To see the other types of publications on this topic, follow the link: Native and invasive populations.
Dissertations / Theses on the topic 'Native and invasive populations'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Native and invasive populations.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Sarvela, Erika Renee. "DIFFERENTIATING BETWEEN INVASIVE AND NATIVE POPULATIONS OF BIGHEAD AND SILVER CARP USING MS-AFLP." OpenSIUC, 2020. https://opensiuc.lib.siu.edu/theses/2807.
Full textAbstract:
When a species is introduced outside their native range, the genetic diversity of the introduced population is generally decreased due to the founder effect, and the fitness of individuals in the introduced population may decrease due to inbreeding depression. Invasive species are a paradox to this paradigm because while the initial population size of an invasive species may be small in their non-native range, the individuals are able to survive, eat, and reproduce so successfully, that they have deleterious effects on native species. One mechanism that invasive species use to overcome a lack of genetic diversity and adapt to their new environment is CpG methylation, a heritable and environmentally influenced epigenetic modification that regulates the expression of certain genes to alter phenotypes without altering an organism’s DNA sequence.Bighead and silver carps, two species of bigheaded carp native to eastern Asia, are believed to have been introduced to the United States in the 1970s. Since that time, populations of both bighead and silver carp have surged, particularly in the Mississippi River drainage, where they compete with native planktivores for food, injure boaters, and threaten the multi-million dollar fisheries industry in the Great Lakes. In this study, methylation-sensitive amplified fragment length polymorphisms (MS-AFLPs) were used to analyze the genetic and epigenetic diversity of bighead and silver carp from the Gan, Pearl, and Yangtze rivers in their native China and from the Illinois River in the United States. While the heterozygosity of silver carp in Illinois was not found to be significantly lower than that of silver carp in China, the silver carp in Illinois did show a significantly higher level of methylation compared to Chinese silver carp. There is evidence that CpG methylation may play a significant role in allowing silver carp to adapt and thrive in an introduced environment.
2
Harrison, Laura Jane. "Density and reproduction in native and invasive Linaria vulgaris populations at multiple spatial scales." Thesis, University of Leeds, 2013. http://etheses.whiterose.ac.uk/5751/.
Full textAbstract:
Comparing invasive plants in their native and invasive ranges can answer questions about invasion mechanisms and inform management options. However, few studies have considered how density varies with spatial scale or how individual fitness is affected by conspecific density at different spatial scales. A census was carried out of 15 native UK populations of the perennial herb Linaria vulgaris Miller (Plantaginaceae), and of seven invasive populations from a climatically matched area of Alaska. There was no difference in density between native and invasive populations when compared at spatial scales of 0.0625, 0.5, 1 or 4 m2, or when density was measured as a mean field of each population. However, invasive populations covered a larger area, so density was greater at broad spatial scales. The effect of conspecific density on the height and reproduction of ramets varied with the spatial scale and between ranges. Invasive ramets were shorter than native ramets, and therefore produced fewer mature fruit. However, this was more than compensated for by the greater number of viable black seed in invasive fruit than native fruit. One of the reasons for this was the presence of the seed feeding weevil Rhinusa antirrhini in over half of the native, but none of the invasive, fruit. The majority of seed was estimated to fall within 1 m of maternal plants when surrounded with vegetation, but seed travelled further in an unvegetated area. Germination rates were very low in both the field and laboratory. The thesis ends with a description of the biology of L. vulgaris. This work demonstrates that invasion and escape from natural enemies can occur at a broad spatial scale, without increased density and vigour at a fine spatial scale.
3
Berman, Maïa. "Impacts of anthropogenic fires and invasive ants on native ant diversity in New Caledonia : from genes to communities." Thesis, Montpellier 2, 2012. http://www.theses.fr/2012MON20086/document.
Full textAbstract:
La destruction de l'habitat, les invasions biologiques et leur interaction sont des menaces majeures pour la biodiversité. La Nouvelle-Calédonie est menacée à la fois par des feux d'origine humaine, et par des fourmis invasives : il est important de comprendre leur impact sur ce biotope unique. Pour ce faire, une approche hiérarchique intégrant différents aspects de la biodiversité (composition, structure et fonction) a été adoptée. Les fourmis ont une grande importance écologique, en particulier en milieu tropical, et leur classification en groupes fonctionnels facilite l'interprétation de leur réponse aux perturbations environnementales. Les objectifs de cette étude étaient donc d'évaluer les impacts des feux, des fourmis invasives, et de leur interaction, sur les fourmis natives de Nouvelle-Calédonie, et ce à différentes échelles spatiales (globale, régionale, locale) et temporelles (court et long terme), ainsi qu'à divers niveaux d'organisation biologique (communautés, espèces, gènes). L'étude contribue à une meilleure connaissance de la myrmécofaune calédonienne, en révélant l'absence de fourmis souterraines spécialisées, et en documentant la distribution et composition des communautés de fourmis à l'échelle de l'île, en lien avec l'habitat et les fourmis exotiques. Les mécanismes par lesquels les feux impactent les fourmis natives, y compris en association avec les fourmis invasives, sont révélés. Le feu, en créant les conditions de micro- et macrohabitat favorisées par les fourmis invasives, facilite l'invasion, qui cause ensuite d'avantage de perte de diversité, soit quelques années après un incendie ou dans le contexte de la fragmentation à long terme. L'approche hiérarchique a permis de détecter des réponses contrastées au niveau des espèces et de la génétique, liées à différents traits d'histoire de vie, en plus des réponses mesurées au niveau des communautés. Cette étude souligne l'avantage d'une approche holistique pour adresser des problèmes liés à la biodiversitéHabitat destruction, biological invasions and their interaction are global drivers of biodiversity loss. The New Caledonian hotspot of biodiversity is threatened by both anthropogenic fires and invasive ants: it is important to understand their impacts on its biota. Because biodiversity spans several levels of organisation (from genes to communities) and relates to different attributes (compositional, structural and functional), this thesis takes a hierarchical approach to address this issue. Ants are of great ecological importance, especially in tropical biomes, and their classification into functional groups provides a global framework for analysing their response to disturbance. My aims were therefore to investigate the impacts of anthropogenic fires and invasive ants, and their interaction, on the native New Caledonian ant fauna at different spatial (global, regional, local) and temporal (short and long term) scales, and at different levels of biological organisation (community, species, genes). The study contributes to an improved knowledge of the New Caledonian ants, by revealing the lack of specialised subterranean species, and by investigating island-scale patterns of ant communities, in relation to habitat and invasion. The mechanisms by which fire impacts native ants, either as a standalone process or in association with invasion could be identified. In particular, I show that fire, by creating macro- and microhabitats favoured by invasive ants, facilitates invasion, which then causes further diversity declines, either in the short- (post-burning) or long-term (forest fragmentation). The hierarchical approach used enabled the detection of contrasting trait-derived responses at the species and genetic level, in addition to responses measured at the community level. This study highlights the advantage of a holistic approach to investigating biodiversity-related issues
4
Wilson, Sarah Jane. "Freshwater macroinvertebrate communities on exotic and native plants." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=101665.
Full textAbstract:
Aquatic plants play an important role in the survival and proliferation of invertebrates in freshwater ecosystems. Exotic plants are now common in North American lakes and rivers, where they may displace native plants, thereby potentially altering epiphytic invertebrate communities. Differences in aquatic invertebrate communities on native and exotic plants are examined here through (1) a meta-analysis of published data, and (2) two field surveys in northeastern North America that compared invertebrates on the exotic Myriophyllum spicatum and Potamogeton crispus to those on their native congeners. The meta-analysis revealed that exotic plants generally support lower invertebrate abundance than do natives, while invertebrate taxa richness tends to be similar on exotic and native plants. The field surveys demonstrated that M. spicatum and P. crispus support significantly different invertebrate densities and lower taxa richness than their structurally similar native congeners. These results suggest that the replacement of native plants by exotics---even those with similar morphology---may cause concomitant changes to aquatic ecosystems.
5
Romanek, Daniel M. "Competition and allelopathic effects of native and invasive populations of Lonicera maackii: a comparative analysis." Wright State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=wright1261414983.
Full text
6
Beckmann, Michael [Verfasser]. "In Search of Similarities in Invasive Plant Species - Comparing Native and Invasive Populations of Six Clonal Plant Species in Germany and New Zealand / Michael Beckmann." Kiel : Universitätsbibliothek Kiel, 2018. http://d-nb.info/1153400855/34.
Full text
7
Tsutsui, Neil Durie. "Population genetics of the invasive Argentine ant in its native and introduced ranges /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2000. http://wwwlib.umi.com/cr/ucsd/fullcit?p9984805.
Full text
8
Jelbert, K. "The comparative demography of invasive plants." Thesis, University of Exeter, 2018. http://hdl.handle.net/10871/34994.
Full textAbstract:
Biodiversity, ecosystems, industry and human health are threatened by invasive plant species. The costs of mitigating damages run into billions of pounds per annum. Fundamental to the control of invasive plant species is an ability to predict which species will become invasive. Yet identification of predictive differences between invasive and non-invasive species has proven difficult to pinpoint. In this thesis I identify several weaknesses within published literature, and using field experiments and meta-analyses we address these to find consistent predictors of invasiveness amongst plants. Specifically, I recognize that predictors of invasiveness can be identified by studying plant species in the native range because species may undergo phenotypic and demographic changes following naturalization (Chapters 2 – 5). I also recognize the importance of comparing globally invasive and non-invasive species, and the importance of accounting for phylogenetic relationships so as not to inflate or conceal differences (Chapters 2 – 4). Finally, I investigate whether particular analyses are more appropriate for investigating life history and demographic differences (Chapter 5). This thesis comprises an introductory chapter (Chapter 1), four data chapters (Chapters 2 - 5) and a general discussion (Chapter 6). Chapters 2 and 3 compare life history traits of plant species known to be invasive elsewhere, with their exported but non-invasive sympatric relatives in the native range. Chapter 4 utilizes Population Projection Matrices held within the COMPADRE Plant Matrix Database, to compare demographic projections of stable and transient dynamics of invasive and non-invasive plants; and Chapter 5 compares ten metrics, derived from Population Projection Matrices, of seven invasive species between the native and invaded range to determine if there are demographic or life history differences that facilitate invasion, and to identify those analyses that are most likely to reveal such differences. I find reproductive capacity to be a predictor of invasiveness, and that analyses of transient dynamics are more likely than analyses of projected stable dynamics to reveal demographic or life history differences between invasive and non-invasive species or populations of plants. I discuss these findings in the context of invasive risk assessment protocols and highlight future research opportunities.
