In light of human-mediated environmental change, a fundamental goal for biologists is to determine which phenotypic characteristics enable some individuals, populations or species to be more adept at coping with such change, while rendering others more vulnerable. Studying ongoing range expansions provide a unique opportunity to address this question by allowing documentation of how novel environments shape phenotypic variation on ecological timescales. At range-edges, individuals are exposed to strong selective pressures and population genetic challenges (e.g. bottlenecks and/or founder effects), which make genetic adaptation difficult. Nevertheless, certain species, such as the house sparrow (Passer domesticus), seem to thrive in their introduced ranges, despite genetic challenges, resulting in a genetic paradox. Increasing evidence suggests that rapid phenotypic differentiation at range-edges may be facilitated by phenotypic plasticity among individuals. Further, a role for epigenetic mechanisms as molecular drivers of such plasticity—particularly in genetically depauperate populations—has recently garnered empirical support across a broad range of taxa. For my dissertation, I investigated the role of epigenetic mechanisms (i.e. DNA methylation) as a potential mediator of range expansion success in vertebrates. Specifically, I proposed that success or failure at range-edges may be underlain by variation in the capacity for epigenetically-mediated plasticity (i.e. epigenetic potential) and used extant literature on an inherently plastic and highly integrated physiological system (i.e. the HPA-axis) to support this hypothesis (Chapter I). I then tested these ideas empirically by examining the relative contribution of genetic and epigenetic variation to immunological variation in Kenyan house sparrows (Chapter II) and explored whether mediators of neural plasticity (i.e. BDNF) and epigenetic potential (i.e. DNA methyltransferases; DNMTs) varied among populations of Senegalese house sparrows, including the potential for covariation among BDNF, DNMTs and corticosterone (CORT) within individuals (Chapter III). Flexibility in the regulation of glucocorticoids (GCs) via the HPA-axis is crucial for survival at range-edges because (i) GCs act as integrators capable of coordinating diverse physiological and/or behavioral responses and (ii) the HPA-axis contains multiple regulatory checkpoints which may help to buffer organisms from maladaptive responses (via redundancy) while simultaneously allowing for the fine-tuning of phenotypic responses to future stressors contingent on current and past experiences. GC regulatory flexibility can be influenced by (and in some cases have an effect on) variation in the capacity for epigenetic mechanisms to regulate environmentally-induced phenotypic changes (i.e. epigenetic potential). DNMTs are capacitators of epigenetic change, thus provide one such example of how variation in epigenetic potential could arise via genetic (e.g. variation in coding regions of DNMT genes) and/or environmental (e.g. developmental programming of DNMT expression) factors. For my first chapter, I conducted a literature review to explore where within the HPA-axis epigenetic potential was most likely to occur and to demonstrate how such variation could promote/constrain range expansion success via its impact on GC regulatory flexibility. Results from the literature search revealed that within the HPA-axis, evidence for epigenetic regulation was highest for receptors, suggesting that variation in epigenetic potential of these targets may be most impactful for variation in GC regulatory flexibility. Using a physiological regulatory network (PRN) framework, I showed how variation in epigenetic potential can modify plasticity of PRN states by altering the regulatory relationships (e.g. connectivity) between HPA elements (e.g. GCs as central hubs) and other physiological/behavioral traits (e.g. subnetworks). As such, I portrayed how genetic forms of epigenetic potential can dictate the upper/lower limits of an individual’s homeostatic range, while environmental forms can act to further titrate GC regulatory flexibility through plasticity of PRN states or stabilization of PRN states. The concept of epigenetic potential in the HPA-axis demonstrates how plasticity at the molecular level can influence plasticity at the whole-organism level, which is likely to be important when coping with novel challenges at range-edges. Among the strongest of selective pressures faced by range-edge populations is exposure to parasites, particularly those with which individuals have little to no evolutionary history. Previous work from our lab on house sparrows in Kenya—site of an ongoing range expansion—revealed that range-edge birds had higher expression of Toll-like receptor 4 (TLR4—a microbial surveillance gene) than birds from the range-core. Moreover, extensive inter-individual variation in genome-wide DNA methylation was found among Kenyan house