Dissertations / Theses: 'Invasions'

1

White, Laura Linsey Fallaize. "Mechanisms underlying marine macroalgal invasions : understanding invasion success of Sargassum muticum." Thesis, University of British Columbia, 2010. http://hdl.handle.net/2429/23713.

Full text

Abstract:

This thesis examines different aspects of invasion success of the brown macroalga Sargassum muticum. Chapter two investigates the relationship between native diversity and invasibility by S. muticum in experimental and unmanipulated communities of low intertidal macroalgae. I found that diversity effects on invasion varied from positive to negative with life history stage of the invader. Native diversity facilitated recruitment of S. muticum, but decreased growth and or survivorship. Phenological differences between S. muticum and native macroalgal species may contribute to the success of this invader in British Columbia. Chapter three explores the effects of S. muticum on native macroalgal diversity at different densities by manipulating exotic density in natural communities. I found that the effects of S. muticum on native macroalgal richness were both density and time dependent, and are mediated through competition for light. The reciprocal interaction between S. muticum and native macroalgal diversity has shown effects in both directions, and suggest some degree of symmetry in the interaction between non-native S. muticum and native macroalgae. Chapter four examines whether non-native S. muticum is less grazed than native macroalgae in British Columbia, and whether the concentrations of defensive polyphenolic compounds in the tissue of the exotic differ from native conspecifics. In contrast to the predictions of the Enemy-Release Hypothesis, I showed that when presented a choice, native herbivores do not discriminate between native and non-native macroalgae. The levels of polyphenolic defenses in the exotic were similar to some native macroalgae, suggesting differences in polyphenolic concentrations are not influencing herbivore choice. Reduced grazing of non-native S. muticum by native herbivores is not contributing to the success of this invasive in British Columbia. Chapter five tests two predictions of the Evolution of Increased Competitive Ability hypothesis; whether S. muticum in non-native regions attains greater sizes and lower chemical defenses than conspecifics in the native region. We compared the size (as a measure of performance) and levels of polyphenolic defenses of S. muticum from its native and invaded regions. My preliminary results suggest that in non-native regions, S. muticum attains larger sizes with lower levels of defensive polyphenolic compounds than native regions.

APA, Harvard, Vancouver, ISO, and other styles

2

Shucksmith, Richard. "Biological invasions : the role of biodiversity in determining community susceptibility to invasion." Thesis, University of Aberdeen, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485655.

Full text

Abstract:

Invasion by non-native species has the potential to change native biodiversity, community structure, food webs and interactions between species.. Small scale manipUlative experiments :using sessile organisms have shown that increasing biodiversity reduces community susceptibility to invasion by non-native species. However, large scale observational studies have shown that some ofthe most diverse systems are the most invaded. The search fora generalised mechanism that may make a resident community resistant to invasion by a non-native species has proven difficUlt and has provided contrasting resUlts. Small scale experiments have been criticised for their dinllnptive spatial scale and -rdatively homogeneous environmental conditions. _ The contrasting results between the experimental and observational studies may be due to the heterogeneous nature ofmost environments which iilllY promote invasion as well as coexistence. In this thesis I study the relationship between invasion and competition in heterogeneous en'ir0nments using the North-East Asian amphipod Caprella mutica. Caprellids have been shown to live on marine sessile species such as, algae, hydroids, tunicates, mussels, bryozoans and sponges which attach to a hard substratum and form '. . erect structures that project into the wat~r column. Species-rich epifaunal comm.unities . can create a structurally diverse habitat. In choice experiments using different structural patches and structure types in the laboratory, there was no effect ofthe number of different types ofstructures in a patch on the number of C. mutica attached to a patch, but structure type was critically important. Caprella mutica preferred the filament.ous structures long tÃ‚Â¢and short turf .over mussel mimics. In field experiments, densities were 7 times greater than the laboratory experiments.. There were twice as many caprellids on the structurally heterogeneous patches than on the structurally homogeneous patches. However, invasion patterns in the field did follow the same structure type as the laboratory experiments. Intraspecific competition appeared to be stronger on the homogeneous patches, whereas there were more refuges and microhabitats on the heterogeneous patches and this may have reduced the aggressive interactions between conspecifics. Artificial and live habitats were placed together in laboratory experiments and there was .t'. no difference in the number of caprellids attached to the artificial and live habitats. Lack ofdifferences between live biota and the artificial mimics showed that C. mutica habitat choice is most likely due to the physical characteristics ofthe habitat. Furthermore, choice oftype ofstructure did not differ betWeen the artificial and live patches. I In competition experiments between C. mutica and two native cap~ellids Caprella linearis and Pseudoprotella.phasma, C. mutica successfully displaced both species from homogeneous artificial habitat patches after 24 hours. Patches that had a refuge attached reduced the number of C. linearis being displaced but only when C. mutica was at a low density. Further experiments, using 3 different levels of structural heterogeneity with C. linearis .and C. mutica, showed that the two species could occupy the structurally heterogeneous patches at similar densities after the 24 hour experimenta~ period. On structurally homogeneous patches C. mutica significantly displaced C. linearis. Aggressive interactions were likely to have been more intense on the homogeneous than structurally heterogeneous patches and this study suggests that C. mutica displaces C. linearis through agonistic interactions. The same processes that reduced intraspecific competition in the first set ofexperiments also promoted coexistence between the two ecologically similar species. Consequently, structurally diverse habitats have the potential to promote invasion while at the same time reducing the impact of an invader on native species. Kelp communities consisting ofLaminaria hyperborea and Saccharina latissima in close proximity to known populations of C. mutica were surveyed and showed that C. mutica did disperse to the kelp communities but was not found on any ofthe kelp plants in the upper zone of the kelp bed. This study was limited to only sampling kelp plants to a depth of 1 to 2 m on spring tides and it is possible that C. mutica may inhabit kelp ' . plants that are deeper. However, laborat~ experiments showed Carcinus maenas predated on C. mutica and may provide biotic resistance to benthic emjronments from 'the invasion by C. mutica. Even at small spatial scales where environmental conditions were similar for both the laboratory and field experiments, the probability of invasion cannot be predicted ' reliably from aggregate community 'measures such as species richness (analogous to the number ofdifferent types ofstructures). Individual characteristics ofthe invading ,' species and positive'associations with structure types, even at small spatial scales, may increase the probability ofinvasion regardless of species richness. Thus, invasion by C. mutica is likely if an appropriate structure type is prese.nt and the success ofinvasion increases with an increasing richness of structure-forming epibiota. For native fauna, which have a similar ecological requirement to the invader, structural heterogeneity appears to reduce the impact ofthe invading species. Habitat heterogeneity may be essential for co-existence between a superior and inferior competitor, as structurally complex habitats offer a variety of different microhabitats and niches. The invasibility of a community, therefore, depends on the diversity and composition of the community being invaded, and the invasive potential of a species depends not only on the community properties, but also on the characteristics of the invader.

APA, Harvard, Vancouver, ISO, and other styles

3

Britton, Andrea Jane. "Modelling invasions on heathlands." Thesis, University of Liverpool, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284563.

Full text

APA, Harvard, Vancouver, ISO, and other styles

4

Minors, Kevin. "Deterministic and stochastic population invasions." Thesis, University of Bath, 2018. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.761030.

Full text

Abstract:

This thesis concerns three models of deterministic and stochastic population invasions, starting from individual-level interactions and deducing population level behaviour. Firstly, we model a bacteria population near obstacles using the 2D FisherKolmogorov-Petrovskii-Piscounov (FKPP) equation with mixed boundary conditions along a corridor and in the half-plane. For a deterministic population, we calculate the smallest corridor width required for survival, the angle the population level sets make with the boundaries, and the population speed. As the hostility of the mixed boundaries increases, the condition for collapse behind the front is achieved before the condition to achieve speed zero ahead of the front. Secondly, we model an invasive fish population using the 1D FKPP equation and explore the effect that sexual conflict between individuals has on the diffusion rate, and hence the invasion speed, of the population. After introducing a stochastic model for the microscopic movement, we demonstrate how sexual conflict can increase the effective diffusion rate of a pair of individuals by determining the mean speed, separation, and time required for a direction change. In large populations, sexual conflict can increase the diffusion rate ahead of the front, where the speed of the invasion is determined. Finally, we model the spread of an opinion using the voter model with nonlocal interaction and diffusion. Individuals can either persuade others who are close by very strongly or persuade others who are far away very weakly. In low density populations, we determine the probability of either individual persuading the other when two different individuals meet in a pair. In a high density population, a small noise expansion determines whether the proportion of either type in the population increases or decreases on average. In both regimes, we find that wide and weakly persuading individuals have an advantage.

APA, Harvard, Vancouver, ISO, and other styles

5

Pujol, Buxó Eudald. "Biological invasions: a temporal, spatial and plastic point of view: the case of Discoglossus pictus in Europe = Invasions biològiques: un punt de vista temporal, espaial i plàstic : el cas de Discoglossus pictus a Europa." Doctoral thesis, Universitat de Barcelona, 2017. http://hdl.handle.net/10803/456898.

Full text

Abstract:

The rates at which allochthonous species are introduced and become invasive worldwide are unprecedented and accordingly, the number of studies on invasion biology have increased during the past years. However, biological invasions are still seemingly underused as natural laboratories to test essential biological theory. In this sense, the nine studies – ordered in three parts, which function as thematic blocks – presented in this thesis try to globally give an evolutionary – apart from ecologic – point of view on the ongoing invasion of the Mediterranean Painted Frog (Discoglossus pictus) in Europe. This frog is native to Northern Africa and was introduced from Algeria in Southern France approximately a century ago, being nowadays present on a wide coastal strip of approximately 250km in SE France and NE Spain, constantly colonizing new areas. The aim of “PART A: Intraspecific variation along the invasive range of Discoglossus pictus” is the examination at a phenotypic and genomic level of possible differences across populations within the invasive range of the species. We observe that the Mediterranean Painted Frog is not a uniform unit in its invasive range in Europe: mean size of adults and life-history traits related to mean annual precipitation, while substantial genetic differences among populations are most probably created by the expansion history itself. The aim of “PART B: Intraguild competition in tadpoles of Discoglossus pictus” is to study and discuss the role of Discoglossus pictus tadpoles as potential competitors for the larvae of native anurans. We here see that the Mediterranean Painted Frog represents, physiologically, a unique addition to the local tadpole guild, characterized by a very rapid and consumption-oriented growth, and that these tadpoles are able to increase the quality and quantity of its food intake when these possibilities are provided. This poses these tadpoles as potentially very disruptive of the natural dynamics of native anurans. Concerning the competitive relationship between the Natterjack Toad (Epidalea calamita) and the Mediterranean Painted Frog, we can observe that it changes according to previous evolutionary history of populations. In this sense, populations of the native toad that have had a greater number of generations of contact with the invasive frog are able to inflict a greater competitive distress on the invasive tadpoles. Both competitors also differ mildly in their breeding preferences, but nevertheless, both species seem forced to end up competing very often at a pond level. Within ponds, the trophic position of both species can respond either to evolutionary or to ecological patterns with the data gathered hitherto. Finally, in “PART C: Tadpoles of Discoglossus pictus as prey for aquatic native predators”, two studies examine if invasive tadpoles modify its phenotypes in front of an array of – native and invasive – predators, testing also the effectiveness of the possible changes. Interestingly, the invasive frog presents a pattern of inducible defences which would be expected for a native anuran, responding to all native predators effectively, while lacking responses in front of introduced or invasive predators. Globally, the complex evolutionary history of the local anuran assemblages poses the Mediterranean Painted Frog as a good model for ecological and evolutionary studies reaching beyond invasion biology, as it is very particular case of invasive species, in which effects of previous recurrent shared evolutionary history with similar competitor / predator species are probably present.
Les invasions biològiques estan essent aparentment infrautilitzades com a laboratoris naturals per investigar certs aspectes teòrics fonamentals de la biologia. En aquest sentit, els nou estudis presentats en aquesta tesi – ordenats en tres blocs temàtics – intenten donar un punt de vista evolutiu – a part d'ecològic – sobre la invasió de la granota pintada (Discoglossus pictus) a Europa. Aquesta granota es va introduir des d'Algèria a Banyuls de la Marenda (Catalunya Nord) fa aproximadament un segle, arribant ara des de Montpeller fins a Sant Celoni, colonitzant contínuament noves àrees. A la "PART A: variabilitat intraespecífica al llarg de la distribució invasora de Discoglossus pictus" observem que la granota pintada no forma un conjunt uniforme de poblacions en la seva distribució invasora europea, ni fenotípica ni genòmicament: la mida i els trets de la història vital dels adults es relacionen amb la precipitació mitjana de cada zona, mentre que la diferenciació genètica entre poblacions ha estat molt probablement creada pel procés d'expansió en sí. A la "PART B: Competència intra-gremi en capgrossos de Discoglossus pictus" veiem que la granota pintada representa, fisiològicament, una addició única al gremi local de capgrossos, caracteritzada per un creixement molt ràpid i orientat al consum, amb bones capacitats d'augmentar la qualitat i quantitat de la ingesta d'aliments quan n'hi ha possibilitats. Pel que fa a la freqüent relació de competència entre Epidalea calamita i Discoglossus pictus, podem observar que els capgrossos autòctons que han tingut un major nombre de generacions de contacte amb els invasors són capaços d'infligir un major estrès competitiu en aquests. Els dos competidors també difereixen lleugerament en les seves preferències de cria, però semblen estar obligats a acabar competint molt sovint a nivell de bassa. Dins d'aquestes, la posició tròfica d'ambdues espècies pot respondre tant a patrons evolutius com a patrons ecològics amb les dades recollides fins ara. Finalment, a la "Part C: Capgrossos de Discoglossus pictus com a presa per depredadors aquàtics autòctons" veiem que la granota invasora presenta un patró de defenses induïbles que s'emmotlla al que s'esperaria per a un anur autòcton, responent a tots els depredadors nadius eficaçment, mancant respostes davant de depredadors introduïts. La complexa història evolutiva dels conjunts d'anurs del mediterrani occidental posa la granota pintada com un cas molt particular d'espècie invasora, on no ses poden descartar els efectes d'una història co-evolutiva prèvia entre espècies similars.

