Tesi sul tema "Introduced species"

Humankind has redistributed a large number of species outside their native geographic ranges. Although the majority of introduction attempts fail to establish populations, the cumulative negative effect of successful non-native species has been and will continue to be large. Historical records of land bird introductions provide one of the richest sources of data for testing hypotheses regarding the factors that affect the successful establishment of non-native populations. However, despite comprehensive summaries of global avian introductions dating back two decades only very recent studies have examined the successful establishment of non-native bird species worldwide. It is clear that a non-random pattern exists in the types of land bird species that have been chosen by humans to be introduced outside their native range. Out of the 44 avian families from which species have been chosen for introduction almost 70% of introduction attempts have been from just five families (Phasianidae, Passeridae, Fringillidae, Columbidae, Psittacidae). Notably, these families include game species, insectivorous song birds, and species from the pet trade. It has been hypothesised that the fate of introduced species may be determined in part by heritable characteristics that are shared by closely related taxa. In my analyses, I have used current comparative methods to demonstrate that intrinsic eco-physiological characteristics are significant predictors of the worldwide success of introduced land bird species. The results of my analyses contribute to a greater ecological understanding of the traits that correlate with the successful establishment of non-native species. Notably, the three major conclusions that I have drawn from this thesis are: 1. Non-random patterns of successful establishment exist for introduced land bird taxa that have experienced a repeated number of introduction attempts. This result supports the idea that introduced species have an inherent likelihood of either succeeding or failing to establish non-native populations. 2. Eco-physiological traits are important correlates for determining the variability in introduction outcome for non-native land bird species. With reliable information on introduction attempts and taxa-specific traits predictive models are possible that quantify the outcome of repeated introduction attempts across non-native species. 3. Islands are not universally less resistant than mainland regions to the successful establishment of non-native species. This perception is a reflection of the greater number of introduction attempts to islands rather than an effect of biotic resistance. Any differences in the success of introduction attempts can be attributed largely to differences in the proportion of introductions that have been made across biogeographic regions. I have highlighted that data are accessible for global analyses of the variability in the successful establishment of non-native species. Although establishment success is not a deterministic process, the characteristics of an introduced species can influence the probability of its succeeding. I have shown that with adequate eco-physiological information, and for introduced land bird species at least, this probability can be predicted. These results refute previous suggestions that the stochastic component of species introductions will always overshadow any emerging patterns of successful establishment among non-native populations.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Australian School of Environmental Studies
Science, Environment, Engineering and Technology
Full Text

The surveillance and control of introduced species has become an increasingly important, yet often controversial, form of environmental management. I investigate why and how introduced species management is initiated; whether, why and how it is contested; and what relations and outcomes emerge ‘in practice’. I examine how introduced species management is being done in the United Kingdom through detailed social scientific analyses of the processes, practices, and disputes involved in a series of management case studies. First, I demonstrate how some established approaches to the design and delivery of management initiatives can render them conflict-prone, ineffective and potentially unjust. Then, examining a disputesurrounding a state-initiated eradication of monk parakeets (Myiopsitta monachus), I show why and how ‘parakeet protectors’ opposed the initiative. I identify the significance of divergent evaluations of the risks posed by introduced wildlife; personal and community attachments between people and parakeets; and campaigners’ dissatisfaction with central government’s approach to the issue. By following the story of an unauthorised (re)introduction of Eurasian beavers (Castor fiber) to England, I show how adiverse collective has, at least temporarily, been united and empowered by a shared understanding of beavers as ‘belonging’ in the UK. I consider how nonhuman citizenship is socio-politically negotiated, and how the beavers have become enrolled in a ‘wild experiment’. Finally, through a multi- sited study of grey squirrel (Sciuruscarolinensis) control initiatives, I find important variations in management practitioners’ approaches to killing squirrels, and identify several ‘modes of killing’ that comprise different primary motivations, moral principles, ultimate aims, and practical methods. I identify multiple ways in which people respond and relate to introduced wildlife, and demonstrate how this multiplicity produces both socio-political tensions and accords. Furthermore, throughout this thesis I make a series of propositions for re-configuring the management of introduced species in ways that explicitly incorporate inclusive, constructive, and context-appropriate socio-political deliberations into its design and implementation.

The introduced common warthog, Phacochoerus africanus, in the Eastern Cape is increasing rapidly both in numbers and distribution, despite attempts by landowners to reduce numbers and exclude warthogs. These control attempts are motivated by concerns over the impacts of warthogs, on vegetation, soil and other animal species. This expansion of warthog populations is paradoxical given that a species of warthog occurred historically in this part of the world, apparently at low densities and was wiped out in the mid-1800s. The question therefore arises as to why warthogs are able to overcome population regulation attempts now, and this becomes an invasive species issue as the species now occurring in the Eastern Cape is in fact an introduced species. The objectives of the study were to investigate the status of warthogs as an introduced invasive species in the Eastern Cape by documenting the rate and direction of population expansion, ecological impacts and possible dietary shift of the introduced species, P. africanus compared to the extinct species P. aethiopicus. The research approach adapted here was to test the hypotheses that, (1) the success of P. africanus in the Eastern Cape reflects dietary differences of the two species based on observations of different dental adaptations, as P. africanus has functional incisors, which are absent in P. aethiopicus. Stable carbon isotope analysis of the tooth enamel was used to determine the diet of the two species. (2) Common warthogs are specialized grazers and will impact on a limited range of grass species, this hypothesis was addressed by describing the diet of common warthogs in one site in the Eastern Cape to identify plant species at risk due to invasion by P. africanus, and microhistological faecal analysis was used. (3) Common warthogs have successfully expanded their range in the Eastern Cape since their introduction and are now showing impact, this was addressed by describing the range of expansion of P. africanus in the Eastern Cape, as well as reviewing landowner perceptions of the impacts of warthogs, this was based on questionnaire surveys distributed in the Sundays and the Fish River valleys. The results of the study showed that there are differences in the diet of Cape warthog P. aethiopicus and common warthog P. africanus. The Cape warthog was largely a grazer (86 percent C4 grasses in their diet), while P. africanus is also a grazer (71 percent of C4 grasses in their diet), but with a larger proportion of browse in their diet. These results support the hypothesis that the presence of functional incisors in the common warthog might provide the common warthog with foraging advantages over the Cape warthog. This might be a contributing factor to the success of this invasive species in the Eastern Cape, and might explain the rapid disappearance of Cape warthogs in the 1800s, which coincided with rapid expansion of herds of domestic grazers. A total of twelve grass species are used by common warthogs and are therefore most vulnerable to impacts of this invasive species. Common warthogs are rapidly expanding their range particularly around the Sundays and the Great Fish River valleys and they are perceived by landowners to have impacts on grass cover, soils and fencing. This spread of warthog in the Eastern Cape exhibits characteristics of an invasive species. In light of the findings of this study, it is therefore important that government authorities and other parties concerned recognize that common warthogs are invasive in the Eastern Cape.

Deer have been introduced outside their native ranges numerous times worldwide, causing significant economic and environmental impacts. The scale of problems caused by some introduced deer species is expected to increase, while others are relatively harmless and may be important for conservation as their numbers decline in native regions. This thesis examines the factors promoting invasion in non-native deer, and investigates the population genetics of two deer species introduced to Great Britain. Factors hypothesised to predict invasion success were tested using a comparative analysis of the outcomes of introductions of non-native deer populations. Two modelling approaches were taken to account for confounding effects in species-level and population-level analyses, and different factors were found to explain success at different stages of the invasion process. Populations of roe deer expanding from refugia and reintroductions were examined, and differences in genetic diversity between core and peripheral populations, alongside a decline in diversity with rate of expansion from the core were found. High levels of differentiation between and among core and peripheral populations suggest that genetic drift is the major factor causing these patterns. Using a genome scan of British and European roe deer, loci potentially under selection were identified. Association between some of these loci and environmental variables suggests that climatic extremes may have a role in exerting selective pressures on roe populations. The Chinese water deer is severely declining in range and number in its native habitat, but rapidly expanding after being introduced to Great Britain. Relatively high levels of diversity in native Chinese populations, and significant differentiation between the Chinese and British populations were found. The source population of the British deer is likely to be extinct, and the level of genetic structuring indicates that conserving populations across both ranges is important to maintaining their diversity.

Humankind has redistributed a large number of species outside their native geographic ranges. Although the majority of introduction attempts fail to establish populations, the cumulative negative effect of successful non-native species has been and will continue to be large. Historical records of land bird introductions provide one of the richest sources of data for testing hypotheses regarding the factors that affect the successful establishment of non-native populations. However, despite comprehensive summaries of global avian introductions dating back two decades only very recent studies have examined the successful establishment of non-native bird species worldwide. It is clear that a non-random pattern exists in the types of land bird species that have been chosen by humans to be introduced outside their native range. Out of the 44 avian families from which species have been chosen for introduction almost 70% of introduction attempts have been from just five families (Phasianidae, Passeridae, Fringillidae, Columbidae, Psittacidae). Notably, these families include game species, insectivorous song birds, and species from the pet trade. It has been hypothesised that the fate of introduced species may be determined in part by heritable characteristics that are shared by closely related taxa. In my analyses, I have used current comparative methods to demonstrate that intrinsic eco-physiological characteristics are significant predictors of the worldwide success of introduced land bird species. The results of my analyses contribute to a greater ecological understanding of the traits that correlate with the successful establishment of non-native species. Notably, the three major conclusions that I have drawn from this thesis are: 1. Non-random patterns of successful establishment exist for introduced land bird taxa that have experienced a repeated number of introduction attempts. This result supports the idea that introduced species have an inherent likelihood of either succeeding or failing to establish non-native populations. 2. Eco-physiological traits are important correlates for determining the variability in introduction outcome for non-native land bird species. With reliable information on introduction attempts and taxa-specific traits predictive models are possible that quantify the outcome of repeated introduction attempts across non-native species. 3. Islands are not universally less resistant than mainland regions to the successful establishment of non-native species. This perception is a reflection of the greater number of introduction attempts to islands rather than an effect of biotic resistance. Any differences in the success of introduction attempts can be attributed largely to differences in the proportion of introductions that have been made across biogeographic regions. I have highlighted that data are accessible for global analyses of the variability in the successful establishment of non-native species. Although establishment success is not a deterministic process, the characteristics of an introduced species can influence the probability of its succeeding. I have shown that with adequate eco-physiological information, and for introduced land bird species at least, this probability can be predicted. These results refute previous suggestions that the stochastic component of species introductions will always overshadow any emerging patterns of successful establishment among non-native populations.