sparrows, including an inverse relationship between epigenetic diversity and genetic diversity across populations. For my second chapter, I investigated whether these two observations were related, asking whether and how DNA methylation and/or genetic variation within the putative promoter of the TLR4 gene contributed to variation in TLR4 expression. I found that DNA methylation status at CpG1, which varied from only ~73-100%, was a strong predictor of TLR4 expression within individuals. Interestingly, other studies have shown that similar magnitudes of variation in DNA methylation of TLR4 can result in differences in the susceptibility/resistance to bacterial pathogens, thus, it’s plausible that the variation we observed could have functional implications for host defense. I also discovered four genetically linked polymorphisms within the TLR4 promoter that grouped into two general genotypes. We revealed a trend that suggests that genotype differences may influence TLR4 expression, confirmation of which may be possible with increased representation from individuals with the rare genotype. Given that DNA methylation did not vary systematically among populations and evidence for extensive genetic admixture at the Kenyan range-edge, it seems likely that individual-level factors (e.g. genotype, early-life experience, infection history, etc.) may be more predictive of variation in DNA methylation of TLR4 than population-level processes. Coping with novel challenges often requires coordinated adjustments to environmentally-sensitive (i.e. plastic) traits. Findings from my first dissertation chapter, as well as previous research from the Martin lab, revealed that CORT regulation, exploratory behavior and epigenetic mechanisms likely contribute to range expansion success in house sparrows. Within the hippocampus, mediators of neural plasticity such as brain-derived neurotrophic factor (BDNF), play a unique role in the bidirectional regulation of CORT and exploratory behavior, with important implications for hippocampal-dependent learning and memory. Moreover, evidence suggests that the regulatory capacity of CORT and BDNF to influence learning and memory relies heavily on the catalytic capacity of epigenetic modification enzymes—including DNA methyltransferases (DNMTs). For my third chapter, I explored whether previous CORT/behavioral/epigenetic patterns contributed to population-level differences in hippocampal BDNF expression and/or hippocampal expression of DNMTs (mediators of epigenetic potential), including potential covariation among CORT, BDNF and DNMTs within individuals. I collected house sparrows from three populations in Senegal—site of an ongoing range expansion—and measured stressor-induced CORT, hippocampal BDNF, DNMT1 and DNMT3a expression. Given the potential importance of neural plasticity and epigenetic potential for coping with novel challenges, I hypothesized that BDNF and DNMT expression would be highest at the range-edge, while positive covariation would occur between CORT, BDNF and/or DNMT expression within individuals. I found that intermediate levels of CORT resulted in the highest BDNF expression within individuals, suggesting that interactions between CORT and BDNF are likely important for balancing homeostatic and progressive (e.g. cognitive) changes within the hippocampus in response to environmental challenges. I also found that CORT positively covaried with DNMT1 expression in one, but not both, range-edge populations, while the reverse was true at the range-core. These findings suggest that in newly established population, CORT may promote epigenetic potential, allowing for rapid and fine-tuned organism-wide responses to novel stressors, while at the range-core, where stressors are presumably less novel, CORT may inhibit epigenetic potential as a means of diverting resources away from cognitive processes and towards maintaining homeostasis. Altogether, my dissertation has demonstrated how inherently plastic sub-organismal level traits (i.e. molecular, physiological, and neurological) may interact and contribute to range expansion success in an introduced bird. Specifically, my research has not only shown that epigenetic variation can influence an ecologically-relevant trait, but also that variation in the regulatory potential of epigenetic mechanisms can be mediated by intrinsic and extrinsic factors. These studies have expanded our understanding about how epigenetic mechanisms act as regulatory mediators of plasticity at the molecular level and can influence (and be influenced by) variation at multiple phenotypic levels, with implications for whole-organism performance in natural populations. I hope that my work contributes to the field of ecological epigenetics by providing the framework for epigenetic potential as an additional tool for assessing how epigenetic processes contribute to phenotypic outcomes in the face of rapid environmental change.

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.