APA, Harvard, Vancouver, ISO, and other styles

6

Berwill, Wilhelm. "Invasions- och insatsförsvaret : En professionsteoretisk jämförelse." Thesis, Swedish National Defence College, Swedish National Defence College, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:fhs:diva-739.

Full text

Abstract:

This essay is on the subject of the changes that the Swedish military is undergoing. This essay will take the old ways of alignment thinking, were the military was to protect the nation against an invasion and compare it to the newer way of alignment thinking, where the military is to go abroad and do peacekeeping operations as there main objective. This comparison will be done by using Bengt Abrahamson theory about professions. He uses three parts one is specialised theoretical knowledge, another is ethics and the last is corps spirit. This theory will then be connected to four interviews. Two with officers representing the defence thinking and two officers representing the peacekeeping thinking. Through this theory and interviews there will be a comparison which tells the different skills and mental attribute the soldiers of the different alignment way of thinking requires. The results shows that the soldiers from the defensive alignment are not capable to do the samet hings as the soldiers from the peacekeeping alignment, but the soldiers from the peacekeeping alignment can handle both the defence and the peaces keeping. Most importantly it shows that there is a difference in the mental attitude between the two ways of alignment thinking. Something I think should be looked upon further to show if it has any effect on how the different soldiers act depending on which alignment they have been trained under. Can the soldiers from these two alignments be combined, or are they too different to do so?

APA, Harvard, Vancouver, ISO, and other styles

7

Hirsch, Philipp E. "Phenotypic Processes Triggered by Biological Invasions." Doctoral thesis, Uppsala universitet, Limnologi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-158697.

Full text

Abstract:

Individuals within a single population can vary widely in their phenotype e.g. in their body shape. These differences are an important source of biodiversity and they can precede evolutionary divergence within a population. In this thesis we use the biological invasion of the zebra mussels into Swedish lakes to investigate which processes create or maintain phenotypic diversity within populations of the two native fish species perch and roach and the mussel itself. Both fishes have specially adapted body shapes that depend on whether they feed in the near-shore or open-water habitat of lakes. This habitat-specific divergence was more pronounced in lakes with zebra mussels, probably because resources in both habitats were in higher supply due to the mussels’ effects on the lakes. Divergence in perch body shapes between habitats was also higher in lakes with a higher water clarity, suggesting that visual conditions can affect the resource use and thus also the expression of a habitat-specific body shape. When investigating the diversity of body shapes in the mussel itself we found that mussels from one lake changed their shell shape when exposed to different predators: fish predators induced a more elongated shell shape while crayfish predators induced a rounder shell. These specific shell shapes probably serve as two alternative predator defenses protecting the mussel from predation. We conclude that the availability and use of distinct resources is an important source of diversity within populations. Abiotic conditions can play a previously underappreciated role by promoting or impairing the use of the distinct resources thus affecting the divergence. The diversity of shell shapes we found in the zebra mussels complements our study by demonstrating that not only consumer responses to resources but also resources’ responses to predators can generate phenotypic diversity.

APA, Harvard, Vancouver, ISO, and other styles

8

Gilbert, Mark. "Modelling species invasions in heterogeneous landscapes." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:944d15d3-257a-47e5-acb9-9bdfba26985b.

Full text

Abstract:

Biological invasions are devastating ecosystems and economies world-wide, while many native species' survival depends on their ability to track climate change. Characterising the spread of biological populations is therefore of utmost importance, and can be studied with spatially explicit, discrete-time integro-difference equations (IDEs), which reflect numerous species' processes of demography and dispersal. While spatial variation has often been ignored when implementing IDE models, real landscapes are rarely spatially uniform and environmental variation is crucial in determining biological spread. To address this, we use novel methods to characterise population spread in heterogeneous landscapes. Asymptotic analysis is used for highly fragmented landscapes, where habitat patches are isolated and smaller than the dispersal scale, and in landscapes with low environmental variation, where the ecological parameters vary by no more than a small factor from their mean values. We find that the choice of dispersal kernel determines the effect of landscape structure on spreading speed, indicating that accurately fitting a kernel to data is important in accurately predicting speed. For the low-variation case, the spreading speeds in the heterogeneous and homogeneous landscapes differ by ϵ², where ϵ governs the degree of variation, suggesting that in many cases, a simpler homogeneous model gives similar spread rates. For irregular landscapes, analytical methods become intractable and numerical simulation is needed to predict spread. Accurate simulation requires high spatial resolution, which, using existing techniques, requires prohibitive amounts of computational resources (RAM, CPU etc). We overcome this by developing and implementing a novel algorithm that uses adaptive mesh refinement. The approximations and simulation algorithm produce accurate results, with the adaptive algorithm providing large improvements in efficiency without significant losses of accuracy compared to non-adaptive simulations. Hence, the adaptive algorithm enables faster simulation at previously unfeasible scales and resolutions, permitting novel areas of scientific research in species spread modelling.

APA, Harvard, Vancouver, ISO, and other styles

9

Vogl, Gero, Marcus Rennhofer, Bogdan Sepiol, Manfred Smolik, Franz Essl, and Ingrid Kleinbauer. "Invasions of isotopes and of neobiota." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-194174.

Full text

Abstract:

We report on invasions with low diffusivity: one in materials science and one in ecology. What is interesting in materials science is to describe diffusivities in order to model technological important materials. In ecology on the other hand predictions into the future appear the most challenging issue.

APA, Harvard, Vancouver, ISO, and other styles

10

Vogl, Gero, Marcus Rennhofer, Bogdan Sepiol, Manfred Smolik, Franz Essl, and Ingrid Kleinbauer. "Invasions of isotopes and of neobiota." Diffusion fundamentals 6 (2007) 76, S. 1-2, 2007. https://ul.qucosa.de/id/qucosa%3A14256.

Full text

Abstract:

We report on invasions with low diffusivity: one in materials science and one in ecology. What is interesting in materials science is to describe diffusivities in order to model technological important materials. In ecology on the other hand predictions into the future appear the most challenging issue.

APA, Harvard, Vancouver, ISO, and other styles

11

Fournier, Alice. "Modéliser et prédire les invasions biologiques." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS144/document.

Full text

Abstract:

Les invasions biologiques, deuxième cause de perte de biodiversité à l’échelle mondiale, représentent un risque majeur auquel nos sociétés doivent faire face. On parle d’invasion biologique lorsque des activités humaines permettent à une espèce de franchir des barrières qui jusqu’alors limitaient sa dispersion ou sa multiplication, entrainant une explosion géographique et démographique de l’espèce dans un nouvel écosystème et s’accompagnant éventuellement d’impacts économiques, sociétaux ou écologiques. La façon la plus efficace et la moins coûteuse de limiter les impacts causés par les espèces envahissante et de les prévoir en amont afin de mettre en place des mesures de prévention ciblées et efficaces et d’essayer de les éviter.L’objectif de cette thèse est de démontrer qu’il est possible d’améliorer la prédiction des invasions biologiques en développant et combinant différentes approches de modélisation de façon innovante. Les questions posées sont de savoir s’il est possible de prévoir quelles pourraient-être ces espèces, où elles pourraient devenir envahissantes et quels impacts elles pourraient avoir. Toutes les méthodes développées dans cette thèse ont été appliquées à des hyménoptères sociaux ; nombreuses espèces de fourmis (famille des Formicidés) ou frelon asiatique (famille des Vespidés, vespa Velutina nigrithorax), mais elles sont généralisables et réutilisables pour tout autre taxa.Je montre dans cette thèse qu’il est possible de développer un outil statistique de détection des espèces risquant de devenir envahissantes. J’applique cet outil aux fourmis, je fournis une liste de 15 espèces de fourmis risquant de devenir envahissantes à travers le monde et je cartographie les zones du globe risquant d’être envahies par ces espèces. Chacun des continents est menacée par au moins une de ces invasions potentielles. Dans un deuxième temps, je mets au point d’un cadre méthodologique permettant d’améliorer les prédictions d’aires de distribution des espèces en combinant leurs exigences climatiques et d’habitat, tout en respectant l’échelle géographique à laquelle ces facteurs agissent sur la distribution des espèces. J’applique cette méthode au frelon asiatique, ce qui me permet d’identifier les habitats qui lui sont les plus favorables et d’utiliser ces informations pour raffiner la prédiction de son aire favorable. En combinant le climat et l’habitat, je prédis une aire potentielle de distribution 56% plus restreinte par rapport aux estimations basées sur le climat uniquement. Enfin, dans un troisième temps, je m’intéresse au développement d’une méthode permettant de prédire spatialement les impacts causés par une invasion biologique. Pour ce faire, je prédis d’abord l’abondance potentielle du frelon asiatique en France. Je couple ensuite cette prédiction avec des données de présence de ruches et un modèle présidant l’impact du frelon asiatique sur la survie des colonies d’abeilles. J’estime enfin que cette invasion peut conduire à l’effondrement de 41% des colonies d’abeilles domestiques en France.Cette thèse met en lumière l’utilité d’intégrer la modélisation dans la construction du savoir autour des invasions biologiques, approche relativement nouvelle dans ce champ disciplinaire. De plus, elle illustre comment la modélisation et l’élaboration de prédictions peuvent aider à objectiver la prise de décision concernant la gestion des espèces envahissantes et optimiser leur efficacité en ciblant les habitats, les régions et les espèces d’action prioritaires
Biologicals invasions, the second cause of biodiversity loss worldwide, represent a major threat that our societies have to face. Invasive species correspond to species that, due to human activities, cross geographic and reproduction barriers and expand into new areas in large numbers. This spread into new ecosystems may have severe socio-economic or ecological impacts. The most efficient way to limit these impacts is to predict and avoid biological invasions before they occur by setting up appropriate management plans.The aim of this PhD thesis is to demonstrate that existing predictive models can be further developed and combined together to improve biological invasion predictions. All of the methods developed in this thesis have been applied to social Hymenoptera: ant species (Formicidae) and the Asian hornet (Vespa velutina nigrithorax), but they are generalizable to any other taxa. The questions asked are: can we predict future invader species? Can we improve the spatial predictions of their distribution? Can we predict invasive species impact?First, I show in this thesis that it is possible to develop a model that detects future invasive species, even before they have had the chance to be moved outside their native range. I apply this screening tool to more than 2000 ant species, provide a list of the 15 ant species that are highly likely to become invasive and map their global suitability to highlights the area the most at risk from these invasions. All continents are threatened by at least one of these potential invasions. Second, I set up a methodological framework to improve species distribution predictions by combining multi-scale drivers. I apply this method to the invasive Asian hornet, identify its high affinity habitats, and use this information to refine suitability maps. I show that integrating multiple drivers, while still respecting their scale of effect, produced a potential range 55.9% smaller than that predicted using a climatic model alone. Finally, I propose a method to predict invasive species impacts in a spatially explicit way and I apply it to the estimate the Asian hornet’s impact on honeybee colonies in France. To do so, I estimate the Asian hornet nest density across France and combine it with an agent-based hive model to estimate honeybee mortality risk. I show that up to 41% of the honeybee colonies are likely to collapse due to the Asian hornet.Overall, these studies demonstrate how modelling techniques can provide valuable inputs to improve invasive species management decision by offering tools to optimize prevention strategies and target areas, species or habitats where action is needed in priority. Biological invasions involve our scientific, political and cultural perceptions in an intricate way; this PhD thesis highlights the usefulness of bringing together modelling techniques and the rest of biological invasion knowledge to better grasp invasion science complexity

APA, Harvard, Vancouver, ISO, and other styles

12

Harris, Kyle Robert. "Arthropod assemblages in a savanna invaded by Opuntia stricta (Cactaceae) in the Kruger National Park, South Africa." Pretoria : [s.n.], 2009. http://upetd.up.ac/thesis/available/etd-11292009-211107.

Full text

APA, Harvard, Vancouver, ISO, and other styles

13

Rehage, Jennifer Schöpf. "Traits underlying invasiveness a comparison of widespread and endemic species in the genus gambusia (poeciliidae) /." Lexington, Ky. : [University of Kentucky Libraries], 2003. http://lib.uky.edu/ETD/ukybiol2003d000107/JSRdiss.pdf.

Full text

Abstract:

Thesis (Ph. D.)--University of Kentucky, 2003.
Title from document title page (viewed June 1, 2004). Document formatted into pages; contains x,143 : ill. Includes abstract and vita. Includes bibliographical references (p. 125-141).

APA, Harvard, Vancouver, ISO, and other styles

14

Banks, Christopher Mark. "New Zealand Calanoid Copepod Invasions: Has Artificial Lake Construction Facilitated Invasions, and are our Coastal Waters Uninvaded?" The University of Waikato, 2007. http://hdl.handle.net/10289/2269.

Full text

Abstract:

Non-indigenous species have become a global issue of increasing importance in recent years, with many causing significant environmental and economic damage. Identifying locations vulnerable to invasion allows for focus of management efforts towards prevention of invasions at those locations. In order to determine whether constructed water bodies, such as reservoirs, ornamental lakes or retired mines, are more easily invaded environments than natural water bodies, owing to decreased biotic resistance, the distributions of native and non-indigenous freshwater calanoid copepod species in the North Island were examined. Calanoid copepods in ports and other coastal environments were also examined, in order to determine whether ports are more frequently invaded owing to increased propagule supplies from visiting ships and other sources. The distributions of the native freshwater calanoid copepod species Boeckella hamata, B. propinqua, B. delicata and B. tanea are confined in the North Island of New Zealand to specific technostratigraphic terranes when natural waters only are examined, and as such each species can be considered to have a native range. The recently colonised calanoid copepod species Boeckella minuta (6 locations), Skistodiaptomus pallidus (3 locations) and Sinodiaptomus valkanovi (2 locations) are to date confined to constructed water bodies. Boeckella symmetrica (2 locations) may be confined to constructed water bodies, but the status of one location is unclear. Boeckella triarticulata, a species common in the South Island, is known only from a single farm dam in the North Island. The native species Boeckella hamata, B. propinqua and B. delicata were found to occur in constructed waters, but only B. propinqua was found in constructed water bodies outside their natural ranges (9 locations). Calamoecia lucasi is found in lakes throughout most of the North Island, and is not confined to any one terrane. My results indicate that constructed water bodies are more easily invaded by non-indigenous species than natural water bodies, represents a potential pathway for future invaders to establish, and provides locations for species to spread. In order to determine whether recently established freshwater calanoid copepod species have the potential to spread from their present habitats into other water bodies, the prosomal lengths of non-indigenous calanoid copepod species were measured and compared with those for native species. The results suggest that dietary overlap should prevent the non-indigenous species present to date from spreading into any water bodies with established Boeckella populations, although Sinodiaptomus valkanovi and Boeckella triarticulata could potentially spread to lakes containing only Calamoecia lucasi. Data on the co-occurrences of native freshwater calanoid copepod species support the theory of dietary exclusion, as Boeckella species have not been found to coexist. In order to test whether New Zealand marine environments have been invaded by non-indigenous calanoid copepods, and whether ports have been more regularly invaded than non-port areas, calanoid copepods were sampled from various coastal locations around the North Island. With the possible exception of Sulcanus conflictus, no non-indigenous species were found, indicating that non-indigenous marine calanoid copepod species are not establishing in New Zealand despite a history of invasion elsewhere.