9
Snyder, Matthew Robert. "Environmental DNA Detection and Population Genetic Patterns of Native and Invasive Great Lakes Fishes." University of Toledo / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1564680483342507.
Full text
10
Bailey, R. J. E. "Predatory interactions between the invasive amphipod Gammarus tigrinus and the native Opossum shrimp Mysis relicta." Thesis, Queen's University Belfast, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368463.
Full text
11
Hertzberg, Jillian M. "Investigating the effects of the invasive Euonymus fortunei on populations of native species in an on campus forest and assessing campus population social value in developing a protection plan." Miami University Honors Theses / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=muhonors1303763035.
Full text
12
Cairns, Christine Elizabeth. "Effects of invasive Africanized honey bees (Apis Mellifera Scutellata) on native stingless bee populations (Meliponinae) and traditional Mayan beekeeping in Central Quintana Roo, Mexico." FIU Digital Commons, 2002. http://digitalcommons.fiu.edu/etd/1970.
Full textAbstract:
The Maya of the Yucatan region have a long history of keeping the native stingless bees (subfamily Meliponinae). However, market forces in the last two decades have driven the Maya to favor the use of invasive Africanized honey bees (Apis mellifera scutellata) for producing large quantities of high quality honey which has an international market. Furthermore, the native bees traditionally used by the Maya are now disappearing, along with the practice of keeping them.
An interdisciplinary approach was taken in order to determine the social factors behind the decrease in stingless beekeeping and the ecological driving forces behind their disappearance from the wild. Social research methods included participant observation with stingless beekeepers, Apis beekeepers, and marketing intermediaries. Ecological research methods included point observations of commonly known melliferous and polliniferous plants along transects in three communities with different degrees of human induced ecosystem disturbance.
The stingless bee species most important to the Maya, Melipona beecheii, has become extremely rare, and this has caused a breakdown of stingless beekeeping tradition, compounded with the pressure of the market economy, which fuels Apis beekeeping and has lessened the influence of traditional practices. The community with the heaviest amount of human induced ecosystem disturbance also had the lowest degree of bee diversity, while the area with the most intact ecosystem had the highest diversity of stingless bees, though Apis mellifera was still the dominant species. Aggressive competitive behavior involving physical attacks by Apis mellifera against stingless bees was observed on several occasions, and this is a new observation previously unreported by science. Human induced disturbance of the ecosystem and competition with the Africanized honey bee are affecting the diversity and abundance of various bee species.
13
Wang, Shasha [Verfasser]. "Is fouling a determinant of invasion success? - A comparison of the susceptibility to fouling between native and non-native populations of Gracilaria vermiculophylla / Shasha Wang." Kiel : Universitätsbibliothek Kiel, 2017. http://d-nb.info/1129685470/34.
Full text
14
Gleen, Wendy. "Life on the Edge: Population and Behavioural Responses of the Native Bush Rat to Invasive Species at the Urban Edge." Thesis, The University of Sydney, 2013. http://hdl.handle.net/2123/9822.
Full textAbstract:
Invasive species are a common feature of urban edges and pose a significant threat to biodiversity globally. While it is well known that urban edges provide a point of incursion for invasive species into bushland, there is poor understanding of the effect this has on native wildlife. In this thesis I explored bush rat Rattus fuscipes responses to two invasive species, the weed lantana Lantana camara, and the black rat Rattus rattus at the urban edge. Using a multi-scaled and mechanistic approach, I examined bush rat population abundance and demographic patterns in weedy urban edge, weedy core and core macrohabitat types and used a Giving Up Density experiment to examine perceived predation risk in weedy and native habitat. I demonstrated that urban edges were poor quality habitat for bush rats, and found that dense lantana functioned as a buffer, apparently ameliorating other deleterious edge effects. Lantana reduced bush rat Perceived Predation Risk (PPR), however plant structure was more important than species as a predictor of PPR. I then explored whether competition from black rats explains poor habitat quality for bush rats at the urban edge. Contrary to prediction there were no negative associations in population abundance between black and bush rats which co-existed at several sites. This lack of evidence for inter-specific competition may be explained by the patchy distribution of black rats in the study area, or the presence of lantana which may have reduced competition by providing visual and physical barriers, facilitating co existence. My results demonstrate that invasive species do not always have a negative impact on fauna at urban edges in Australia, and in fact may enhance habitat quality at certain ecological scales. Further work into the mechanistic basis for the nature of the interactions between native and alien species at urban edges is warranted in order to balance the competing consequences of the management of entrenched alien species.
15
Zhang, Bo. "Evolutionary genetics and human assisted movement of a globally invasive pest (Russian wheat aphid : Diuraphis noxia)." Thesis, Queensland University of Technology, 2012. https://eprints.qut.edu.au/60959/1/Bo_Zhang_Thesis.pdf.
Full textAbstract:
This PhD study has examined the population genetics of the Russian wheat aphid (RWA, Diuraphis noxia), one of the world’s most invasive agricultural pests, throughout its native and introduced global range.
Firstly, this study investigated the geographic distribution of genetic diversity within and among RWA populations in western China. Analysis of mitochondrial data from 18 sites provided evidence for the long-term existence and expansion of RWAs in western China. The results refute the hypothesis that RWA is an exotic species only present in China since 1975. The estimated date of RWA expansion throughout western China coincides with the debut of wheat domestication and cultivation practices in western Asia in the Holocene. It is concluded that western China represents the limit of the far eastern native range of this species. Analysis of microsatellite data indicated high contemporary gene flow among northern populations in western China, while clear geographic isolation between northern and southern populations was identified across the Tianshan mountain range and extensive desert regions.
Secondly, this study analyzed the worldwide pathway of invasion using both microsatellite and endosymbiont genetic data. Individual RWAs were obtained from native populations in Central Asia and the Middle East and invasive populations in Africa and the Americas. Results indicated two pathways of RWA invasion from 1) Syria in the Middle East to North Africa and 2) Turkey to South Africa, Mexico and then North and South America. Very little clone diversity was identified among invasive populations suggesting that a limited founder event occurred together with predominantly asexual reproduction and rapid population expansion. The most likely explanation for the rapid spread (within two years) from South Africa to the New World is by human movement, probably as a result of the transfer of wheat breeding material. Furthermore, the mitochondrial data revealed the presence of a universal haplotype and it is proposed that this haplotype is representative of a wheat associated super-clone that has gained dominance worldwide as a result of the widespread planting of domesticated wheat.
Finally, this study examined salivary gland gene diversity to determine whether a functional basis for RWA invasiveness could be identified. Peroxidase DNA sequence data were obtained for a selection of worldwide RWA samples. Results demonstrated that most native populations were polymorphic while invasive populations were monomorphic, supporting previous conclusions relating to demographic founder effects in invasive populations. Purifying selection most likely explains the existence of a universal allele present in Middle Eastern populations, while balancing selection was evident in East Asian populations. Selection acting on the peroxidase gene may provide an allele-dependent advantage linked to the successful establishment of RWAs on wheat, and ultimately their invasion potential.
In conclusion, this study is the most comprehensive molecular genetic investigation of RWA population genetics undertaken to date and provides significant insights into the source and pathway of global invasion and the potential existence of a wheat-adapted genotype that has colonised major wheat growing countries worldwide except for Australia. This research has major biosecurity implications for Australia’s grain industry.
16
Piacenza, Teresa. "Population Densities of the Cuban Treefrog, Osteopilus septentrionalis and Three Native Species of Hyla (Hylidae), in Urban and Natural Habitats of Southwest Florida." [Tampa, Fla] : University of South Florida, 2008. http://purl.fcla.edu/usf/dc/et/SFE0002392.
Full text
17
Cilliers, Charl Daniel. "Post-fire effects of invasive exotic plants on seed banks, regeneration, soil chemistry and selected soil microbial populations in the Silvermine Nature Reserve, Cape Peninsula, South Africa." Thesis, Stellenbosch : Stellenbosch University, 2002. http://hdl.handle.net/10019.1/53006.