abstract: Megafauna species worldwide have undergone dramatic declines since the end of the Pleistocene, twelve thousand years ago. In response, there have been numerous calls to increase conservation attention to these ecologically important species. However, introduced megafauna continue to be treated as pests. This thesis evaluates the extent of this conservation paradox in relation to changing megafauna diversity from the Pleistocene to the Anthropocene and finds that introductions have provided refuge for a substantial number threatened and endangered megafaunal species and has restored generic diversity levels per continent to levels closer to the Pleistocene than the Holocene. Furthermore, this thesis describes a previously unstudied behavior of wild burros (Equus asinus), an introduced megafauna whose pre-domestic ancestors are Critically Endangered. Wild burros dig wells to access groundwater and in doing so substantially increase water availability on several scales, create sites that are visited by numerous species and are comparable to natural water sources in terms of species richness, and provide germination nurseries for important riparian pioneer plant species. My results suggest that relaxing concepts of nativity in an age of extinction will provide new understandings of ecological function and can help focus attention on broader conservation goals. / Dissertation/Thesis / Appendix C / Appendix F / Masters Thesis Biology 2017

A introdução de espécies nos ecossistemas pode levar a conseqüências difíceis de serem controladas, sendo que a competição por recursos alimentares talvez seja o principal meio pelo qual uma espécie introduzida possa afetar as espécies nativas, podendo ocasionar a extinção. Neste sentido, os estudos de alimentação tornam-se importantes ao fornecerem subsídios para compreender o funcionamento trófico de um ecossistema. Considerando estes aspectos, o objetivo da pesquisa foi conhecer a ecologia trófica das espécies introduzidas (Plagioscion squamosissimus e Cichla cf. ocellaris) e da espécie nativa (Geophagus brasiliensis), avaliando as possíveis interações entre elas. Para o estudo da dieta das espécies escolhidas, foram utilizados os exemplares capturados durante o desenvolvimento do projeto PROBIO 2. As coletas foram realizadas nos seis reservatórios do Médio e Baixo rio Tietê, no período de novembro de 2002 a fevereiro de 2004. Foram realizadas análises quantitativas (freqüência de ocorrência, método volumétrico e método gravimétrico) dos itens encontrados, caracterizando a preferência alimentar das espécies. Neste trabalho o acará (Geophagus brasiliensis), apresentou um hábito alimentar onívoro, consumindo principalmente larvas de Diptera, insetos aquáticos e microcrustáceos. A espécie (Cichla cf. ocellaris) apresentou um hábito alimentar piscívoro, consumindo principalmente peixes e crustáceos. A corvina (P. squamossisimus) foi considerada piscívora, apresentando um amplo espectro alimentar, consumindo principalmente peixes, insetos aquáticos e crustáceos. A ampla distribuição da espécie P. squamosissimus nos seis reservatórios do médio e baixo rio Tietê e a plasticidade alimentar evidenciada pela análise de conteúdo estomacal sugerem que a corvina exerce uma forte pressão sobre as espécies nativas, cuja dinâmica populacional pode ser alterada. / The species introduction into the ecosystems may lead to difficult consequences hard to be controlled and the competition for food resources being the main factor by which introduced species can affect the native species, even causing their extinction. In this sense, the feeding studies are important by supplying subsidies to understand the trophic functioning of an ecosystem. Considering these aspects, the objective of this research was to know the trophic ecology of the introduced species Plagioscion squamosissimus and Cichla cf. ocellaris and of the native species (Geophagus brasiliensis), evaluating the possible interactions between them. For the diet study of the chosen species, were used the samples collected during the development of the project PROBIO 2. Sampling was carried out in six reservoirs of the Middle and Low Tietê river, between November 2002 and February 2004. Qualitative analysis was done (occurrence frequency, volumetric method e gravimetric method) on the found items, characterizing the species feeding preference. In this work, the acará (Geophagus brasiliensis) presented an omnivorous feeding habit, mainly consuming Dipteral worms, aquatic insects and micro crustaceans. The species (Cichla cf. ocellaris) presented a piscivorous feeding habit, mainly consuming fishes and crustaceans. The curvina (P. squamossisimus) was considered piscivorous, presenting an ample feeding spectrum, mainly consuming fishes, aquatic insects and crustaceans. The ample distribution of the specie P. squamosissimus in the six reservoirs of the Middle and Low Tietê river and the plasticity revealed by the stomach content analysis, suggests that the curvina exercises a strong pressure over the native species, in which population dynamics can be changed.

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.