APA, Harvard, Vancouver, ISO, and other styles

15

Moodley, Desika. "Determinants of introduction and invasion success for Proteaceae." Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/79851.

Full text

Abstract:

Thesis (MSc)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: Successful biological invasions take place when species introduced to regions outside their natural dispersal range overcome several barriers and establish, persist, proliferate and spread potentially resulting in major threats to biodiversity. The success of invasive alien plants depends on species-specific traits and characteristics of the introduced environment. In this thesis I explore which species traits are important and which environmental barriers need to be overcome for an invasion to occur using Proteaceae as a test case. Firstly, I assessed the global introduction history and invasion ecology of Proteaceae - a large plant family with many taxa that have been widely disseminated by humans, but with few known invaders. This revealed that at least 402 species (i.e. 24% of 1674 species in this family) are known to have been moved by humans out of their native ranges, 58 species (14%) have become naturalized and 8 species (2%) are invasive. The probability of naturalization was greatest for species with large native range sizes, low susceptibility to Phytophthora root-rot disease, larger seeds, mammal-dispersed seeds and those with the capacity to resprout after fire or other disturbances. The probability of naturalized species becoming invasive was greater for species with larger range sizes, species used as barrier plants, taller species, species with smaller seeds, serotinous species, and those that regenerated mainly through re-seeding. Secondly, I looked at mechanisms underlying naturalization on a regional scale, using species which are not already classified as major invaders. At least 26 non-native Proteaceae species have been introduced to, and are cultivated in, South Africa. Propagule pressure facilitated the naturalization of Hakea salicifolia populations in climatically suitable areas, but in suboptimal climates human-mediated land disturbance and land management activities are important for naturalization. Similar drivers are important for naturalization of other alien Proteaceae: a long residence time, fire regimes, poor land management, and propagule pressure were important mechanisms for naturalization. Thirdly, I determined whether reproduction, which in part drives propagule pressure, serves as a barrier for naturalization. I examined several Australian Proteaceae species introduced to South Africa and observed that all species were heavily utilized by native nectar-feeding birds and insects. The five Banksia species that were assessed are self-compatible but four species have a significantly higher reproductive output when pollinators visit inflorescences. Fruit production in H. salicifolia does not differ between naturally-pollinated and autonomously-fertilized flowers. Moreover, no significant difference in fruit production was observed between the five pollination treatments (i.e. natural, pollen-supplementation, autonomous, hand-selfed and hand-crossed treatments) and naturalized and non-naturalized populations. However, pollen limitation was detected in non-naturalized populations which received fewer pollinator visits than naturalized populations. Thus, reproduction limits but is not a fundamental barrier to invasion for H. salicifolia. I conclude that reproductive success of the studied Proteaceae, which is a key barrier determining invasiveness, is not limited by autonomous seed set or mutualisms in the introduced range. In this thesis I highlight biogeographical characteristics, a set of life-history traits and ecological traits as important determinants of invasiveness. These traits are in turn dependent on the stage of invasion. Characteristics of the recipient environment are also important drivers of invasions. This study provides a better understanding of plant invasions in general, but the patterns and processes of invasions highlighted in this thesis will be particularly useful for the current and future management of alien Proteaceae in South Africa and elsewhere, as well as, other species that are adapted to Mediterranean and nutrient poor ecosystems. For example, combining traits of invasiveness and susceptible environments will help to identify which non-native species pose a high risk of becoming invasive (e.g. species with large home ranges and barrier plants) and which conditions in the target area are likely to facilitate or exacerbate invasions (e.g. strong climate match and high propagule pressure).
AFRIKAANSE OPSOMMING: Suksesvolle biologiese indringing vind plaas wanneer ŉ spesie geïntroduseer word in ŉ area buite sy natuurlike verspreidings area, sekere versperrings oorkom, vestig, bly voortbestaan, vermenigvuldig en versprei en potensieel ŉ groot bedreiging inhou vir biodiversiteit. Die sukses van uitheemse indringer plante hang af van spesifieke kenmerke van die spesie en kenmerke van die omgewing waarin dit geïntroduseer word. In hierdie tesis maak ek gebruik van Proteaceae om te ondersoek watter kenmerke is belangrik en watter omgewing versperrings moet oorkom word vir indringing om plaas te vind. Ten eerste assesseer ek die wêreldwye introduksie geskiedenis en indringers ekologie van Proteaceae – ŉ groot plant familie wat wyd gebruik word deur mense, maar met min indringer spesies. Dit het gewys dat mense ten minste 402 spesies (dus 24% van die 1674 spesies in die familie) uit die inheemse areas verskuif het, 58 spesies (14%) genaturaliseer het en 8 spesies (2%) indringers geword het. Die moontlikheid van naturalisasie was die grootste vir spesies met ŉ groot inheemse streek, lae vatbaarheid vir Phytophthora wortelvrot, groter sade, dier verspreide sade en die met ŉ vermoë om weer uit te spruit na ŉ vuur of ander versteuring. Die moontlikheid van genaturaliseerde spesies om indringers te word, was groter vir spesies met groter streek grootte, spesies wat as versperring plante gebruik word, hoër spesies, spesies met kleiner sade, serotiniese spesies, en die wat hoofsaaklik voortbestaan as saadspruiters. Tweedens, het ek gekyk na onderliggende meganismes op ŉ regionale skaal, deur gebruik te maak van spesies wat nie alreeds as belangrike indringers geklassifiseer is nie. Ten minste 26 nie-inheemse Proteaceae spesies is alreeds geïntroduseer en word gekultiveer in Suid Afrika. Propaguul druk fasiliteer die naturalisering van Hakea salicifolia populasies in areas met geskikte klimaat, terwyl in areas met ŉ sub optimale klimaat, versteurings deur mense en grond bestuurs aktiwiteite belangrik is vir naturalisering. Die selfde drywers is belangrik vir die naturalisering van ander uitheemse Proteaceae: lang verblyftyd, vuur bestel, swak land bestuur en propaguul druk. Derdens het ek bepaal of reproduksie, wat gedeeltelik propaguul druk dryf, ŉ versperring is vir naturalisasie. Ek het gekyk na verskeie Australiese Proteaceae spesies wat geïntroduseer is in Suid Afrika, en het gevind dat al die spesies besoek word deur inheemse nektar etende voëls en insekte. Die vyf Banksia spesies wat geassesseer is, kan self bestuif, maar vier van die spesies het ŉ betekenisvolle hoër reproduksie wanneer bloeiwyses deur bestuiwers besoek word. Vrug produksie verskil nie tussen natuurlik bestuifde en self bestuifde blomme in H. salicifolia nie. Verder was daar geen verskil tussen vrug produksie van die vyf bestuiwings behandelinge (naamlik: natuurlik, stuifmeel bygevoeg, self, hand self en hand kruis) en tussen genaturaliseerde en nie genaturaliseerde populasies. Ewenwel, stuifmeel beperking is gevind in nie-genaturaliseerde populasies wat egter ook minder besoeke ontvang het dan die genaturaliseerde populasies. Dus, reproduksie kan die verspreiding beperk maar is nie ŉ fundamentele versperring vir indringing van H. salicifolia nie. My konklusies is dat die reproduktiewe sukses, wat andersins ŉ sleutel versperring is vir indringing, in die bestudeerde Proteaceae nie beperk word deur outonomiese saad produksie of mutualismes in die geïntroduseerde gebied nie. In hierdie tesis beklemtoon ek die biogeografiese karakters, lewens geskiedenis kenmerke en ekologiese kenmerke as belangrike bepalers van indringing. Hierdie kenmerke is op hulle beurt weer afhanklik van die stadium van indringing. Karakters van die ontvangende omgewing is ook belangrike dryfvere van indringing. Hierdie studie verbeter hoe ons plant indringing in die algemeen verstaan, maar die patrone en prosesse van indringing wat beklemtoon word in hierdie tesis sal besonder bruikbaar wees vir huidige en toekomstige bestuur van uitheemse Proteaceae in Suid Afrika en op ander plekke, asook vir ander spesies wat aangepas is tot Mediterreense en nutriënt arm ekosisteme. Byvoorbeeld, die kombinasie van kenmerke van indringing en vatbare omgewings sal help om te identifiseer watter uitheemse spesies ŉ hoë risiko inhou om ŉ indringer te word (byvoorbeeld spesies met ŉ groot streek grootte en versperring spesies) en watter kondisies in die teiken area die waarskynlikste indringing fasiliteer of vererger (byvoorbeeld sterk klimaat ooreenstemming en hoë propaguul druk).

APA, Harvard, Vancouver, ISO, and other styles

16

Lesieur, Vincent. "Invasion de la punaise américaine Leptoglossus occidentalis en Europe : une contribution à la compréhension des invasions fulgurantes." Thesis, Orléans, 2014. http://www.theses.fr/2014ORLE2045/document.

Full text

Abstract:

Les dernières décennies représentent un tournant majeur concernant les invasions biologiques avec une augmentation sans précédent de leur rythme et de leur ampleur, en lien direct avec les activités humaines, en particulier la mondialisation. Certains invasifs se propagent à une vitesse très rapide dans leur nouveau milieu. L’invasion européenne de la punaise Leptoglossus occidentalis, illustre parfaitement ce phénomène et offre un modèle d’étude particulièrement intéressant. Cette thèse a pour but de tester des hypothèses permettant d’expliquer la rapidité de cette invasion. Pour répondre à cet objectif, nous avons choisi d’utiliser une approche pluridisciplinaire combinant des études de génétique des populations (natives et introduites) à des études de biologie et d’écologie des populations invasives. Grâce à l’utilisation de marqueurs moléculaires et de méthodes Bayésiennes (ABC), nous démontrons que l’invasion en Europe suit un scénario " tête de pont ", au sens où la population invasive de l’Est de l’Amérique du Nord a servi de source pour l’invasion européenne. Nos résultats confirment les soupçons d’introductions multiples dans des zones géographiquement déconnectées. En outre, l’étude de génétique des populations, associée aux mesures expérimentales des capacités de vol, indique que les capacités intrinsèques de dispersion de cette espèce sont particulièrement élevées. Les conditions rencontrées en Europe par les populations introduites ne sont pas un frein à l’invasion. L’espèce s’accommode parfaitement des nouvelles essences de conifères rencontrées sur le continent. La polyphagie observée dans la zone native est confirmée dans la zone d’introduction européenne, constituant un atout pour l’établissement des populations. De plus, cette étude révèle les risques écologiques que cette espèce représente pour la flore native européenne. Les dégâts occasionnés semblent s’additionner à ceux des ravageurs natifs, diminuant ainsi le potentiel de régénération naturelle. L’ensemble de ces résultats constitue une contribution à la connaissance des mécanismes sous-tendant les invasions biologiques, notamment sur la rapidité de propagation de certains invasifs, et met l’accent sur des phénomènes sous-estimés il y a encore peu de temps comme le scénario d’invasion " tête de pont "
During the last decades, biological invasions were observed to increase exponentially, at an unprecedented rate and magnitude, in direct relation with the human activities, especially globalization. In this context, some invasive species spread very quickly in the area of introduction. The European invasion of Leptoglossus occidentalis is a good example of this phenomenon. This study aimed at testing some hypotheses to explain the rapidity of this invasion. To reach this goal, we used a multidisciplinary approach combining population genetics (analyzing samples from native and invaded areas) with a study of biological and ecological characteristics of the invasive populations. Through the use of molecular markers and Bayesian methods (ABC), we confirmed previous suspicions and demonstrated that the European invasion proceeded from multiple introductions in distant geographic areas. Our results also indicated that a primarily invaded area of Eastern North America acted as a bridgehead for the invasion in Europe. Moreover, population genetics, combined with an experimental measurement of the bug flight capabilities using flight mills, revealed that the intrinsic capacities of dispersion of this species are particularly high. The environmental conditions of the newly invaded areas in Europe did not constitute a barrier to the invasion of L. occidentalis. Its high degree of polyphagy was confirmed on European conifers, quite all species being susceptible to be exploited, thus favoring population establishment. . Furthermore, this study highlights the ecological threat represented by this insect which can affect the native flora in Europe. Actually, bug damage which can be important, seems to be additive to those of native insects exploiting cone and seed resources, thus decreasing the potential of natural regeneration. This work contributes to improve knowledge on biological invasions, especially to understand the reasons underlying the rapid spread observed in some invasive species, and highlights phenomenon underestimated until recently such as the Bridgehead scenario

APA, Harvard, Vancouver, ISO, and other styles

17

Wu, Shan-Huah. "Naturalized plants and their invasions in Taiwan /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2004. http://uclibs.org/PID/11984.

Full text

APA, Harvard, Vancouver, ISO, and other styles

18

Vall-llosera, Camps Miquel. "Avian invasions: from basic to applied research." Doctoral thesis, Universitat Autònoma de Barcelona, 2012. http://hdl.handle.net/10803/96891.