Biological invasions represent both an urgent conservation problem and an opportunity to advance ecological theory. Development of pertinent research questions and proactive management strategies require knowledge of which introduced species are present and of spatiotemporal trends in the distribution of natives and invaders. In Chapter 2 we developed a quantitative framework to identify spreaders and decliners and estimate invasion chronologies based on a historical fish presence data set for upper and middle New River (UMNR) tributaries. Our framework accounts for spatiotemporal variability in sampling effort by aggregating presences by watershed and expressing range size as a function of the number of watersheds sampled per time period. The majority (55%) of fish species present in the study area were introduced, 51% of which were spreaders. Most spreaders (84%) appeared to be spreading exponentially. The rate of new introductions detected in the study area has slowed since the mid-20th century. Two natives, the mound-spawning bluehead chub Nocomis leptocephalus and its strong nest associate (reproductive mutualist), mountain redbelly dace Chrosomus oreas, were among the most rapid spreaders. Four natives showed evidence of decline. Our framework leverages historical presence data to reconstruct temporal trends in species distributions. It sets the stage for further study of factors driving stream fish invasions and declines in the Appalachian region, and is transferable to diverse taxonomic groups and geographic regions. Species traits and human activities mediating stream-fish invasions remain poorly understood. In Chapter 3 we modeled the contribution of species traits to invasion success of UMNR tributary fishes during the colonization and spread stages. Biological traits accurately explained colonization and spread success, whereas ecological traits resulted in less accurate models. Colonization success was positively related to time since introduction, benthic feeding, an equilibrium life history, and nest spawning. Successful spread was positively related to winter air temperature in the native range and an equilibrium life history. Variables estimating human use and propagule pressure were non-informative. Traits that influenced invasion success were consistent with the hypothesis that human land-use practices have increased the invasibility of highland watersheds by creating novel conditions suited to lowland and equilibrium invaders.
Master of Science

Fire is a natural component of, and serves as a tool for, the restoration of forested ecosystems worldwide; however, disturbance due to fire also has been implicated in the proliferation of invasive species. How these fires affect occupancy and use of the forest by wildlife is of great concern, in particular, the differential response of non-native and native species. In the North American Southwest, prior to European settlement, frequent wildfires helped to maintain forest structure. We examined the effect of a large wildfire on an introduced population of the Abert's squirrel (Sciurus aberti) that has invaded the high elevation forests inhabited by the critically endangered Mt. Graham red squirrel (Tamiasciurus fremonti grahamensis). We found that introduced Abert's squirrels were more common than native red squirrels in burned areas. Abert's squirrels did not abandon burned areas but nested, foraged, and did not adjust their home range size in burned areas. This suggests that invasive Abert's squirrels are better able to exploit burned areas than native red squirrels and that fire can favor non-native species. This interaction between non-native species, native species, and fire adds new insight into the complexities of conservation and restoration of ecosystems and helps to inform conservation activities worldwide.

The long-term success of an introduced population depends on the ecological conditions in its new environment, but is also influenced by stochasticity. This is particularly clear in the first stage of an invasion when the population is still small and either goes extinct quickly or establishes a self-sustaining population. Once established, some populations grow and spread spatially, with potential impacts on native communities and ecosystems. The role of stochasticity during these later invasion stages remains unclear. Furthermore, little is known about the population genetic and evolutionary consequences of stochastic invasion trajectories. With this dissertation, I would like to contribute to a stochastic eco-genetic theory of the entire invasion process—from the first introduction up to potential impacts. The overarching questions in this dissertation are: a) How does a population’s movement through the invasion process depend on ecological factors influencing its average growth rate? b) How does it depend on factors influencing the stochastic variability in the population dynamics? c) How much genetic diversity do introduced populations harbor on average upon reaching a certain point in the invasion process? d) To what extent can the population-genetic consequences of invasion trajectories feed back onto the population dynamics? Together with my advisors and coauthors, I have conducted four studies, each addressing two or more of these questions for specific ecological scenarios. We employ several types of stochastic models: Markov chains, Markov processes, their diffusion approximations, and coalescent-like genealogy simulations. In Chapter 1 (Wittmann et al., 2013a, appeared in Theoretical Population Biology), we focus on a factor influencing the introduced population’s average growth rate: the intensity of competition with an ecologically similar native species. Our results indicate that the expected time until the introduced species drives the native competitor to extinction is smallest for intermediate competition intensity. This phenomenon results from the opposing effects of competition intensity at different points of the invasion process: On the one hand, intense competition renders the establishment of the introduced population more difficult; on the other hand, it facilitates the later exclusion of the native species. In Chapter 1, we also investigate to what extent the native species’ extinction is accelerated if a reduction in population size entails a reduction in genetic diversity and thus a reduced ability to adapt to a changing environment. We find this eco-genetic feedback to be particularly strong at small competition intensities. In Chapter 2 (Wittmann et al., 2013b, in press at Oikos), we compare introduction regimes with the same average number of individuals introduced per time unit, but with a different temporal distribution. Relative to regimes with many small introduction events, regimes with few large introduction events generate more variability in population-size trajectories. We show that this variability helps introduced populations to overcome difficult stages in the invasion process (those with a negative average growth rate), but is disadvantageous during easy stages (those with a positive average growth rate). In the light of our results, we can reinterpret three published data sets on invasion success under different introduction regimes. In Chapters 3 and 4 (Wittmann et al., 2013c,d), we examine levels of genetic diversity in populations that have successfully overcome a strong demographic Allee effect. In this ecological scenario, the average population growth rate is negative below a certain critical population size and positive above, such that the first stage in the invasion process is difficult and the second one easy. In Chapter 3, we assume Poisson-distributed offspring numbers. We show that compared to successful populations without an Allee effect, successful Allee-effect populations are expected to harbor either more or less genetic diversity, depending on the magnitude of typical founder population sizes relative to the critical population size. Part of the explanation is that, counter-intuitively, successful Allee-effect populations escape particularly fast from the range of small population sizes where genetic drift is strongest. In Chapter 3, we also identify conditions under which the critical population size can be estimated from genetic data. In Chapter 4, we consider a range of offspring-number models leading to either more or less variability in population dynamics than the Poisson model. For a fixed founder population size, we observe that the Allee effect has a negative influence on genetic diversity for small amounts of variability, but a positive influence for large amounts of variability. We show that the differences between our various offspring-number models are so substantial that they cannot be resolved by rescaling the parameters of the Poisson model. Taken together, these results offer some general conclusions with respect to the four main questions raised above. a) How fast an introduced population completes the invasion process is mainly determined by the presence and severity of difficult stages. Therefore, an ecological change promotes invasion success if it lessens such difficult stages. b) From the perspective of the introduced population, variability is advantageous during difficult but not during easy stages of the invasion process. c) Because the strength of genetic drift depends on population size, a key to understanding the population genetic consequences of invasion trajectories is to consider how much time the population of interest spends in different population-size ranges. d) Feedbacks between a reduction in population size and a loss of genetic diversity are strongest in ecological scenarios where the population of interest spends considerable time at small population sizes. Some of the most striking results in this dissertation cannot be understood from a deterministic point of view, but only when considering stochasticity. Thus, stochasticity does not just add “noise” to some average outcome, but can qualitatively change the behavior of biological systems.
Der langfristige Erfolg einer eingeführten Population hängt von den ökologischen Bedingungen in ihrer neuen Umgebung ab, aber auch vom Zufall. Besonders offensichtlich ist die wichtige Rolle des Zufalls für kleine Populationen im Anfangsstadium einer Invasion. In diesem Stadium entscheidet sich, ob die eingeführte Population nach kurzer Zeit ausstirbt oder sich dauerhaft etablieren kann. Manche etablierten Populationen wachsen dann weiter und breiten sich räumlich aus, zum Teil mit schwerwiegenden Folgen für einheimische Gemeinschaften und Ökosysteme. Bislang ist nicht klar, welche Rolle der Zufall in diesen späteren Invasionsstadien spielt und welche populationsgenetischen und evolutionären Auswirkungen vom Zufall geprägte Invasionsverläufe haben. Mit dieser Dissertation möchte ich beitragen zu einer stochastischen öko-genetischen Theorie des gesamten Invasionsprozesses – von der Einführung bis hin zu möglichen Auswirkungen. Meine übergreifenden Fragen sind: a) Welche Rolle für den Invasionsverlauf spielen ökologische Faktoren, die die durchschnittliche Wachstumsrate der eingeführten Population beeinflussen? b) Und welche Rolle spielen Faktoren, die die stochastische Variabilität der Populationsdynamik beeinflussen? c) Wie viel genetische Diversität weisen eingeführte Populationen im Durchschnitt auf, wenn sie einen bestimmten Punkt im Invasionsprozess erreichen? d) Inwiefern können die populationsgenetischen Auswirkungen von Invasionsverläufen wiederum die Populationsdynamik beeinflussen und so zu einer Rückkopplung führen? Zusammen mit meinen Betreuern und Koautoren habe ich vier Studien durchgeführt, die sich für bestimmte ökologische Szenarien jeweils mit mindestens zwei dieser Fragen befassen. Dazu kommen im Verlauf der Dissertation verschiedene Typen von stochastischen Modellen zum Einsatz: Markov-Ketten, Markov- und Diffusionsprozesse sowie Coalescent-artige Genealogie-Simulationen. In Kapitel 1 (Wittmann et al., 2013a, erschienen in Theoretical Population Biology) konzentrieren wir uns auf einen Faktor, der die durchschnittliche Wachstumsrate der Population beeinflusst: die Stärke der Konkurrenz mit einer ökologisch ähnlichen einheimischen Art. Unsere Ergebnisse deuten darauf hin, dass die erwartete Zeit bis zum Aussterben des einheimischen Konkurrenten für mittlere Konkurrenzstärken am kleinsten ist. Das können wir dadurch erklären, dass die Konkurrenzstärke gegensätzliche Auswirkungen in verschiedenen Stadien des Invasionsprozesses hat: Einerseits erschwert eine hohe Konkurrenzstärke die Etablierung der eingeführten Art, andererseits führt eine hohe Konkurrenzstärke aber auch dazu, dass die einheimische Art schnell verdrängt werden kann. Zusätzlich untersuchen wir in Kapitel 1, wie stark eine öko-genetische Rückkopplung das Aussterben der einheimischen Population beschleunigen würde. Dazu berücksichtigen wir, dass ein Rückgang der einheimischen Populationsgröße zu einem Verlust an genetischer Diversität führt, und das wiederum zu schlechterer Anpassung an veränderte Umweltbedingungen und darum weiterem Schrumpfen der Population. Unsere Ergebnisse legen nahe, dass diese öko-genetische Rückkopplung dann besonders stark ist, wenn die Konkurrenz zwischen einheimischer und eingeführter Art eher schwach ist. In Kapitel 2 (Wittmann et al., 2013b, im Druck bei Oikos) untersuchen wir für feste durchschnittliche Einführungsraten (Individuen pro Zeiteinheit), welche Rolle die zeitliche Verteilung der Individuen spielt. Besonders wichtig ist hierbei die Beziehung zwischen zeitlicher Verteilung und der Variabilität in der Größenentwicklung der Population. Wir zeigen, dass Fälle mit wenigen großen Einführungsereignissen zu mehr Variabilität führen als Fälle mit vielen kleinen Einführungsereignissen. Diese Variabilität hilft den eingeführten Populationen dabei, schwierige Stadien im Invasionsprozess (also solche mit einer negativen durchschnittlichen Wachstumsrate) zu bewältigen, ist aber anderseits in einfachen Stadien mit positiver durchschnittlicher Wachstumsrate von Nachteil. Im Lichte unserer Ergebnisse können wir aus der Literatur bekannte Daten zu Invasionsprozessen neu interpretieren. In den Kapiteln 3 und 4 (Wittmann et al., 2013c,d) untersuchen wir die genetische Diversität von Populationen, die einen starken demografischen Allee-Effekt erfolgreich überwunden haben. Laut Definition ist dabei die durchschnittliche Wachstumsrate bei Populationsgrößen unterhalb einer gewissen kritischen Größe negativ und in größeren Populationen positiv, so dass das erste Stadium des Invasionsprozesses schwierig ist und das zweite einfach. In Kapitel 3 zeigen wir unter der Annahme Poisson-verteilter Nachkommenzahlen, dass erfolgreiche Allee-Effekt-Populationen je nach Startgröße entweder eine höhere oder eine niedrigere durchschnittliche genetische Diversität aufweisen als erfolgreiche Populationen ohne Allee-Effekt. Das kommt zum Teil daher, dass erfolgreiche Allee-Effekt-Populationen besonders schnell das schwierige erste Stadium des Invasionsprozesses verlassen, wo genetische Drift am stärksten ist. Außerdem untersuchen wir in Kapitel 3, unter welchen Bedingungen sich die kritische Populationsgröße aus genetischen Daten schätzen lässt. In Kapitel 4 betrachten wir eine Reihe von Modellen für die Anzahl an Nachkommen von Individuen oder Paaren in der Population. Manche dieser Modelle führen zu mehr stochastischer Variabilität in der Populationsdynamik, andere zu weniger Variabilität als das in Kapitel 3 betrachtete Poisson-Modell. Für feste Startgröße beobachten wir, dass der Allee-Effekt bei kleiner Variabilität einen negativen Einfluss auf die genetische Diversität hat und bei großer Variabilität einen positiven Einfluss. Wir zeigen weiterhin, dass die Unterschiede zwischen unseren Nachkommenzahl-Modellen so substanziell sind, dass sie sich nicht durch eine Umskalierung der Parameter des Poisson-Modells erklären lassen. Zusammen genommen erlauben uns diese Ergebnisse einige allgemeine Schlussfolgerungen bezüglich der vier oben aufgeführten übergreifenden Fragen. a) Wie schnell eine eingeführte Population den Invasionsprozess durchläuft, hängt hauptsächlich davon ab, ob es schwierige Stadien gibt, und wie schwierig diese sind. Deshalb begünstigt eine ökologische Veränderung den Invasionserfolg dann, wenn sie schwierige Stadien im Invasionsprozess mindert. b) Aus der Perspektive der eingeführten Population ist Variabilität in schwierigen Stadien des Invasionsprozesses von Vorteil, aber in einfachen Stadien von Nachteil. c) Da die Stärke der genetischen Drift von der Populationsgröße abhängt, können wir die populationsgenetischen Auswirkungen von Invasionsverläufen verstehen, indem wir analysieren, wie viel Zeit die betrachtete Population in verschiedenen Populationsgrößenbereichen verbringt. d) Rückkopplungen zwischen einem Rückgang der Populationsgröße und einem Verlust genetischer Diversität sind am stärksten, wenn die Population viel Zeit im Bereich kleiner Populationsgrößen verbringt. Einige der wesentlichsten Ergebnisse dieser Dissertation können aus einer deterministischen Perspektive nicht verstanden werden, sondern sind ein direktes Produkt von Stochastizität. Dies macht deutlich, dass Stochastizität nicht einfach einem gewissen Durchschnitts- ergebnis etwas Rauschen hinzufügt, sondern das Verhalten biologischer Systeme qualitativ verändern kann.