Nonnative fishes are a major threat to biodiversity and new species continue to be introduced. In this dissertation, I described patterns and assessed determinants of fish invasions in the Mid-Atlantic region of the United States. Data on nonnative fish distributions were obtained from the United States Geological Survey's Nonindigenous Aquatic Species Database (NASD). Nonnative fishes are introduced by a variety of pathways, and prevention efforts can be optimized by focusing on pathways posing the greatest risk of new invasions. To assess the importance of existing pathways, I described the species associated with each pathway, analyzed the number of species introduced by decade for certain pathways, and estimated the detectability and probability of establishment of species introduced by each pathway. Additionally, I reviewed the efficacy of existing regulations for preventing introductions via each pathway. Historically, the intentional introduction of centrarchids and salmonids for sport was the dominant pathway. Pathways currently posing the greatest risks included bait release, illegal introductions, stocking of private ponds, and several pathways associated with economic activities. These pathways involved cyprinids, catostomids, and species exotic to North America. Regulations varied considerably among states, and I suggest that region-wide prohibitions on the release of nonnative species into the wild would help prevent additional introductions. Mid-Atlantic region watersheds differ considerably in nonnative species richness (NNSR), suggesting they are not equally invasible. I analyzed relationships between ecosystem characteristics and invasibility by compiling data on watershed characteristics and correlating these with NNSR. I included measures of colonization pressure (i.e., the number of species introduced) and research effort, which can bias patterns of NNSR. After controlling for these factors, the range in elevation in a watershed explained the greatest variation in NNSR. Highland watersheds had greater NNSR, probably because of greater habitat heterogeneity due in part to human activity. I suggest that NNSR can be reduced by restoration activities that reduce the diversity of artificial habitats available in highland watersheds. Ecosystems with similar NNSR may be invaded by different species, because differences in ecosystem characteristics may regulate the types of species that are able to establish. To explain differences in nonnative species among ecosystem types, I grouped Mid-Atlantic region watersheds by nonnative community and tested for differences in ecosystem characteristics among groups. Four groups were identified. A large, speciose group in the north-west portion region was characterized by smallmouth bass (Micropterus dolomieu). A large, speciose group in the south-west portion of the region was characterized by largemouth bass (Micropterus salmoides). Two smaller groups with few species were found on the coastal plain; one to the north, characterized by black crappie (Pomoxis nigromaculatus) and a second to the south characterized by white crappie (Pomoxis annularis). Nonnative community type was correctly predicted 80% of the time by models based on temperature and range in elevation. Relatively uninvaded watersheds in the south-east part of the region were predicted to host the most diverse nonnative community, suggesting that risks of invasion are high there. These results demonstrate the importance of species identity in determining ecosystem invasibility. There is no consensus on how to estimate the relative impacts of nonnative species. I developed and compared several approaches for doing so. I estimated impact by surveying fish biologists regarding the abundance and socioeconomic and ecological impacts of each species. I obtained fish collection records as an additional estimate of abundance and consulted reports of impacts in the NASD. I consulted reports of impacts in global invasive species databases as a basis for comparison. I compared top-ranked species among approaches, and game and non-game biologists' ratings of game and non-game species for each survey question. Top-ranked species differed considerably among approaches. Non-game biologists gave higher ecological impact ratings to both game and non-game species. Approaches assessing socioeconomic impacts are most appropriate for informing social decisions, such as restricting the possession or trade of a species. A combination of data from approaches assessing ecological impacts and abundance is most appropriate for studies of ecological patterns, such as testing for differences in traits between high- and low-impact species. These approaches are transferrable to other regions and taxa, and can inform management decisions and improve efforts to identify factors correlated with high-impact invaders. Collectively, my results can aid in reducing the effects of nonnative fish invasions by enabling managers to focus prevention efforts on high-impact species likely to invade particular ecosystems via known pathways. For example, bait releases, illegal introductions, private stocking, and several pathways associated with economic activities present the highest risks of future invasions, and warrant attention aimed at preventing invasions. Prevention could also be focused on several watersheds in the south-east part of the region, which currently have few established species but were predicted to be invasible by bluegill (Lepomis gibbosus), bluntnose minnow (Pimephales notatus) channel catfish (Ictalurus punctatus), and warmouth (Lepomis gulosus). This work represents major advancements in invasion biology, including new links between species identity and ecosystem invasibility and the development of methods for quantifying impact. / Ph. D.