Full text

Abstract:

La preocupació pels greus problemes ambientals i econòmics causats per les invasions biològiques ha provocat un enorme interès en tractar de comprendre els factors que influeixen en el procés invasiu. Aquesta informació és essencial per prevenir, avaluar i mitigar els impactes de les espècies invasores. En aquest context, aquesta tesi té dos objectius principals. El primer és descobrir què fa que una espècie tingui èxit en la invasió, i el segon investigar si aquests descobriments poden ser útils per prevenir els impactes dels invasors. Aquesta tesi explora aquestes qüestions utilitzant les aus com a objecte d'estudi. Per entendre per què hi ha espècies exòtiques que, tot i començar amb poblacions sovint petites i genèticament empobrides, arriben a vegades a establir-se en ambients on no havien tingut oportunitat d’adaptar-se, sovint s’invoca que les espècies bones invasores tenen adaptacions que els permeten superar aquests problemes. La teoria ecològica proposa que una d’aquestes adaptacions haurien de ser les històries de vida. Les característiques de les espècies relacionades amb la reproducció i la supervivència haurien de jugar un paper destacat en disminuir el risc d’extinció per factors estocàstics just després de la introducció. Els resultats indiquen que els bons invasors es caracteritzen per donar prioritat a la reproducció futura en lloc de la actual, segurament perquè un gran èxit en la reproducció en el futur redueix els costos d'un fracàs reproductiu en condicions d'incertesa i augmenta les oportunitats per explorar i respondre a les pressions ambientals noves. A més, les espècies exòtiques haurien de tenir adaptacions que els permetin trobar un nínxol ecològic apropiat on sobreviure i prosperar, per evitar l’extinció per creixement poblacional negatiu. Aquest nínxol no només ha d’incloure els recursos necessaris, però també pocs competidors i enemics. La teoria suggereix dues formes de trobar aquest nínxol: o les espècies invasores són capaces de desplaçar competitivament les espècies natives dels seus nínxols, o bé els invasors són oportunistes i troben nínxols ecològics desaprofitats. En aquesta tesi la importància relativa d’aquestes dues hipòtesis s’ha contrastat mitjançant l’estudi de l’invasió del Rossinyol del Japó (Leiothrix lutea) a la serra de Collserola. L'invasor s'ha establit amb relativament poca resistència de les espècies natives, el que reflecteix la seva naturalesa oportunista i generalista i que els seus requeriments ecològics estaven poc representats en la comunitat nativa. No obstant, durant el període d’expansió de l’invasor s’ha detectat la disminució d’una espècie nativa ecològicament similar, presumiblement deguda a desplaçament competitiu. Aquests resultats mostren que les dues hipòtesis no són mútuament exclusives, sinó que conjuntament poden ajudar a millorar la comprensió de les invasions. Finalment, aquesta tesi planteja si és possible utilitzar les característiques proposades d’estar relacionades amb l’èxit invasor per desenvolupar una metodologia per detectar les espècies potencialment invasores i així poder evitar futurs problemes. Els resultats indiquen que l’èxit invasor pot ser predit per la mida de la població fundadora, l'ús de l'hàbitat, la mida del cervell i la capacitat de les espècies de prioritzar la reproducció futura. Tot i que són poques característiques, els models generats van predir la probabilitat d'èxit de l'establiment de les aus a Europa i Austràlia, amb una precisió molt alta. Així doncs, es demostra que fer avaluacions de risc basades en les característiques relacionades amb l'èxit de l'establiment és difícil, però possible, i proporcionen una eina útil per orientar les estratègies de prevenció destinades a mitigar els impactes d'espècies invasores. Tot i així, aquesta tesi també demostra que per ser del tot efectives cal que aquestes metodologies siguin implementades realment en les polítiques de gestió ambiental si de debò volem evitar un futur dominat per les espècies invasores.
Serious concern for environmental and economic problems caused by biological invasions has caused a huge interest in trying to understand the factors that influence the invasive process. This information is essential to prevent, assess, and mitigate the impacts of invasive species. In this context, this thesis has two main goals. The first is to ask what makes a species a successful invader, and second to investigate whether this information can be useful for preventing the impact of the invaders. This thesis explores these questions using birds as the object of study. To understand why exotic species, whose initial populations are generally small and genetically depleted, can sometimes succeed to establish themselves in environments to which they have had no opportunity to adapt it has often been invoked that successful invaders have adaptations that allow them to overcome these problems. Ecological theory suggests that life histories should be part of these adaptations. The characteristics of the species related to reproduction and survival should play an important role in reducing the risk of extinction by stochastic factors at the initial stages of the invasion process. The results indicate that successful invaders are characterized by prioritizing future over current reproduction, probably because a great success in reproducing in the future reduces the cost of reproductive failure under conditions of uncertainty and increases the opportunities to explore and respond to new environmental pressures. In addition, alien species should have adaptations to find an appropriate niche to survive in and prosper, to avoid extinction by negative population growth. This niche should include not only necessary resources, but also few competitors and enemies. Theory suggests two ways to achieve this niche: or invasive species are competitively superior and displace native species from their current niches, or invaders are opportunistic and have the ability to find unused ecological niches. In this thesis the relative importance of these two hypotheses has been contrasted trough the study of the invasion of the Red-billed Leiothrix (Leiothrix lutea) in the Collserola forest reserve. The invader established with relatively little resistance from the native species, reflecting its generalist and opportunistic nature and that its ecological requirements were underrepresented in the native community. However, there has been a decline of a native species ecologically similar to the invader during the period of expansion, presumably due to competitive displacement. These results show that both hypotheses are not mutually exclusive, but taken together can help to better understand of the establishment process. Finally, this thesis asks whether it is possible to use the species features proposed to be related to the invasive success to develop a methodology to detect potentially invasive species and, thus, to be able avoid future problems. The results show that invasive success can be predicted by the founder population size, habitat use, brain size, and the ability of species to prioritize future reproduction. Although there are few traits, the models predicted the probability of successful establishment for birds in Europe and Australia with high accuracy. Therefore, it is demonstrated that risk assessments based on characteristics related to the success of the establishment are difficult but feasible and provide a useful tool for guiding preventive polices aimed at mitigating the impact of invasive species. However, this thesis also shows that, to be fully effective, these methods have indeed to be applied in the environmental management policies if we really want to avoid a future dominated by invasive species.

APA, Harvard, Vancouver, ISO, and other styles

19

Cruickshank, Isla. "The dynamics of ecological invasions and epidemics." Thesis, University of Strathclyde, 1999. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=21436.

Full text

Abstract:

The systems of interest in this study are the spread of epidemics and invasions from a small propagule introduced into an arena that was initially devoid of the given species or stage of illness. In reaction-diffusion models, populations are continuous. Populations at low densities have the same growth functions as populations at high densities. In nature, such low densities would signify extinction of a population or of a disease. This property can be removed from reaction-diffusion models by small changes in the formulation so that small populations become extinct. This can be achieved by the use of a threshold density or an Allee effect, so there is negative growth at low densities. Both these alterations were made to the Fisher model, a predator-prey model and a two stage and a three stage epidemic model. A semi-numerical method, termed the Shooting method, was developed to predict the shapes and velocities of these wave fronts. This was found to correctly predict the velocity, the peak density of the invading stage or species and the width of the wave front. It was found that in oscillatory cases of the multi species models, a high threshold can remove the wave train or wake which would normally follow the wave front, so the wave becomes a soliton. The next step is to investigate probable causes of persistence behind the initial wavefront. To do this, discrete time and space versions of the models were formulated so that experiments investigating persistence can be carried out in a two dimensional arena with less computational effort. The formulations were chosen so that at reasonable time and space steps the discrete models show no behaviour different to that of the reaction diffusion model, and so that the Shooting method could also be used to make predictions about these wavefronts. Three mechanisms of persistence are investigated; environmental heterogeneity, long range dispersal and self organised patterns.

APA, Harvard, Vancouver, ISO, and other styles

20

Krug, Rainer Michael. "Modelling seed dispersal in restoration and invasions." Thesis, Stellenbosch : Stellenbosch University, 2008. http://hdl.handle.net/10019.1/1155.

Full text

Abstract:

Thesis (PhD (Conservation Ecology and Entomology))--Stellenbosch University, 2008.
Dispersal plays an essential role in determining the distribution of populations of species, especially species expanding their ranges. Two disciplines are concerned with gaining understanding of spread of species, namely restoration ecology and invasion biology. Con- ceptual understanding of dispersal, its mechanisms and its management is essential to both disciplines. Nevertheless, the disciplines have quite opposite objectives: in restoration ecol- ogy, spread of indigenous species into transformed landscapes is promoted, while invasion biology aims to prevent the (further) spread of alien species into pristine or restored habi- tats. Despite these two opposite objectives of facilitating spread and preventing spread of their respective target species, these disciplines have essentially the same requirements in terms of information needed for restoration. In this thesis, I will present two modelling studies—one looking at the impact of two different seed-feeding alien control agents on the spread of Hakea sericea, the other investigating the recolonisation by Dicerothamnus rhinocerotis of an old field dominated by Cynodon dactylon. Based on these studies, I will draw conclusions for the management in each case. In a second step, I will compare these two seemingly-different studies and draw conclusions on how these two disciplines can learn from each other, and how conclusions drawn and management recommendations developed for the one discipline can be translated for the other. The invasion biology study concluded that seed-feeding biocontrol agents do have a considerable impact on the velocity of the spread of the target species. In addition, management recommendations included the possibility of substituting seed-feeding biocontrol agents with an increased fire frequency where the negative impact on natural vegetation, on the site invaded by the target species, is acceptable. The restoration study concluded that the main impact on the velocity of spread, and the speed of the return of the shrub species onto the old fields, is the availability of micro-sites. A sensitivity analysis showed the even a slight change from 1% to 2% increases the velocity and pattern of spread dramatically. The other parameters playing an important role are the mean rate of establishment and the time span between

APA, Harvard, Vancouver, ISO, and other styles

21

Schonegevel, Lucille. "Modelling alien vegetation invasions and clearing strategies." Thesis, Stellenbosch : Stellenbosch University, 2001. http://hdl.handle.net/10019.1/52341.

Full text

Abstract:

Thesis (MSc)--Stellenbosch University, 2001.
ENGLISH ABSTRACT: The burgeoning problem of alien plant invasions in South Africa necessitates effective decision-making based on an understanding of the complex processes that govern these invasions. Due to the spatial nature of the problem, this study explored the use of Geographic Information Systems and spatial models for predicting the spread of alien vegetation and assessing the effectiveness of clearing strategies. The Spatially Explicit Individual Based Simulation (SEIBS) model was identified as a potentially useful tool for alien plant management. This thesis documents the further investigation and development that was necessary before recommendations could be made regarding the future use of the model. The landscape version of the SEIBS model was adapted to allow for the convenient input and output of spatial data, making it possible to simulate invasions in different areas. An ArcView extension was developed in order to facilitate the pre- and post-processing of the spatial data required and created by the model. Changes were also made to the fire routine of the model. The new version of the model was called Clear. A series of model tests for Pinus pinaster were conducted to assess the sensitivity of the Clear model to spatial resolution, initial spatial fragmentation and heterogeneity. These tests revealed that the model was sensitive to changes in resolution and needed to be reparameterised when using different resolutions. The initial level of fragmentation was shown to have a major influence on the invasion rate. Although greater levels of spatial heterogeneity with respect to vegetation age did not significantly affect the spread rate, it did increase the effectiveness of clearing strategies based on clearing juvenile or sparse vegetation. Based on these tests, it is concluded that the model can be readily applied to different areas, provided the influence of spatial characteristics is understood and accommodated. The Clear model was shown to be a useful tool for evaluating clearing strategies and for investigating invasion rates. It is recommended that the model be introduced to a wider audience, in order to obtain user feedback and further improve the accessibility of the model.
AFRIKAANSE OPSOMMING: Die toenemende probleem van uitheemse indringerplante in Suid Afrika, noodsaak effektiewe besluitneming wat gebaseer is op 'n begrip van die ingewikkelde prosesse wat indringing beheer. As gevolg van die ruimtelike geaardheid van die probleem, is die gebruik van Geografiese Inligtingstelsels en ruimtelike modelle vir die voorspelling van die verspreiding van indringerplante en die evaluasie van die effektiwiteit van opruimingstrategieë in hierdie studie ondersoek. Die Spatially Explicit Individual Based Simulation (SEIBS) model is as 'n moontlike geskikte hulpmiddel vir die bestuur van uitheemse indringerplante geïdentifiseer, alhoewel verdere ondersoeke en ontwikkeling nodig was voordat aanbevelings vir die gebruik van die model gemaak kon word. Vir hierdie studie is die landskapweergawe van die SEIBS model aangepas om die maklike toevoer en afvoer van ruimtelike data te fasiliteer. 'n ArcView uitbreiding is ontwikkel om met die voor- en naprosessering van ruimtelike data, wat deur die model gebruik en geskep is, te fasiliteer. Veranderinge is ook aan die vuur sub-roetine van die module gemaak. Die nuwe weergawe van die model word Clear genoem. 'n Reeks toetse is vir Pinus pinaster gedoen om die sensitiwiteit van die Clear model te toets teenoor ruimtelike resolusie, aanvanklike vlak van versnippering en vlak van heterogeniteit. Vanuit die toetse het dit geblyk dat die model sensitief was ten opsigte van verandering in resolusie en dat die model se parameters verstel moes word wanneer verskillende resolusies gebruik word. Daar is ook gewys dat die die vlak van aanvanklike versnippering 'n groot impak op die verspreidingstempo het. Alhoewel hoër vlakke van ruimtelike heterogeniteit teenoor plantegroei nie 'n merkbare impak op die verspreidingstempo gehad het nie, het dit wel die effektiwiteit van opruiming-strategieë, gebaseer op die opruiming van jong of yl verspreide plante, verbeter. Die gevolgtrekking wat uit die toetse gemaak kan word is dat die model geredelik op verskillende areas toegepas kan word, op die voorwaarde dat die invloed van ruimtelike eienskappe in ag geneem word en in berekening gebring word. Dit word aanbeveel dat die model wyer bekendgestel word om sodoende gebruikersterugvoer te bekom.

APA, Harvard, Vancouver, ISO, and other styles

22

Coxner, Mina, and Jacobsson Stina Närvä. "Parental Privacy Invasions and Adolescent Depressive Symptoms." Thesis, Örebro universitet, Institutionen för juridik, psykologi och socialt arbete, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:oru:diva-68912.