Full textAbstract:
Thesis (MSc) -- University of Stellenbosch, 2002.ENGLISH ABSTRACT: The fires, which occurred during January 2000 on the Southern Cape Peninsula, Cape Province, South Africa, focused attention on the importance of sound, informed management of exotic plant invaders in fynbos, especially at the urban interface. The fires also highlighted the relative lack of knowledge about the combined impacts of fire, exotic plants and the exotic-clearing programme on soil seed banks and regeneration. This study examines soil borne seed banks, regeneration, soil chemistry and micro biota in different postfire environments, focusing on three components of exotic plant management: The post-fire effects of standing invasive exotic plants; stacks of slashed exotic plant material which were deliberately burnt and stacks reduced to heat scars by a wildfire. The primary hypothesis addressed is that post-fire vegetation regeneration patterns, seed bank diversity and seed bank abundance are linked to pre-fire vegetation characteristics and, in particular, to the treatment of exotic plant species. It is also hypothesised that soil microbe population sizes are linked to pre-fire vegetation and soil chemical composition. Differences in soil seed banks, soil micro biota and vegetation regeneration patterns occur in different post-fire environments. High volumes of (live or dead) woody exotic biomass negatively impact upon postfire indigenous species diversity and abundance, both above and below-ground. Soil seed banks and above-ground regeneration decline with increasing fire intensity, wildfire burnt stack treatments showing the largest declines followed by wildfire burnt standing exotics, control burnt stacks, wildfire burnt cleared areas and wildfire burnt Mountain Fynbos treatments. Persistent indigenous seed banks are found under some exotic dominated stands. Heat damage, associated with high woody exotic biomass, affects seeds of all species into deep soil layers. Depth of burial is a more important determinant of seed survival during fires than seed size. Soil microbial populations are variably affected by exotic plants, their management and increases in fire intensity. The most drastic microbial population changes are in post-fire treatments of high exotic plant biomass. Soil chemistry affects microbial population sizes as does seasonal climatic changes. In this thesis vegetation, seed bank and microbial responses to various exotic plant management practices are shown and management recommendations are made. Keywords: exotic plants, fire, Fynbos Siome, microbes, post-fire succession, soil seed banks.
AFRIKAANSE OPSOMMING: Die Januarie 2000 vure op die Suid Kaapse Skiereiland het fokus gerig op die belangrikheid van goeie, ingeligte bestuur van uitheemse indringerplante in fynbos, veral naby stedelike gebiede. Die vure het ook 'n relatiewe .gebrek aan kennis aangaande die gekombineerde impakte van vuur, uitheemse plantegroei en indringer plant beheer programme op grond saadbanke en die hergroei van plante na 'n vuur aan die lig gebring. Hierdie projek bestudeer die invloed van vuur op grond saadbanke, hergroei van plante, grond chemie en mikro-organismes. Die klem lê op drie komponente van uitheemse plant bestuur: waar staande uitheemse plante voorkom; waar skoongekapte uitheemse plante in hope gestapel is en gekontraleerd gebrand is en waar soortgelyke hope in 'n onbeplande weghol vuur gebrand is. Die primêre hipotese is dat plant herstelpatrone, saadbank diversiteit en grootte gekoppel is aan veldtoestande voordat daar gebrand is, en veral aan die bestuur van uitheemse plantspesies. Nog 'n sentrale hipotese is dat die grootte van grond mikrobiale populasies gekoppel is aan veld toestande voor die brand en aan grond chemiese samestelling. Hierdie studie dui verskille aan in grond saadbanke, mikro-organismes en plant hergroeipatrone onder verskeie toestande na vuur. Die brand van hoë volumes (lewende of dooie) houtagtige uitheemse plant biomassa benadeel inheemse plant spesie diversiteit en getalle (bo en onder die grond oppervlak). Grond saadbanke neem af met vehogings in vuur intensiteit. Die grootste afnames is in wegholvuur gebrande gestapelde uitheemse plantmateriaal gevolg deur wegholvuur gebrande staande uitheemse plante, opsetlik gebrande hope uitheemse plante, gebrande skoongekapte areas en wegholvuur gebrande Berg Fynbos. Ou inheemse saadbanke is gevind onder sommige areas wat voor die vuur oorheers was deur uitheemse plantegroei. Hitteskade, geassosieer met hoë volumes houtagtige uitheemse biomassa, affekteer sade van alle spesies tot diep in die grond. Saad oorlewing tydens brande is meer geaffekteer deur diepte van begrawing in die grond as deur saad grootte. Grond mikro-organisme populasies is geaffekteer deur uitheemse indringer plante, die bestuur van uitheemse plante en vuur intensiteit. Die grootste veranderinge is waar die biomassa van uitheemse plantegroei baie hoog is. Grond chemiese samestelling en seisoenale veranderinge in weerspatrone affekteer die grootte van mikrobiale bevolkings. In hierdie tesis word verskille in plantegroei, saad store en grond mikrobes, soos geaffekteer deur uitheemse plant beheer programme uitgewys en voorstelle vir toekomstige bestuur gemaak. Sleutelwoorde: Fynbos Bioom, grond saad stoor, mikrobes, plant hergroei, uitheemse plante, vuur.
18
Tocko, Marabena Brice Kette. "Richesse spécifique, diversité génétique et structuration des populations du complexe d’espèces Bemisia tabaci sur le manioc et plantes associées dans la zone CEMAC (Communauté économique et monétaire en Afrique centrale)." Electronic Thesis or Diss., La Réunion, 2015. https://tel.archives-ouvertes.fr/tel-04136842.
Full textAbstract:
L’étude de la richesse spécifique et génétique des ravageurs des cultures, vecteurs de virus phytopathogènes, dans un contexte d’invasion biologique en milieu continental, est indispensable pour la compréhension des mécanismes qui sous-tendent les émergences virales en Afrique Sub-saharienne. Le complexe d’espèce cryptique de Bemisia tabaci est composé de nombreuses espèces dont le groupe d’espèces Sub-Sahariennes qui sont inféodées au manioc en Afrique. Celles-ci sont directement impliquées dans la vection de nombreux virus provoquant la maladie de la mosaïque du manioc (CMD) ou celle de la striure brune (CBSV). Ces maladies entrainent de fortes pertes de rendement sur les cultures de manioc, qui figurent parmi les principales plantes à racine amylacées cultivées du continent Africain. Malgré les études réalisées, la diversité des espèces d’aleurodes sur manioc dans certains pays reste inconnue. En outre, peu d’information existe sur les flux de gènes au sein des espèces et potentiellement des sous-groupes génétiques récemment décrit au sein de ces espèces. C’est dans ce contexte que nous avons réalisé une étude génétique de 898 échantillons de Centrafrique et de 667 échantillons du Cameroun au moyen de marqueurs nucléaires (microsatellites) et mitochondrial (COI). Ces analyses ont permis la caractérisation de la variabilité génétique et de la différenciation intra et inter espèce. L’effet de possibles facteurs tels que la plante-hôte et l’origine géographique des individus analysés, souvent rapportés comme facteurs de structuration génétique chez l’espèce B. tabaci ont également été testés pour (i) déterminer la nature des espèces en circulation dans ces pays, (ii) comprendre la répartition de ces populations, (iii) évaluer l’étendue de leur diversité et structuration génétique, et (iii) considérer l’apport de ces connaissances dans la gestion des populations d’Afrique centrale. Nous avons ainsi pu décrire la présence en Centrafrique et au Cameroun de 6 espèces du complexe de B. tabaci et de 5 des sous-groupes d’une espèce (SSA1) de ce complexe (SSA1-SG1, SSA1-SG2, SSA1-SG1/2, SSA1-SG3, SSA2, SSA3, MED, MEAM1 et l’IO). Les abondances des populations d’aleurodes dénombrés sur manioc coïncident à des niveaux de type « pullulation » dans l’ensemble des zones échantillonnées, mettant en avant le statut de ces pays comme situés en zone épidémique. Ce travail de thèse a permis en outre de mettre en exergue le rôle de l’espèce SSA1-SG1 (P9H9/P18F5) dans la pullulation et l’expansion de la mosaïque africaine du manioc en Afrique centrale. Les populations de cette espèce et de cet haplotype en particulier ont été détectées comme dominantes et polyphages dans les pays échantillonnés. De même, au Cameroun, il été mis en avant que l’invasion et la pullulation de cet haplotype majoritaire pourrait être réalisé selon un processus d’invasion par hybridation avec les populations résidentes. Les données actuelles sur la distribution de cet haplotype dans ces deux pays tendent à montrer que non seulement le Cameroun et la RCA sont impactés par cette vague d’invasion mais pourraient l’être dans les pays limitrophesThe study of species and genetic richness of crops pest vector of plant viruses in a biological context of invasion in continental environment, is essential for understanding the mechanisms that underlay viral emergencies in sub-Saharan Africa. The cryptic Bemisia tabaci species complex is composed of many species, including the Sub-Saharan group of species that are subservient to cassava in Africa. They are directly involved in the vection of many viruses causing cassava mosaic disease (CMD) or the cassava brown streak diseases (CBSD). These diseases cause severe yield losses in cassava crops, which are among the leading starchy root crops in the African continent. Unfortunately very few studies on the vector of these diseases had been made in numerous African countries where the disease is of great concern. The diversity of whiteflies species on cassava in some countries remains broadly unknown. Furthermore, little information is available on the gene flow within species and between genetic subgroups recently described within these species. It is in this context that we conducted a genetic study on 898 samples from Central Africa and 667 samples from Cameroon using nuclear (microsatellites) and mitochondrial (COI) markers. These analyzes have allowed the characterization of the genetic variability at the intra- and inter-species level. The possible effect of factors such as the host plant and the geographical origin of analyzed individuals, often reported as genetic structuring factors in the species B. tabaci were also tested for (i) determining the nature of the species in circulation in these countries, (ii) understand the distribution of these populations, (iii) assess the extent of their diversity and genetic, structure, and (iii) consider the contribution of this knowledge in the management of whitefly populations in Central Africa. We were able to describe the presence of 6 species of B. tabaci complex and 5 subgroups of a species (SSA1) of this complex in CAR and Cameroon (SSA1-SG1, SG2-SSA1, SSA1- SG1 / 2, SSA1-SG3, SSA2, SSA3, MED, MEAM1 and IO). The abundances of whitefly populations on cassava coincide with levels of "outbreak" in all sampled areas, highlighting the status of these countries as in an epidemic area. This thesis has allowed also highlighting the role of the species SSA1 and its subgroup -SG1 with a specific haplotype P9H9 / P18F5 in the proliferation and expansion of the African cassava mosaic in Central Africa. Populations of this species and this particular haplotype were detected as dominant and polyphagous in sampled countries. Similarly, in Cameroon, it was emphasized that the invasion and overgrowth of this haplotype could be achieved through a process of invasion by hybridization with resident populations. Current data on the distribution of the dominant haplotype in both countries tend to show that not only the Cameroon and the CAR are affected by this wave of invasion but could be also in the neighboring countries
19
Mealor, Brian A. "Native plant population resilience to exotic invasion." Laramie, Wyo. : University of Wyoming, 2006. http://proquest.umi.com/pqdweb?did=1221731861&sid=7&Fmt=2&clientId=18949&RQT=309&VName=PQD.