Using a comparative approach, the presented study explores the ecology of ten species of native New Zealand broom, Carmichaelia, and their vulnerability to competition and herbivory, with the aim of gaining a better understanding of the significance of introduced species as a threat to rare indigenous plants in New Zealand. In particular, the study focuses on the relationship between characteristics of the Carmichaelia species and their vulnerability, as well as on other factors influencing the significance of introduced species as a threat. To gain a better understanding of the ecology of the Carmichaelia species, their current habitats and associated plant communities were investigated using quantitative-descriptive methods in the field. The effect of competition with introduced plants was studied in two glasshouse experiments, differentiating above ground competition for light from below ground competition for nutrients and water. The experiments focussed on the early life-stage of seedling establishment of the Carmichaelia species. The impact of herbivory by introduced mammals was studied in four field-based exclosure trials, focussing on the effects on survival and reproductive activity of adult Carmichaelia plants. The results showed that the effects of competition and herbivory vary between the different species. Furthermore, they provided a set of species characteristics that can be used as indicators to predict the vulnerability of Carmichaelia to the impact of introduced species. These indicators provide a useful tool for threatened species management, as they allow the identification of the most vulnerable species as well as the most significant threat to each species. Furthermore, the indicators can be used to group species, combining those with similar vulnerability profiles, and therefore, likely similar management needs. However, the example of the Carmichaelia species also illustrated that the use of indicators for the vulnerability of threatened species is limited and needs to be combined with case-by-case studies to verify the actual significance of threats for each population of concern. The vulnerability profiles derived from species’ characteristics can be used to guide such site specific studies, ensuring they focus on the most relevant threat factors. This combination of the understanding of general patterns in the vulnerability of species with targeted species and site-specific studies will lead to increased efficiency in the conservation management of threatened plant species.

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.

La variation de la diversité des communautés d’hôtes réservoirs peut modifier le risque de maladies impliquant ces espèces. En particulier, l’introduction d’une espèce potentiellement réservoir est susceptible d’augmenter le risque de maladie, en agissant comme un réservoir supplémentaire et/ou en amplifiant la circulation des agents pathogènes chez les réservoirs autochtones. L’objectif du travail de thèse est de quantifier la contribution, d’une espèce introduite, le tamia de Sibérie (Tamias sibiricus barberi), au risque d’une maladie multi-hôtes, la borréliose de Lyme, due à des bactéries appartenant au complexe d’espèces Borrelia burgdorferi sensu lato et transmises par des tiques, principalement Ixodes ricinus en Europe. Dans un premier temps, nous avons testé si le tamia est un réservoir compétent pour la maladie de Lyme en milieu naturel, c'est-à-dire s’il est capable de transmettre B. burgdorferi sl aux tiques I. ricinus et de maintenir l’infection. Le tamia est fortement infesté par les tiques et infecté par les bactéries et il peut transmettre B. burgdorferi sl aux tiques. Nos résultats ne montrent pas clairement que le tamia peut maintenir l’infection. Une des deux composantes du risque de la maladie de Lyme pour l’homme est le risque acarologique, c'est-à-dire la densité de nymphes infectées en quête d’hôtes. Dans un deuxième temps, nous avons calculé la contribution du tamia au risque acarologique et l’avons comparé à celles du campagnol roussâtre (Myodes glareolus) et du mulot sylvestre (Apodemus sylvaticus), réservoirs avérés de B. burgdorferi sl. Puis, nous avons étudié la variation temporelle de la contribution du tamia et testé si sa présence influençait la contribution des réservoirs rongeurs natifs. Pour calculer la contribution au risque, nous avons utilisé deux approches, l’une basée sur des captures des rongeurs, et l’autre sur l’identification des espèces hôtes sur lesquelles se sont gorgées les tiques. Le tamia produit plus de nymphes infectées à l’affût que le campagnol et le mulot. La contribution du tamia varie entre années suivant la densité de tamias et intra-années suivant la disponibilité en tiques. Sa plus forte infestation par I. ricinus et infection par B. burgdorferi sl, que les rongeurs natifs, peuvent être expliquées par sa plus forte exposition aux tiques. En conclusion, le tamia semble un réservoir compétent pour B. burgdorferi sl, avec une forte contribution au risque acarologique et une amplification possible de la circulation des pathogènes dans les communautés natives. Sa présence peut augmenter le risque pour la