Full text

APA, Harvard, Vancouver, ISO, and other styles

23

Hutchison, Melissa Alice Sarah. "Interactions between habitat fragmentation and invasions: factors driving exotic plant invasions in native forest remnants, West Coast, New Zealand." Thesis, University of Canterbury. School of Biological Sciences, 2009. http://hdl.handle.net/10092/3218.

Full text

Abstract:

Habitat fragmentation and biological invasions are widely considered to be the most significant threats to global biodiversity, and synergistic interactions between these processes have the potential to cause even greater biodiversity loss than either acting alone. The objective of my study was to investigate the effects of fragmentation on plant communities in native forest fragments, and to examine potential interactions between these effects and invasions by exotic plants at multiple spatial scales. I examined edge, area and landscape effects on plant invasions using empirical data from fragmented landscapes on the West Coast of New Zealand. My research revealed significant interactions between the amount of native forest cover in the landscape and the strength of edge and area effects on plant communities in forest fragments. The dominance of exotic plants in the community was highest at forest edges and decreased towards fragment interiors, however the interiors of very small fragments were relatively more invaded by exotic plants than those in larger fragments, reflecting a significant interaction between edge and area effects. Similarly, exotic dominance increased in more heavily deforested landscapes, but this effect was only apparent in very small fragments (<2 ha). The combined effects of small fragment size and low forest cover in the landscape appear to have promoted invasions of exotic plants in very small remnants. I explored the mechanisms underlying edge-mediated invasions in forest fragments and examined whether propagule availability and/or habitat suitability may be limiting invasions into fragments. Experimental addition of exotic plant propagules revealed that landscape forest cover interacted with edge effects on germination, growth and flowering rates of two short-lived, herbaceous species, and this appeared to be driven by elevated light and soil phosphorus levels at edges in heavily deforested landscapes. I also examined the role of traits in influencing plant responses to forest fragmentation. Different traits were associated with exotic invasiveness in edge and interior habitats of forest fragments, indicating that the traits promoting invasiveness were context dependent. Traits also had a major influence on responses of native plants to forest fragmentation, with generalist species appearing to benefit from fragmentation, as they can utilise both forest and open habitats, whereas native forest specialists have been negatively impacted by fragmentation.

APA, Harvard, Vancouver, ISO, and other styles

24

Law, Hang-heung Sharon. "Invasive species : what can Hong Kong do? /." View the Table of Contents & Abstract, 2006. http://sunzi.lib.hku.hk/hkuto/record/B37121005.

Full text

APA, Harvard, Vancouver, ISO, and other styles

25

Merchant, Sandra M. "Spatiotemporal patterns in mathematical models for predator invasions." Thesis, University of British Columbia, 2009. http://hdl.handle.net/2429/17988.

Full text

Abstract:

Much attention has been given to oscillatory reaction-diffusion predator-prey systems recently because, in the wake of predator invasions, they can exhibit complex spatiotemporal patterns, notably wave trains and associated irregular spatiotemporal oscillations, thought to occur in natural systems. This thesis considers the generation and stability of spatiotemporal patterns behind invasion in these models and an extension that includes non-local intraspecific prey competition. In the first part, we study the mechanism by which a single member is selected from a continuous family of wave train solutions behind the invasion. This was first studied by Sherratt (1998), where the author develops a selection criterion that is valid near a supercritical Hopf bifurcation in the kinetics and when the predator and prey diffuse at equal rates. We formulate a ``pacemaker" selection criterion that generalizes the criterion of Sherratt (1998), but does not depend on these assumptions. We test this pacemaker criterion on three sample systems and show that it provides a more accurate approximation and can apply to unequal diffusion coefficients. In the second part of the thesis, we study the effect of including non-local intraspecific prey competition in these systems. We first study the qualitative effect of non-local competition on the spatiotemporal patterns behind predator invasions in these models, and in a related caricature system. We find that non-local prey competition increases the parameter range for spatiotemporal pattern formation behind invasion, and that this effect is greater for lower kurtosis competition kernels. We also find that sufficiently non-local competition allows the formation of stationary spatially periodic patterns behind invasion. Second, we revisit the selection and stability of wave train solutions. We modify the selection criterion from the first part, also applying it to the non-local system, and study how the properties of selected wave trains vary with the standard deviation of the non-local prey competition kernel. We find that the wavelength of selected wave trains decreases with the standard deviation of the non-local kernel and also that unstable wave trains are selected for a larger parameter range, suggesting that spatiotemporal chaos may be more common in highly non-local systems.

APA, Harvard, Vancouver, ISO, and other styles

26

Dreiwi, Hanan Ali. "Using transfer function analysis in modelling biological invasions." Thesis, University of Exeter, 2012. http://hdl.handle.net/10036/3749.

Full text

Abstract:

This thesis is made up of seven chapters and two appendices. Chapter 1 provides an introduction whilst Chapter 7 o ers a conclusion. In Chapter 2 we provide preliminaries on population projection models and robustness analysis. In Chapter 3 we introduce a stage-structured model in a context of biological invasions. Using a Transfer Function Approach, we provide a detailed analysis of the invasion model where the existence and local stability of all possible equilibria are characterised in terms of the underlying parameters of the model. In Chapter 4, a Lyapunov function approach is used to estimate the basin of attraction for each equilibrium. In Chapter 5, harvesting is incorporated into the model and we speci cally examine the e ect of harvesting on whether one or both of the species are eliminated. In Chapter 6 we introduce a novel technique to measure the possibility of invasion in non-normal systems where the traditional invasion exponent technique is unreliable.

APA, Harvard, Vancouver, ISO, and other styles

27

Oudaer, Guillaume. "La pseudo-histoire du mythe des invasions d'Irlande." Thesis, Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLEP064/document.

Full text

Abstract:

Cette thèse a pour objectif d'analyser les origines de la pseudo-histoire mythique des invasions d'Irlande : les sources classiques antiques ou judéo-chrétiennes de ce cycle légendaire, les survivances indigènes, le processus d'élaboration et sa signification socio-politique. La méthodologie utilisée a été de comparer les éléments dont la source pouvait être indigène à d'autres traditions celtiques ou indo-européennes
The object of this thesis is an analysis of the origins of the mythic pseudo-history of the invasions of Ireland: the classical or judeo-christian sources of this legendary cycle, its native remnants, the elaboration process and its socio-political significance. The methodology we used was to compare the native elements with other Celtic or Indo-European traditions

APA, Harvard, Vancouver, ISO, and other styles

28

Caut, Stéphane. "Invasions biologiques, réactions en chaîne et relations trophiques." Paris 11, 2006. http://www.theses.fr/2006PA112357.

Full text

Abstract:

L’invasion des écosystèmes par les espèces invasives est vue comme l’une des plus importantes sources de perte de la biodiversité. La meilleure réponse à ces effets est presque toujours le contrôle, ou bien lorsque cela est possible l’éradication de tous les individus de la population invasive. Dans beaucoup de cas, l’élimination de l’espèce invasive est suivie par un rapide et spectaculaire rétablissement des populations locales. Cependant, la disparition soudaine de l’espèce invasive peut générer plusieurs déséquilibres, entraînant des dommages similaires ou encore plus importants sur l’écosystème. Ces phénomènes sont appelés « effets surprises ». Etant donné le nombre et la complexité des interactions entre espèces, il est toujours difficile de prédire les résultats de la suppression d’espèces clés, comme les prédateurs supérieurs. Cela justifie l’importance des études pré-éradication au préalable pour initier l’éradication de l’espèce invasive, afin d’éviter toute catastrophe écologique. Ce projet concerne l’étude de la place des espèces invasives dans les réseaux trophiques envahis, afin de prédire et donc d’éviter les potentielles réactions en chaîne qui pourraient découler de la suppression soudaine de l’espèce invasive. La mise en place de cette méthodologie est basée sur une combinaison d’études empiriques de travail de terrain, d’études de régimes alimentaires classiques et d’isotopes stables en laboratoire et de modélisation mathématique. La partie terrain de mon projet est basée sur un inventaire floristique et faunistique complet de la communauté locale, la détermination des relations trophiques et d’une campagne d’éradication d’une espèce invasive. Le site d’étude sélectionné est l’île Surprise, dans le récif d’Entrecasteaux, en Nouvelle Calédonie, qui est un site de ponte majeur de tortues et d’oiseaux marins, mais aussi un écosystème riche qui est envahi par le rat noir. Mon étude souligne l’importance de considérer les espèces invasives au sein des communautés, pour prendre en compte tous les liens avec les autres espèces, qu’elles soient exotiques ou indigènes. Je montre aussi les avantages et les limites de l’utilisation des analyses en isotopes stables pour la reconstruction du régime alimentaire et des réseaux trophiques. Finalement, j’insiste sur l’impact des rats introduits sur l’île Surprise et la nécessité de l’éradiquer, tout en prenant garde à minimiser l’impact sur les espèces non visées par l’éradication et le risque de déclenchement d’une relâche des plantes exotiques, des fourmis ou des souris
The invasion of ecosystems by exotic species is viewed as one of the most important sources of biodiversity loss. The best response to these effects is almost always to control the alien population, when possible by eradicating the whole alien population from the island. In many cases, the elimination of the alien invasive species is followed by a rapid and often spectacular recovery of the impacted local populations. However, the sudden removal of the alien species may generate further disequilibria, resulting in similar or greater damages to the ecosystem. This has been called the "surprise effect"; Given the numerous and often complex population interactions among species, it is difficult to predict the outcome of the removal of key species, such as a top predator. This justifies a careful pre-control study prior to initiating the eradication of alien species eradication, in order to avoid an ecological catastrophe. This project concerns the study of the place of invasive species in invaded trophic webs in order to predict, and thus avoid, potential chain reactions that could be triggered by alien species sudden removal. The setting of this methodology is based on a combination of empirical work in the field, classical diet and stable isotope analyses in the lab, and mathematical modelling. The field part of my project is based on a complete floristic and faunistic inventory of the local communities, the determination of the resulting trophic webs and an invasive species eradication campaign. The selected field site is Surprise Island, in the Entrecasteaux reef, New Caledonia, a major breeding site for sea turtles and seabirds, and a rich ecosystem that is invaded by black rats. My study highlights the importance of considering the invasive species within the invaded communities, taking into account all link with other species, be they exotic or indigenous. I also show the advantages and limits of using stable isotope analyses for the reconstruction of diet composition and trophic webs. Finally, I stress out the impact of the rats introduced on Surprise island, and the need to eradicate them, while taking care of minimising both the impact on non-target species and the risks of triggering a release of exotic plants, ants or mice

APA, Harvard, Vancouver, ISO, and other styles

29

Wikström, Sofia A. "Marine seaweed invasions : the ecology of introduced Fucus evanescens /." Stockholm : Botaniska institutionen, Univ, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-132.

Full text

APA, Harvard, Vancouver, ISO, and other styles

30

Jankovic, Masha. "Modelling biological invasions : population cycles, waves and time delays." Thesis, University of Leicester, 2015. http://hdl.handle.net/2381/31392.

Full text

Abstract:

Biological invasions are rapidly gaining importance due to the ever-increasing number of introduced species. Alongside the plenitude of empirical data on invasive species there exists an equally broad range of mathematical models that might be of use in understanding biological invasions. This thesis aims to address several issues related to modelling invasive species and provide insight into their dynamics. Part I (Chapter 2) documents a case study of the gypsy moth, Lymantria dispar, invasion in the US. We propose an alternative hypothesis to explain the patchiness of gypsy moth spread entailing the interplay between dispersal, predation or a viral infection and the Allee effect. Using a reaction-diffusion framework we test the two models (prey-predator and susceptible-infected) and predict qualitatively similar patterns as are observed in natural populations. As high density gypsy moth populations cause the most damage, estimating the spread rate would be of help in any suppression strategy. Correspondingly, using a diffusive SI model we are able to obtain estimates of the rate of spread comparable to historical data. Part II (Chapters 3, 4 and 5) is more methodological in nature, and in a single species context we examine the effect of an ubiquitous phenomenon influencing population dynamics time delay. In Chapter 3 we show that contrary to the general opinion, time delays are not always destabilising, using a delay differential equation with discrete time delay. The concept of distributed delay is introduced in Chapter 4 and studied through an integrodifferential model. Both Chapters 3 and 4 focus on temporal dynamics of populations, so we further this consideration to include spatial effects in Chapter 5. Using two different representations of movement, we show that the onset of spatiotemporal chaos in the wake of population fronts is possible in a single species model.

APA, Harvard, Vancouver, ISO, and other styles

31

Silva, Rui Manuel Roque da. "Using data from citizen-science to monitor bird invasions." Master's thesis, Universidade de Évora, 2018. http://hdl.handle.net/10174/23690.

Full text

Abstract:

As consequências ecológicas da introdução de espécies exóticas, é uma das questões de conservação mais preocupantes mundialmente. A utilização de dados de ciência cidadã, tem sido proposta como uma solução alternativa para analisar este problema. Assim, o nosso principal objectivo foi avaliar a adequabilidade de dados de ciência cidadã para monitorizar as tendências populacionais e de distribuição de espécies exóticas (Psittaciformes and Sturnidae) na região urbana de Lisboa, utilizando três principais grupos de fontes de dados. Estes dados foram validados, uma vez que foram recolhidos por colaboradores experientes, a quantidade de registos foi considerável, e os padrões espácio-temporais relativamente homogéneos. Entre as oito espécies mais registadas, o periquito-rabijunco e o mainá-de-crista, tiveram o maior aumento populacional e de distribuição. Para o periquitão-de-cabeça-azul, foi igualmente registado um aumento, mas menos marcado, enquanto as restantes espécies registadas ocasionalmente. Desta forma, a ciência cidadã demonstrou ser uma ferramenta útil alternativa à ciência convencional; Abstract: The ecological consequences from the introduction of non-native species are among the major conservation concerns worldwide. Using citizen-science data has been proposed as an alternative solution to asses this problem. Thus, our main goal was to evaluate the suitability of citizen-science data to monitor the population and distribution trend of non-native species (Psittaciformes and Sturnidae) in the urban region of Lisbon. The evaluation included three major groups of data sources. We validated the suitability of citizen-science data since the contributors' expertise is in general high, the amount of records is considerable, and the spatio-temporal patterns are relatively homogeneous. Among the eight most recorded species, the Ring-necked Parakeet and the Crested Myna showed a noticeable increase in population and distribution range. The Blue-crowned Parakeet also increased but less markedly, while for the remaining species there were only occasional records. Therefore, the citizen-science showed to be a valuable alternative to conventional science.