Adaptive radiation – the proliferation of species from a single ancestor and diversification into many ecologically different forms – has long been heralded as an important process in the generation of phenotypic diversity. However, the early stages of adaptive radiation are notoriously elusive to observe and study. In this dissertation, I capitalize on communities of introduced non-native Anolis lizards as analogues of early stage adaptive radiations. In Chapter II, I begin by reviewing the concept of “ecological opportunity” – a classic hypothesis put forward as a potential key to understanding when and how adaptive radiation occurs. In Chapter III, I investigate the mechanisms which allow for coexistence and community assembly among ecologically-similar species. To do this I investigate range dynamics and assembly patterns of introduced anoles on the oceanic island of Bermuda. I discover that interspecific partitioning of the structural environment facilitates species coexistence, however the order of species assembly was an important predictor of final community composition. In Chapter IV, I then investigate how interspecific interactions between coexisting species may drive phenotypic divergence. This is the process of character displacement, which has been widely hypothesized to be an important mechanism driving phenotypic divergence in adaptive radiations. To do this I investigate sympatric and allopatric populations of introduced Cuban brown anoles (Anolis sagrei) and Puerto Rican crested anoles (A. cristatellus) in Miami FL, USA. I identify morphological shifts in sympatry, driven by divergence in habitat use and decreases in abundance. This study provides evidence of how selection on both ecologically and sexually-important traits can both drive phenotypic divergence during character displacement. Finally, in Chapter V, after taking advantage of non-native species as model eco-evolutionary systems in previous chapters, I investigate the potentially harmful effects that their presence may have on vulnerable native biodiversity. To do this I investigate the conservation risk posed by newly-discovered populations of A. sagrei on Bermuda to Critically Endangered endemic Bermuda skinks (Plestiodon longirostris). Through a detailed analysis of habitat use, diet, population size, and morphology of A. sagrei on Bermuda, we conclude it likely poses a high conservation threat to P. longirostris through interspecific competition.

Understanding broad patterns of biodiversity requires developing a unified and rigorously tested theory that explains how species coexist despite the risk of competitive exclusion. Species interactions are fundamentally shaped by environmental variability. Recent theoretical development has predicted a set of general mechanisms that promote species coexistence under variable environments. Nevertheless, this theoretical framework has received limited empirical tests. Biological invasions offer excellent opportunities to empirically test coexistence mechanisms in communities in which the stability of coexistence is likely affected by introduced species. I took this opportunity to directly test the theory of species coexistence in this dissertation work by investigating how environmental variability affected the invasion of introduced species and their coexistence with native species. My collaborators and I started the investigation of diversity maintenance by first examining the range expansion of introduced species. Studying range shifts can reveal drivers of diversity patterns, which are formed by overlapping ranges of different species. We used a novel spatial analysis to determine the scale-dependent expansion rate of an invasive winter annual species, Brassica tournefortii over North America as well as to infer the drivers of this scale dependency. We found that this species expanded rapidly on scales from 5 to 500 km historically but had ceased its current expansion on the 100-500 km scales due to climatic constraints. This finding left open the question why this species continued its spread on the 5-50 km scales and how it would impact native species within its invaded range. To address these questions, we examined relatively local scale interactions between B. tournefortii and its competitors. We compared key demographic rates of B. tournefortii with other invasive and native winter annuals over a Sonoran Desert landscape to check conditions necessary for their spatial and temporal niche differentiation. We found the presence of two essential requirements for their niche differentiation: species-specific germination responses that could differentiate species by their favored environments and buffered population growth in time and space that could prevent catastrophic population declines when species faced unfavorable conditions. These conditions could provide niche opportunities to promote both the establishment of B. tournefortii and the persistence of native species under its presence. Building upon this finding, we directly quantified one general mechanism of spatial niche differentiation between B. tournefortii and its native competitors. We measured the strength of this mechanism, the spatial storage effect, across a hierarchy of spatial scales (subhabitat -> habitat -> landscape). We found that this mechanism did not promote species coexistence on any of these scales over the study period. These species were not differentiated over their tested spatial niches because weak competition following dry growing conditions failed to intensify intraspecific competition relative to interspecific competition. The strength of this mechanism increased from occasionally producing negative effects on lower scales to consistently being non-negative on the highest scale. This scale-dependent pattern was in line with the expectation that coexistence potential would increase with scales as species interacted over a wider range of environmental heterogeneity. Our findings demonstrated empirically that environmental variability in time and space led to scale-dependent patterns of the coexistence potential between introduced and native species. This work showed that introduced and native species could be differentiated by their environmental responses given spatial and temporal environmental heterogeneity on higher scales. However, for those species to stably coexist on higher scales, competitive effects had to follow environmental responses to separate species by their own density-dependent feedback loops. This work is among the first few empirical tests of a body of theory that holds the promise to generalize the mechanisms of spatial and temporal niche differentiation. Its success and limitation can motivate more studies to adopt the guiding mathematical principles and to use similar yet more innovative approaches to address the grand question of biodiversity maintenance.

A seine net (3 mm mesh), and where necessary other methods, were used to collect three native species (Galaxias occidental is, Bostockia porosa and Edelia vittata) and two introduced species (Gambusia affinis and Perea fluviatilis) at regular intervals from the southern branch of the Collie River. The same net was used to sample the native species Galaxiella munda from a tributary of the Warren River 120 km further south in Western Australia. Annuli on otoliths and the seasonal trends shown by gonadal development, including changes in oocyte diameter, were used to determine the age and the duration and peak time of spawning of each of the four native species. Spawning of all four native species, which follows a movement into either tributary creeks or flood waters, takes place between mid-winter and mid-spring, with the peak time of spawning differing slightly amongst species. While sexual maturity is reached by G. occidentals, E. vittata and G. munda at the end of the first year of life, it is not attained by B. porosa until the end of the second year of life. Each species can live for five or six years, except G. munda which dies before it reaches two years of age. The breeding of G. afTinis occurs in the shallows between mid-spring and late summer, while that of P. fluviatilis takes place in deeper water in the spring. Amongst the native species, G. occidentals and B. porosa spawn only once in a breeding season, whereas E. vittata and G. munda are multiple spawners, producing clutches of eggs at intervals throughout the spawning period. The relationships between the age and size at first maturity and the growth rate and spawning mode of these four species are discussed. The influence of growth of the females of G. affinis during the spring and summer on the number of live young they produce is determined. All of the above native and introduced species are carnivorous. At most times of the year, the diets of G. occidentals and 0+ P. fluviatilis, which were characterised by insects from the water surface and copepods from the plankton respectively, showed little overlap with those of other species. Although B. porosa and E. vittata both fed predominantly on benthic invertebrates, the former species ingested a greater amount of larger prey and fed at night rather than during the day. The diets of G. affinis varied considerably at different times and in different locations, indicating that this species was particularly opportunistic and could focus on prey which were abundant. Comparisons are made between the biology of native fish in the highly seasonal environment of south-western Australia and those of the same and other families in eastern Australia and New Zealand.

Introduced species present one of the greatest threats to biodiversity of native species, and knowledge of introduced species ecology is imperative for the development of management plans to ensure conservation of native species populations. We sought to determine the distribution and nesting behavior of an introduced population of red-bellied squirrels (Sciurus aureogaster) on islands of the Florida Keys currently managed as part of Biscayne National Park, and document potential for the species to impact native flora and fauna. Squirrels were difficult to observe in the dense vegetation of the subtropical forest, so we relied on their leaf nests, which were highly visible in the canopy of trees, to determine current presence and distribution on the Park's islands. We found nests throughout the mixed-hardwood forests of Elliott Key and Sands Key, and also documented a single, old nest on Old Rhodes Key, the first ever documentation of the species that far south in the Upper Keys. Nests were located in tall trees with more canopy linkages than random focal trees, and nests were placed in the upper canopy on the north side of the nest tree more often than expected by chance. Squirrels selected West Indies mahogany (Swietenia mahagoni) to place nests more often than available in the forest. Squirrels used areas with greater tree density and canopy cover, but lower recent hurricane damage and fewer woody shrub stems, than areas available at random in the forest. Squirrels built nests only in mixed-hardwood forest. Overall, this introduced species exhibited nest site selection behavior similar to other tree squirrels, and appears capable of continued spread despite the initial site of introduction on an oceanic island. Knowledge obtained from this research is being used by managers and applied to an eradication program to remove this invasive species from Biscayne National Park.