borréliose de Lyme chez l’homme en augmentant la prévalence d’infection des nymphes, mais pas les densités de nymphes à l’affût. / The variation of the composition of host communities can modify the risk of diseases involving these species. In particular, the introduction of a potentially reservoir species may increase the disease risk, by acting as an additional reservoir or by amplifying the circulation of pathogens in the native reservoirs. We quantified the contribution of an introduced species, the Siberian chipmunk (Tamias sibiricus barberi), to the risk of a multi-host vector-borne disease, Lyme borreliosis (LB), due to bacteria that belong to the Borrelia burgdorferi sensu lato complex and transmitted by bites of hard ticks, especially by Ixodes ricinus ticks in Europe. First, we verified if the Siberian chipmunk is a competent reservoir host for LB in the field, by testing if chipmunks can transmit B. burgdorferi sl to I. ricinus ticks and maintain the infection. Chipmunks were highly infested by ticks and infected by B. burgdorferi sl, and they are able to transmit the bacteria to ticks. Our results did not show clear maintenance patterns. Second, one of the parameter of LB risk for human is the acarologic risk, which is the density of infected questing nymphs. We evaluated the contribution of chipmunks to this risk and compared it with the one of bank voles (Myodes glareolus) and wood mice (Apodemus sylvaticus), two known reservoir rodents. Moreover, we studied the variation of the contribution. We used two approaches, the one based on captures of rodents and the other one on host-blood meal analysis of questing nymphs. Chipmunks produced more infected nymphs than voles and mice. The contribution of chipmunks varies between years according to chipmunk density and during the year according to tick availability. The higher infestation by I. ricinus and infection by B. burgdorferi sl of chipmunks in comparison to native reservoir rodents, could be due to its higher exposition to ticks. As Siberian chipmunk seems to be a competent reservoir host for LB with strong contribution, they can “spillback” infection to native communities and increase the risk for LB to humans by increasing infection prevalence in nymphs, but not nymph density.

Two conceptual approaches which offer promise for improved understanding of biological invasions are conceptualizing the invasion process as a series of distinct stages and explicitly incorporating human actions into analyses. This study explores the utility of these approaches for understanding the invasion of Trifolium (true clover) species in New Zealand. From the published literature, I collected a range of Trifolium species attributes, including aspects of global transport and use by humans, opportunistic association with humans in New Zealand, native range attributes, habitat characteristics, and biological traits. I also searched historical records to estimate the extent to which each species had been planted in New Zealand, a search facilitated by the enormous importance of Trifolium in New Zealand’s pastoral agriculture system. Regression analysis and structural equation modelling were then used to relate these variables to success at each invasion stage. Fifty-four of the 228 species in the genus Trifolium were intentionally introduced to New Zealand. Species introduced for commercial agriculture were characterised by a large number of economic uses and presence in Britain, while species introduced for horticulture or experimental agriculture were characterised by a large native range area. Nine of these 54 intentionally introduced species subsequently naturalised in New Zealand. The species that successfully naturalised were those that had been planted extensively by humans and that were well-matched to the New Zealand climate. A further 16 species (from the pool of 174 species that were never intentionally introduced) arrived and naturalised in New Zealand without any recorded intentional aid of humans. Several attributes appeared to assist species in unintentional introduction-naturalisation, including a good match to the New Zealand climate, a large native range area, presence in human-influenced habitats, a widespread distribution in Britain, and self-pollination capability. The 25 total naturalised species varied greatly in their current distributions and in the rates at which they had spread to achieve those distributions. Species that had spread quickly and are currently more widespread had been frequent contaminants in the pasture seed supply and have a long flowering period in New Zealand. Other biological traits and native range attributes played supporting roles in the spread process. Attributes facilitating success clearly varied among invasion stages. Humans played a dominant role at all stages of this invasion, although biological traits had increasing importance as a species moved through the invasion sequence. My findings suggest that incorporation of human actions and the stage-based framework provide valuable insight into the invasion process. I discuss potential avenues by which these approaches might be integrated into predictive invasion models.