APA, Harvard, Vancouver, ISO, and other styles

32

Stojanov, Darko. "Les villes de l’Illyricum protobyzantin face aux grandes invasions." Paris, EPHE, 2013. http://www.theses.fr/2013EPHE4005.

Full text

Abstract:

Cette thèse a pour but d’analyser la diversité et l’intensité de certaines transformations provoquées dans les villes de la préfecture du prétoire d’Illyricum par les vagues successives des grandes invasions (dans ce cas, 374-618). Centrée sur les centres urbains, tels Thessalonique, Sirmium, Viminacium, Stobi, Dyrrachium, Athènes, Corinthe etc. , la recherche se développe dans deux directions : la réaction des villes (voir des citadins) face aux invasions et les traces matérielles laissées par les envahisseurs. En se fondant sur une analyse détaillée des sources littéraires et archéologiques, ainsi que, dans une moindre mesure, les témoignages épigraphiques et numismatiques, la thèse avait essayée de découvrir le comportement, y compris les réactions, les sentiments et les destins différents, de la population urbaine de l’Illyricum durant l’un des plus importants processus historiques. A part les petites indications et nouvelles opinions, la recherche effectuée a mené à trois résultats principaux : 1. A l’image de la ville face au péril barbare il faut ajouter l’image de la ville en double ou multiples périls, afin d’ arriver à une compréhension plus complète et plus nuancée de la position compliquée des villes au temps des grandes invasions ; 2. Il est important d’accentuer la possibilité d’une nouvelle vie en Barbaricum, aux dépens de l’image « eschatologique » qui voit les grandes invasions comme la fin pour les citadins des villes protobyzantines ; 3. Les grandes invasions avaient la capacité surprenante de provoquer des turbulences chaotiques « ex nihilo » dans les villes protobyzantines qui n’étaient pas des cibles particulières
This dissertation aims to analyse the diversity and the intensity of certain transformations which the Great Invasions caused in the cities of the praetorian prefecture of Illyricum (in this case, 374-618). Focused on the urban centres such as Thessalonika, Sirmium, Viminacium, Stobi, Dyrrachium, Athens, Corinth, etc. , this research addresses two topics: the reaction of the cities (or citizens) facing the barbarian invasions, and the material traces left by the invaders. Based on a detailed analysis of literary and archaeological sources and, to a lesser degree, on epigraphic and numismatic evidence, this dissertation tries to understand how the presence of barbarian invaders impacted the behaviors, perceptions, and physical and material circumstances of the urban population in Illyricum. Besides the small indications and new opinions, my research yielded three principal conclusions: 1. Cities in Illyricum faced threats not only from barbarian invaders, but also form the presence of imperial military forces; we must understand this “double” or multiple danger if we are to arrive at a more complete and nuanced image of the complicated position of cities at the time of the Great Invasions; 2. Contrary to the traditional "eschatological" image which sees the Great Invasions as the end for citizens of early Byzantine cities, the evidence from Illyricum shows that some citizens were able to accommodate themselves to barbarian rule, and successfully make new lives and livelihoods for themselves in Barbaricum; 3. The invasions had a surprising capacity to cause chaotic turbulences “ex nihilo” in some early Byzantine cities, which were not a target of a particular attack

APA, Harvard, Vancouver, ISO, and other styles

33

Bishop, Tara Boyce. "Of Fire, Mammals, and Rain: Mechanisms of Plant Invasions." BYU ScholarsArchive, 2019. https://scholarsarchive.byu.edu/etd/8572.

Full text

Abstract:

Biological invasions are driving environmental state changes on a global scale. Exotic plant species must be successful at passing several abiotic and biotic filters to establish and disrupt the native plant community assembly. Understanding where exotic plants are on a regional scale and being able to characterize how exotic plants are generally interacting with their environment is crucial information for exotic species management (chapter 1). In the western United States human-related activities are augmenting the spread of exotic plant species by increasing the ignitions of wildfire. Wildfire can lead to nutrient pulses through the removal of intact native communities and returning some mineral content into the soil. Exotic plant species that have traits that efficiently acquire nutrients accompanied by rapid growth rates may outcompete native plants. In chapters 2, 3, and 4 experimental fires demonstrated that the direct effect of fire may not be as critical as the potential indirect effects of fire such as altering the behavior of consumers (chapter 2) and reducing competition (chapters 3 and 4). In the Mojave desert, rodent consumers can have strong top-down effects on plant community assembly through foraging selection preferences. Life history traits such as seedling and seed size can lead to differential herbivory and positively benefit some plant species while inhibiting others (chapter 1) which could indirectly alter plant-plant interactions. Plant competition is a biotic filter than can determine establishment success or failure. Species that with rapid growth rates and plastic growth responses are likely to be able to capitalize on fluctuations in available resources. In the Great Basin, forecasts in climate change models predict that precipitation timing will lead to heavier fall rains and more rain than snow in the winter. Water availability is one of the main limiting factors in semi-arid and arid ecosystems where native plants have adaptive traits to maximize resource use. The interaction of wildfire and changes in climate, specifically timing of precipitation is critical to understand to be able to predict and protect against increasing wildfire frequency and severity. In chapter three, the responses by a key exotic annual grass, Bromus tectorum, and keystone native perennial shrub Artemisia tridentata subsp. wyomingensis, were positive for increased early fall precipitation but much more pronounced for B. tectorum. Exotic annual plants are able to respond to changes in timing of fall precipitation and have extreme growth which leads to superior competitive abilities through interference and priority effects (chapter 4). Native plants can compete with exotics but the magnitude of the effects are diminished compared to the negative interaction from exotics. Together these findings demonstrate that across several regions exotic annual grasses are capable of passing through abiotic filters and disrupting biotic interactions of the native plant community. This is likely to lead to increased spread of exotic annual species and may indicate potential and availability of fine fuel production supporting increases in size and frequency of wildfires in the western United States.

APA, Harvard, Vancouver, ISO, and other styles

34

Shimode, Sayumi. "Multiple invasions of an infectious retrovirus in cat genomes." Kyoto University, 2015. http://hdl.handle.net/2433/199206.

Full text

APA, Harvard, Vancouver, ISO, and other styles

35

Berry, Katharine M. "The role of parasites in the invasion ecology of Harmonia axyridis." Thesis, University of Stirling, 2017. http://hdl.handle.net/1893/27336.

Full text

Abstract:

The success of an invasive alien species is often attributed to the ecological advantage gained from natural enemy release. Numerous factors have been suggested as contributing to the success of Harmonia axyridis as an invasive alien species, including enemy release. This thesis studied the interactions of several parasites with H. axyridis, investigating parasite transmission, growth and virulence as well as host immune responses, thereby shedding light on the potential role of enemy release in the invasion biology of this ladybird. Benefits gained by invasive alien species from enemy release diminish if parasites of native species shift hosts to exploit the novel invader. The fungal ectoparasite Hesperomyces virescens began infecting H. axyridis shortly after it invaded the UK, probably as a result of a host shift from Adalia bipunctata. This study found a rapid increase in H. virescens prevalence over three years in London H. axyridis populations. Laboratory study showed H. virescens transmission and growth to be more efficient on A. bipunctata than the novel host. In addition, reciprocal interspecific transfers of H. virescens strains isolated from A. bipunctata and H. axyridis revealed that the infection characteristics of the fungi from these two hosts differed, suggesting strains may have diverged after the initial shift from A. bipunctata to better exploit the host from which they were derived. Laboulbenialian fungi were previously thought to have negligible impacts on host fitness. A detailed examination of H. virescens infecting H. axyridis found distinct virulence, with infections resulting in a 50% reduction in host lifespan. In addition, chronic H. virescens infection in males caused acceleration in the age-associated decline in body condition while for females, infection triggered fecundity senescence and a faster age-related decline in fertility. While their role in accelerating ageing is debated, the results presented here provide evidence that infectious diseases can drive the ageing process in this insect species. In nature, multiple parasites affecting a single host are common. The effect of co-infection on the virulence caused by two fungal infections was characterised using H. axyridis and A. bipunctata hosts. The ability of two ladybird species to defend against an acute fungal parasite, while infected with the relatively avirulent H. virescens was found to be sex-specific. While for females, the presence of co-infection did not alter the virulence seen in singly infected females, a higher mortality rate existed for co-infected males compared with those infected singly. Previously, H. virescens has been considered to be avirulent, however, this study provides evidence that this chronic fungal parasite may be important when considering the mortality associated with co-infections in the field. The invasive success of H. axyridis has, in part, been attributed to a more vigorous immune ability compared with other competitor species. Previously, field studies have shown that the prevalence of the parasitoid wasp Dinocampus coccinellae in H. axyridis is considerably lower than in the UK primary host of this wasp, Coccinella septempunctata. The extent to which the prevalence asymmetry in the field is driven by differences in host encapsulation response was tested by first comparing the encapsulation ability of C. septempunctata and H. axyridis directed against an artificial implant. Following this, the encapsulation response of D. coccinellae parasitized individuals was assessed and compared between the two host species. While encapsulation ability did not differ between the host species, and D. coccinellae did not affect the immune response of H. axyridis, wasp parasitism did alter the encapsulation ability of C. septempunctata, although it was inconsistent across sexes and populations. Overall, this thesis furthers our understanding of the fungal parasite H. virescens and its association with the notorious invader H. axyridis. The research presented here also demonstrates the use of H. axyridis as a model system in areas other than invasion ecology and furthermore, contributes to understanding the role of infectious disease in the rate of ageing. Finally, sex-specific effects were found across the chapters of this thesis, demonstrating the use of H. axyridis in the study of sex-specific effects of infections.

APA, Harvard, Vancouver, ISO, and other styles

36

Murphy, Jennifer E. "The Beginning and Legacy of Rosa multiflora Invasions: Understanding the Mechanisms that Drive Its Success Across Stages of Invasion." Case Western Reserve University School of Graduate Studies / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=case1561484787925341.

Full text

APA, Harvard, Vancouver, ISO, and other styles

37

Chandler, Brad James. "The effects of disturbance and deer herbivory on plant invasions." Thesis, University of Canterbury. Biological Sciences, 2009. http://hdl.handle.net/10092/3852.

Full text

Abstract:

Despite the negative impacts invasive plants can impose on forest communities and the potential for these impacts to increase with global change, little has been done in New Zealand to examine what facilitates the establishment and spread of these species within native beech (Nothofagus solandri) forest. This study examines the role which forest canopy gaps and deer herbivory have on the dispersal, germination, establishment and spread of invasive plant species within the Nothofagus forests of the Hopkins and Huxley valleys, near Twizel, New Zealand. Propagule dispersal was enhanced by the presence of a gap in the above canopy, resulting in an increased number of seeds being caught on the sticky traps in these plots (159 compared to only 2 in the control plots). Seed bank samples were assessed by germination in a glasshouse for one year. The invasive seed bank was larger in the fenced plots and conversely to the other results of this study, the presence of a canopy gap had no effect on the size of the seed bank. Aboveground cover of these invasive plants was primarily driven by the existence of a canopy gap, suggesting that canopy gaps are the main cause of plant invasions into Nothofagus forest (9% mean cover in the gap plots compared to 0% in the control and fence plots). However, there was a further increase in the aboveground cover of these invasive plants where a deer exclusion fence was situated around the perimeter of an open canopy plot (27.5% mean cover in the gap fence plots compared to 9% in the gap plots). Thus, suggesting that deer herbivory could be decreasing the abundance of invasive plants in areas of forest where gaps have been created. The canopy gaps allowed invasive plants to spread back into the forest away from the openings but only for a short distance, as in all cases invasive plants were absent by 6-7m from the plot edge. This localised establishment and spread of invasive plants where canopy gaps have been created could pose a threat to New Zealand’s native Nothofagus forests, as many small populations spread out across a landscape can cause more ecosystem adversity than larger single populations. If not kept in check these invaders could increase further with global change however, if herbivory is assisting in the control of plant invasions management strategies for both invasive plants and introduced deer may need to be revised.

APA, Harvard, Vancouver, ISO, and other styles

38

Sagerman, Josefin. "Marine seaweed invasions : Impacts and biotic resistance in native ecosystems." Doctoral thesis, Stockholms universitet, Institutionen för ekologi, miljö och botanik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-116788.

Full text

Abstract:

Marine seaweeds constitute one of the most productive plant systems known on Earth and a rich fauna including juvenile fish and crustaceans is dependent on the habitats they form. Human influence on marine costal ecosystems has resulted in large scale changes to the abundance and distribution of species, where species introductions constitute an obvious part. The aims of this thesis were to 1) explore how non-native seaweeds impact on ecosystem functions (primary production and decomposition), and 2) study how interactions between non-native seaweeds and native communities affect invasion success. I used a combination of laboratory assays, outdoor mesocosms and field experiments. Paper I and II revealed that the impact on ecosystem functions were substantially different depending on the identity of the invader. The highly successful non-native red alga Heterosiphonia japonica had a large effect on community productivity. Due to the rapid growth of the invader, the primary production increased by more than four times in mixed species communities with the invader compared to communities with only native species. In contrast, the morphologically similar and equally successful non-native red alga Bonnemaisonia hamifera grew slowly and had no effect on community production. But B. hamifera produces a potent defense compound that deters native herbivores and reduces the growth of micro-organisms. As a direct or indirect effect of this chemical defense, the litter from B. hamifera decomposed considerably slower compared to native seaweed litter. Rapid growth and defense against predation are likely important in explaining how the two invaders have become successful in the invaded range. These results show that traits related to invasion success may determine impacts on native communities. Paper III shows that the rapidly growing invader H. japonica is avoided as food by native herbivores, which likely enables the invader to survive during colder seasons with sub-optimal growth conditions. In paper IV I found that competition from the native brown alga Fucus vesiculosus decreased growth of the non-native congener Fucus evanescens. Native herbivores caused more damage to the native competitor but it did not relieve F. evanescens from competitive pressure. Several native brown algae grow in the niche of F. evanescens, which may explain why the species only is growing sparingly in the invaded range. The results indicate that competition with native seaweeds have potential to reduce the success of non-native seaweeds in the new range. In summary, this thesis shows that non-native seaweeds differ strongly in their effect on ecosystem functions. Knowledge of which traits are present among abundant non-native species and how these traits relates to different effects may enable us to gain a better understanding of invasion impacts on native communities. The thesis also highlights that competitive interactions can be of importance for invasion success in seaweed communities.