The introduction of exotic species is one of the greatest threats to freshwater biodiversity. Brown trout are native to Eurasia, but have been introduced to much of the rest of the world, including the United States. In other parts of their introduced range, brown trout have caused substantial negative effects to native species‟ abundances and distributions, and have altered the structure of some aquatic communities. In the United States, studies of some streams and watersheds have shown that brown trout can negatively affect native species, but I found no study that considers the effect of brown trout across a large portion of their introduced range. For this study, I examined if (1) the abundance and distribution of two ecologically different native fish taxa (sculpins and speckled dace) and (2) the structure of entire stream vertebrate assemblages were negatively associated with the presence and abundance of brown trout. I based my analyses on existing, standardized survey data collected across streams of the western United States. I found no relationship between brown trout and the abundance, presence-absence, or probability of detection of sculpins or speckled dace. I also found that brown trout were not associated with the structure of native stream vertebrate assemblages. My results imply that native stream vertebrates in western US streams are able to coexist with brown trout across the western United States, despite the negative effects brown trout can have on some taxa in individual watersheds or rivers.

Doutoramento em Biologia
In marine ecosystems, organisms are exposed to a variety of stressors such as metal/metalloid contamination, climate change, and introduction or spread of invasive species. One of the most successful invasive species is the clam Ruditapes philippinarum but this species may also co-habit in coastal ecosystems with the native species (Ruditapes decussatus). Although some researchers have studied these species to assess environmental contamination, little information is available about both species from different ecosystems. In addition, the effects induced by contaminants and climate change related factors on both species remain poorly understood. Therefore, the present thesis aimed to understand if the native species, R. decussatus, and the introduced species, R. philippinarum, co-exist in the same areas of the Ria de Aveiro and the Óbidos lagoon, and to study their metal(loi)s accumulation, partitioning, and biochemical performances when co-habiting. In addition, in the laboratory, it was also assessed the response of sympatric clam species when exposed to single (As concentrations and salinity, temperature, pH shifts) or combined stressors (pH and As concentrations). Field studies in the Ria de Aveiro and Óbidos lagoon revealed that native and introduced species co-exist in both marine ecosystems and in 2013/2014 the introduced species has not yet supplanted the native one. When present in the same area, both species presented similar metal(loid)s concentrations, cellular metal partition, and biochemical performance, independently of the contamination level of each area and ecosystem. This study also revealed that both species from both ecosystems accumulated higher metal(loid)s concentrations in the least contaminated areas than in the most contaminated areas. In addition to the fieldwork, laboratory studies showed that both species exposed to As contamination presented similar tolerance, being able to regulate As toxicity up to 8.2 mg/L. However, both species under As contamination scenario above 8.2 mg/L were negatively affected, not being able to maintain detoxification mechanisms against As exposure leading to its death. Relatively to temperature exposure, the native species was the most tolerant species to future chronic warming environmental conditions since the temperature rises induced less subcellular and molecular changes in native, than in introduced species. In addition, native species were also tolerant to seawater acidification (7.3) when compared to introduced one. However, low (14) and high (35) salinities affected negatively native species. Similar results were observed for introduced species at high salinity. Regarding the combined effects exposure, results showed that both species were not negatively affected by the predicted seawater acidification. However, the introduced species accumulated higher amount of As than the native clams, suggesting that the predicted seawater acidification may potentiate health risks associated with the consumption of this species. In conclusion, findings reported in this thesis improved the knowledge and provide an important data base about the distribution, contamination and the performance of both species from different ecosystems and the response of both species exposed to different environmental conditions, such as arsenic contamination, temperature increase, salinity shifts, and seawater acidification.
Nos ecossistemas marinhos os organismos estão expostos a uma enorme variedade de stresses tais como a contaminação por metais/metaloides, as alterações climáticas e a introdução de espécies invasoras. Uma das espécies invasoras mais bem-sucedidas é a amêijoa Ruditapes philippinarum, no entanto esta espécie pode também coabitar em ecossistemas costeiros com espécies nativas de amêijoas tais como Ruditapes decussatus. Embora alguns estudos utilizem estas espécies para avaliar a contaminação ambiental, pouca informação está disponível relativamente à abundância e distribuição de R. decussatus e R. philippinarum em diferentes ecossistemas. Além disso, os impactos induzidos por contaminantes e por fatores relacionados com as alterações climáticas em ambas as espécies continuam pouco conhecidos. Posto isto, a presente tese teve como objetivos perceber se a espécie nativa, R. decussatus, e a espécie introduzida, R. philippinarum, coabitam na Ria de Aveiro e na Óbidos lagoon, estudar a acumulação de metais e arsénio, a sua compartimentação e as alterações bioquímicas induzidas nestas espécies quando no ambiente. Para além destes objetivos, pretendeu-se também avaliar, através de ensaios laboratoriais, a resposta de ambas as espécies quando expostas a um stress isolado (contaminação por arsénio e variações de salinidade, temperatura ou pH), ou à combinação de diferentes stresses (contaminação por arsénio e variações de pH). Os estudos de campo efetuados na Ria de Aveiro e na Óbidos lagoon mostraram que as duas espécies coabitam e que a espécie introduzida em 2013 e 2014 ainda não tinha substituído a espécie nativa. Quando presentes na mesma área, ambas as espécies apresentam concentrações e compartimentação semelhante de metais e de arsénio, independentemente da contaminação de cada área e ecossistema. Esta semelhança reflete-se também ao nível da resposta bioquímica. Este estudo evidenciou também que, no ambiente ambas as espécies bioacumularam maior concentração de metais e arsénio nas áreas menos contaminadas do que nas áreas mais contaminadas. Para além dos trabalhos de campo, os estudos de laboratório mostraram que ambas as espécies quando expostas a arsénio apresentaram tolerância semelhante, sendo capazes de tolerar a toxicidade do arsénio até 8.2 mg/L. Contudo, quando expostas a um cenário de contaminação acima desta concentração, ambas as espécies apresentaram elevada mortalidade e reduzida capacidade em manter os seus mecanismos de desintoxicação. Relativamente à exposição a temperaturas elevadas, a espécie nativa provou ser a mais tolerante, uma vez que se verificaram menores alterações celulares e moleculares nesta espécie comparativamente à espécie introduzida. A espécie nativa também evidenciou uma elevada tolerância face à acidificação da água do mar comparativamente à espécie introduzida. No entanto, salinidades altas (35) e baixas (14) afetaram negativamente a espécie nativa. O mesmo se verificou para a espécie introduzida a salinidade 35. Em relação à exposição combinada a pH e arsénio os resultados mostraram que a resposta bioquímica de ambas as espécies não foi afetada negativamente. Contudo a espécie introduzida acumulou mais arsénio que a espécie nativa, pelo que a acidificação da água do mar poderá potenciar o risco associado ao consumo desta espécie. Em conclusão, os resultados reportados nesta tese contribuem para uma melhor compreensão sobre a coexistência de ambas as espécies em diferentes ecossistemas, da acumulação e toxicidade de metais/metaloides e da resposta de ambas as espécies quando expostas a diferentes condições ambientais tais como contaminação por arsénio, aumento da temperatura, flutuação da salinidade, e acidificação da água do mar.

The detrimental impact of invasive, non-native species on biodiversity conservation and ecosystem function is widely recognised. The invasion of predatory species can have particularly deleterious consequences on native species in the invaded range and there is an increasing awareness of, and necessity for, management action to minimise these impacts. There is a growing body of literature identifying the impacts of invasive species and priorities for conservation action. However, there is a noticeable gap between the rising scientific output regarding invasive species control and conservation measures, and the management action required to implement recommendations. The American mink (Neovison vison, hereafter mink) has been a recent focus of invasive species research and management. Mink are semi-aquatic mustelids and generalist predators and were introduced to countries around the world for fur farming. Feral populations have established across the introduced range with devastating consequences for native species, particularly birds and mammals. In the UK, mink are held partly responsible for the decline in water voles (Arvicola amphibius) and in Scotland in particular, breeding seabirds are significantly impacted by mink predation. Control of mink in North East Scotland has proven successful using an adaptive management, community-based approach but there is currently no equivalent project in the complex, coastal landscape of west Scotland. This study aimed to provide information that could refine and further develop management plans for mink in north and west Scotland by acquiring a better understanding of the ecology of mink in Scotland to inform the implementation of control. Mink were distributed across all but the far north of Scotland. There was spatial and temporal variation in the pattern and rate of their expansion which was attributed to landscape heterogeneity. In northwest Scotland, availability of suitable habitat was restricted to the coastline and consequently, the availability of prey was hypothesised to be limited to coastal areas. Indeed, the diet of mink in northwest Scotland had a greater input from marine resources than those in southwest Scotland, where habitat availability and, therefore, terrestrial food resources, extended inland. Landscape features were shown to affect the direction of colonisation, with mountains restricting and valleys facilitating dispersal. Population genetic studies confirmed that mink dispersal in northwest and northeast Scotland was limited by mountain barriers. Additionally, populations in northwest Scotland were likely to have originated from southwest Scotland. These results suggest that mink control should be primarily focussed in coastal habitats in west Scotland and that the risk of reinvasion from relatively close populations in northeast Scotland is minimal. Volunteer involvement in conservation projects is being accepted increasingly as a cost-effective way to gather ecological information and implement conservation over large spatial scales. The landscape of west Scotland, particularly in northern areas, is complex, remote and sparsely populated by humans which consequently creates challenges for executing mink control. Ecotourism boat operators were concerned about the presence of mink and their effect on local wildlife in coastal areas and were willing to volunteer in mink management. Consequently ecotourism boat operators could provide a key link between management recommendations and implementation. This study combined methodologies from ecological modelling, population genetics, chemical analyses and social science to address questions regarding invasive species management. This holistic approach has resulted in a thorough overview of the distribution and ecology of an invasive species as well as recommendations for management action and implementation that will be applicable to a range of invasive species.