Full text
20
Sherpa, Stéphanie. "Histoire de la colonisation et déterminants du succès invasif des populations du moustique tigre Aedes albopictus en Europe." Electronic Thesis or Diss., Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAV049.
Full textAbstract:
Le moustique tigre, Aedes albopictus, originaire d’Asie du Sud-Est, a colonisé l’ensemble des continents excepté l’Antarctique depuis les dernières décennies. En revanche, les raisons du succès invasif des populations à l’échelle mondiale sont encore peu connues. Nous nous sommes concentrés sur l’invasion de l’Europe, et avons combiné différentes méthodes d’analyse et des données multi-sources afin de distinguer le rôle des processus historiques et contemporains, neutres et adaptatifs, dans la structuration de la variabilité génétique des populations invasives. L’analyse de la variabilité génétique de 1000 individus appartenant à 150 populations invasives et natives a révélé trois introductions indépendantes en Europe (en Albanie, au Nord de l’Italie, et au Centre de l’Italie), à partir des Etats-Unis (aire envahie) et de la Chine (aire native). Les populations initialement introduites ont constitué des centres de dispersion en Europe et les voies de migration corrèlent avec la géographie des transports humains. Différents évènements d’admixture au moment de l’introduction ou durant l’expansion subséquente, ainsi qu’une forte connectivité des populations, ont favorisé le maintien d’une forte diversité génétique. Des adaptations au froid préexistantes dans l’aire native de l’espèce et un fort conservatisme de niche entre les populations introduites et leurs sources suggèrent que les populations introduites étaient déjà pré-adaptées pour coloniser les environnements tempérés de l’Europe. Néanmoins, des changements de fréquences alléliques le long des gradients environnementaux en Europe suggèrent également une réponse adaptative après l’introduction. Le potentiel adaptatif des populations, ainsi que la dispersion longue distance assistée par l’homme, ont favorisé l’expansion rapide en Europe. Bien que souvent négligée dans le contexte des invasions biologiques, la dispersion naturelle semble également jouer un rôle dans l’expansion des populations à l’échelle du paysage. L’étude des caractéristiques démo-génétiques des populations invasives et des caractéristiques environnementales de l’aire envahie en Europe a permis d’identifier les processus favorisant deux étapes clés du processus d’invasion: l’établissement et l’expansionThe Asian tiger mosquito, Aedes albopictus, is native to Southeast Asia and has colonized all continents but Antarctica in the last decades. However, the factors determining the invasive success of populations at the global scale remain to be elucidated. Focusing on the European invasion, we used a comprehensive framework and multi-source data for distinguishing the role of historical and contemporary processes, both neutral and adaptive, in structuring the genetic variability of invasive populations. Examining the genetic variability of 1,000 individuals from 150 invasive and native populations revealed three independent introduction events in Europe (in Albania, North Italy, and Central Italy), from the United States (previously invaded area) and from China (native range). Primary introduced populations constituted dispersal centers for the colonization of Europe, and migration routes correlate with the geography of human transportation networks. Several admixture events either during introduction or subsequent expansion, as well as high connectivity between invasive populations, promoted the maintenance of high levels of genetic diversity. Pre-existing cold adaptation within the native range of the species and niche conservatism between introduced populations and their sources suggest that these populations were already prepared for establishing under temperate European climate. Nonetheless, shifts in allele frequencies along environmental gradients within Europe suggest post-introduction adaptive changes. The adaptive potential of populations and long-distance human-aided dispersal facilitated the rapid expansion of populations. Although often neglected in the context of biological invasions, natural dispersal at the landscape scale further contributed to range filling in range edge populations. The study of the demo-genetic and environmental characteristics of the European invasion allows a better understanding of processes at play during two key stages of the invasion process: establishment and expansion
21
Hautier, Louis. "Intraguild predation in Harmonia axyridis and its effects on native coccinellids." Doctoral thesis, Universite Libre de Bruxelles, 2012. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209619.
Full textAbstract:
During the 1990s, over a period of just a few years, the multi-colored Asian lady beetle, Harmonia axyridis (Pallas) invaded the entire area of northern Europe. In parallel with this invasion, a decline in native coccinellid species was recorded in Belgium, Britain, and Switzerland, affecting mainly one common species: the two-spot ladybird, Adalia bipunctata L. An impressive trait of H. axyridis, that could explain both its high invasiveness and the decline of native coccinellids, is its predation behaviour. Intraguild predation is a trophic interaction between species that share the same prey – in this case, aphids. In order to determine the precise impact of this predation on the native coccinellid species, the predation behaviour of H. axyridis larvae was observed in Petri dishes and on plants. The resistance of H. axyridis to predation was also studied by exposing it without dorsal spines to native predator larvae, in order to test whether or not the dorsal spines are a physical defence against intraguild predation. In addition to these laboratory experiments, an original method was developed and used to track predation under field conditions. This method is based on the gas chromatography–mass spectrometry (GC-MS) detection of exogenous alkaloids in H. axyridis, especially alkaloids from native coccinellids likely to be subject to intraguild predation. My results show that, in the absence of aphids, H. axyridis consumes both A. bipunctata eggs and all larval instars in Petri dishes. On plants, depending to aphid density, this interaction can change with regards to larvae but not eggs. In addition to intraguild predation, competitive exclusion can occur because of quite aggressive behaviour towards competitors. Dorsal spines significantly reduce the number of bites inflicted, and thereby complement the other defense mechanisms of H. axyridis that enable it to remain dominant in competition for food resources. In semi-natural conditions, predation on the native coccinellids Adalia spp. Calvia spp. Coccinella septempunctata L. and Propylea quatuordecimpunctata (L.) was detected. The number of sites where this predation was observed suggests that this interaction is frequent. It was also observed that an H. axyridis larva can ingest several native coccinellid species, confirming its status as a predator of coccinellids. We can therefore conclude that intraguild predation by H. axyridis leads, as does resource competition, to a decline in native coccinellids./Introduite pour la lutte biologique dans les années 90, la Coccinelle asiatique, Harmonia axyridis (Pallas), a envahi en quelques années toute l’Europe du Nord. Parallèlement à cette invasion, un déclin de plusieurs espèces de coccinelles indigènes dont la très commune Coccinelle à deux points, Adalia bipunctata L. a été observé dans différents biotopes en Belgique, en Angleterre ainsi qu’en Suisse. Un des traits remarquables de la Coccinelle asiatique est son comportement de prédateur intraguilde qui pourrait expliquer à la fois ce déclin mais aussi en partie son caractère hautement invasif. La prédation intraguilde est une interaction trophique entre des espèces qui se nourrissent d’une même proie, dans ce cas-ci les pucerons. Afin de mieux connaître l’impact de cette prédation sur les coccinelles indigènes, le comportement de prédation des larves d’H. axyridis a été décrit en boîtes de Petri et sur plantes. Sa résistance à la prédation a également été étudiée en exposant des larves dépourvues d’épines dorsales à un prédateur indigène, dans le but de tester le rôle de ces épines en tant que défense physique à l’égard d’un prédateur intraguilde. En plus de ces expériences de laboratoire, une méthode originale a été développée et utilisée pour suivre cette prédation en conditions semi-naturelles. Elle se base sur la détection, en GC-MS, des alcaloïdes exogènes chez H. axyridis et en particulier des alcaloïdes produits par d'autres espèces de coccinelles susceptibles de subir une prédation intraguilde. Mes résultats montrent qu'en l'absence de pucerons, H. axyridis a un comportement de prédation vis-à-vis des œufs et de tous les stades larvaires d’A. bipunctata. La présence de pucerons, suivant leur densité, peut modifier cette interaction à l’égard des larves indigènes mais pas des œufs. En plus de la prédation intraguilde, une compétition par exclusion peut être aussi suspectée et expliquée par le comportement très agressif d’H. axyridis à l’égard de ses concurrents. Quant aux épines dorsales, elles permettent de réduire significativement le nombre de morsures et complètent ainsi les autres lignes de défense utilisées par H. axyridis pour s’imposer dans des ressources déjà exploitées par d’autres prédateurs. En conditions semi-naturelles, cette prédation à l’égard des coccinelles indigènes a été confirmée vis-à-vis d’Adalia spp. Calvia spp. Coccinella septempunctata L. et Propylea quatuordecimpunctata (L.). Vu le nombre de sites où cette prédation a été détectée, elle peut être considérée comme une interaction fréquente. De plus, une même larve de coccinelle asiatique peut ingérer plusieurs espèces de coccinelles indigènes confirmant indéniablement son statut de prédateur de coccinelles. Ainsi, nous pouvons conclure que la prédation intraguilde par H. axyridis sur les coccinelles indigènes participe très certainement au déclin de celles-ci et ceci très probablement au même titre que des phénomènes de compétition pour les ressources.Doctorat en Sciences agronomiques et ingénierie biologique
info:eu-repo/semantics/nonPublished
22
Howery, Larry D., Ed Northam, Walt Meyer, Jennifer Arnold, Emilio Carrillo, Kristen Egen, and Mary Hershdorfer. "Non-Native Invasive Plants of Arizona." College of Agriculture, University of Arizona (Tucson, AZ), 2016. http://hdl.handle.net/10150/625545.