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript.

Alien-native trophic interactions: consequences for invasion success and ecosystem effects of invasions

APA, Harvard, Vancouver, ISO, and other styles

39

QuiÌlez-Badia, Gemma. "Alien invasions : the introduction of zooplankton via ships' ballast water." Thesis, University of Newcastle Upon Tyne, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.424152.

Full text

APA, Harvard, Vancouver, ISO, and other styles

40

Bell, Sally Sue. "Mathematical models assessing the importance of disease on ecological invasions." Thesis, Heriot-Watt University, 2010. http://hdl.handle.net/10399/2316.

Full text

Abstract:

A general understanding of the role that both shared disease and competition may play in ecological invasions is lacking. We develop a theoretical framework to determine the role of disease, in addition to competition, in invasions. We first investigate the e ect of disease characteristics on the replacement time of a native species by an invader. The outcome is critically dependent on the relative e ects that the disease has on the two species and less dependent on the basic epidemiological characteristics of the interaction. This framework is extended to investigate the e ect of disease on the spatial spread of an invader and indicates that a wave of disease spreads through a native population in advance of the replacement. A probabilistic simulation model is developed to examine the particular example of the replacement of red squirrels by grey squirrels in the United Kingdom. This model is used to examine conservation strategies employed within red squirrel refuges and compared to observations from Sefton Coast Red Squirrel Refuge. Our findings indicate that culling greys may be e ective at protecting red populations from replacement, but none of the conservation strategies currently employed can prevent periodic outbreaks of infection within red squirrel refuges.

APA, Harvard, Vancouver, ISO, and other styles

41

Gichohi, Nathan W. "Ecological impacts of biological invasions on native birds in Africa." Master's thesis, University of Cape Town, 2010. http://hdl.handle.net/11427/4747.

Full text

Abstract:

The impacts of biological invasions on native avian diversity have been the subject of many studies in Africa. However, a holistic synthesis of available information from different taxa and their impacts on native birds is lacking. From published information, I analysed the negative and positive effects of biological invaders on native African birds from five taxa: plants, invertebrates, fish, mammals and birds. In order to assess functional gains and losses, native birds were categorized into their functional guilds defined by their primary diet. I limited my scope to mainland Africa at the biome level. ArcView GIS 3.3 software was used to map locational data of impacts within the major biomes. The results indicate that a minimum of 572 native birds are negatively impacted by invasive species from the five taxa. This represents ca 29% of all the bird species in Africa. In contrast, only 191 species of native birds benefited from such invasions. Birds whose diet was primarily insects were disproportionally impacted. The majority of the impacts were caused by invasive plants. At the biome level, the greatest numbers of native birds impacted were in the Montane grassland and shrubland biome. It is predicted that native birds will continue to lose more than they gain from biological invasions in the continent.

APA, Harvard, Vancouver, ISO, and other styles

42

Ruland, Florian [Verfasser]. "The Role of Behavioural Changes in Biological Invasions / Florian Ruland." Berlin : Freie Universität Berlin, 2020. http://d-nb.info/1212031970/34.

Full text

APA, Harvard, Vancouver, ISO, and other styles

43

Adan, Farhiya, and Olivia Schibort. "Privacy invasions and their association with poor parent-adolescent relationship." Thesis, Örebro universitet, Institutionen för juridik, psykologi och socialt arbete, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:oru:diva-75557.

Full text

Abstract:

In this study we examine whether privacy invasions are associatedwith poor parent-adolescent relationship. We also examined if therewere differences between mothers and fathers in the frequency oftheir invasions, as well as the intent of those invasions. Lastly, welooked at associations between privacy invasions and parentadolescentrelationships and if these were modified by parent oradolescent gender. We hypothesized that intentional and frequentprivacy invasions would have a stronger association with poorparent-adolescent relationship than accidental and infrequentinvasions of privacy. The data for this study was selected from alarger database. Participants consisted of 78 adolescents, 39 girlsand 39 boys. Data were collected through questionnaires that bothadolescent and parent answered separately. The adolescents filledout the questionnaires at school in different classrooms. Weconcluded that frequent privacy invasions had a significantassociation with poor parent-adolescent relationship for mothers,but not fathers. Furthermore, the interaction between the frequencyof privacy invasions and the intent was significant for mattering tomothers. However, no significant relations were found for fathers.
I den här studien undersöker vi huruvida integritets-inkräktande ärförknippade med dålig förälder-ungdom relation. Vi undersökteockså om det fanns skillnader mellan mammor och pappor ifrekvensen av deras invasioner, liksom avsikten med dessainvasioner. Slutligen såg vi på associationer mellan integritetsinkräktandeoch föräldra-ungdoms relationer och om dessamodifierades av föräldrar eller ungdomars kön. Vi förutsåg attavsiktligt och frekvent integritets-inkräktande skulle ha en starkareförknippning med dålig förälder-ungdom relationer än oavsiktligaoch sällsynta invasioner av integritet. Uppgifter för denna studievaldes från en större databas. Deltagarna i studien bestod av 78ungdomar, 39 flickor och 39 pojkar. Uppgifterna samlades ingenom flera frågeformulär som både ungdomar och föräldrarbesvarade separat. Ungdomarna fick besvara frågeformulären iskolan i olika klassrum. Slutsatsen var att mängden integritetsinskränkandefaktiskt hade en signifikant koppling med dåligförälder-ungdom relation för mödrar, men inte för fäder. Äveninteraktionen mellan mängden integritetskränkande och derasavsikt visade sig vara signifikant för mödrar. Dock fanns ingensignifikant relation för fäder.

APA, Harvard, Vancouver, ISO, and other styles

44

Siesa, M. E. "FRESHWATER COMMUNITIES AND BIOLOGICAL INVASIONS: ODONATA, AMPHIBIA AND PROCAMBARUS CLARKII." Doctoral thesis, Università degli Studi di Milano, 2011. http://hdl.handle.net/2434/154018.

Full text

Abstract:

This research work analyses processes and dynamics occurring during the early stages of a biological invasion in freshwater habitats. I analysed processes determining the Procambarus clarkii invasion and the impact on native amphibians and odonates that have complex life cycles, I surveyed 148 among temporary and permanent wetlands of running and standing waters in a region that is at the edge of the invasion range of P. clarkii, I performed repeated sampling sessions in each wetland obtaining both qualitative and quantitative data on freshwater communities, I characterized each wetland using standard parameters, and I used GIS software for the description of the surrounding landscape. I analysed all data using spatial models and considering the spatial autocorrelation. Data analysis showed that the environmental features are important in determining the early phases of the crayfish invasion; in the study area, P. clarkii spreads more frequently in association with large and permanent wetlands in human-altered landscapes, and the autocorrelation of its populations is stronger at distances up to 2500 m suggesting that dispersion affect invasion processes up to this distance. Further analysis showed that environment shapes both alien invasive species (AIS) and freshwater communities, but considering the optimal environmental features for P. clarkii and for amphibians and odonates, I observed important differences related to wetland size, depth, hydroperiod, exposition, presence of aquatic macrophytes, and surrounding landscape features. The observed relationships among distribution and composition of native communities and distribution of P. clarkii suggests that the invasive crayfish has only a limited direct impact on adult amphibians and odonates, but the analysis of juvenile stages of native communities (larvae of amphibians, larvae and exuviae of odonates) showed the dramatic loss of their abundance and richness in wetlands invaded by the crayfish, indicating that, despite adults attempt reproduction in invaded sites, P. clarkii causes, with its activities, the fall down of their reproductive success. This research confirms the strong negative impact of AIS on native communities. My data indicate that P. clarkii determines the loss of reproductive sites, and the decrement of the reproductive success when native populations use the invaded sites for breeding. This research highlights the importance of studying the early stages of an invasion, confirming that in this phase AIS populations have larger environmental needs that might make them more vulnerable at management actions. Through the analysis and description of the mechanisms determining the AIS impact on native communities, this research helps to identify the ongoing processes at early stages of the AIS invasion, and the consequences that the invasive crayfish will have in the near future, allowing managers to start conservation actions before that the invasion consequences become irreversible.

APA, Harvard, Vancouver, ISO, and other styles

45

Potgieter, Luke. "Casuarina invasions : a multi-scale assessment of an important tree genus." Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/86203.

Full text

Abstract:

Thesis (MSc)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: Understanding the processes that drive the invasion of non-native species is often essential for effective management. This thesis focuses on Casuarina spp. – an economically and ecologically important tree genus with taxa that have been widely disseminated by humans. I explore the effects certain taxa can have on community dynamics in recipient environments, investigate the factors that mediate invasion of Casuarina species, and from this aim to develop recommendations for managing the group. First, I assessed the global introduction history, invasion ecology and the evolution of management approaches of Casuarina. Ten of the 14 species in the genus have been introduced outside their native ranges to over 150 countries, but only three species are recorded as naturalized or invasive. As with other groups there is a correlation between native range size and invasiveness – the three invasive species also have the largest introduced ranges. Propagule pressure explains much more of the variance in observed invasiveness between Casuarina taxa than any known combination of life-history traits. Large-scale plantings of casuarinas in some climatically suitable areas have not yet resulted in large-scale invasions; there is a substantial global Casuarina invasion debt. Experiences in Florida and the Mascarene Islands highlight that casuarinas have the potential to transform ecosystems with significant control costs. Despite modest progress with managing invasions in some areas, substantial problems remain. As with most other invasive tree taxa, complex conflicts of interest are particularly challenging. Second, I looked at mechanisms underlying naturalization and assessed invasion risk at a regional scale. Here, I examined Casuarina cunninghamiana invasions in the south-western Cape of South Africa – the part of the country with the largest contiguous area climatically similar to the native range of the species. Propagule pressure is a key driver of naturalization of C. cunninghamiana populations in climatically suitable areas. The species also naturalizes in regions with suboptimal bioclimatic conditions, but then only very near (<10 m) planted trees. Risk models indicate that C. cunninghamiana is likely to spread across a greater region of the Western Cape than it currently occupies. Naturalized populations of C. cunninghamiana are young and expanding. The capacity of the species to resprout and attain reproductive maturity at an early age suggests that this species could become a widespread and damaging invader in South Africa. We conclude with some recommendations for management, and argue that if particular steps are taken (e.g. the immediate removal of all female plants from proximity to dams and water-courses; all future sales and plantings to be restricted to male plants) then it might be possible to safely utilise the species in future. Third, I examined the invasion dynamics of a single Casuarina species at the landscape scale. I explored how interactions between disturbance and invasion govern successional trajectories, using the remarkable invasion of C. equisetifolia on the volcanic island of Réunion. Invasive populations of C. equisetifolia have increased substantially in extent over 40 years. Lava flows have facilitated the spread of C. equisetifolia and invasion of this species has radically changed successional trajectories, increasing the rate of succession sevenfold. This case mirrors work done on Morella faya and Falcataria moluccana on Hawa'ii, which shows the extent to which invasive species can alter ecosystem function and benefit from natural disturbances generated by volcanic lava flows. The continued spread of C. equisetifolia poses a major threat to the small area of remaining native lowland rainforests on Réunion which cover < 2 % of their original extent. The studies in this thesis have uncovered patterns, processes and invasion risks for invasive trees that are not well represented in the literature. Some insights derived from well-studied tree genera, such as Acacia and Pinus, seem to apply fairly well to tree invasions in general. However, special ecological features of Casuarina species and the ways they are used by humans call for unique considerations when piecing together changing global distributions and creating effective strategies for management.
AFRIKAANSE OPSOMMING: ‘n Deeglike begrip van die prosesse wat die indringing van uitheemse spesies fasiliteer is noodsaaklik vir effektiewe besturing. Hierdie tesis fokus op Casuarine spp. – ‘n ekonomiese en ekologiese belangrike boom genus, met menigte spesies binne hierdie genus wyd verspreid deur mense. Ek ondersoek die effekte wat sekere taksa kan hê op die gemeenskap dinamika in die ontvanger omgewing, sowel as die faktore wat Casuarina indringing bemiddel, en deur hierdie doelwitte beoog ek om aanbevelings te maak aangaande die effektiewe bestuur van hierdie groep. Eerstens evalueer ek die invoerings geskiedenis van die genus wêreldwyd, die indringer ekologie en ook die evolusie van bestuurs benaderinge ten opsigte van Casuarina. Tien van die 14 spesies binne hierdie genus is ingevoer na meer as 150 verkillende lande buite hul inheemse streek, maar slegs drie van hierdie spesies word beskou as genaturaliseerd of indringers. Soos met ander groepe is daar ‘n korrelasie tussen inheemse streeks-grote en indringerheid – die drie indringer spesie het ook die grootste ingevoerde streke. Propaguul druk verduidelik die meerderheid van die variasie in die waargeneme indringer Casuarina taksa as enige ander kombinasie van lewens geskiendenis eienskappe. Groot skaalse plantasies van casaurina taksa in sommige klimaat geskikste areas het nog nie na groot skaalse indringing gelei nie; daar is wêreldwyd ‘n aansienlike Casuarina indringer skuld. Ervarings in Florida en die Mascarene Eilande beklemtoon dat casuarinas die potensiaal het om ekosisteme te transformeer met geweldige beheer omkostes. Ten spyte van redelike vordering aangaande die besturing van indringers in sekere areas, is daar steeds aansienlike probleme. Soos met meeste ander indringer boom taksa, is die botsing van belange veral uitdagend. Tweedens, het ek die meganismes van die naturalisasie bemiddel as ook indrigner risiko op die plaaslike skaal ondersoek. In hierdie deel het ek Casuarina cunninghamiana indringers in die Suid-Wes Kaap van Suid-Afrika ondersoek – die deel van die land met die grootste aangrensende area wat ‘n ooreenstemmend klimaat het met die inheemse areas van die spesie. Propaguul druk is ‘n belangrike drywer vir die naturalisasie van C. cunninghamiana populasies in areas met ‘n geskikte klimaat. Hierdie spesie het ook genaturaliseer in areas met suboptimale klimaats kondisies, maar slegs baie naby (<10m) aan plantasies. Risiko modelle dui aan dat C. cunninghamiana die potensiaal het om te versprei na ander dele van die Wes-Kaap waar dit huidiglik afwesig is. Natuurlike populasies van C. cunninghamiana is jonk en in die proses van uitbreiding. Die kapasiteit van die spesie om te hergrooi en voortplantings volwassenheid op n vroeë ouderdom te beriek stel voor dat hierdie spesie ‘n wyd verspreide en skadelike indringer kan word. Ons sluit af met aanbevelings vir effektiewe bestuur en stel voor dat indien sekere stappe geneem word (bv. ontmiddelike verwydering van die vroulike plante naby damme en water areas; alle verdere verkope beperk word tot manklike plante), dit moontlik sal wees om hierdie spesie op ‘n omgewings-veilige manier te gebruik. Derdens het ek die indringing dinamika van ‘n enkele Casuarina spesie on landskap skaal ondersoek. Ek het verken hoe interaksies tussen versteurings en indringing plantegroei prosesse dryf, deur gebruik te maak van die merkwaardige indringing van C. equisetifolia op die vulkaniese eiland van Reunion. Indringer populasies van C. equisetifolia het aansienlik vermeerder in die afgelope 40 jaar. Lava vloei het die verspreiding van C. equisetifolia gefasiliteer en indringing van hierdie spesie het plantegroei prosesse radikaal verander, deur die tempo van opvolging sewevoudig te verhoog. Hierdie studie weerspieël werk wat op Morella faya en Falcataria moluccana in Hawa’ii gedoen is en toon tot watter mate indringer spesies ekosisteem funksies kan verander en voordeel kan trek uit natuurlike versteurings wat gegenereer word deur vulkansiese lava vloei. Die voortgesette verspreiding van C. equisetifolia hou ‘n groot bedreiging in vir oorblywende inheemse laeveld reënwoude op Reunion wat tans < 2% van hul oorspronlike area dek. Die studies in hierdie tesis het patrone, prosesse en indringer risikos vir indringer bome ontdek wat nie goed in die literatuur verteenwoodig word nie. Sommige insigte wat deur goed bestudeerde boom genera, soos Acacia en Pinus, ontdek is, blyk om redelik goed van toepassing te wees op boom indringers in geheel. Alhoewel, sekere ekologiese funksies van Casuarina spesies en die manier wat hulle deur mense gebruik word, vra vir unieke oorwegings aangaande hul wêreldwye verspreiding en effektiewe beheer.