Since globalization have promoted the ornamental trade and accelerated the movement of freshwater fishes around the world, non-native species pose a high potential to be released into local freshwater habitats, and to spread and establish as invasive and nuisance species with adverse ecological, economic and social impacts. This study aimed to investigate the potential of the ornamental freshwater fish trade as an invasion pathway in Hong Kong, assess the ecological risk of common aquarium freshwater fish species being traded in the local market, identify species of concern and recommend ways for their management with a view to minimizing biological invasion risk associated with the aquarium trade. Based on a series of systematic market surveys through visiting 46 major aquarium shops in Hong Kong, about 167 freshwater fish species were found in the local aquarium trade between summer 2012 and spring 2013. Twenty-five species were randomly selected to go through two standard ecological risk assessment protocols (i.e., FISK & IFRA). The assessment results indicated that the goldfish (Carassius auratus), common carp (Cyprinus carpio carpio) and Wel’s catfish (Silurus glanis) have a high invasive risk in Hong Kong. The ornamental trade is one of the significant sources of freshwater fish invasions in Hong Kong. An integrated invasive species management plan is recommended to apply and implement in Hong Kong. The key elements of this management plan include (1) development of law and regulation on invasive species, (2) establishment of an early detection programme (like the current study), (3) implementation of control and eradication measures, (4) setting up invasive species handling guidelines and (5) fostering public education programs on biological invasion prevention. The plan should involve the participation of all stakeholders, such as government, industry, social community organization and public in order to engage them to jointly effectively tackle and manage invasive species and thereby conserve Hong Kong’s aquatic biodiversity.
published_or_final_version
Environmental Management
Master
Master of Science in Environmental Management

Rates of species invasion are rising globally, particularly in freshwater ecosystems. The impacts of only a small fraction of these invasions have been studied, and some have been found to cause substantial ecological and socio-economic damage. Nevertheless, there have been recent claims that the impacts of non-native species have been exaggerated, that native species have an equal propensity to cause damage, and therefore the biogeographic origins of species should not be considered in management decisions. Here, I address these claims by comparing the socio-economic impacts of native and non-native species in freshwater systems. Using data from North American and European watersheds, I find that non-native species are five times more likely than natives to become pests. Another major issue concerning the impacts of non-native species is that managers lack predictive tools for prioritizing invasion threats, because very few general correlates of impact have been identified. The functional distinctiveness of a non-native species within the invaded assemblage has been proposed as a predictor of its impact on native species populations. Using a global dataset of non-native freshwater molluscs and taxonomic relatedness as a proxy for functional similarity, I find that novel taxa comprise disproportionately large numbers of high-impact invaders. Moreover, more taxonomically distant taxa have the highest proportions of high-impact species. These results support the use of taxonomy and biogeographic origin in invasion risk assessment.
Les taux d'invasions d'espèces sont en hausse dans le monde, et particulièrement dans les écosystèmes d'eau douce. Seuls les impacts d'une petite fraction de ces invasions ont été étudiés. Il a été démontré que certaines d'entre elles peuvent causer des dommages environnementaux et socioéconomiques considérables. Toutefois, certains écologistes suggèrent que l'impact des espèces non indigènes pourrait avoir été exagéré. Selon eux, les espèces indigènes auraient la même propension à causer des dommages environnementaux et socioéconomiques. L'origine biogéographique d'une espèce ne devrait alors pas être considérée lors d'une prise de décision. Je tente ici de vérifier la validité de ces affirmations en faisant la comparaison des impacts socioéconomiques des espèces indigènes et non indigènes dans les écosystèmes d'eau douce. En analysant des données provenant de bassins d'eau douce nord-américains et européens, il s'avère que les espèces non indigènes ont cinq fois plus de chances de devenir nuisibles. Un problème majeur relié à l'impact des espèces invasives est que les preneurs de décisions manquent d'outils de prédiction leur permettant de prioriser les menaces d'invasion. Le caractère distinctif de la fonction écologique d'une espèce non indigènes au sein de la communauté envahie à été proposé comme prédicteur de son impact sur la population indigène. En construisant un ensemble de données mondial sur les mollusques non indigènes et en utilisant la parenté phylogénique comme indicateur de la similarité fonctionnelle des espèces, il ressort que les taxons nouveaux sont plus susceptibles de devenir des envahisseurs à haut impact. De plus, les taxons les plus distants phylogéniquement ont la plus haute proportion d'espèces envahissantes à haut impact. Ces résultats soutiennent l'utilisation de la phylogénie et de l'origine biogéographique pour l'évaluation des risques associés à une invasion par une espèce non indigène.

nÃo hÃ
In the present work we performed a study and characterization of benthic macrofauna of the intertidal fringe of PecÃm beach between the years 2006 and 2011 in order to obtain information about the taxonomic diversity of species and deepen knowledge about the ecology of these organisms in the face of new environmental conditions imposed by the deployment of Marine Terminal of Port of PecÃm. Seventy-one taxa belonging to seven taxonomic groups: Porifera, Cnidaria, Mollusca, Annelida (Polychaeta), Arthropoda (Crustacea), Echinodermata and Chordata were listed. Six species of marine benthic invertebrates introduced: the bivalve mollusc Isognomon bicolor, Donax gemmula and Heterodonax bimaculatus, the crustacean Decapoda Charybdis hellerii and the polychaete Phragmatopoma caudata were listed. The species Phragmatopoma caudata, Donax gemmula and Heterodonax bimaculatus were classified as cryptogenic and Isognomon bicolor and Charybdis hellerii as exotic detected in the natural environment. Heterodonax bimaculatus is first recorded in the state of CearÃ, extending its distribution along the Brazilian coast. Specific preferences of benthic macrofauna in relation to the variability of substrates were found. This fact influences the composition and distribution of taxa, has been identified a greater number of taxonomic groups (seven) in consolidated substrate when compared to taxonomic groups (three) identified in the unconsolidated substrate. There were no significant changes in the composition of local benthic macrofauna when compared to other coastal regions of the state. The quantitative fluctuations observed in populations seem to be related to a response of organisms to coastal dynamics, indicating an adaptive process of species to new environmental conditions of the area. It was observed a decrease in the average percentage of coverage of organisms in consolidated substrate, and there were no significant differences in the average number of organisms in unconsolidated substrate between the years 2008 and 2011. With reference to the collect frequency (monthly, bimonthly and quarterly) was observed that the average percentage of coverage of organisms in consolidated substrate and the average amount of organisms in unconsolidated substrate showed no significant differences among the three study periods during the years 2008 and 2011. The quantitative and qualitative data obtained in this study suggest that the introduced species in the intertidal fringe PecÃm beach have not, so far, caused significant impacts on local benthic macrofauna, although they may be considered as a potential threat to the structure of these communities. Shipping accomplished through the Marine Terminal of Port of PecÃm seems to be the vector responsible for the introduction of new species in local macrozoobenthos.
No presente trabalho foi realizado o levantamento e carac-terizaÃÃo da macrofauna bentÃnica da faixa entremarÃs da praia do PecÃm, no perÃodo de 2006 a 2011, com a finalidade de obter informaÃÃes sobre a diversidade taxonÃmica das espÃcies e aprofundar o conhecimento sobre a ecologia desses organismos frente Ãs novas condiÃÃes ambientais impostas pela implantaÃÃo do Terminal PortuÃrio do PecÃm. Foram identificados 71 tÃxons pertencentes a 7 grupos taxonÃmicos: Porifera, Cnidaria, Mollusca, Annelida (Polychaeta), Arthropoda (Crustacea), Echinodermata e Chordata. Como espÃcies introduzidas foram identificados os moluscos bivalves Isognomon bicolor, Donax gemmula e Heterodonax bimaculatus, o crustÃceo decÃpoda Charibdys hellerii e o poliqueta Phragmatopoma caudata. As espÃcies Phragmatopoma caudata, Donax gemmula e Heterodonax bimaculatus foram classificadas como criptogÃnicas e Isognomon bicolor e Charibdys hellerii como exÃticas detectadas em ambiente natural. Heterodonax bimaculatus à registrado pela primeira vez para o estado do CearÃ, ampliando sua distribuiÃÃo na costa brasileira. Foram constatadas preferÃncias especÃficas da macrofauna bentÃnica com relaÃÃo à variabilidade dos substratos o que influencia na composiÃÃo e distribuiÃÃo dos tÃxons, tendo sido identificada uma maior quantidade de grupos taxonÃmicos (7) no substrato consolidado quando comparada aos grupos taxonÃmicos (3) identificados no substrato inconsolidado. NÃo foram observadas alteraÃÃes significativas na composiÃÃo da macrofauna bentÃnica local quando comparada com a de outras localidades costeiras do estado. As flutuaÃÃes quantitativas observadas nas populaÃÃes parecem estar relacionadas a uma resposta dos organismos à dinÃmica costeira, indicando um processo adaptativo das espÃcies Ãs novas condiÃÃes ambientais da Ãrea. Foi verificado um decrÃscimo no percentual mÃdio de cobertura dos organismos no substrato consolidado, nÃo tendo sido observado diferenÃas significativas na quantidade mÃdia de organismos no substrato inconsolidado entre os anos de 2008 e 2011. Com relaÃÃo à periodicidade de coleta (mensal, bimestral e trimestral) observou-se que o percentual mÃdio de cobertura de organismos no substrato consolidado e a quantidade mÃdia de organismos no substrato inconsolidado nÃo apresentaram diferenÃas significativas entre os trÃs perÃodos analisados durante os anos de 2008 e 2011. Os dados quantitativos e qualitativos obtidos nesse estudo sugerem que as espÃcies introduzidas na faixa entremarÃs da praia do PecÃm nÃo tÃm, atà o momento, causado impactos significativos na macrofauna local, embora possam ser consideradas como uma potencial ameaÃa à estrutura dessas comunidades. O transporte marÃtimo realizado atravÃs do Terminal PortuÃrio do PecÃm parece ser o vetor responsÃvel pela introduÃÃo de novas espÃcies no macrozoobentos local.

xvi, 109 p. : ill.
Invasions by introduced plant species cost billions of dollars each year in the United States and threaten native habitat. The primary goal of my dissertation research was to examine the role that natural enemies (pathogens and herbivores) play in these invasions in both unmanaged and restored plant communities. In two related studies in seasonal wetland prairies in the Willamette Valley, Oregon, USA, I surveyed natural enemy attack on common native and introduced plant species in a restoration experiment designed to test the effects of site preparation techniques on plant community composition. Restoration treatments had little influence on enemy attack rates. Attack rates depended on idiosyncratic differences in the relationships between host species and plant community characteristics, suggesting that existing theories concerning these relationships have limited predictive power. Another field experiment tested the potential for enemy spillover from introduced to native species and dilution of natural enemy attack on introduced species by native species. I examined natural enemy attack on three native and three perennial grasses that commonly co-occur in the Willamette Valley. The native species are commonly used in restoration. The introduced species are common throughout North America and potentially harbor enemies that could affect both crops and natural communities. There was no compelling evidence of enemy spillover from the introduced to the native species, but dilution of enemies on the introduced species by the native species was evident in year 2 and even stronger in year 3 for two of the three introduced species. Using the same three introduced species from the spillover/dilution study, I tested the enemy release hypothesis, which proposes that introduced species lose natural enemies upon introduction and are thus "released" from population control. I surveyed populations of the three grass species across a wide geographic area in their native and naturalized ranges in Europe and the United States, respectively. I also compared my results to those of a previously published literature survey. My field survey supported release from herbivores but not from fungal pathogens. In contrast, the literature survey found evidence of release from fungal pathogens. This dissertation includes unpublished co-authored material.
Committee in charge: Brendan Bohannan, Chairperson; Bitty Roy, Co-Advisor; Scott Bridgham, Co-Advisor; Eric Seabloom, Member; Robert Mauro, Outside Member

Invasive Non-Native Species (INNS), or Invasive Alien Species, are organisms introduced by humans outside their natural range that have “negative impacts on biodiversity, socio-economy or human health”. Growing awareness of the ecological and socio-economic impacts of INNS has led to a mushrooming of control attempts across the UK. The costs of such environmental management has grown far in excess of the availability of funds to afford control by professionals and led to widespread involvement of volunteers in INNS management and monitoring. This thesis aimed to identify challenges in collaborations between lay people and experts in ecological restoration and to critically examine some of the claims made about the benefits of citizen participation on the sustainability and democratisation of environmental management and on citizen empowerment. Qualitative research methodology was employed to explore in depth motivations, experiences, intentions and views of volunteers and of the organisations that attempt to enrol them in practical conservation work and monitoring activities. We found that caring for nature, the experience of nature and the activities, and social interactions were the three main drivers of volunteering. Importantly, over time, motivations were shaped by the interplay between individual expectations and experiences with the social and ecological context and changed from identifiable personal goals and functions to more complex attachments to the place and the group. Our research also revealed that while some of these key motivations may be recognised by project managers, their description of costeffectiveness, local ownership and empowerment as complementary volunteering goals were often not aligned in practice. Moreover, decision-making may remain largely expert-based, with volunteers not perceiving their knowledge to be valid or a useful contribution to decision-making. Enhancing the sustainability and democratic nature of INNS management requires reflexive practice of citizen engagement that explicitly considers different interests and views but also invites citizens to reflect on their role in the co-production of conservation practice and knowledge.

This study examined the physiological and behavioural effects of a stress-inducing stimulus (predator odour) on potential prey species (Australian native and exotic). The aim was to determine if differences in the response of prey were related to the scent of evolutionary known predators compared to unfamiliar or short-term introduced ones. In laboratory experiments, responses were always restricted to changes in respiratory variables, with brushtail possums (Trichosurus vulpecula), rabbits (Oryctolagus cuniculus) and tammar wallabies (Macropus eugenii) showing no variation in metabolic rate after exposure to predator odours.Brushtail possums showed strong changes in ventilatory rate only when faced with the scent of an historical predator, increasing respiratory frequency (ratio after/before exposure = 4.55 ± 1.007) and decreasing tidal volume (ratio after/before exposure = 0.38 ± 0.113 ) in response to stale dingo urine. The changes were short-lived, lasting for only one minute of exposure. For this reason, it is unclear if the response observed could be considered as a fear reaction. However, there was no habituation after three exposures and this may indicate that possums were initially displaying an investigative approach to a predator scent and then relaxing once assessment was completed.The effect of predator and novel odours on the ventilation of rabbits appeared to be in general mediated by anxiety, as shown by the responses elicited by both predator and control scents. However, stronger reactions were observed in response to feral cat and quoll odours for both respiratory frequency (ratio after/before exposure to feral cat = 4.39 ± 0.721 and to quoll = 3.75 ± 0.486) and tidal volume (ratio after/before exposure to feral cat = 0.47 ± 0.065 and to quoll = 0.64 ± 0.129). This could be due to different intensity of the olfactory stimuli. Nevertheless, the effects of noxious odours on rabbits clearly demonstrate that they become highly vigilant at any sudden change in their environment.Tammar wallabies appeared to possess a mechanism for the recognition of predator odours as ventilatory responses were restricted to particular predator scents. After investigation, fox and cat odour provoked a stronger and more prolonged change in respiratory frequency (ratio after/before exposure to fox = 3.58 ± 0.918 and to feral cat = 2.44 ± 0.272) and tidal volume (ratio after/before exposure to fox = 0.84 ± 0.110 and to feral cat = 0.98 ± 0.155) compared to the other scents, suggesting that wallabies may have perceived these species as more immediate threats.For wild, free-living brushtail possums and southern brown bandicoots (Isodoon obesulus), there was no pattern of avoidance of historical or introduced predator odours, with no difference in number of animals captured in predator and control scented traps. This may indicate that predator odour avoidance has not evolved in these species and that they have poor possibilities of escaping potential predators. However it may also be explained by the long-term predator-free environment in which the study was conducted, and suggests loss of anti-predator behaviour in populations without predation risk.Wild, free-ranging western grey kangaroos (Macropus fuliginosus) reacted to the odour of both historical (dingo) and novel (fox) predators by reducing number of feeding events (5.2±2.08 for fox and 5.9±1.33 for dingo) and time spent foraging (17.7±7.2 sec for fox and 22.2±4.6 sec for dingo) when predator scents were present and by escaping areas tainted with predator odours (41.4±17.5 sec for fox and 33.8±13 sec for dingo). Clearly these results suggest that kangaroos are scared of predator odours. However, a close investigation of predator scents was necessary before a response could be elicited and feeding areas were not completely abandoned.It is still unclear if small Australian prey, such as southern brown bandicoots and brushtail possums, respond to olfactory cue of predation in the wild, as different results were obtained in the studies conducted in the laboratory and in free populations. However, this research showed that medium and large-sized macropods respond to both native, long-term and introduced predator odours. This indicates that at least some Australian prey species can recognise the odour of potential predators, although responses usually occur after a period of investigation, and do not always result in avoidance behaviour. Differential responses appear to be based on the perceived risk. Use of predator odour is unlikely to be an effective mechanism of deterring herbivores from preferred feeding locations.

Includes bibliographical references (p. 206-231).
The use of bruchid beetles for biologicval control of mesquite, Prosopsis species, in South Africa is deemed to have failed because the beetles are supposed to be unable to compete with livestock which utilise the seed pods of mesquite extensively as forage. These assumptions have been made without any evidence as to how the beetles and livestock interact or as to whether mesquite is site or seed limited in South Africa. This study was initiated to test the hypothesis that the beetles are not coping with competition with livestock and that mesquite is site limited and not seed limited in South Africa.

Species translocations result in demographic bottlenecks that may produce inbreeding depression and reduce genetic variation through random sampling and drift, an outcome that could decrease long-term fitness and adaptive potential of many New Zealand species. Despite considerable evidence for costs associated with inbreeding and reduced genetic variation, some species have recovered from a small number of individuals and are thriving, perhaps via high growth rates, differential survival of heterozygous individuals or inbreeding avoidance. I examined the genetic consequences of species translocations in saddlebacks (Philesturnus carunculatus) with additional data provided for robins (Petroica australis) where possible. I first assessed whether contemporary genetic variation represented historical levels or a decline following demographic bottlenecks. I then examined whether sequential demographic bottlenecks caused sequential genetic bottlenecks and reviewed whether populations founded with a small number of birds were likely to go extinct. This analysis was followed by an investigation of two mechanisms that may maintain or reduce fitness costs, differential survival of heterozygous individuals and mate choice to avoid genetically similar individuals. Evidence from museum specimens suggests that low levels of genetic variation in contemporary saddlebacks is no different to historical genetic variation in the only source population, Big South Cape Island. An ancient founding event to Big South Cape Island is probably the cause of severe genetic bottlenecking rather than the demographic bottleneck caused by rats in the 1960s. In robins, genetic variation decreased slightly between museum and contemporary samples suggesting that recent population declines and habitat fragmentation have caused reductions in current levels of genetic variation. Serial demographic bottlenecks caused by sequential translocations of saddlebacks did not appear to decrease genetic variation. Loss of genetic variation due to random sampling was probably minimized because the low level of genetic variation remaining in the species was probably represented in the number of birds translocated to new islands. Models assessing future loss of genetic variation via drift showed that high growth rates combined with high carrying capacity on large islands would probably maintain existing genetic variation. In contrast, low carrying capacity on small islands would probably result in considerable loss of genetic variation over time. Saddleback populations on small islands may require occasional immigrants to maintain long-term genetic variation. Saddleback and robin populations established with a small number of founders did not have an increased risk of failure, suggesting that inbreeding was not substantial enough to prevent populations from growing and recovering. However, modelling showed that translocated saddleback and robin populations grow exponentially even when egg failure rates (a measure of inbreeding depression) are extremely high. Although inbreeding depression may be considerable, populations may be judged healthy simply because they show strong growth rates. Discounting the problem of inbreeding depression may be premature especially under novel circumstances such as environmental change or disease. Finally, two mechanisms proposed to avoid or delay the costs of inbreeding depression and loss of genetic variation do not appear to be important in saddlebacks or robins. Heterozygosity was not related to survivorship in saddlebacks that successfully founded new populations, and neither saddlebacks nor robins chose genetically dissimilar mates to avoid inbreeding. In conclusion, most saddleback populations should not require genetic management, although populations on small islands will probably need occasional immigrants. In robins, large, unfragmented populations should be protected where possible.

New Zealand has no native mammalian herbivores, and the recent introduction of deer to the country is having a major impact on native vegetation. This thesis explores aspects of the foraging ecology of introduced deer and the responses of native plant species to browsing. In Chapter 1, I introduce the study system and the conceptual themes of the thesis, which run along two main axes. The first theme relates to the importance of traits of individuals (both plants and deer) versus landscape or community-level characteristics in determining diet selection. The second theme is concerned with two mechanisms by which native plant species can cope with ungulate herbivores: avoidance versus tolerance of damage. In Chapter 2, I use a pre-existing vegetation and browsing survey dataset to explore the capacity of 53 forest plant species to avoid damage. At a community level, plants were more heavily browsed if their neighbours were of high palatability. At the level of the individual, the strongest predictor of the palatability of species was the dichotomy between woody and non-woody plants (mostly ferns). Among woody plant species, the primary predictor of palatability was low content of phenolics. There were weaker associations between palatability and high SLA, large leaf size, and low lignin, but the significance of these weaker traits depended on the index by which palatability was defined. The considerably lower palatability of ferns compared with woody plants could not be explained by foliar traits measured in this study. Differences in palatability between fern species were small, and not related to any foliar trait. In Chapter 3, I use a pre-existing rumen contents dataset to explore major sources of variation in diet.

For this dissertation, I measured how plant communities in Appalachian forests responded to disturbances caused by forest management activities. I had two primary objectives including (1) testing theories of biological diversity and invasions by nonnative species; and (2) providing empirical data that will help guide the sustainable use of forest resources. This work is part of the Southern Appalachian Silviculture and Biodiversity (SASAB) experiment that was established in the early 1990s to investigate ecosystem responses to a gradient of timber harvesting disturbances. Ranging from undisturbed controls to silvicultural clearcuts, the disturbance gradient is replicated at sites located throughout the Appalachian mountains of Virginia and West Virginia. The plant community was sampled across a wide range of spatial scales (2 hectares to 1 m2) using a nested sampling design and was also sampled at three times including pre-disturbance, one year post-disturbance, and ten year post-disturbance. For one element of the study I tested modern theories of biological invasions and investigated how the forest disturbance gradient interacted with species diversity to influence invasion by nonnative species (Chapter 2). Contrary to popular ecological theories of biotic resistance, the most diverse sites tended to be more easily invaded following intense canopy disturbance. Interestingly, none of the sites in this study were dominated by invasive plants, which led me to ask whether dominant tree species in forests provided resistance to nonnative plant establishment and growth through the quality of the litter they produce. I also asked how might animals that are known to alter litter layers interact with dominant tree species to influence plant invasions. Therefore, I conducted an experiment investigating how changes in litter from dominant tree species and invasions by nonnative earthworms might influence invasibility of forests using forest floor mesocosms (Chapter 3). I found that plant invasion was inhibited by native oak litter even when earthworms were present, suggesting that oak forests may resist plant invasions via oak tree litter. In contrast, plant invasion was greater under invasive tree litter and earthworm activity tended to facilitate invasive plant success only under invasive tree litter. I was also interested in understanding how disturbance might alter relationships between local and regional diversity. The long-term data of the forest disturbance experiment allowed me to investigate how local species richness is mediated by regional species richness after disturbance and during forest community development (Chapter 4). Local richness depended strongly on regional richness only after disturbance via colonization of species, but this relationship changed during forest aggradation. These results suggest that regional species pools are important to maintain local diversity following disturbance, but that local interactions (through canopy closure of dominant trees) exert control over species diversity during community reorganization. Lastly, I tested current theories on how diversity influences compositional stability after disturbance (Chapter 5). Disturbance consistently resulted in decreased compositional stability, but diversity was associated with stability in complex ways, which depended on how stability was measured and at what scale. Species-rich areas were in some instances less stable; in other instances areas with intermediate levels of diversity were more stable. These results suggest that disturbance causes shifts in species composition via colonization, but the ways in which diversity of sites influences compositional stability is complex and depends on methods used and the scales of observation. Taken together, these results suggest that disturbance influences invasibility, species saturation, and compositional stability of ecological communities. These properties change immediately following disturbance, and during forest development and canopy closure. Data from this project were useful in testing existing theories of community ecology, and may ultimately prove useful for forest managers as they decide how to protect biodiversity while planning for other uses of forest resources. Overall, these results suggest that colonization of species is the primary process driving plant community patterns in Appalachian forests following disturbance.
Ph. D.

Invasive non-native species are believed to be one of the biggest threats to biodiversity. Until now biological invasions have been mainly studied from a biological perspective and much research has been undertaken to investigate species’ ecology and potential options for management. Comparatively little attention has been devoted to questions regarding the social construction of the issue. This is despite invasion biologists increasingly acknowledging the fundamental importance of human perceptions, beliefs, attitudes and values inherent in debates about invasive non-native species. This thesis employs a mix of methods from the social sciences to investigate the social construction of biological invasions. Research conducted here is based on the theory of social representations. Thus, taking a social scientific perspective, the thesis contributes to both the development of the theory and an identification of beliefs inherent in the debate on biological invasions and their relationship to people’s attitudes towards species and their management. Those species attributes that predominantly shape the debate – but yet appear to be under-researched – are identified. Based on the findings in this thesis I argue that invasion biology would benefit from a more explicit and transparent use of its concepts and terminology. This will have implications also for the communication with policy makers, conservation managers and the general public. Recommendations for future research are discussed along with limitations of the thesis.

The aim of the thesis was to document patterns in breeding and migration in Swedish Canada geese Branta canadensis, to explain these against the genetic and historical background of the population, and to test predictions of hypotheses pertaining to parental investment. The Canada goose population in Sweden was founded by the introduction of a few individuals in the 1930's. DNA fingerprint similarity between geese breeding in Sweden was on average at the same level as between inbred close relatives in other wild bird species. The genetic variability of the population appeared to be considerably reduced in comparison to that of Canada geese breeding in North America. Dispersal and migration patterns were studied using plastic neck-bands that could be identified at long distance. Most Canada goose females nested at the lake where they grew up. Males were more prone to disperse than females, although most of them still returned to breed close to their area of origin. Geese from three breeding areas in Sweden had different winter distributions, although wintering areas overlapped considerably. Individual geese tended to return to the same wintering area as they had used in previous years. The females' investment in the egg clutch was related to the migration distance from spring foraging areas to the nesting area, suggesting an energetic cost of migration for egg production. Within breeding seasons, clutch size decreased with later initiation of nesting, but only in years with early breeding. A probable reason for this decrease was that body reserves available for egg production were larger in early layers. In years with late breeding, clutch size did not decrease, most likely because late-nesting females could supplement their body reserves by foraging on fresh vegetation. Nest defence intensity was studied by recording the behaviour of the female geese when a human approached the nest. The results largely confirmed predictions for nest defence intensity extracted from parental investment theory.

Diss. (sammanfattning) Umeå : Umeå universitet, 1993, härtill 6 uppsatser

digitalisering@umu

The introduction of trout has been implicated in the declines in native fish fauna in New Zealand and worldwide. Since the introduction of brown (Salmo trutta) and rainbow (Oncorhynchus mykiss) trout to New Zealand in 1867, their distribution has spread and they have been implicated in the fragmentation of native fish distributions, particularly native non-migratory galaxiids. However, in the Upper Waimakariri basin the co-occurrence of trout and galaxiid populations is relatively common, even in streams where trout reach sizes known to be piscivorous. To investigate mechanisms that may regulate trout and galaxiid co-occurrence, I investigated differences in antipredator behaviour and growth rate between stream types with varying levels of trout presence. Using quantitative survey data collected between 1997 and 2006, I found that trout abundance was low and varied annually in frequently disturbed sites compared their high abundance in stable streams. This finding was used to classify streams into three population types, barrier (trout absent), disturbed (trout presence intermittent) and sympatric (constant trout presence). Using this classification, I tested the effects of trout chemical cues on galaxiid activity and refuge use in artificial channels. There were no differences in activity or refuge use between trout odour and there were no effects of population type or galaxiid size during both the day and the night. Using otolith weight-fish length relationships in galaxiids collected from each population type, I found that galaxiid growth rate was higher in disturbed streams than in stable streams either with or without trout. An experiment manipulating trout size and presence, over two months in a natural stream, found galaxiids from treatments without trout grew slower than those with trout. Slow growth rates in galaxiids above trout-migration barriers and in sympatry, combined with low growth rates in treatments without trout suggest that the mechanisms that regulate galaxiid growth are more complex than previously thought.

Thesis (PhD)--Stellenbosch University, 2008.
ENGLISH ABSTRACT: Introduced species displace native species and alter ecological communities, affect agriculture as well as human health and are economically costly to eradicate. Long term monitoring of introduced species including the documentation of levels of genetic variation is therefore of the utmost importance. This study investigated the distribution of genetic variation in two introduced species distributed across South Africa the bud gall-forming wasp Trichilogaster acaciaelongifoliae and the Argentine ant Linepithema humile. The bud gall-forming wasp was introduced into South Africa as a biological control agent to curb the spread of the invasive long-leaved wattle Acacia longifolia. In addition to the intended (target) host, the bud gall-forming wasp has also colonised A. floribunda, a noninvasive ornamental plant. Limited genetic variation was found across South Africa based on the mitochondrial DNA cytochrome oxidase subunit I (COI) gene. Only 3 haplotypes characterized 53 individuals collected from 23 localities (nucleotide diversity £k = 0.002 ¡Ó 0.001, haplotype diversity h = 0.482 ¡Ó 0.045). No significant partitioning of genetic variation was found across South Africa including between host plants (target host = A. longifolia, non target host = A. floribunda) or between the core (sites of introduction) and edge (naturally dispersed) sites (ƒ¶ST = 0.094, P = 0.288). The limited genetic variation and the absence of significant genetic structure are congruent with patterns described for many other introduced species and may suggest that propagule pressure plays only a minor role in species establishment and spread of the gall-forming wasp across South Africa. Mitochondrial and nuclear markers were used to describe the distribution of genetic variation within Argentine ants across their introduced range in South Africa. For the mitochondrial DNA, low genetic diversity was found for the COI gene with only five haplotypes, separated by single mutational changes, characterizing 101 specimens from 35 localities (nucleotide diversity π = 0.001 ± 0.001, haplotype diversity h = 0.151 ± 0.048). Notwithstanding the low levels of genetic diversity, mitochondrial variation was significantly structured (ST = 0.54, P < 0.001) across the landscape. In contrast, microsatellite analyses of 230 ants from 23 localities, employing six polymorphic microsatellite markers, revealed a relatively high amount of genetic diversity (HE = 0.51 ± 0.22). Significant population structure was similarly evident (RST = 0.14, P < 0.001) with the localities of Elim2, Porterville2 and Bloemfontein2 clustering as a distinct population from the remainder of the localities. Importantly, individuals from these localities also had a unique mitochondrial haplotype and, when taken with the nuclear results, may indicate the occurrence of more than one introduction event (and possibly more than one colony) in South Africa. This is further underscored by the presence of unique microsatellite alleles in these three populations. In an attempt to establish the source populations for the introduction of Argentine ants into South Africa, mitochondrial cytochrome b sequences were generated for a subset of ants representing the two major genetic clades across South Africa. A comparison with the published data from across the world including the native range of the Argentine ant in South America grouped Argentine ants from South Africa with three potential source populations namely Ocampo and Rosario in Argentina and Passo do Lontra in Brazil. The results of this study underscore the role of human-mediated dispersal in shaping the levels of genetic variation in both species. Human-mediated dispersal can lead to genetic homogenization across populations.
AFRIKAANSE OPSOMMING: Indringer spesies verplaas of verander ekologiese gemeenskappe, beinvloed landbou asook menslike gesondheid en is ekonomies duur om te verwyder. Langtermyn monitering van indringer spesies asook die dokumentasie van genetiese variasie is dus baie belangrik. Hierdie studie bestudeer die verspreiding van genetiese variasie in twee indringer spesies wat regoor Suid-Afrika voorkom, naamlik die kroongal-vormende wespe Trichilogaster acaciaelongifoliae en die Argentynse mier Linepithema humile. Die kroongal-vormende wesp is na Suid Afrika gebring as biologiese beheeragent om die verspreiding van indringer lang-blarige wattle Acacia longifolia te beveg. Die kroongalvormende wespe het sowel die teiken spesies, asook A. floribunda, ‘n nie-indringer ornamentele plant gekoloniseer. Beperkte genetiese variasie is gevind regoor Suid Afrika gebasseer op die mitochondriale DNA sitokroom-oksidasie subeenheid I (COI) geen. Slegs 3 haplotipes karakteriseer 53 indiviue van 23 bevolkings (nukleotied diversiteit π = 0.002 ± 0.001, haplotiep diversiteit h = 0.482 ± 0.045). Geen beduinde groepering van genetiese variase is gevind regoor Suid Afrika nie (ST = 0.094, P = 0.288). Hierdie bevinding geld onafhanklik van die gasheer plant (teiken gasheer = A. longifolia, nie-teiken gasheer = A. floribunda). Ook is geen beduidende genetiese groepering gevind tussen die sentrale (plek van inisiele blootstelling) en perifêre (natuurlik verspreide) lokaliteite nie. Die kleinskaalse genetiese variase en die afwesigheid van beduidende genetiese struktuur wat hier gevind is, verskil van die patrone wat voorheen vir baie ander indringer-spesies beskryf is. Dit mag daarop dui dat ‘propagule’ druk slegs ’n klein rol speel in spesies-vestiging en verspreiding van die galvormende wespe regoor Suid-Afrika. Mitochondriale asook kern merkers is gebruik om die verspreiding van genetiese variasie in Argentynse miere in Suid Afrika te beskryf. Vir die mitochondriale DNA is lae genetiese variase gevind vir die COI geen, met slegs 5 haplotipes, gedifferensieer deur enkele mutasie veranderinge wat 101 monsters van 35 lokaliteite karakteriseer (nukleotied diversiteit π = 0.001 ± 0.001, haplotiep diversiteit h = 0.151 ± 0.048). Desondanks die lae genetiese variasie, is gevind dat mitochondriale variasie beduidend gestruktureerd is (ST = 0.54, P < 0.001) oor die landskap. Hierteenoor het mikrosatelliet analises van 230 miere van 23 lokaliteite, deur gebruik te maak van ses polimorfiese mikrosatelliet merkers, ’n relatiewe hoë hoeveelheid genetiese diversiteit aangedui. Beduidende bevolkingstruktuur was ook gevind (RST = 0.14, P < 0.001) in die areas Elim2, Porterville2 en Bloemfontein2 wat saam groepeer as eiesoortige bevolkings vergeleke met die res van die areas. Ook van belang is dat individue van die areas ’n unieke mitochondriale haplotipe besit, en in kombinasie met die kern resultate, mag dit die voorkoms van meer as een blootstellingsgeleentheid (en moontlik meer as een kolonie) in Suid Afrika aandui. Hierdie bevinding word verder beklemtoon deur die teenwoordigheid van unieke mikrosatelliet allele in die drie bevolkings. In ‘n poging om die oorsprong van die oorsprong-bevolking vir die blootstelling van Argentynse miere in Suid Afrika vas te stel, is mitochondriale sitokroom b volgordes gegenereer vir ’n substel miere wat die twee hoof genetiese klades in Suid Afrika voorstel. Vergelyking met gepubliseerde data van regoor die wêreld, insluitende die endemiese gebied van die Argentynse mier in Suid Amerika, het die Argentynse mier van Suid Afrika met drie potensiele oorsprong-bevolking verbind, naamlik Ocampo en Rosario in Argentina en Passo do Lontra in Brazil.

Invasive species constitute a major threat to global biodiversity and cause important economic losses and ecological impacts. In the marine realm, ascidians include several aggressive invasive species, some of which have worldwide colonisation ranges, such as Didemnum vexillum. In this thesis, some biological and ecological characteristics implicated in the invasiveness of the species are assessed. First, we performed a 20 month monitoring to determine settlement and growth preferences of invasive ascidian species in the Ebro Delta aquaculture facility, including D. vexillum. Our results indicated that D. vexillum has a preference for complex substrates. To minimise fouling on bivalves, spat immersion during fall and below 1 m depth is recommended. To detect new introduced species, a follow-up program based on occurrences would be sufficient. Second, a protocol for small DNA samples combining whole genome amplification (WGA) and genotyping-by-sequencing (GBS) was developed and applied to D. vexillum using a single zooid per colony to determine patterns of genomic diversity and differentiation, describe the colonisation history of the species, and study its capability to form chimeras. Our results confirmed that Japan is in the native area of the species and only one clade spread worldwide. We found that the two main mitochondrial clades are strongly differentiated at the genomic level suggesting reproductive isolation, we determined that three independent colonisation events shaped the global distribution of the species, and we found that populations are diverse and well differentiated indicating a high expansion potential of D. vexillum. Third we detected high prevalence of chimerism, and fusion was unlinked to global genetic relatedness. Finally, we analysed the microbiome of D. vexillum that showed markedly different composition than a congeneric species and water. The invasive clade had a small but abundant core and a highly diverse variable microbiome component with a strong capacity to enrich the symbionts from the environment. The microbiome structure correlated to host genetic distance, temperature and geographical distances, pointing to vertical and horizontal transmission. In conclusion, D. vexillum is an aggressive invasive species with a high adaptive capacity that may contribute to the invasiveness of this global pest.

Aquatic invasive species (AIS) are biological pollutants that cause detrimental ecological, economic, and sociological effects on non-native communities. With increasing globalization through maritime trade, coastal ports are vulnerable to AIS introductions transported by commercial vessels. As Cuba’s Port Mariel becomes a competitive transshipment hub within the Caribbean, it is essential to identify the potential threat that AIS may pose with a likely increase in shipping activity. It is equally important to understand the status of established AIS in Cuba and control measures presently being implemented by the country. This information can provide guidance for establishing or improving Cuban AIS preventative and remedial actions. For this study, publically accessible information was used to conduct threat assessments of present and potential AIS in Cuba and to identify feasible international donors of AIS due to trade with Port Mariel. Fifteen species were identified as established Cuban AIS, eight of which were associated with harmful impacts to the environment, economy, and human health. Only one established AIS, Perna viridis (the Asian green mussel), was recorded as having repeated, negative influences in Cuba. Regional trade partners of Port Mariel were identified as the most likely donors of AIS due to ecological similarity and minimal voyage duration between countries. These trade partners also represented the busiest ports and transshipment hubs in the wider Caribbean region and, therefore, could expose Port Mariel to ‘stepping-stone’ invasions. Five species associated with international trade partners were identified as potentially detrimental to Cuba if introduced into Port Mariel. There were no significant differences between the salinity and temperature tolerances of the AIS already established in Cuba and the possible AIS of concern, suggesting that these potential invaders could survive the environmental conditions of Port Mariel and subsequently become established throughout Cuba. The results presented herein are a preliminary assessment of AIS threats in Cuba and emphasize the importance of prioritizing AIS prevention and management. This study also establishes a baseline inventory of potential AIS in Cuba and a methodology that can be followed for future analyses outside of the study region.

The Southwest region of Western Australia is a recognised ‘biodiversity hotspot’, as it possesses high levels of biodiversity and endemism; it also holds a number of species threatened by habitat loss. The arrival of Europeans in the region wrought major changes on the natural landscape. Extensive tracts of bushland were cleared for housing, infrastructure, forestry, farming, and mining. Another challenge to regional biodiversity was the spread of exotic plants and animals (including birds); the latter provide the focus for the present study. The research examines four bird species that colonised the Southwest region following European settlement: Australian White Ibis (Threskiornis molucca); Spotted Dove (Streptopelia chinensis); Laughing Dove (S. senegalensis) and Laughing Kookaburra (Dacelo novaeguineae). The study examines how the feeding and breeding ecology of the species influenced colonisation success and dispersal, specifically in relation to geographic i.e. climate and anthropogenic (e.g. landuse) features of the region. Each of these species has been identified as a ‘generalist’ feeder, with flexible ecological needs. The species have been able to adapt their food preferences and way of life to living in proximity to human settlements. It appears that each utilised resources made available through human endeavour and activities. It appears that the most rapid spread of invaders occurs in areas of modified habitat, in which the proportion covered by natural ecosystems has declined: i.e. in urban areas, pastoral lands and agricultural areas, although conserved natural habitats have also been invaded. The results indicate clear associations between the extent of colonisation success in the first wave of dispersal, and anthropogenic phenomena. Such is evidenced by the range expansion of Australian White Ibis into coastal urban areas, within which foraging success is assisted by access to alternative food sources and roost sites; whereas the species’ movement inland is linked to habitats associated with dairy farming and cattle production. However, the biology of each species and the extent of its ecological flexibility are also influencing factors, as attested by the wide-spread dispersal of the Laughing Kookaburra throughout the study area. This species possesses physiological features that give it an energy advantage over other species and it possesses social behaviours which offer further ecological advantages. Although it is a combination of factors: the biological attributes of the species (which define the ecological aspects of its survival), the geographical features of the adopted landscape, and the impact of human imprint upon that landscape that affect the process of biological invasion, the outcomes are specific to each species. This is shown in the development of markedly different patterns of dispersal, as between the two Streptopelia doves, despite their arriving in the study area under (approximately) the same conditions, and sharing almost identical ecological profiles. As, despite being released into rural areas, the Spotted Dove retained a localised, mainly urban, population, whilst the Laughing Dove has become spread across both urban and rural environments. This may be due to differences in the ability of each species to tolerate dryland conditions, which appear to better suit the Laughing Dove, perhaps due to similarities in climate between the adopted range and the areas from which it originates. It is felt that the study has augmented existing knowledge of biological invasion events in the study area, and contributed towards a greater understanding of biological invasion phenomena, particularly those associated with wheat production, processing, and transport. The study design incorporated Geographic Information Systems (GIS) technology as a means of processing large volumes of historical data. The methodology developed for the study could be adapted to other species, regions and eras, provided sufficient data are available. It produces temporal snapshots of changes in distributions, which can be considered in relation to changes in climate conditions and landuse practices.

While there is increasing interest in the evolutionary consequences of species invasions on native plant communities, the connection between the phylogenetic relatedness of invaders and natives, and its evolutionary consequences, has not yet received much attention. One way to examine the role of relatedness on the impact of species invasions is through the use of meta-analytical techniques combined with a phylogenetic framework. I apply this technique and expand on a prior meta-analysis by Oduor (2013), in order to compare how native plant species that either have prior experience coexisting with an invasive (‘experienced’) or do not (‘naïve'), differ in terms of their growth and reproduction in the presence of the invasive for evidence of a phylogenetic signal in their response to plan invasions. My results suggest that the effects of a species invasion on native growth and reproductive traits may be greater when the native and invasive species are distantly related, and/or when the invasive species is allelopathic, but only in the presence on the invader. I also found that the negative effect of competition with an invader on native growth traits tended to be greatest when the native and invasive species were closely related, suggesting that the strength of competition and the evolutionary response of native plants to invasive plants may not be as closely associated as it is often assumed. Overall, my analysis suggests that future studies may benefit from integrating phylogenetic relatedness when exploring native evolutionary responses to invasions, but that considerable work need sot be done to tease apart the roles of relatedness and competition.

Les rongeurs de la savane soudanienne du Sénégal-Oriental ont été examinés en relation avec l'intensité des changements liés à l'homme. Un des moteurs principaux du changement global, l'usage des terres, a causé une augmentation significative des abondances de rongeurs dans les milieux cultivés par rapport aux savanes naturelles du Parc National du Niokolo-Koba. Ceci est du surtout à l'augmentation des effectifs de l'espèce ubiquiste Mastomys erythroleucus. Au niveau des populations, la fragmentation et la déforestation de la savanne boisée, potentiellement facilités par les changements climatiques subsahariens, ont eu des conséquences sur la diversité génétique d'une autre espèce partiellement arboricole : Praomys daltoni. La richesse allélique et l'hétérozygotie attendue sont significativement plus basses, et la différentiation inter-populations plus forte dans la limite nord de sa répartition, où des populations isolées ne survivent que dans les villages, alors que dans les localités du sud sa répartition est continue dans les savanes. Un autre aspect majeur du changement global est l'introduction et la propagation du rat noir Rattus rattus, dont la colonisation du Sénégal a été décrite en utilisant une approche Bayesienne récemment développée et basée sur les données de microsatellites. Le scénario évolutif le plus probable indique des introductions multiples d'individus d'origines diverses, ce qui peut expliquer son succès invasif. Des conséquences substantielles de l'impact humain sur les rongeurs ont été observées au niveau des communautés et des populations, avec des effets importants sur la biodiversité et le bien-être des populations humaines
Rodent communities and populations in the Sudanian savanna of Eastern Senegal were investigated in relation to the intensity of human-made changes of the environment. One of main drivers of the global change, land use, caused significantly higher abundances of rodent communities in agriculture landscape via to increasing dominancy of the ubiquitous murid species Mastomys erythroleucus, than was observed for pristine savannas inside the Niokolo Koba National Park. At population level, the fragmentation and deforestation of wooded savanna, potentially facilitated by climatic changes in this sub-Saharan region, indicated significant changes in genetic diversity of another species, the partly arboreal Praomys daltoni. Microsatellite allelic richness and expected heterozygosity were significantly lower, and population differentiation higher in isolated populations in the northern limit of its distribution area, where they have left deforested landscape and survive only in villages, than in southern localities with continuous P. Daltoni distribution. Another main aspect of the global environmental change is the human-mediated introduction and spread of the invasive black rat Rattus rattus, whose colonization of Senegal was described using recently developed Bayesian approach based on microsatellite data. The most likely evolutionary scenario indicated multiple introductions and several subsequent admixture events, which might support its invasion success. Substantial consequences of human impact on rodents were found at both community and population levels, implying important effects on biodiversity and human well-being