Full textAbstract:
84 pp. / First Edition Published 2001The noxious weed problem in the western United States has been described as, a biological forest fire racing beyond control because no one wants to be fire boss. Indeed, when small weed infestations are left unchecked, they can grow exponentially and spread across the land much like a slow-moving biological wildfire. However, land consumed by fire usually recovers and is often more productive than before the fire occurred. On the other hand, land consumed by noxious weeds may be irreversibly changed and never again reach its full biological potential. Reviewed 12/2016, First Edition Published 2001
23
Howery, Larry D., Ed Northam, Walt Meyer, Jennifer Arnold, Emilio Carrillo, Kristen Egen, and Mary Hershdorfer. "Non-Native Invasive Plants of Arizona." College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2009. http://hdl.handle.net/10150/146922.
Full textAbstract:
84 pp.First Edition Published, 2001
The noxious weed problem in the western United States has been described as, a biological forest fire racing beyond control because no one wants to be fire boss. Indeed, when small weed infestations are left unchecked, they can grow exponentially and spread across the land much like a slow-moving biological wildfire. However, land consumed by fire usually recovers and is often more productive than before the fire occurred. On the other hand, land consumed by noxious weeds may be irreversibly changed and never again reach its full biological potential.
24
Buckley, Yvonne Maria. "Ecology, evolution and manipulation of invasive plant populations." Thesis, Imperial College London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271748.
Full text
25
Bell, Brian P. "Growth and Water Relations of Native Wheatgrass Populations." DigitalCommons@USU, 2008. https://digitalcommons.usu.edu/etd/7499.
Full textAbstract:
Screening populations for development into released plant materials can be done inexpensively and in a timely manner. A common approach has been to quantify the amount of shoot dry mass produced as a surrogate for competitiveness. Besides dry mass production , other morphological characteristics have been employed , but physiological parameters have received less emphasis. Dry mass production may be an important characteristic, but identifying the traits responsible can be just as imperative . Populations with greater drought tolerance may be less impacted by competition for water from weeds, which could lead to greater establishment of desirable grasses on disturbed landscapes.
The objective for chapter 2 was to evaluate the effects of cheatgrass competition on the growth and water relations of three Snake River wheatgrass (Elymus wawawaiensis) populations and two bluebunch wheatgrass (Pseudoroegneria spicata) populations in the seedling stage in a greenhouse setting. The treatments were 1) containers with a single wheatgrass plant or 2) containers with one wheatgrass and one cheatgrass plant. Containers were watered gravimetrically to 11.5% soil-water content, regard less of treatment, every few days until harvested on day 35. Cheatgrass competition reduced root dry mass, shoot dry mass, leaf area, leaf number, tiller number, xylem pressure potential, and stomata} conductance. The bluebunch wheatgrass populations generally had more negative xylem pressure potential, higher stomata! conductance, and higher shoot dry mass, while the Snake River populations had higher specific leaf area and less negative xylem pressure potentials .
The objective for chapter 3 was to evaluate the effects of planting density on the growth and water relations over a 2-year period among five Snake River wheatgrass populations, one thickspike wheatgrass (Elymus lanceolatus) population , and three interspecific hybrids. High (25 plants/m 2 ) and low-density (7.8 plants/m2) plots of each grass were transplanted to Millville, Utah in the spring of 2005 and 2006 intended to generate low and high resource availability environments, respectively. Thickspike wheatgrass had the highest shoot dry mass and least negative xylem pressure potential , the hybrids were intermediate, and the Snake River wheatgrasses were least productive and more water stressed.
The primary benefit of this thesis will be through identifying the potential for developing these populations into improved plant materials and releasing them for commercial use in degraded rangelands across the Intermountain West. These new plant materials may also help transition damaged rangelands towards more desirable stable states composed of lower abundances of invasive annual grasses.
26
Wint, Ashley A. "Genetic Diversity in Native and Invasive Rubus (Rosaceae)." TopSCHOLAR®, 2008. http://digitalcommons.wku.edu/theses/17.
Full textAbstract:
Invasive species are an increasing threat to biological diversity as well as a leading cause of recent species’ extinctions. Invasives spread quickly and efficiently, and the U.S spends millions of dollars annually in the control and eradication of these species. More information is necessary in order to predict which species may become invasive. Rubus (Rosaceae) was chosen for study because this genus includes various ploidy levels, reproductive modes, and species that are invasive as well as native.
Three Rubus species were chosen to represent apomictic and tetraploid invasives (Rubus armeniacus), a sexual and diploid native species (R. occidentalis), and a sexual and diploid invasive species (R. phoenicolasius). Specimens were collected across the U.S. and two different genetic fingerprinting techniques were used; Amplified Fragment Length Polymorphism (AFLP) and Randomly Amplified Fingerprints (RAF).
Using three AFLP primers and two RAF primers, genetic similarity was determined and phylograms were constructed. Through statistical analysis and phylogram data it was determined that there might be slightly more genetic diversity in native R. occidentalis than in invasive R. phoenicolasius. Genetic diversity between apomictic and tetraploid Rubus armeniacus and the two sexual and diploid Rubus species were so similar that no distinction could be made, although the mean pairwise distances and mean number of alleles were significantly different. It was also found that geographic distance and genetic similarity do not appear to be related in these three Rubus species. During the course of this study it was also observed that the AFLP technique produced more alleles than the RAF technique, although this difference was not significant.
27
Curtis, Joseph Schmidt. "Resource Use Overlap in a Native Grouper and Invasive Lionfish." Scholar Commons, 2016. http://scholarcommons.usf.edu/etd/6488.
Full textAbstract:
Invasive species can severely disrupt biological communities through their interactions with native organisms, yet little is known about the response of marine predators to the establishment of a competitive invasive fish. In the western Atlantic, invasive Indo-Pacific lionfishes (Pterois spp.) may represent a novel competitor to several commercially and ecologically important native species. However, there is a scarcity of empirical research documenting comparative resource use of cohabitant lionfish and native fishes, as well the physiological consequences that may result from interspecific interactions with the invasive species. For this thesis, I conducted two studies designed to elucidate the strength of resource use overlap and potential competition among invasive lionfish and an ecologically similar serranid, the Graysby (Cephalopholis cruentata), along a contiguous coral-reef ledge in Biscayne National Park, South Florida.
My first study aimed to determine whether lionfish and Graysby could be classified as competitors through comparisons of Graysby population size, diet, and condition across a range of ambient lionfish biomass. Using stable isotope and gut content analyses, I measured a difference in Graysby diet on sites with larger populations of lionfish, specifically a smaller breadth of resource use and lower consumption of teleost fish prey. Despite a shift in diet, Graysby condition did not vary with lionfish biomass, and thus this study did not provide unequivocal evidence of competition between the two species. However, based on a high amount of apparent overlap in interspecific resource use, competitive interactions between lionfish and species such as Graysby remain likely in systems with more limiting prey or shelter.
For my second study, I measured stable isotope values of muscle, liver, and eye lens layers in lionfish and Graysby to further compare individual and population-level patterns of diet and habitat use. The use of eye lenses as metabolically stable chronological recorders of stable isotopes has vast potential to provide insight about animal life history, but has not yet been applied to describe trends in resource use among invasive and native species. To aid these analyses I created a rudimentary map of spatial isotopic variation along the reef ledge of Biscayne National Park, which could serve as a frame of reference to study local-scale animal movements. Isotopic differences between liver and muscle samples suggested a broader range of movement in lionfish than Graysby, important for understanding the relative scale of habitat use in these species. In eye lenses, stable isotope values increased logarithmically with lens radius (i.e. fish size), likely reflecting patterns of trophic growth. There was a high amount of variability among the shapes of eye lens isotopic chronologies, particularly those of lionfish, yielding further information about movement and individual resource use specificity in these species.
The results of this thesis are the first to compare native predator diet and condition across a range of invasive lionfish biomass, as well as the first to measure size-structured trends in the resource use of individual lionfish. Together, these results enhance our understanding of the potential for competition among lionfish and native mesopredators, an important objective for researchers studying how this highly invasive species interacts with surrounding ecological communities.
28
Mas, Sandoval Àlex 1989. "Native American genetic history through admixed populations of Brazil." Doctoral thesis, Universitat Pompeu Fabra, 2018. http://hdl.handle.net/10803/666982.
Full textAbstract:
Most of the Native American populations that lived in nowadays Eastern Brazil when the Europeans established in the area in the 16th century do not exist anymore. The colonization of Brazil implied huge migrations from Europe and brought more than four million people from sub-Saharan Africa from the 16th to the 19th centuries to work as slaves. This process disrupted the demography of the Native American populations from eastern Brazil, which disappeared or experienced admixture events with the European colonizers, the sub-Saharan slaves and their descendants to become urban admixed Brazilian populations. Therefore, the genetic history of Native American populations from eastern Brazil might only be traced from urban admixed Brazilians or through the few surviving Native American populations that also received, in a lesser extent, geneflow from European and sub-Saharan sources. This thesis presents two novel methodologies to isolate and analyse the Native American ancestry from these populations to reconstruct the Native American genetic structure before the arrival of Europeans. The main findings reveal a population landscape shaped by a dichotomy of Tupi and Je ancestries and contribute to the revision and rescheduling of the major demographic events before 1500CE.La gran part de les poblacions natives americanes que vivien a les terres que avui en dia són l’est del Brasil ja no existeixen. La colonització del Brasil va comportar grans migracions des d’Europa i va arrencar més de quatre milions de persones de l’Àfrica sub-sahariana des del segle XVI fins al segle XIX per treballar esclavitzades al Brasil. Aquest procés va alterar la demografia de les poblacions Natives Americanes de l’est del Brasil, que van desaparèixer o es van mesclar amb els colonitzadors europeus, els esclaus sub-saharians, o els seus descendents per esdevenir poblacions brasileres mestisses. Com a conseqüència, per tal de conèixer la història genètica de les poblacions natives americanes de l’est del Brasil cal traçar-la a través de les poblacions brasileres mestisses urbanes o de les poques poblacions natives americanes supervivents, que en menor mesura també han rebut l’impacte genètic de poblacions d’origen europeu o sub-saharià. Aquesta tesi presenta dues noves metodologies per aïllar i analitzar la part ancestral nativa americana d’aquestes poblacions per tal de reconstruir l’estructura genètica de les poblacions natives americanes abans de l’arribada dels europeus. Els descobriments principals revelen un escenari modelat per una dicotomia de les ancestralitats Tupi i Je i contribueixen a la revisió i reestructuració dels principals esdeveniments demogràfics abans del 1500.
29
Ballard, Meg. "Insect populations on early successional native and alien plants." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 50 p, 2006. http://proquest.umi.com/pqdweb?did=1203553531&sid=1&Fmt=2&clientId=8331&RQT=309&VName=PQD.
Full text
30
Calvo, Ugarteburu Miren Gurutze. "Parasitism and invasive species : an ecological study of mussel populations." Thesis, Rhodes University, 1997. http://hdl.handle.net/10962/d1005422.
Full textAbstract:
The Mediterranean mussel Mytilus galloprovincialis, was introduced accidentally to South Africa and has since become invasive. One possible explanation for the success of this species is that it has been released from the effects of parasites which affect the indigenous species of mussels. The aim of this work was to examine the parasitic load of different mussel populations along the southern African coast and to assess the effects of parasites on their hosts. A survey was done to quantify the levels of parasitism in indigenous populations of Perna perna from Southern Africa and of Mytilus galloprovincialis from South Africa (where it is exotic) and Spain (where it is indigenous). This survey was carried out at three different geographic scales: small scale (metres), studying the incidence of parasites within a mussel bed; medium scale (kilometres to tens of kilometres), comparing prevalences of infection among different localities; and large scale (hundreds to thousands of kilometres), examining infection rates along the Southern African coast, as well as the coast of the Basque Country (North Spain). During this survey metazoan parasites other than trematodes were rare. Four species of trematodes were commonly found infecting the indigenous mussel Perna perna. These were metacercariae of the genus Proctoeces, bucephalid sporocysts, encysted metacercariae on the labial palps and gelatinous cysts with metacercariae inside. A detailed description of Proctoeces is given; the other parasites are described elsewhere. No parasites were found in M. galloprovincialis either in South Africa or in Spain. This thesis concentrates on the study of prevalences of Proctoeces and bucephalid sporocysts and their effects on Perna perna. Infection rates with Proctoeces are highly dependent on the sex of the host, with more females than males being infected, and are also size dependent, though only for females. Identification of the sex of mussels infected with bucephalid sporocysts is often not possible since the sporocysts spread over the gonad and replace it. Prevalence of infection with this parasite also increases with the size of the host. To study the influence of Proctoeces and bucephalid sporocysts on the ecological fitness of Perna perna, their effects on survival and competitive ability were tested. The results showed significant negative effects. Both parasites significantly depressed condition but only after spawning, when the mussels were already stressed. In order to check for effects on host survival, the effects of both parasites on mortality rates, gaping behaviour and water loss of mussels exposed to air were also examined. Neither parasite affected mortality rate or gaping behaviour of Perna perna. Proctoeces did not affect the amount of water lost by mussels, but the bucephalid sporocysts did. Mussels infected with sporocysts lost significantly more water than non-infected individuals. This increase in water loss was not related to the gaping behaviour, but a test of the strength of the adductor muscles showed that less force was needed to open mussels with bucephalid sporocysts than non-infected mussels. This was not the case for mussels infected by Proctoeces. Weaker mussels will fail to seal the valves properly, resulting in an increase of water loss on exposure to air by evaporation. Another factor that will have an obvious effect on a population is the reproductive output of the animals. Histological sections of the gonad of infected and non-infected females were cut to study the effects of both parasites on reproduction. Statistical tests comparing the numbers and sizes of oocytes in females infected with Proctoeces and non-infected females showed no significant differences. However, bucephalid sporocysts have a dramatic effect on reproduction by castrating the host, leaving no trace of sex products. One of the major factors shaping the composition of a mussel bed is competition for space and food, with smaller mussels being at a competitive disadvantage. Thus, in order to examine effects of both parasites on the competitive ability of Perna perna, summer and winter growth rates were compared for infected and non-infected mussels. Proctoeces reduced growth both in summer and in winter whilst bucephalid sporocysts had no significant effect. Both growth and reproduction are important components of the energy budget of an animal, and each is affected by either Proctoeces or the bucephalid sporocysts. In an attempt to test if Perna perna compensates energetically for these negative effects, filtration rates and oxygen consumption of mussels with and without parasites were measured. Neither parasite had a significant effect on filtration rates or oxygen consumption of the host. All these results indicate that both Proctoeces and the bucephalid sporocysts have a detrimental effect on their host, and that the mussels do not compensate for these negative effects. There is neither an increase in filtration, nor a decrease in respiration to balance the energy lost to the parasite. The two parasites studied affect the host in different but complementary ways. The effects of both parasites are concentrated on those size classes of mussel which channel most energy into the portion of the energy budget affected by the parasite. Proctoeces affects growth only in the smaller individuals, which under normal conditions would put most energy into growth; and the bucephalid sporocysts castrate the bigger mussels, which would expend most energy on reproduction. By reducing growth rates of small mussels or castrating large mussels, these parasites effectively remove them from the breeding population and reduce their competitive abilities. These negative effects, together with the high prevalence of both parasites in Perna perna along the South African coast and their absence in Mytilus galloprovincialis, suggest that parasites may be an important reason for the success of Mytilus.
31
Bell, Spencer Sullivan. "Mountain Lake Revisited: Impacts of Invasion on Native Symbiotic Systems." Thesis, Virginia Tech, 2018. http://hdl.handle.net/10919/96193.
Full textAbstract:
Organismal invasions have repeatedly been cited as both a driving force behind global change and beneficiaries of that change. Although many drivers of these invasions have been well studied, few studies have addressed invasions through the perspective of native symbiont communities. In the Mountain Lake region of Virginia, crayfish host diverse assemblages of obligate cleaning symbionts known as branchiobdellida. This cleaning symbiosis has been found to result in significant fitness benefits for native crayfish. Historical survey work showed that invasive crayfish, known to be intolerant of symbionts, were introduced into the region by the 1960s. I carried out an extensive regional survey to determine how this invasion has progressed and what impacts it is having on the native crayfish-branchiobdellida symbiosis. Survey results show that invasive crayfish have successfully spread throughout the region, resulting in the displacement of native crayfish. Additionally, findings suggest that invasion results in significantly reductions in abundance and richness in native symbiont communities. To determine mechanisms contributing to observed impacts on native symbionts, I carried out a study that simulated displacement of native crayfish by invasive crayfish in a controlled setting. This study found that as native crayfish are increasingly displaced by invasive crayfish, both symbiont dispersal and survival are negatively affected. This potential loss of symbiosis caused by invasion may reduce symbionts on native crayfish below abundances necessary for fitness benefits, exacerbating the negative impacts of invasions and presenting a major conservation issue in invaded systems.M. S.
32
Jokela, Anneli. "Factors affecting the impact of invasive mussels on native freshwater mussels." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=101146.
Full textAbstract:
Biological invasions are among the leading causes of species diversity loss; however, the impacts of invasion are context-dependent and can vary with the local environment. The mechanisms governing variation in impact and their relationship to specific abiotic and biotic factors remain largely unexplored. Recent local declines in native unionid mussels have been attributed to the invasion of North American lakes and rivers by the Eurasian zebra mussel ( Dreissena polymorpha), as a result of intense fouling of unionid shells by zebra mussels. My research investigated the role of abiotic and biotic factors in mediating the impact of zebra mussels on native mussels. I examined the impact of zebra mussels on unionids in a habitat thought to be suboptimal for zebra mussels and compared this to the impact observed in other invaded habitats. A predictive model relating fouling intensity to local environmental variables (calcium concentration, sediment particle size) was developed, and a predator-exclusion experiment was conducted to investigate the role of predation in mediating fouling intensity. Overall, I found that two abiotic factors of the local environment were significant predictors of fouling intensity and that relationships used to predict the impact of zebra mussels could be extended to a broader range of habitats.
33
Kelly, D. W. "The role of native and invasive amphipods (Crustacea) in freshwater communities." Thesis, Queen's University Belfast, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390875.
Full text
34
Harvey, Joshua Thomas. "Stoichiometric Homeostasis in Two Native and Two Invasive South Dakotan Grasses." Thesis, South Dakota State University, 2019. http://pqdtopen.proquest.com/#viewpdf?dispub=13807215.
Full textAbstract:
Increased nutrient availability has been widely linked to the success of invasive plants, however a general mechanism explaining these observations is lacking. Stoichiometric homeostasis (H), which is the regulation of internal nutrient concentrations, has been used to explain changes in plant community diversity under alterations in nutrient availability. One hypothesis holds that plants with high regulation (larger H) decrease in abundance in nutrient enriched conditions but are stable in nutrient deficient and drought conditions, likely due to extensive root systems. Additionally, plants with low regulation (lower H) increase in abundance under nutrient enriched conditions but are sensitive to drought conditions. I tested the hypotheses that H would be higher in native grasses than in invasive grasses, that H would be modulated by environmental conditions, and that differences in H would be associated with differences in growth and biomass allocation. I calculated H and measured plant growth and growth traits in two native ( Pascopyrum smithii and Elymus canadensis) and two invasive (Bromus inermis and Agropyron cristatum ) grasses grown in two experiments. Both experiments contained a range of N:P fertilizer supply concentrations and the first experiment contained a two-level drought treatment while the second experiment contained a two-level mycorrhizal inoculation treatment.
In the first experiment, I found support for the hypothesis that H is higher in native than invasive plants, that environmental conditions (i.e. water availability) affect the value of H, and that differences in H were associated with differences in growth. In the second experiment, there was no successful mycorrhizal inoculation, resulting in no differences in H between mycorrhizal treatment groups. There were significant differences in total growth between the second experiment native and invasive grasses, despite there being no significant differences in H. Differences in H values between control-treated grasses in the two experiments may be due to differences in greenhouse temperature and light conditions. These results show first, significant differences exist in H between invasive and native grasses, with invasive grasses expressing lower values of H, second, environmental conditions effect the expression of H, and third, that differences in the expression of H are matched by differences in growth.
35
Rosewarne, Paula Joy. "Native and invasive freshwater decapods in the UK : conservation and impacts." Thesis, University of Leeds, 2013. http://etheses.whiterose.ac.uk/7807/.
Full textAbstract:
Crayfish species have been translocated by humans, with both positive and negative consequences. Conservation-led translocations of the endangered white-clawed crayfish (Austropotamobius pallipes) to safe ‘Ark sites’ where threats are minimised are underway. Restored quarries may represent ideal Ark sites and several questions pertaining to their suitability were addressed, along with a 3-year case study of Ark site creation in a limestone quarry. Quarries contain large quantities of unconsolidated sediment and crayfish experienced gill fouling and reduced aerobic scope after exposure to suspended solids concentrations of 62 mg L-1 and above. A novel parasite detected in the gills of A. pallipes caused gill pathology, highlighting the need for health assessment of donor stock prior to translocation. Most Ark sites do not historically hold crayfish and their introduction may cause strong effects on existing freshwater communities. In a mesocosm study, juvenile and adult A. pallipes reduced the abundances of grazers and shredders; however consumption of the gastropod Physa fontinalis and detritus varied between life-stages. The American signal crayfish (Pacifastacus leniusculus) is rapidly invading catchments and replacing A. pallipes. In a field-based telemetry study, a flow-gauging weir reduced upstream movements of P. leniusculus by 45%, highlighting the need to balance invasion risk with EU targets for improved riverine connectivity. P. leniusculus co-occurs with another invasive decapod, the Chinese mitten crab (Eriocheir sinensis), and their feeding behaviour was compared. Both consumed a range of prey items, including fish eggs. Juvenile E. sinensis had a higher per capita intake of the keystone shredder Gammarus pulex than native A. pallipes and showed greater preference for this prey item than did P. leniusculus. Overall, E. sinensis is likely to have an equal, if not higher, per capita impact on prey species than P. leniusculus. Recommendations for quarry Ark site creation and management of invasive decapods were formulated.
36
Morghan, Kimberly Jo Reever. "Competitive interactions between native grasses and invasive species in California grasslands /." 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
37
Mahoney, Catherine R. "Anthropometric Variation in California: A Study of Native American Populations." The University of Montana, 2008. http://etd.lib.umt.edu/theses/available/etd-05082008-132023/.
Full textAbstract:
Physical anthropologists study the patterns of human morphology to observe the influence of genetics and environment on cranial form. The following study compares cephalic and nasal index means from four Native American populations using modern statistical methods, including one-way ANOVA tests and Games-Howell comparison tests. The individuals used were of only Native American ancestry, over the age of seventeen when the data was collected, and were divided into male and female samples. The climatic conditions of each of the regions are compared to examine the relationship between the mean cranial and nasal indices and the environments in which the populations lived. Previous research suggests that larger cephalic indices should be found in populations from colder climates and larger nasal indices should be found in populations from warmer climates. Some cases in which a significant difference in means was found between populations it followed the pattern predicted from the environmental differences, though one population (the Miwok) provided an exception.
38
Mahoney, Catherine Rose. "Anthropometric variation in California a study of Native American populations /." CONNECT TO THIS TITLE ONLINE, 2008. http://etd.lib.umt.edu/theses/available/etd-05082008-132023/.
Full text
39
Mullins, Lydia R. "Testing the effects of glyphosate and a possible tradeoff with immunity on native and non-native species of crickets." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1587642768787223.
Full text
40
Maspero, Matteo <1976>. "Managing invasive populations of Anoplophora chinensis and A. glabripennis in Lombardy." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amsdottorato.unibo.it/7184/1/Maspero_Matteo_tesi.pdf.
Full textAbstract:
Two Asian longhorned beetles (Coleoptera: Cerambycidae), commonly known as Citrus Longhorned Beetle (CLB), Anoplophora chinensis (Forster), and Asian Longhorned Beetle (ALB), A. glabripennis (Motschulsky), are considered the most destructive wood borers introduced in Lombardy (northern Italy).
This research aimed at (1) improving laboratory rearing methods for the biological control agent Aprostocetus anoplophorae (Hym.: Eulophidae), an egg parasitoid specific to CLB, and defining release techniques allowing its establishment; (2) test the efficacy of the sentinel tree technique for the early detection of CLB; and (3) evaluating the efficacy of traps baited with artificial lures in attracting adults of ALB and possibly CLB.
Several problems were faced while rearing the egg parasitoid in laboratory. It appeared that the rate of parasitism of the hosts could depend on the age of the host eggs and/or age of the laying parasitoid females. Data results from the field experiments about A. anoplophorae release-capture showed that the percentage of slits containing a CLB egg was particularly low on most sentinel trees and the percentage of CLB eggs that were killed, because of natural predators, was high. Only one egg amongst those exposed was attacked by the released parasitoid. These negative results were anyway very useful, since they provided evidence and information on the type of host plants to be used, the time necessary for the exposure of the plants to the egg-laying CLB females, the number of laying parasitoid females to be inserted per cage.
The sentinel trees technique revealed to be not successful; signs and symptoms of CLB presence were not recorded during the two seasons of field observations (2012-2013).
Extremely positive was instead the trial with artificial lures carried out during summer 2013. A total of 32 beetles were captured (4 ALB and 28 CLB) deploying 50 baited traps.
41
Maspero, Matteo <1976>. "Managing invasive populations of Anoplophora chinensis and A. glabripennis in Lombardy." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amsdottorato.unibo.it/7184/.
Full textAbstract:
Two Asian longhorned beetles (Coleoptera: Cerambycidae), commonly known as Citrus Longhorned Beetle (CLB), Anoplophora chinensis (Forster), and Asian Longhorned Beetle (ALB), A. glabripennis (Motschulsky), are considered the most destructive wood borers introduced in Lombardy (northern Italy).
This research aimed at (1) improving laboratory rearing methods for the biological control agent Aprostocetus anoplophorae (Hym.: Eulophidae), an egg parasitoid specific to CLB, and defining release techniques allowing its establishment; (2) test the efficacy of the sentinel tree technique for the early detection of CLB; and (3) evaluating the efficacy of traps baited with artificial lures in attracting adults of ALB and possibly CLB.
Several problems were faced while rearing the egg parasitoid in laboratory. It appeared that the rate of parasitism of the hosts could depend on the age of the host eggs and/or age of the laying parasitoid females. Data results from the field experiments about A. anoplophorae release-capture showed that the percentage of slits containing a CLB egg was particularly low on most sentinel trees and the percentage of CLB eggs that were killed, because of natural predators, was high. Only one egg amongst those exposed was attacked by the released parasitoid. These negative results were anyway very useful, since they provided evidence and information on the type of host plants to be used, the time necessary for the exposure of the plants to the egg-laying CLB females, the number of laying parasitoid females to be inserted per cage.
The sentinel trees technique revealed to be not successful; signs and symptoms of CLB presence were not recorded during the two seasons of field observations (2012-2013).
Extremely positive was instead the trial with artificial lures carried out during summer 2013. A total of 32 beetles were captured (4 ALB and 28 CLB) deploying 50 baited traps.
42
McReynolds, Kim, and Cori Dolan. "Invasive Plants on Small Acreage Properties in Arizona." College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2010. http://hdl.handle.net/10150/144770.
Full textAbstract:
3 pp.Tips for Arizona's Rural Landowners Series -- Plants Unit
The Tips for Arizona's Rural Landowners Fact Sheet Series is intended to educate homeowners who have recently purchased small acreages in Arizona. The purpose of the series is to give homeowners information about living in rural settings. The Plant Unit includes fact sheets on Arizona's native plant law, small-scale gardening, pasture establishment, invasive plants, and assessing plant damage.
43
Innis, Anne Foss. "Comparative ecology of the invasive rubus phoenicolasius and the native rubus argutus." College Park, Md. : University of Maryland, 2005. http://hdl.handle.net/1903/2634.
Full textAbstract:
Thesis (Ph. D.) -- University of Maryland, College Park, 2005.Thesis research directed by: Biology. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
44
Jewett, Elizabeth Bromley. "Epifaunal disturbance by periodic low dissolved oxygen native versus invasive species response /." College Park, Md. : University of Maryland, 2005. http://hdl.handle.net/1903/2714.
Full textAbstract:
Thesis (Ph. D.) -- University of Maryland, College Park, 2005.Thesis research directed by: Biology. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
45
MacNeil, Calum. "The ecology of freshwater amphipods : a study of invasive and native species." Thesis, Queen's University Belfast, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312638.
Full text
46
Fincham, William Norman Whitlock. "Quantifying the impacts of invasive non-native species using key functional traits." Thesis, University of Leeds, 2018. http://etheses.whiterose.ac.uk/21380/.
Full textAbstract:
Invasive non-native species place high pressures on native communities and can result in ecological impacts often associated with differences in key functional behaviours that mediate top-down and bottom-up forces. In this thesis, I use two model systems, the UK Coccinellidae system and the UK freshwater amphipod system, to quantify per-capita differences between native and invasive non-native species. I scale these studies up to more complex ecological communities and attempt to account for additional environmental pressures (e.g. pathogenic infection). First, I present a laboratory experiment to quantify the per-capita differences in predatory behaviour between native and invasive non-native Coccinellidae with a pathogen (Beauveria bassiana) exposure treatment. H. axyridis was the most effcient predator and pathogenic infection reduced the forage ability in all species. Second, I used existing H. axyridis distribution and aphid abundance data to quantify H. axyridis' impact through top-down forces. The arrival of H. axyridis is correlated with significant changes in aphid abundance and, of the 14 species studied, five declined in abundance, four increased, while the remaining five showed no significant change. Third, I measured the per-capita differences in detrital processing rates between native and invasive freshwater amphipods when provided with three diets of differing resource quality and maintained at three temperatures. The rates of detrital processing varied between the native and invasive non-native species and between the temperature and resource quality treatments. Fourth, I applied native and invasive amphipods at two density treatments (high and low) to a field mesocosm experiment to measure how the per-capita differences impacted more complex ecological systems. The presence of invasive amphipods changed the macroinvertebrate community composition and ecosystem functioning. I finish by highlighting that our understanding as to how the pressures of invasive non-native species interact with additional environmental stressors remains limited and an area that warrants further investigation.
47
Costa, Sofia Conde. "Antagonistic interactions between dominant invasive and native ant species in citrus orchards." Master's thesis, ISA, 2017. http://hdl.handle.net/10400.5/14836.
Full textAbstract:
Mestrado em Engenharia Agronómica - Proteção das plantas / Instituto Superior de AgronomiaThe Argentine ant, Linepithema humile (Mayr) established in the South of Portugal (Algarve), about 120 years ago. Zina et al. (2017) compared the composition of ant communities foraging in tree canopy in citrus orchards among the three ecological subregions of Algarve (Litoral, Barrocal and Serra) and observed that the invasive dominant species L. humile was absent from Serra. In this work, we tested the hypothesis that dominant native ant species, such as Tapinoma nigerrimum (Nylander) and Lasius grandis Forel could prevent the Argentine ant from invading Serra. Laboratory experiments were carried out, using both Petri dish arenas and cages to assess the antagonistic interactions between the Argentine ant and two dominant native species, at the individual and colony level, respectively. Overall, our results support the tested hypothesis. At the individual level, both T. nigerrimum and L. grandis showed higher aggression and survival levels than Argentine ant. At the colony level, the results suggest that both the Argentine ant and T. nigerrimum were able to recruit a relative large number of individuals from the colony when trying to colonise a food resource defended by the competitor species. In our experimental conditions, T. nigerrimum showed to be more efficient than Argentine ant in this type of competition, as it was able to defend a food resource in four out of five times from the attack of the former species, as well as to dominate a resource defended by Argentine ant in four out of five times
N/A
48
Bennett, Lindsay. "Invasive plant removal strategies and native plant community recovery in Ontario, Canada." Thesis, Université d'Ottawa / University of Ottawa, 2020. http://hdl.handle.net/10393/41240.
Full textAbstract:
The introduction and spread of invasive species are of major conservation concern. Invasive plant species are hypothesized to impact the population dynamics of native flora, including species at risk (SAR), and may disrupt the functioning of the plant communities which they invade. Some native plant populations may be more vulnerable due to pre-existing factors such as fragmented habitat, poor competitive nature, and/or limited geographical ranges. Because of this, the presence of one or more invasive species is frequently cited as a leading cause of at-risk species decline. However, the actual evidence for this link is weak and the mechanisms are unclear. In this study, I aimed to (1) determine the effect of invasive management schemes on the recovery of native plant communities and to (2) examine the role of factors such as method of removal and duration of invasive removal at two conservation areas in southern Ontario. After 12 candidate study areas were surveyed, two were chosen for the study (for logistical reasons). Specifically, pairs of ‘control’ and ‘invasive’ removal sites were established at St. Williams Conservation Reserve, near Turkey Point Provincial Park, ON (N = 10) and Bruce Peninsula National Park, ON (N = 8) through May - August 2018. Plots were surveyed for native and invasive plant species richness and abundance using transect methods. I found a significant difference in the abundance of native and invasive plants between control and treatment plots at St. Williams Conservation Reserve and Bruce Peninsula National Park, although the trends were in the opposite direction. Neither site had a significant difference in plant diversity between treatment types. I discuss my findings in light of the differences in land use history and management at the two areas and their implications for invasive removal schemes to manage for native plant conservation.
49
Kadye, Wilbert Takawira. "Assessing the impacts of invasive non-native African sharptooth catfish Clarias Gariepinus." Thesis, Rhodes University, 2012. http://hdl.handle.net/10962/d1005070.
Full textAbstract:
Invasive species are of particular concern as they have the potential to alter community structure and food web relationships within their invaded habitats. African sharptooth catfish Clarias gariepinus, a generalist predator, was introduced through an inter-basin water transfer scheme into the Great Fish and Sundays Rivers, Eastern Cape, South Africa, where it threatens the native riverine biota. This thesis assessed its impact from a trophic perspective. Patterns in catfish distribution and abundance revealed an upstream to downstream gradient that was associated with spatial distribution of most species within the mainstream, and a mainstream to tributary gradient that was associated with the spatial distribution of native minnows. The catfish was predicted to occur widely within the mainstem habitats and to decrease progressively along the mainstrem to tributary gradient with the physico-chemical environment being a good proxy for predicting both its occurrence and abundance. The results suggest the catfish proliferated within mainstem habitats where invasion resistance was possibly reduced due to alteration of flow. Population dynamics and size structuring of two native cyprinid minnows Pseudobarbus afer and Barbus anoplus, threatened by catfish, were examined within uninvaded headwater streams in relation to their proximate physical habitats. Their habitats were characterised by seasonal variation in physico-chemical conditions and a spatial variation in substrata compositions. No evidence of differences was found between seasons for density and capture probability for either species. The population size and density for P. afer was found to increase with increasing proportion of boulders. In comparison, B. anoplus population size and probability of capture increased with increasing proportion of bedrock and bank vegetation, respectively. Size structuring was explained predominantly by seasonality and habitat variables for P. afer and B. anoplus, respectively. Stable isotope ratios of carbon and nitrogen were used to compare the spatial variation in both the community-wide and catfish-specific niches and to estimate catfish prey sources from different habitats within the invaded systems. Aquatic community and catfish niches were statistically different among localities, suggesting that each locality had a distinct community-wide trophic structure. Dispersion metrics indicated no evidence of differences in the clustering among individuals, but provided evidence of differences in path trajectories for the comparisons of catfish populations that suggested dietary plasticity within different localities. Dietary studies revealed both ontogenetic shift and omnivory that suggested that catfish may exhibit less pronounced top-down effects within its invaded habitats. Manipulative experiments were used to test the response of benthic macroinvertebrates within two rivers that were differentially impacted by catfish as a presstype disturbance. Macroinvertebrates were non-responsive to catfish presence within a system where catfish had previously been established. In contrast, excluding catfish in this system indicated a response that suggested the importance of refuge within invaded habitats and the possible recovery pattern of certain macroinvertebrate taxa. By comparison, introduction of catfish within previously uninvaded localities provided evidence of direct catfish impact through elimination of conspicuous taxa. Acoustic telemetry was used to investigate catfish movement patterns within an invaded lentic habitat and provided evidence that habitat utilisation was non-random. The shallow and structured river mouth habitat, which was most utilised, was probably the most ideal for its breeding and feeding. This inferred potential overlap with native species and suggested the risk of predation and competitive interference. Catfish also exhibited both nocturnal and diurnal activity patterns that were probably related to feeding.
50
Horsley, Catherine Anne. "Pollinator-mediated interactions between native plants and the invasive alien Himalayan balsam." Thesis, University of Leeds, 2013. http://etheses.whiterose.ac.uk/5278/.
Full textAbstract:
Invasive alien species threaten global biodiversity and can impose severe economic costs. Some invasive alien plants can be strong competitors for pollinators due to a high abundance of attractive flowers, which can disrupt native plant-pollinator interactions and reduce native plant reproductive success. This thesis explores pollinator-mediated competition between native plants and the invasive alien Impatiens glandulifera, Himalayan balsam. Previous studies have found conflicting effects of I. glandulifera on native plant-pollinator interactions. This study aimed, using a combination of direct field observations and controlled experiments, to explore the reasons behind these differences by examining the relationship between impact and the abundance of I. glandulifera at multiple spatial scales, and the responses of a wide range of cooccurring species. Chapters two and three tested the hypothesis that the composition of plant and pollinator communities and bumblebee-flower visitation vary in response to I. glandulifera abundance and spatial scale of invasion. Chapter four tested the hypothesis that I. glandulifera pollen will reduce the reproductive success of the native Lamium album. Chapter five tested the hypothesis that pollinator-mediated competition will alter the genetic quality of pollen received by co-flowering L. album. I found a relationship between the plant and pollinator community composition and the abundance of I. glandulifera, which was generally stronger at a broad scale. Responses to invasion differed according to pollinator taxa and plant traits, which could be useful for identifying and protecting potentially vulnerable native species. Impacts differed according to the mechanism used to examine its effects: bumblebee-flower visitation patterns changed, and L. album experienced reduced seed set and disruption to its mating system; however alien pollen did not prevent L. album from setting seed. In conclusion, the direction and magnitude of pollinator-mediated effects varied with I. glandulifera abundance, spatial scale, and the way in which impact was assessed. A wide range of approaches are necessary to understand the impact of invasive alien plants.