APA, Harvard, Vancouver, ISO, and other styles

46

Lindon, Heather Lynn. "Genetic variation in Bromus tectorum (L.) (Poaceae) in the Eastern Mediterranean region." Online access for everyone, 2007. http://www.dissertations.wsu.edu/Thesis/Spring2007/H_Lindon_042707.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

47

Riley, Leslie Anne. "Estimating invasive species impact interaction strengths, abundance and the role of productivity in a freshwater invasion /." Pullman, Wash. : Washington State University, 2008. http://www.dissertations.wsu.edu/Dissertations/Fall2008/l_riley_111808.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

48

Tavares, Joana Flor R. "Assessing the importance of biological uncertainties to the control of species introductions via ballast water /." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 90 p, 2009. http://proquest.umi.com/pqdweb?did=1654487631&sid=3&Fmt=2&clientId=8331&RQT=309&VName=PQD.

Full text

APA, Harvard, Vancouver, ISO, and other styles

49

Richard, Joëlle. "Crepidula fornicata : un modèle biologique pour l'étude du rôle de la variabilité des caractères phénotypiques (reproduction, croissance et nutrition) sur les processus de colonisation en milieu marin." Brest, 2005. http://www.theses.fr/2005BRES2033.

Full text

Abstract:

L’étude des processus de l’invasion a été basée sur le schéma conceptuel de l’invasion d’un système par une espèce allochtone, à savoir la succession des phases : i) phase d’installation, ii) phase d’expansion et, hi) phase d’intégration. Le modèle utilisé dans cette étude es Crepidula fornicata, espèce originaire de la côte Est américaine et introduite accidentellement en Europe au début du 19ème siècle. La caractérisation de la reproduction et de la croissance de cette espèce en rade de Brest a été utilisée afin de déterminer ses traits particuliers pouvant promouvoir la phase d’installation. Il en ressort trois points essentiels vie en chaîne avec reproduction « autosuffisante », fenêtre annuelle de reproduction étendue, émissions gamétiques multiples conduisant à augmenter la probabilité du succès du recrutement. L’étude de la phase d’expansion à deux échelles spatiales, européenne et celle de la rade de Brest, a démontré une très forte plasticité phénoptypique au niveau des paramètres de la reproduction et de la croissance. Cette plasticité est aussi forte à petite échelle qu’à grande échelle et peut participer à l’explication de la réussite de cette phase du processus de l’invasion. La phase d’intégration, a été abordée sous la forme de l’étude de la compétition trophique entre la crépidule et Pecten maximum par la méthode de isotopes stables. Bien que aucune réponse tranchée n’ait pu être apportée à cette question, certains points intéressants ont pu être dégagés, notamment une très forte variabilité inter-individuelle de la crépidule. In fine, les résultats de ce travail ont permis d’approcher l’histoire de la colonisation de la crépidule en rade de Brest
The study of the invasion process was based on the conceptual scheme of the invasion of one system by an allochtone species, within the trame of three known phases of succession: i) installation phase, ii) expansion phase and, iii) integration phase. The modal used in this study is Crepidula fornicata, n species native to the East coast of America and introduced accidentally in to Europe at the beginning of the l9th century. The characterisation of reproduction and growth of the species in the Bay of Brest was used to determine the particular traits of the species which promoted the installation phase. It presents three essential points: life in stacks with an “auto-sufficient” reproduction, a wide annual window of reproduction and multiple gamete emissions increasing the probability of settlement success. The study o the expansion phase in two spatial scales, European and Bay of Brest, has demonstrated a high phenotypic plasticity for the reproduction and growth parameters. This plasticity was as high in the small scale as in the larges scale and participates in explaining the success of this phase of the invasion process. The integration phase was tackled by the study of trophic competition between Crepidula fornicata and Pecten maximus using the stable isotopes method. Even though no clearcut answer was supplied to this question, some interesting points were found, notably the high interindividual variability of Crepidula fornicata. In conclusion, the results of this work permitted a clearer picture of the colonisation of the slipper limpet in the Bay of Brest

APA, Harvard, Vancouver, ISO, and other styles

50

Guo, Zhiqiang. "Séparation de niche entre deux espèces invasives de gobies." Toulouse 3, 2012. http://thesesups.ups-tlse.fr/1842/.

Full text

Abstract:

Comprendre la coexistence d'espèces et le maintien de la biodiversité est depuis longtemps un point central en écologie des communautés. La notion de niche, ou théorie des niches, a été largement développée depuis l'explication par Darwin de l'impressionnante diversité de la vie sur Terre. Celle-ci est considérée comme un mécanisme majeur permettant la coexistence d'espèces compétitrice au sein des communautés écologiques. La différenciation en niches spécifiques implique des différences spatiales, trophiques, temporelles et/ou une combinaison de celles-ci. Dans cette étude, la sélection d'habitat, les traits d'histoire de vie, la composition alimentaire et les comportements alimentaires de deux espèces invasives de gobiidés, très abondantes et écologiquement similaires (Rhinogobius cliffordpopei et Rhinogobius giurinus), sont comparées afin de tester si la séparation de niches est un mécanisme qui peut potentiellement permettre leur coexistence stable dans le lac Erhai (un lac superficiel d'eau douce du plateau de Yunnan-Guizhou en Chine). Les résultats montrent qu'il y a séparation des niches de ces deux espèces le long d'un axe d'habitat, d'un axe alimentaire (pour l'habitat littoral et pour les adultes et sub-adultes), et d'un axe temporel (en termes de cycles de ponte). Spécifiquement, R. Giurinus occupe principalement les habitats profonds (PH) alors que R. Cliffordpopei occupe principalement l'habitat littoral (LH). Des analyses corrélatives ont montré que l'abondance de R. Giurinus est positivement associée avec la profondeur de l'eau et les substrats composés de sables limoneux et grossiers, tandis que la distribution de R. Cliffordpopei est corrélée aux fortes densités en macrozooplankton, les fortes abondances en autres espèces de poissons, les fortes concentrations en oxygène dissout et les fortes densités en macrophytes submergées. Concernant le partage en ressources alimentaires, les deux espèces ont montré de clairs changements au niveau de leur diète ontogénique ainsi que dans les patrons de partage des aliments qui sont significativement différents selon le stade de leur histoire de vie et les habitats. Pour les deux espèces, les juvéniles consomment principalement du macrozooplancton (cladocères et copépodes), alors que les sub-adultes et les adultes consomment principalement des larves de Chironomidae et de Tubificidae. En LH, les sub-adultes et adultes des deux espèces présentent des différences significatives dans leur régime alimentaire alors que les juvéniles ont des régimes similaires. Cependant, en PH et SH, nous n'avons trouvé aucune preuve de partage des ressources alimentaires, quelque soit le stade de vie (juvéniles, sub-adultes et adultes). R. Cliffordpopei et R. Giurinus présentent un partage de leur niche temporel. En effet, les deux espèces ont des débuts de période de reproduction ainsi que des pics de reproduction à des moments différents. R. Cliffordpopei se reproduit de Février à Juin avec un pic de ponte entre Mars et Avril alors que l'activité de reproduction de R. Giurinus se fait entre Avril et Août avec un pic de ponte pendant les mois de Mai et Juin. Ces différences ont conduit à un partage temporel des cohortes de taille similaire entre les deux espèces, en particulier pour les larves de petite taille et les juvéniles, qui sont presque exclusivement zooplanctivores et qui exploitent les mêmes ressources alimentaires dans le lac. Cependant, l'activité nycthémérale (activité de locomotion) et le rythme d'alimentation varient légèrement entre les deux espèces, i. E. Les deux espèces présentent deux pics d'activités (6:00 - 10:00 et 18:00 - 22:00) et deux principales périodes d'alimentation (6:00 - 10:00 et 18:00 - 22:00) sur un laps de temps de 24h pour les quatre saisons. De plus, notre étude apporte une compréhension complète de la sélection d'habitat et des traits d'histoire de vie (i. E. Patron de croissance, biologie de la reproduction et dynamique de population) de ces deux espèces invasives de gobies. Ces résultats biologiques sont essentiels pour la mise en place de programmes économiquement et écologiquement efficaces de contrôle pour les deux espèces de ravageurs. De nouveau programmes de gestion sont fortement recommandés en vue de ces résultats. Par conséquent, dans cette étude, plusieurs programmes de restauration spécifiques et innovants sont proposés pour améliorer les stratégies actuelles de gestion dans une perspective de réduction des coûts et une meilleure efficacité
Understanding species coexistence and maintenance of biodiversity in nature has long been a central issue in community ecology. The niche or niche-based theory has been developed since Darwin's explanation of an amazing diversity of life on the Earth and considered as a major theory explaining the coexistence among competing species within ecological communities. Niche differentiation basically involves spatial, trophic, temporal and/or a combination of them. In the present study, habitat selections, life-history characteristics, diet compositions and feeding behaviors of two highly abundant and ecologically similar invasive goby species (Rhinogobius cliffordpopei and Rhinogobius giurinus) are compared to test whether niche separation is a potential mechanism allow ing the stable coexistence of them in Lake Erhai (a shallow freshwater lake in the Yunnan-Guizhou Plateau of China). The results demonstrated that these two species showed niche separation along habitat axis, food axis (in littoral habitat for sub-adults and adults), and temporal axis in terms of spawning cycles. Specifically, R. Giurinus mostly occupied profundal habitat (PH) while R. Cliffordpopei mainly used littoral habitat (LH). Correlation analyses revealed that the abundance of R. Giurinus was positively associated with deep water, silt and coarse sand substrata, whereas the distribution of R. Cliffordpopei was positively associated with high densities of macrozooplanktons and high abundances of other fish species, high concentration of dissolved oxygen and high densities of submerged macrophytes. For food resources partitioning, they showed a clear ontogenetic diet shifts and significantly different food partitioning patterns at different life-history stages and habitats. For both species, macrozooplanktons (Cladocera and Copepoda) were the main food for juveniles while sub-adults and adults primarily consumed Chironomidae larvae and Tubificidae. In LH, sub-adults and adults of the two species significantly differed in their diet compositions while juveniles showed similar diets. In PH and SH, however, there was no evidence for food partitioning between species at all the three life-history stages. R. Cliffordpopei and R. Giurinus showed temporal niche partitioning as they exhibited different onsets of spawning and peaks of spawning seasons, and thus different growth and population dynamics, though both of them are short-lived species with a life span of about one year. R. Cliffordpopei spawned from February to June with a spawning peak occurring in March and April. Spawning activity of R. Giurinus occurred from April to August with a peak activity during May and June. These differences resulted in a temporal partitioning for similar-sized cohorts, especially for small-sized larvae and juveniles, which were almost exclusively zooplanktivorous and exploited the same food resources in the lake. Moreover, their different spawning cycles led to different peak seasons for the highest population density of the two species. However, the diel activity (locomotory activity) and feeding rhythm varied slightly between them, i. E. Both species showed two peaks of activity (6:00 - 10:00 and 18:00 - 22:00) and two main feeding periods (6:00 - 10:00 and 18:00 - 22:00) in the four seasons. Moreover, our study provides a full understanding of habitat selection and life-history characteristics (i. E. Growth pattern, reproduction biology and population dynamic) of the two invasive gobies. These findings are crucial biological aspects for an economically and ecologically effective control programs to the two abundant pest species. The further management programs are highly recommended to give a careful consideration of these findings. Therefore, several specific remediation is suggested to improve the current management strategies from the perspective of cost-efficiency

APA, Harvard, Vancouver, ISO, and other styles

Dissertations / Theses on the topic 'Invasions'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles