Dissertations / Theses on the topic 'Introduced animals'

Thesis (M.S.)--Central Connecticut State University, 2002.<br>Thesis advisor: Kim Wilson. " ... in partial fulfillment of the requirements for the degree of Master of Science in Biology." Includes bibliographical references (leaves 54-58). Also available via the World Wide Web.

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.

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.

In near-shore marine environments, two of the most prevalent anthropogenic disturbances affecting ecosystem diversity and function are the invasion of exotic species, and the release of toxic chemicals. Estuarine and harbour environments worldwide are dually subjected to high levels of toxic disturbance and ever increasing rates of invasion, via activities such as boating and shipping. It is not clear, however, whether the success of invasive species is influenced by the presence of toxic contaminants in these impacted environments. In particular, nonindigenous marine species (NIS) may be advantaged in chemically disturbed environments if they are more tolerant of toxicants. This thesis examines whether nonindigenous and native sessile invertebrate species have differential tolerance to a common aquatic contaminant, copper (Cu), which has links to both the invasion process (via its use in antifouling paints and the vector of hull fouling) and the modification of recipient environments (via human-mediated pollution). A series of laboratory- and field-based experiments showed that the cosmopolitan invasive bryozoans Watersipora subtorquata, Bugula neritina and Schizoporella errata are highly tolerant of copper pollution. The larvae and adults of W. subtorquata and B. neritina in particular were able to survive and grow in copper-polluted environments far exceeding most observed real-world levels (< 100 /??g 1-1). These nonindigenous species also showed very strong postexposure recovery. In contrast, the co-occurring native bryozoans Celleporaria nodulosa and Fenestrulina mutabilis demonstrated comparatively low tolerance to copper, with markedly reduced survival and fitness under Cu contaminated conditions, and inferior recovery abilities post-exposure. These findings were further supported by a long-term manipulative field experiment, examining the effect that varying levels of Cu exposure have on the structure and diversity of developing sessile invertebrate assemblages. Cu exposure decreased native species diversity by up to 50%, yet had no effect on NIS numbers. Consequently, in the presence of copper contamination, NIS dominated sessile communities, often resulting in substantial changes to community structure. Important insights were also gained into the nature of metal tolerance in NIS. Toxicity studies on larvae of the introduced bryozoan Bugula neritina revealed intraspecific differences in tolerance to Cu, associated with the level of pollution experienced by the adult source populations. There was also evidence of fitness costs related with increased Cu tolerance. In summary, we have found evidence that the success of invasive species is influenced by chemical contamination. NIS may be advantaged in contaminated estuaries relative to native species and this may assist in their establishment and persistence in new habitats.

Species diversity is influenced by disturbance in the environment. Ground beetles (Coleoptera: Carabidae) were used as a model taxon to study the effects of disturbance (i.e., time since disturbance) in different habitats along a successional gradient (agricultural fields, old fields, young forests and old forests). Seventy-three species (5139 individuals) were collected during both years of sampling, of which 9 species are introduced species and compose 64.8% of the total catch. In contrast to the predictions of the Intermediate Disturbance Hypothesis, diversity of ground beetles was higher in the agricultural fields and lowest in the old forests. The community composition, as seen with Nonmetric Multidimensional Scaling ordination, in the agricultural fields was the most distinct, while the difference between and among other habitats was less clear, possibly influenced by the introduced species present in the area. The introduced species collected had a significant influence in the total catch as they represented more than half of the total individuals collected and in the ground beetle community composition. The distribution of seven introduced species in Quebec was studied and compared to what was reported in 1975. Five species have a similar distribution, while the distribution range of Harpalus rufipes DeGeer has expanded south and Bembidion obtusum Audinet-Serville might have been dispersing northeast since its introduction.

The Enemy Release Hypothesis proposes that introduced species often achieve larger individual sizes and greater population abundance in their introduced range because they have escaped their natural enemies - predators and parasites - that regulate populations in their native range. The main objective of this study is to test the Enemy Release Hypothesis (ERH) by investigating the identity, prevalence and intensity of parasites in two marine species introduced to New Zealand - the recently introduced but spatially restricted Asian portunid crab, Charybdis japonica, and the longer-established Asian nesting mussel, Musculista senhousia. Host choice of a native generalist parasite presented with the non-native and native mussels, and prey selection by a native predator presented with these bivalves will be examined. This is the first study of its kind in New Zealand. The parasite fauna of the only established New Zealand population of C. japonica (Waitemata Harbour, Auckland), was compared to that from (a) a population of C. japonica from its native region (Japan) and (b) to multiple populations of the native New Zealand crab Ovalipes catharus, a native New Zealand portunid. Results showed the introduced crab harboured only one species of endoparasite (a nematode), and two types of melanised lesions. Neither the parasite nor the lesions were present in the native crab populations. The native crab was host to only one parasite species, which occurred at very low prevalence, and was present in only one of the six populations examined from throughout New Zealand. Carapace width in the introduced crab was no larger than that reported in literature from its native are, but was larger than carapace widths of the Japanese sample. M. senhousia was examined from five sites within New Zealand. Parasites in M. senhousia were compared with a sympatric native bivalve, Austrovenus stutchburyi, two native mytilids, (Perna canaliculus and Xenostrobus pulex) and with samples of M. senhousia from Italy and the USA where it is introduced, and Japan where it is native. Two native generalist parasites, the pea crab Pinnotheres novaezelandiae, and a copepod, were found within M. senhousia in New Zealand, but only at low prevalence. A greater array of organisms was associated with the native bivalves. No parasites were recovered from any of the overseas samples of M. senhousia, including the Japanese samples. This may be caused by the preservation medium used, but could be a true reflection of the parasite fauna in these populations. The site where the two native parasites were exploiting M. senhousia was the only site sampled where two native mussels, P. canaliculus and X. pulex, also occurred. Consequently, effects of these two generalist parasites on the three mussel species were examined. In P. canaliculus, presence of native pea crabs was associated with lower tissue dry weight and greater shell depth. Shell width and depth were both greater in the presence of copepods. However, the prevalence of pea crabs and copepods was much lower in M. senhousia compared to the two native mussels, indicating some release from the effects of these parasites for the non-native species. Experimental choice tests showed that the pea crab, P. novaezelandiae, does not actively select M. senhousia as a host, preferring the larger native mussel, P. canaliculus. Rates of infection of M. senhousia are, therefore, likely to remain low in natural habitats where there are large numbers of native hosts. In addition, a generalist predator, the crab O. catharus, showed no preference when foraging on the three mussel species under experimental conditions. Thus, some predation pressure may be exerted on M. senhousia by this native crab in the natural environment. Investigation of multiple populations of both native and non-native species has shown large variation in parasite prevalence and intensity among populations of each species. After examining C. japonica and the comparable native O. catharus, evidence to support the ERH was found to be weak. As the native crab was relatively free of parasites, it seems unlikely that parasite infection is important within native populations and therefore, the success of C. japonica is unlikely to be caused by comparatively greater freedom from parasites (a central tenet of the ERH). There was also no evidence for host-switching by native parasites into the introduced C. japonica population. In contrast, native parasites were present at very low prevalence in the non-native mussel M. senhousia. Length of time since introduction can be an important factor in host switching between native and introduced hosts, but unless prevalence of these parasites is high, the introduced species still escapes from enemies that could control a population. Therefore every non-native species needs to be examined using multiple populations to investigate variation in parasite fauna, prevalence and intensity, as the same species, if introduced numerous times, could potentially show contrasting results for the ERH unless multiple populations are examined.

The nutria (Myocastor coypus) is a semi-aquatic rodent native to South America that was introduced to the Pacific Northwest, USA, in the 1930s. Primary damage categories from this invasive species include burrowing and herbivory, resulting in habitat degradation. Nutria have become well-established in metropolitan habitats, and anecdotal information suggests the problem has increased in recent years. However, little regional research on the species has been conducted. The scope of this research, which emphasizes metropolitan habitats, includes three primary foci in relation to nutria populations in the Pacific Northwest: modeling habitat suitability, assessing activity and movement patterns, and identifying and managing negative impacts. Large-scale management of any invasive species requires understanding of the current and potential future population distribution. Cold temperatures have been assumed to be a limiting factor for the geographic distribution of nutria populations, but this assumption had not been explicitly tested. A mechanistic habitat suitability model based on winter temperatures performed well in predicting nutria distribution in the Pacific Northwest and nationally. Regional results suggest nutria currently occupy most accessible suitable habitat. However, coupling the model with future climate change data suggests a much larger suitable habitat zone regionally and nationally in the near future. Management of an invasive species on a local scale requires region-specific information about behavior patterns. Radio-telemetry tracking of local nutria populations in metropolitan habitats suggested higher diurnal activity levels than reported elsewhere. Activity areas were also on the lower end of reported nutria home ranges, suggesting the studied metropolitan wetland sites represent core habitat for nutria in the region. Comparison of two transmitter attachment methods, a neck collar and a tail mount, did not identify a clearly superior attachment method for short-term nutria behavior studies. The presence of nutria in metropolitan habitats in the Pacific Northwest necessitates the need to expand the limited management techniques available for these habitats. Standard Vexar® plastic mesh tubes very effectively mitigated nutria herbivory damage to woody vegetation live stakes planted in a metropolitan habitat restoration site. A recently developed nutria multiple-capture cage trap captured larger nutria and reduced non-target captures compared to a standard cage trap. The design of the multiple-capture trap, however, prevented multiple-capture events because small nutria escaped the trap. This research contributes substantially to previously limited information about nutria in the Pacific Northwest and resulted in several new findings. Climate change modeling provides the first evidence that nutria ranges could expand in the near future. Evaluation of new radio-telemetry methods will benefit future behavior studies. The assessment of new damage prevention tools provides more options for the management of nutria in urban habitats. Management recommendations include creating regional nutria management plans, identifying and targeting priority monitoring regions, finding key stakeholders, focusing on public education, and initiating a pilot control program. Recommendations for research include evaluating effects on native fauna, conducting disease surveys, assessing the extent of damage, continuing habitat suitability analysis, and developing population indices.

The invasion of individuals into new habitats can pose a major threat to native species and to biodiversity itself. However, the consequences of invasions for native populations that are not fully reproductively isolated from their invaders are not yet well explored. Here I chose the Trinidadian guppy, Poecilia reticulata, to investigate how different population traits shaped the outcome of Haskins's introduction, a well-documented invasion of Guanapo river guppies into the Turure river. I especially concentrated on the importance of behaviour for invasive success. I investigated if the spread of Guanapo guppies is due to superiority in behaviour, life-history and/or genetics, or if the outcome of this translocation is due to chance. Despite the fact that by today the invasive front has passed the Turure's confluence with the River Quare many kilometres downstream of the introduction site, and the original genotype only survives in small percentages, as was revealed by genetic analysis in this and other studies, no obvious differences between invasive and native populations could be detected in any of the tested behavioural, life-history and genetic traits. When tested for mate choice, neither Guanapo nor Oropuche (Turure) males seemed to be able to distinguish between the population origin of females, but courted and mated at random. At the same time, females did not prefer to school with individuals of the same population over schooling with more distantly related females. The formation of mixed schools after an invasive event is therefore likely. Because female guppies showed a very low willingness to mate, even after having been separated from males for up to six months, sperm transfer through forced copulations will become more important. Taken together, these behaviours could increase the speed of population mixing after an invasion without the need for behavioural superiority of the invasive population. When tested for their schooling abilities, offspring of mixed parentage, in contrast to pure breds, displayed a large amount of variety in the time they spent schooling, a circumstance that can potentially influence survival rates and therefore the direction of gene pool mixing. Guanapo fish did not show reproductive superiority in a mesocosm experiment, where both populations were mixed in different proportions. On the contrary, in two out of three mixed treatments, the amount of Oropuche (Turure) alleles was significantly higher than expected from the proportion of initially stocked fish. The almost complete absence of distinguishable traits other than genetic variation between the examined populations that belong to different drainage systems, opposes the recent split of the guppy into two different species following drainage system borders, as is argued in this thesis. However, the successful invasion of the Turure by Guanapo guppies and the nearly entire disappearance of the original population can be explained in absence of differing population traits. Here I demonstrate how behavioural and genetic interactions between subspecies influence the outcome of biological invasions and second, how factors other than population traits, such as the geographic situation, can produce an advantageous situation for the invader even in the absence of population differences.

Amphibians are a group in worldwide decline. The factors that are causing this decline are not well known, but could be multifactorial, related to the recent expansion of pathogens and habitat disturbance. One of these factors related to the loss of habitat quality is the introduction of alien species. These species can compete with or prey on species of the recipient community, producing deep changes in the structure of these communities. For this reason it is a priority to know which factors act by facilitating the invasion process and which species could be more affected by the presence of this alien species. In Catalonia has become established an alien frog, the painted frog. Introduced in the extreme south of France in the early XXth century, this species has expanded gradually, reaching the Llobregat delta to the south and Llanguedoc to the north. This region is rich in native species of amphibians, some of them endemic, and therefore it is necessary to know how this newcomer species interacts with each of these species. We have used a novel approach when analyzing these interactions, applying the theory of morphospaces. The morphospace is the range of morphological variation observed within a community. This morphology is correlated with the use of a niche, and hence the morphological similarities between the invasive and native species serve as a proxy to assess the functional overlap. These analogies in morphospace were evaluated also in the area of native species and among other species of Discoglossus. The question asked is "Does the invasive species occupy a vacant niche, maintaining a similar morphological gap than that observed in the source assemblage and in the case of other species of the genus Discoglossus?”.<br>Els amfibis són un grup en declivi a nivell mundial. Els factors que estan causant aquest declivi no són coneguts, però podria ser multifactorial, en relació amb l'expansió recent de certs patògens i les alteracions dels hàbitats. Un d'aquests factors que es relacionen amb la pèrdua de qualitat dels hàbitats és la introducció d'espècies exòtiques. Aquestes espècies poden competir o depredar sobre les espècies de la comunitat recipient, produint profundes alteracions en l'estructura d'aquestes comunitats. Per aquesta raó és prioritari conèixer que factors actuen facilitant el procés invasiu i quines espècies es poden veure més afectades per la presència d'una espècie exòtica. A Catalunya s'ha establert una espècie de anur d'origen africà, la granota pintada. Introduïda a l'extrem sud de França a inicis del segle XX, aquesta espècie s'ha anat expandint de forma progressiva, fins a arribar pel sud al delta del Llobregat i pel nord el Llenguadoc. Aquesta regió és rica en espècies natives d'amfibis, algunes d'elles endèmiques, i per tant cal conèixer com interacciona aquesta espècie recent arribada amb cadascuna d'aquestes espècies. Nosaltres hem utilitzat un enfocament nou en el moment d'analitzar aquestes interaccions, aplicant la teoria dels morfoespais. El morfoespai és el rang de variació morfològica que s'observa dins d'un acoblament. Aquesta morfologia es correlaciona amb l'ús d'un nínxol, i per tant les analogies morfològiques entre l'espècie invasora i les espècies natives poden servir com una aproximació per valorar el solapament funcional. Aquestes analogies en el morfoespai s'han avaluat també en l'area nativa de l'espècie i entre altres espècies de Discoglossus. La pregunta formulada és "ocupa l'espècie invasora un nínxol vacant, mantenint una distància morfològica similar que a l'acoblament d'origen i que altres espècies del gènere Discoglossus?".

Aquatic invasive species are a major threat to native freshwater biodiversity. The North American signal crayfish Pacifastacus leniusculus was introduced to Great Britain during the 1970s and is now widely distributed throughout England, Wales and Scotland. First recorded in Scotland in 1995, P. leniusculus is now established at more than twenty sites. The only other introduced crayfish species present in Scotland is the white-clawed crayfish Austropotamobius pallipes. A. pallipes is restricted to only two locations in Scotland, Loch Croispol and Whitemoss Reservoir. P. leniusculus negatively impacts macrophytes, invertebrates and fish though ecological and physical processes. Additionally, P. leniusculus has displaced A. pallipes throughout much of its native range within Great Britain due to competition and disease. Consequently, the two A. pallipes populations in Scotland have a high conservation value. This PhD study aimed to improve understanding of P. leniusculus invasion success by examining trophic dynamics and to develop methodologies that could improve the detection and control of P. leniusculus populations in Scotland. Stable isotope analysis was used to determine the diet composition, trophic position and whether an ontogenetic dietary shift occurs in the Loch Ken population of P. leniusculus. Bayesian mixing models indicated that P. leniusculus in Loch Ken do exhibit an ontogenetic dietary shift. Additionally, individuals of all sizes occupied the trophic position of a predator in Loch Ken suggesting that invertebrates and fish constitute an important component of P. leniusculus diet. Stable isotope analysis was used once again to compare the isotopic niche width and diet composition of P. leniusculus populations from Loch Ken and A. pallipes populations from Loch Croispol and Whitemoss Reservoir. At the species level, A. pallipes exhibited a larger niche width than that of P. leniusculus. At the population level, the isotopic signatures of the A. pallipes populations were considerably different from each other suggesting an overestimation of A. pallipes’ niche width at species level. Results showed no dietary overlap between species and Bayesian mixing models suggested P. leniusculus and A. pallipes were consuming different resources, indicating there would be no direct competition for food resources if they were to co-occur. A plus-maze study was used to determine if P. leniusculus exhibited a preference for one of four food attractants (Oncorhynchus mykiss, P. leniusculus, beef or vegetation), which could be used to improve trapping efficiency. In the maze system, P. leniusculus exhibited no preference for any food attractant presented. This would suggest that either the maze was not a good model or food attractants would not improve trapping efficiency of P. leniusculus. Additionally, a comparative investigation into the use of gill nets as a method to control P. leniusculus was conducted. Results showed that the net type and the presence of fish entangled in the net influenced the number of P. leniusculus caught. Finally, environmental DNA (eDNA) was used and evaluated for detection of P. leniusculus. A robust quantitative Polymerase Chain Reaction (qPCR) assay and DNA extraction protocol were developed. Using the developed qPCR assay, P. leniusculus eDNA was detected in controlled aquaria conditions but not in environmental water samples collected from the field. Furthermore, the quantities of P. leniusculus eDNA declined in aquaria conditions while individuals were still present suggesting the mechanisms for eDNA release by P. leniusculus are complex. Stable isotope analysis indicates that P. leniusculus exhibit an ontogenetic dietary shift, and in each life stage, P. leniusculus function as an omnivore but occupy the trophic position of a predator. Niche width analysis revealed that the diet of P. leniusculus was less general than that observed in A. pallipes and thus diet of P. leniusculus may not be responsible for invasive success. Food attractants will not enhance trapping efficiency but nets may present a potential new method to control P. leniusculus. Similarly, eDNA presents a promising new method for rapid detection of P. leniusculus. It will not be possible to eradicate P. leniusculus in Scotland but the findings of this PhD may help prevent establishment of new populations. These results should be incorporated into future management strategies for P. leniusculus populations in Scotland and may have broader applications in Great Britain and Europe.

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.

Mosquitofish is a small, voracious, highly fecund freshwater fish species originated from northeaster America, that was introduced worldwide to control mosquito populations. In this thesis we have studied the genetics of the invasion of Mediterranean streams by the mosquitofish (Gambusia holbrooki) to discover some of the aspects that drive their successfully invasive life history. Comparison of introduced populations with the American sources of invasion indicated that there was no loss of genetic diversity due to the invasion process. Local genetic diversity levels and overall population structure were maintained among generations in introduced populations. We observed adaptive response to pollutants in the Flix reservoir, Ebro River, but that human perturbations do not prevent mosquitofish dispersal along rivers. Finally, unregulated human-assisted translocations probably increase the opportunities for colonization of new environments, and therefore need to be controlled.<br>La gambúsia és un peix molt voraç i fecund originari de les masses d’aigua dolça del nord-est d’Amèrica, que va a ser introduïda en tot el món pel control biològic de les poblacions de mosquit. En aquesta tesis se analitzen els processos genètics relacionats amb l’èxit invasor de la gambúsia (Gambusia holbrooki) en les conques mediterrànies. Les poblacions de gambusia introduïdes catalanes mantenen els nivells de diversitat genètica presents a les poblacions Americànes que van ser les fonts dels invasors de Europa. En aquestas poblacions introduïdes, els nivells locals i patrons hidrogràfics de diversitat genètica es mantenen entre generacions. Hi a una resposta selectiva als contaminants en les poblacions de gamusia a l’embassament de Flix, riu Ebro, però aquestes pertorbacions humanes no limiten la dispersió de la gambúsia. Finalment, les translocacions d’exemplars per l’home augmenten les oportunitats de colonitzar nous ambients i per això han de ser controlats.

The goldfish (Carassius auratus) is a hardy exotic species that have established sporadically distributed feral populations throughout North America. In one shallow seasonally anoxic pond goldfish formed a large stunted population of 15-17,000 ind ha$ sp{-1}$, with 53% being small young of the year. Goldfish were predominantly benthic herbivores with little diet overlap with resident red-spotted newts (Notapthalmus v. viredescens). Thus in relatively simple systems lacking fish predators goldfish can be very successful. However in systems with a complex native fish community, goldfish have had less success in colonizing. This could be related to an inability of goldfish to cope with native predators.<br>Tests for assortative shoaling between brown and gold coloured morphs showed that gold coloured fish exhibited no colour based assortive shoaling, while brown fish showed slight but significant colour preferences for like-coloured fish. This level of shoaling preference did not improve after visual exposure or interaction with native predators, indicating that goldfish showed limited behaviourial responses to predators, and that they were unable to modify their response to a predation threat. Further trials allowing goldfish to interact with either pike (Esox lucius) or bass (Ambloplites rupestris), in both single species groups of predator-naive goldfish, and mixed species conditions of goldfish with predator-experience minnows, showed that goldfish did not alter their behaviour in the presence of minnows (Pimephales notatus) when the predators were not present. However, with the predators present goldfish altered their activities to a more minnow-like pattern and showed a significant improvement in anti-predator behaviour. This improved behaviour continued by goldfish when they were retested on their own, indicating that the goldfish were reacting to the predator and not the minnows. Goldfish colonization may therefore be limited not so much by predation or competition from native cyprinids, but more by the absence/presence of a suitable, native, predator-experienced fish from which to copy the appropriate anti-predator behaviours.

It is generally accepted that populations which experience severe bottlenecks have a reduction in fitness. One of the most frequently reported fitness costs is increased hatching failure in bottlenecked populations of birds. The mechanism responsible for increased hatching failure is unknown. Research on other animals suggest that reduced population numbers cause unavoidable inbreeding that in turn leads to abnormalities in the gametes. In this thesis I examine some of the possible causes for increased hatching failure in severely bottlenecked populations of introduced birds in New Zealand. I look at three traits identified as a cause for infertility or hatching failure previously and determine whether there is a link with the size of a population s bottleneck. It is possible that reduced numbers of sperm reaching the site of fertilisation is a primary cause of hatching failure. I examined the perivitelline membrane of various species of introduced birds and counted the total number of sperm present to compare to how many would be expected in non-bottlenecked species. Although there was no relationship between the size of the bottleneck and the number of sperm present, all species had lower than expected sperm counts. In many species of mammals, a reduction in the quality of sperm is attributed to inbreeding depression bought about by genetic bottlenecks. I next compared the level of sperm abnormalities, variation in midpiece size sperm, and sperm motility with the size of the bottleneck each species passed through when introduced to New Zealand. There was no significant correlation between either the variation in midpiece size or sperm motility with bottleneck size. However, there was a trend for species that passed through more severe bottlenecks to have a slightly higher level of midpiece size and lower motility. Finally, I examined whether there was a link between abnormalities in the eggshell and the size of the respective bottleneck. There was no significant change in eggshell thickness or any change in the number of pores associated bottleneck size. However, there was a decreased number of round pores in severely bottlenecked species, although the consequences of this are unknown. My findings do not directly link a single cause for increased hatching failure in bottlenecked species of birds, but they do highlight the need for monitoring of reproductive traits in endangered species that have experienced a population bottleneck.

This study presents the results of a study on introduced giraffe diet and feeding effects within the Eastern Cape Province of South Africa. Five sites were selected over a moisture gradient from the mesic east to the arid west of the Eastern Cape to describe giraffe diet and provide baseline data for feeding effect experiments. At each site faecal samples were collected seasonally and diet composition determined by microhistological analysis. Plant species availability was measured using the point intersect method in order to compare plant availability to plant consumption to determine diet preferences. Giraffe diet across the sites showed a unimodal response to rainfall by utilising fewer species in drier areas where plant availability is low and increasing the number of species consumed as the rainfall increases. In higher rainfall areas, giraffe reduced the number of plant species fed upon because of the high availability of important species that reduces the need for a varied diet. Across all sites, plant availability was dominated by woody plant species (more than 90 percent at each site). A total of 57 plants species were recorded as being eaten across the five sites. Several PDI (Principle Diet Items) plant species (Acacia karroo, Schotia afra, Pappea capensis and Euclea undulata) were eaten across sites. Over all the sites, significantly preferred species were Asparagus striatus, Schotia latifolia, Asparagus suaveolens, Commelina benghalensis, Viscum rotundifolium, and Acacia cyclops. Acacia karroo, Schotia afra, Pappea capensis, Rhus crenata, A. tetracantha, and Grewia robusta were utilised in proportion to their availability. Euclea undulata, Rhus longispina and Putterlickia pyracantha were avoided. Feeding effects were tested by erecting exclosures around trees, covering one half of each tree. Ten trees were selected for these manipulative experiments which ran from September 2003 to February 2005. The number of branches, number of leaves, branch orders, branch diameter, branch length, leaf length and leaf width were measured for ten samples per side (enclosed vs. exposed) and analysed using a Wilcoxon matched pairs test and tested for effect size using Cohen’s d. Although no significant differences were detected between the sides measured, the effect size indicated differences in all measurements between sides ranging from low to moderate. Leaf length was greater on the outside of exclosures and showed a moderate difference between the sides in terms of the d-value with the p-value (0.059) tending towards significance. Although leaf width was higher on the inside of exclosures, it only showed a moderate difference for d with no statistical significance. Leaf area was higher on the inside of exclosures and tended to significance (p = 0.059) and similarly the d value indicated moderate differences between the sides in terms of effect size. Similarly branch length was higher on the inside of exclosures although not significantly, the p-value (0.07) approached significance. The effect size for branch length also showed a moderate difference between the sides. The number of branches and the number of leaves showed no statistical differences between the sides although the p-value (0.059) for the number of branches, as well as number of leaves (p = 0.07) approached significance. For both these variables, effect size showed a moderate difference. Giraffe showed diversity in their diet selection across sites but mainly fed upon available species. Some preferred species were however less available and this preference could possibly result in increased pressure on the selected plant species Exclosure experiments showed no significant differences in leaf and shoot characteristics although all measurements showed differences in terms of effect size meriting further investigation. It is concluded that giraffe impact on sites may be reduced if populations are properly managed however, high densities of giraffe could lead to similar vegetation impacts as observed in other areas where giraffe have been introduced and potentially change vegetation structure and plant community composition.

Freshwater fish species have been introduced into freshwater systems around the world, primarily for aquaculture, ornamental fish trade and sport fishing. Their introduction into estuarine systems is uncommon however, instances do occur and their establishment success and impacts on these estuarine systems is not well documented. The extent of invasion by four freshwater fishes in a RAMSAR listed estuarine system, the Wilderness Lakes, Western Cape was investigated. This thesis determined the relative abundance and distribution of alien fishes in relation to the native fish biota, their establishment success in the system, what factors inhibited their establishment and whether the introduction of alien fishes negatively impacted the native fish biota. The distribution and abundance of fishes were assessed primarily using fyke nets, seine nets and gill nets in each of the lakes, interconnecting channels and the Touw Estuary. The fish fauna was made up of euryhaline marine species comprising 46%, native estuarine species comprising 18%, catadromous species comprising 7% and freshwater alien species comprising 29% of the total biomass sampled. A total of 26 species were sampled in the system, three of which were considered alien; Oreochromis mossambicus, Gambusia affinis and Cyprinus carpio, and Micropterus salmoides were not sampled but confirmed in the system. Establishment success was determined by evidence of: a sustainable breeding population, a wide distribution, abundant in the sampling area, and all size classes of fish sampled. Gambusia affinis and Oreochromis mossambicus have been recorded in the system for a minimum of 13 and 26 years respectively. They were widely distributed and highly abundant and are established in the system. Micropterus salmoides was first recorded in the system in 1985 but abundances have remained low with fish appearing to be limited to Island Lake and Langvlei. Reproduction appeared to be limited by higher salinity and these factors indicated that this was a casual species which relies on repeated introductions for population maintenance. Cyprinus carpio spawned successfully in 2010 and was widely distributed but abundances were still low with a total of 15 fish being sampled throughout the system, and was thus in the establishing phase. As these are considered freshwater alien species, the physico-chemical parameters in the estuarine environment inhibiting the establishment success of the alien fishes were investigated. Gambusia affinis and O. mossambicus were not limited by the physical environment, and while O. mossambicus cannot tolerate temperatures below 11⁰C, temperatures only dropped below its tolerance for a total of two days between February 2010 and February 2011. Cyprinus carpio and M. salmoides were restricted by salinity in Rondevlei and Langvlei but could tolerate salinity in Island Lake and the Touw Estuary during closed mouth phases. While adults appeared to tolerate the salinity in the system, egg and larval development could be affected thus reducing the viability of the population. The abundance of alien fishes did not negatively impact the abundance of native fish species. The interactions between the native and alien fish biota tended towards biotic acceptance where, as alien abundance increased so did native fish abundance. The impacts of the alien fishes on the native fish biota were assessed by comparing the fish community from a study completed in 1985 to the findings of this study. From these two studies there were no apparent negative impacts on the native fish biota and the fish community composition would most likely be structured by estuarine mouth opening events.

"Styela plicata" is a solitary ascidian introduced all around the world by ship traffic and seems to have many of the required features to become invasive. The main goal of this PhD thesis was to increase our knowledge on the genetic composition of this species, its reproductive features and its capacity to cope with stress during early life-history stages and adulthood. Results indicate that S. plicata is an ancient introduced species that has been travelling around the globe through maritime transport for centuries. It inhabits harbors, marinas and artificial structures, tolerating high concentrations of pollutants. Adults can respond to moderate levels of stressors by adjusting the production of stress-related proteins, but early stages are comparatively much more vulnerable to the harsh conditions that characterize the habitats where this species thrives. A prolonged reproductive period allows S. plicata to exploit temporal windows of favorable conditions and confers a competitive advantage compared to organisms with limited, seasonal reproduction events. Moreover, high genetic variability and the continual presence of larvae also guarantee further reintroduction events and spreading via ship traffic. At present, the distribution of S. plicata appears to be limited by high temperatures, low salinities and other non-investigated factors such as competition and predation. Further studies should determine the dynamics of the few populations co-habiting with native communities to pinpoint all the factors regulating the spread of this species outside enclosed environments.<br>La ascidia Styela plicata ha sido introducida alrededor del mundo y parece presentar las características necesarias para convertirse en invasora. El objetivo principal de esta tesis Doctoral ha sido incrementar nuestro conocimiento sobre la composición genética de la especie, sus características reproductoras y su habilidad para tolerar condiciones estresantes como adulto pero también a lo largo de las primeras etapas del cliclo de vida. Los resultados han indicado que S. plicata es una introducción antigua, dado que la especie ha estado viajando alrededor del mundo durante los últimos siglos gracias al transporte marítimo. Esta especie habita en puertos, marinas y otras estructuras artificiales, y tolera altas concentraciones de contaminantes. Los adultos pueden responder a niveles moderados de estresores ajustando la producción de proteínas de estrés, pero los primeros estadios del desarrollo son mucho más vulnerables a las condiciones que caracterizan los ambientes en que la especie habita. Un periodo reproductor extenso permite a la especie explotar ventanas temporales de condiciones favorables y confiere a la especie una ventaja competitiva frente a otros organismos con reproducción estacional. Además, la elevada variabilidad genética y la presencia continua de larvas en la columna de agua, garantiza también eventos de reintroducción secundarios y por tanto la dispersión de la especie vía tráfico marítimo. Actualmente, la distribución de S. plicata parece estar limitada por temperaturas elevadas, bajas salinidades y otros factores aún por investigar tales como la competencia y la depredación. La dinámica de las escasas poblaciones en que la especie cohabita con comunidades nativas debería ser estudiada, para detectar los factores que regularían la dispersión de la especie afuera de los ambientes confinados en que actualmente la encontramos.

<p>The decline of the Oregon Spotted Frog (<i>Rana pretiosa</i>), a Pacific Northwest endemic now federally listed as threatened, has been attributed to several aspects of ecosystem alteration, primarily habitat degradation and loss. The introduced American Bullfrog (<i>Rana (Aquarana) catesbeiana </i>) has been widely implicated in those declines, but the basis of that contention has been difficult to characterize. The bullfrog occurring at every site of recent Oregon Spotted Frog extirpation has focused concern about its impact. </p><p> Here, I present a suite of interconnected studies that examine the behavioral ecology of both species to better understand the potential for bullfrog-mediated Oregon Spotted Frog extirpation. I quantified Oregon Spotted Frog anti-predator behavior from the only known population successfully co-occurring with bullfrogs (Conboy Lake) and a population devoid of bullfrog impact (Big Marsh), and compared these behaviors to the predatory traits of the bullfrog. The initial study revealed that captive-reared individuals from the Oregon Spotted Frog population that has successfully co-occurred with bullfrogs respond faster to a predatory stimulus (measured as latency to response) than Oregon Spotted Frogs from a population not to exposed to bullfrogs. Subsequent field investigations of the approach distance allowed by a predator stimulus before taking evasive action (termed the flight initiation distance: FID) conducted with the Oregon Spotted Frog population co-occurring with bullfrogs first demonstrated that FID of recently metamorphosed bullfrogs is consistently greater than that of recently metamorphosed Oregon Spotted Frogs. Further, examination of FID across all post-metamorphic age classes of Oregon Spotted Frogs revealed that older frogs do not allow as close approach as recently metamorphosed Oregon Spotted Frogs. This age class shift in FID did not occur in the Oregon Spotted Frog population not exposed to bullfrogs. In the latter population, FID did not differ among age classes. </p><p> Since the bullfrog might be driving this age-based change in anti-predator behavior, I explored the variation in strike distance of bullfrogs from the site of co-occurrence in both the field and laboratory to determine the extent of overlap with Oregon Spotted Frog FID. I found that the bullfrog strike distance significantly overlaps the FID of all ages of Oregon Spotted Frogs from the bullfrog-free site but only that of youngest (recently metamorphosed) frogs at the site of co-occurrence. Older Oregon Spotted Frogs from the site of co-occurrence generally escaped at distances greater than the strike distance of bullfrogs. </p><p> I also collected > 880 bullfrogs from the site of co-occurrence and analyzed the stomach contents to assess their dietary trends. I found that bullfrogs consume Oregon Spotted Frogs at the site, but do not eat the larger (older) frogs. Moreover, the body size ratio between Oregon Spotted Frogs as prey and bullfrogs as predators suggests that nearly all of the adult size distribution of bullfrogs at Conboy would be incapable of preying on adult Oregon Spotted Frogs. </p><p> Collectively, these studies strongly suggest that bullfrogs have altered the escape behavior of Oregon Spotted Frogs at Conboy Lake and that most adult Oregon Spotted Frogs at Conboy may have a size-based release from predation by bullfrogs. Implicit in this finding is that bullfrogs may pose a real threat via predation to other Oregon Spotted Frog populations with which they might come into contact where the distribution of bullfrog body sizes differ substantially from that at Conboy Lake. </p>

The harsh environmental and poor economic conditions of the Bolivian Altiplano require intervention to assist many of those that live there to become economically self-sufficient. We attempted to find introduced dry season reserve forage grasses that could produce enough biomass to be useful as feed for livestock, and that could also produce enough seed to distribute to farmers. While some of the grasses produced reasonable amounts of biomass, none produced seed in quantities that would be even close to being economically viable. The most likely cause of this is that the timing of resources that the grasses need to flower is very different between Bolivia and the areas from which the grasses originally came. We concluded that either the conditions under which the grasses are grown would need to be changed (i.e., earlier irrigation), or pre-adapted native species should be used. Native forbs are a critical component of any natural ecosystem, and thus should be included in wildland restoration projects. However, because the seed is currently collected by hand from the wild, it is very expensive, and this limits the ability of land managers to utilize it. A possible solution to this dilemma is for growers to commercially produce the seed and thus drive down the cost. In such a situation, it would be necessary to use herbicides to control competing weeds. We analyzed the effects of 5 herbicides on 7 species of native Utah forbs at 3 growth stages to learn which herbicides could safely be used on the test plants. We found that the plants' reaction the herbicides is largely species- and growth-stage specific.

Invasion physiology is an emerging field that endeavors to understand the influence of physiological traits on the establishment of non-native species in novel environments. The invasive European green crab,Carcinus maenas, is one of the world's most successful aquatic invaders, and is currently distributed across temperate marine ecosystems globally. The work presented here explored the thermal physiology of this species, and has highlighted several physiological traits that have likely influenced establishment success. Intraspecific comparisons of crabs sampled from the northern and southern edges of their recipient, or invaded range on the west coast of North America have identified both organismal and cellular physiological difference with respect to upper and lower thermal tolerances. Crabs sampled from British Columbia, Canada (BC) had a significantly lower mean upper thermal tolerance threshold and heat shock protein synthesis, Hsp70, compared to their warm acclimated conspecifics sampled from California (CA). These differential physiologic responses may be rooted in the disparate natural thermal habitats that each population occupies within their respective environments. The ability of this species to extend its current range limits was also investigated. Range expansion to the south has been limited, and is likely restricted by this species lack of adaptation to warmer temperatures. Because range expansion has been chiefly northward, characterizing this species' response to cold stress can identify whether colder temperatures poleward may limit further range expansion. Cold tolerance capacity was determined in the laboratory, and crabs sampled from Vancouver Island, British Columbia were able to withstand the over-wintering thermal regime that occurs in Sitka, Alaska, a site that is currently beyond the range limits of this species. Furthermore, intraspecific assessments found that the cold acclimated BC population exposed to cold shock significantly down regulated protein levels of cyclin D1, cell cycle modulator. Distinct differences in carapace width (CW) were detected along the thermal gradient present in the green crabs' range. This variation in body size was utilized to the test the temperature size rule hypothesis for ectotherms. Simply stated, the temperature size rule is the tendency for ectotherms to develop slower but mature to a larger body sizes at cooler temperatures. The results supported this hypothesis as crabs sampled from the warm portion of the range were found to be smaller than crabs sampled from the colder portion of the range. This pattern was detected along the native range as well. Differences in body size have the potential to influence the scope of invasion; larger individuals are generally more fecund and longer lived, which can increase both the intensity and frequency of larval dispersal that could further propel range expansion. The physiologic properties that the green crab possesses which may influence invasion success were examined using peer-reviewed literature with the aim of determining if these physiological traits confer invasion success across taxa. This analysis tested four hypotheses: 1) Broad geographic temperature tolerances (thermal width) confer a higher upper thermal tolerance threshold when comparing invasive and native species. 2) The upper thermal extreme experienced in nature is correlated with upper thermal tolerance threshold. 3) Protein chaperone expression, a cellular mechanism underlying thermal tolerance threshold, is greater in invasive organisms than in native ones. 4) Acclimation to higher temperatures can promote a greater range of thermal tolerance for invasives compared to natives. These preliminary results generally support the four stated hypotheses, and provide a solid foundation for further studies to explore and identify physiologic traits that facilitate invasion success. Overall, these studies investigated the thermal physiology ofCarcinus maenasfrom an invasive metapopulation and have brought about significant advances in our understanding of what physiologic traits correlate to invasion success in this species. In addition, the data presented here can aid resource managers in identifying habitats, based on thermal tolerance measurements that fit the criteria for invasion. Understanding how invasive organisms vary with respect to thermal tolerance can aid our understanding the patterns and processes of species invasions.

This thesis aims to contribute to the understanding of the invasive success of two invasive fishes (Gambusia affinis and G. holbrooki). We reviewed four Internet databases and the literature to clarify their introduction history and geographical distribution, establish their introduction routes, and analyse predictors of their invasive success. A meta-analysis of the ecological impacts of mosquitofishes shows that the overall impact is: i) similar for the two species; ii) clear and strong for fish, macroinvertebrates, amphibians, and some zooplanktonic groups and more variable for taxa at lower trophic levels and for ecosystem features; iii) general for the number of aggressive acts received and decreases in density and biomass but more variable for other response variables; and iv) highly heterogeneous and context-dependent on a number of features. We estimated the mean critical swimming speed (Ucrit) of G. holbrooki as 14.11 cm s-1, which is lower than for many other fish of similar size and confirms that this species is limnophilic and its invasive success might be partially explained by hydrologic alteration. However, we demonstrate that Ucrit and maximal metabolic rate vary markedly with fish size and sex, with males having much higher values for the same weight, and thus probably being more resistant to strong water flows.<br>Aquesta tesi té com a objectiu contribuir a millorar la comprensió de l'èxit invasor d'aquests dos peixos (Gambusia affinis and G. holbrooki). Es van revisar quatre bases de dades d'Internet i la bibliografia per aclarir la seva història d’introducció i distribució geogràfica, establir les rutes d'introducció i analitzar els predictors del seu èxit invasor. Una meta-anàlisi de l'impactes ecològics de les gambúsies mostra principalment que l'impacte global és: i) similar per a les dues espècies; ii) clar i fort per a peixos, macroinvertebrats, amfibis, i alguns grups de zooplàncton i més variable per als tàxons de nivells tròfics més baixos i a nivell d’ecosistema; iii) general per al nombre d'agressions rebudes i la disminució de la densitat i la biomassa, però més variable per altres variables; i iv) altament heterogeni i dependent del context per una sèrie de característiques. Hem estimat la velocitat crítica de natació mitjana (Ucrit) de G. holbrooki com 14.11 cm s-1, que és inferior a la de molts altres peixos de mida similar i confirma que aquesta espècie és limnòfila i el seu èxit invasor parcialment s'explica per l'alteració hidrològica. No obstant això, vam demostrar que Ucrit i la taxa metabòlica màxima varien notablement amb la mida i el sexe dels peixos, amb valors molt més alts als mascles que a femelles del mateix pes, els quals deuen ser per tant menys vulnerables a cabals forts.

La Corse, avec ses 3 000 km de linéaire de cours d’eau, possède un réseau hydrographique particulièrement dense et complexe. A cette complexité vient s’ajouter celle des peuplements piscicoles actuels, fruits de vagues successives d’introductions d’espèces dans les cours d’eau et les plans d’eau de l’île. Si la Corse est caractérisée par une faune piscicole native faiblement diversifiée (seulement quatre espèces), plus d’une vingtaine d’espèces introduites sont venues augmenter artificiellement cette diversité depuis la fin du 19ème siècle. Les impacts des espèces introduites sur les écosystèmes aquatiques sont multiples (e.g., compétition, prédation, modification d’habitat, impacts génétiques) et parmi ceux-ci, la co-introduction de pathogènes, dont les parasites, est particulièrement préoccupante et encore trop faiblement documentée. Il est de plus intéressant d’aborder ce type de sujet en milieu insulaire. Les travaux présentés ici ont par conséquent pour objectifs de déterminer la composition de la parasitofaune des poissons natifs et introduits en Corse, d’évaluer sa richesse, de déterminer si des transferts de parasites des poissons introduits vers les natifs ont pu se produire, et si les parasites présents sont susceptibles d’avoir un impact en termes de santé animale ou humaine.Afin de réaliser ce travail, des campagnes d’échantillonnage ont été réalisées sur une sélection d’espèces natives (Anguilla anguilla, Salmo trutta, Salariopsis fluviatilis et Atherina boyeri) et introduites (vairons du genre Phoxinus, Perca fluviatilis, Squalius cephalus et Gobio spp.), dont quatre ont été particulièrement ciblées en raison de leur accessibilité et des problématiques parasitologiques qu’elles offraient. Ainsi, le travail mené a permis, d’une part, de déterminer la composition des communautés parasitaires d’A. anguilla dans deux lagunes de la plaine orientale et, pour la première fois, dans de nombreux cours d’eau répartis sur l’ensemble du territoire insulaire. D’autre part, ce travail a mis en évidence la présence dans toute la Corse de parasites invasifs : les Monogenea Pseudodactylogyrus bini et P. anguillae et le Nematoda Anguillicola crassus, ainsi que leur maintien et l’augmentation de leur prévalence et abondance dans la lagune de Biguglia depuis la décennie précédente. Ces résultats montrent l’intérêt du suivi des parasites invasifs. L’étude de la truite S. trutta a permis de proposer une détermination spécifique du Gyrodactylus qui provoque des pathologies chez certaines populations de Corse. Pour ce qui est des espèces introduites, les travaux menés chez les Phoxinus ont révélé la présence de quatre espèces de ce genre dans l’île, avec un premier signalement pour Phoxinus csikii et Phoxinus septimaniae. Les parasites des vairons ont été étudiés en Corse pour la première fois et la répartition des Monogenea du genre Gyrodactylus a permis de retracer les voies d’introduction secondaires de leurs hôtes. Ces résultats montrent la nécessité d’une clarté taxonomique pour la parasitologie et l’apport de l’étude des parasites pour la biologie des invasions. Bien que réalisée sur un faible effectif, l’étude des parasites de Perca fluviatilis a révélé la présence de deux parasites zoonotiques chez ce poisson : le Nematoda Eustrongylides spp. et le Digenea Clinostomum complanatum, tous deux rapportés pour la première fois en France, et susceptibles d’impacter la santé de la faune sauvage et la santé humaine. Ces observations confirment la nécessité d’une approche systémique du type One Health pour ce genre de problématique. Des données, moins fournies, ont aussi été apportées pour la première fois sur la parasitologie d’autres espèces introduites et natives de Corse (S. fluviatilis, A. boyeri, S. cephalus et Gobio spp.)<br>With 3,000 km of waterways, Corsica has a particularly dense and complex hydrographic network. This complexity is compounded by the complexity of current fish populations, which is the result of successive waves of species introductions into the island's rivers and reservoirs. Although Corsica's native fish fauna is poorly diversified (only four species), more than twenty introduced species have artificially increased this diversity since the end of the 19th century. The impacts of introduced species on aquatic ecosystems are multiple (e.g., competition, predation, habitat modification, genetic impacts) and among these, the co-introduction of pathogens, including parasites, is of particular concern and still too poorly documented. Moreover, it is interesting to approach this type of subject in an insular environment. The work presented here therefore aims to determine the composition of the parasitofauna of native and introduced fish in Corsica, to assess its richness, to determine whether transfers of parasites from introduced fish to native fish have occurred, and whether the parasites present are likely to have an impact in terms of animal or human health. Sampling campaigns were carried out on a selection of native species (Anguilla anguilla, Salmo trutta, Salariopsis fluviatilis and Atherina boyeri) and introduced species (Phoxinus minnows, Perca fluviatilis, Squalius cephalus and Gobio spp.), four of which were particularly targeted for their accessibility and the parasitological problems they presented. The work carried out enabled us to determine the composition of A. anguilla parasite communities in two lagoons on the eastern plain and, for the first time, in numerous watercourses throughout the island. In addition, this work has highlighted the presence throughout Corsica of invasive parasites: the Monogenea Pseudodactylogyrus bini and P. anguillae and the Nematoda Anguillicola crassus, as well as their maintenance and the increase in their prevalence and abundance in the Biguglia lagoon since the previous decade. These results demonstrate the value of monitoring invasive parasites. The study of S. trutta trout has enabled us to propose a specific determination of Gyrodactylus, which causes pathologies in certain Corsican populations. As for introduced species, work on Phoxinus has revealed the presence of four species in this genus on the island, with the first records of Phoxinus csikii and Phoxinus septimaniae. Parasites of minnows have been studied in Corsica for the first time, and the distribution of Monogenea (Gyrodactylus) has enabled us to trace the secondary introduction routes of their hosts. These results demonstrate the need for taxonomic clarity in parasitology, and the contribution of parasite studies to invasion biology. Although carried out on a small number of fish, the study of Perca fluviatilis parasites revealed the presence of two zoonotic parasites in this fish: the Nematoda Eustrongylides spp. and the Digenea Clinostomum complanatum, both reported for the first time in France, and likely to have an impact on wildlife and human health. These observations confirm the need for a systemic approach such as One Health to this type of problem. Less extensive data were also provided for the first time on the parasitology of other introduced species and those native to Corsica (S. fluviatilis, A. boyeri, S. cephalus and Gobio spp.)

Les rats introduits (Rattus spp.) sont des espèces invasives majeures menaçant la biodiversité sur la plupart des îles de laPlanète. Deux espèces, le rat noir (R. rattus) et le rat du Pacifique (R. exulans) vivent en sympatrie au sein des forêts deNouvelle-Calédonie, où la question de la faisabilité et de l' intérêt de leur contrôle (i.e. limitation locale de leur 'abondance)pour la conservation de la biodiversité native est posée. En raison d'un manque de cadre conceptuel des projets de contrôle,nous avons d'abord réalisé une synthèse et une analyse des opérations de contrôle de rats invasifs dans les milieux naturelsdes îles du monde. Puis, nous avons cherché à caractériser et à comprendre la dynamique des populations de ces deux espècesde rats sympatriques ainsi que leurs interactions avec la biodiversité native en forêt dense humide du massif du Mont Panié.Des opérations de piégeage létal et de capture-marquage-recapture ont montré que les rats noirs étaient plus abondants que lesrats du Pacifique. Les analyses de leur régime alimentaire ont révélé que les deux espèces ont à la fois des proies communeset des proies qui leur sont propres impliquant un renforcement ainsi qu'un élargissement de leurs impacts sur la biodiversiténative. Les rats consomment une grande majorité de fruits et de graines, d'invertébrés et de Squamates mais les oiseaux, quijustifient souvent la mise en place de projets de gestion de rats, ne semblent pas ici être une de leur proie préférentielle. Depotentiels effets positifs des rats sur la dispersion des graines ont également été mis en évidence au travers d'une comparaisondu potentiel germinatif de graines après passage par leur tractus digestif et celui de frugivores natifs. Enfin, nous avons puproposer des stratégies de piégeage létal afin de contrôler efficacement les populations de rats invasifs. Une meilleurecompréhension des impacts des rats en situation de sympatrie ainsi qu' une meilleure connaissance du lien entre densité de ratset intensité des effets sur la biodiversité permettraient d'optimiser les stratégies de contrôle de rats invasifs lorsquel'éradication n'est pas envisageable<br>Introduced rats (Rattus spp.) are one of the major invasive species threatening native biodiversity on islands worldwide. Twospecies, the black rat (R. rattus) and the Pacifie rat (R. exulans) are sympatric in New Caledonian rainforests, where questionsasto the feasibility and the utility of their control (i.e. local limitation of their abundance) for the conservation of nativebiodiversity remain unanswered. ln response to the lack of a conceptual framework for control projects, we fi rst conducted areview of invasive rat control operations in island natural areas worldwide. Then we sought to characterize and understand thepopulation dynamics of these two sympa tric rat species and the ir interactions with native biodiversity in the rainforest of MontPanié mountain. Lethaltrapping operations and capture-mark-recapture showed that black rats were more abundant thanPacifie rats. Diet analysis revealed that the two species consume both shared and unshared prey likely resulting in astrengthening and a broadening oftheir impacts on native biodiversity, relative to the impact that each species would haveal one. Rats consume a large quantity of fruits and seeds, invertebrates, and Squamates. However, birds, which often justify theimplementation of rat management projects, do not appear here to be one of the ir preferred prey, either as adults or throughnest predation. A potential positive rat impact on seed dispersal was a Iso highlighted through a comparison of seedgermination after seeds had passed through rat versus native frugivore digestive tracts. Finally, we propose lethal trappingstrategies to efficiently control invasive rat populations. A better understanding ofboth rat impacts in sympatric situations,and the link between rat density and the intensity of their effects on biodiversity would allow optimizing rat control strategieswhen eradication is not feas ible

Les changements globaux, qu’ils soient d’origine climatique ou anthropique ont diverses conséquences en santé humaine et animale, mais aussi sur les écosystèmes mondiaux. L’une des plus importantes est la modification des aires de répartitions géographiques des espèces et de celle des pathogènes qui leurs sont associés. C’est dans ce contexte que nous assistons ces dernières années à une recrudescence des cas d’émergences et de réémergences de maladies infectieuses dans le monde. Alors que les efforts de recherche menés dans ce domaine se focalisent principalement sur les maladies virales, les maladies transmises par les mollusques d’eau douce, qui affectent plus d’un milliard d’individus dans le monde, sont également sujettes à ces évènements d’émergences devenus fréquents. Cependant, l’étude de la dynamique des parasites associés à ces maladies se focalisent essentiellement sur le diagnostic et le traitement des hôtes définitifs, en particulier l’Homme. Toutefois, une telle approche ne permet pas de prévenir de la transmission de ces parasites à l’Homme et encore moins de prévenir d’un évènement d’émergence, et les outils actuels utilisés pour le suivi de ces parasites dans l’environnement sont difficilement applicables à large échelle. Ce travail de thèse se propose donc d’apporter une vision plus environnementale de la dynamique de ces maladies. Avec l’exemple de l’émergence de bilharziose urogénitale en Corse, nous avons analysé cette émergence en intégrant l’étude des traits d’histoire de vie du parasite tropical en cause, notamment sa thermo tolérance, ainsi que le rôle des hôtes intermédiaires mollusques et des hôtes définitifs sauvages et domestiques dans le maintien local du cycle parasitaire. Dans un second temps nous avons développé des outils de diagnostic par ADN environnemental pour la détection de mollusques hôtes dans l’environnement afin d’identifier les zones à risque d’émergence, ainsi que des outils de détection intramolluscal de schistosomes pour identifier les sites de transmission actif, et donc permettre un suivi environnemental des acteurs de ces maladies. Pour compléter ces approches, nous avons développé un outil plus généraliste de metabarcoding environnemental pour caractériser les communautés de mollusques d’eau douce, et initié le développement d’un outil similaire pour la caractérisation des communautés de trématodes, ceci afin d’étudier les interactions entre ces organismes. Enfin nous discutons de l’intégrations de tous ces éléments dans de nouvelles stratégies de contrôle à l’encontre de maladies transmises par les mollusques d’eau douce<br>Global changes, whether climatic or anthropogenic, have various consequences in human and animal health, as well as for worldwide ecosystems. One of the most important is the modification of geographical ranges of species and those of their associated pathogens. It is in this context that in recent years we have witnessed a resurgence in the emergence and re-emergence of infectious diseases around the world. While research efforts in this field are mainly focused on viral diseases, freshwater snail-borne diseases, that affect more than 1 billion peoples around the world, are also subject to these outbreaks, which have become frequent. However, the study of the dynamics of parasites associated with these diseases focuses primarily on the diagnosis and treatment of the definitive hosts, particularly humans. Such an approach does not prevent the transmission of these parasites to humans and even less prevent an emergence event, and the existing tools used to monitor these parasites in the environment are difficult to apply at large scale. This thesis work, therefore aims to provide a more environmental vision of the dynamics of these diseases. With the example of the emergence of urogenital bilharziasis in Corsica, we analysed this emergence by integrating the study of the life history traits of the tropical parasite in question, particularly its thermo tolerance, as well as the role of mollusc intermediate hosts and wild and domestic definitive hosts in the local maintenance of the parasite lifecycle. In a second step, we have developed environmental DNA diagnostic tools for the detection of molluscs hosts in the environment in order to identify areas at risk of emergence, as well as tools for intramolluscal detection of schistosomes to identify active sites of transmission, and thus allow the environmental monitoring of the actors of these diseases. To complete these approaches, we have developed a more generalised environmental metabarcoding tool to characterise freshwater mollusc communities and initiated the development of a similar tool for the characterisation of trematode communities, in order to study the interactions between these organisms. Lastly, we discuss the integration of all these elements into new control strategies against snail-borne diseases

Les espèces exotiques envahissantes sont un sujet de préoccupation grandissant, mais sont-elles,pour le droit international, un objet comme un autre ? Une espèce exotique envahissante a comme particularité d’être une espèce vivante qui, par sa seule présence dans un écosystème qui lui est étranger, va engendrer des effets délétères alors qu’elle n’en aurait causé aucun dans son écosystème d’origine. Le droit de la mer est-il armé pour répondre à cette menace ? La question de la qualification de leur atteinte en droit international et plus précisément en droit de la mer est autant novatrice que capitale. Le traitement juridique des espèces exotiques envahissantes a consisté, jusqu’à maintenant, à les rattacher de facto à la lutte pour la conservation de la diversité biologique sans même que soit posée la question, en amont, de leur qualification. Et si les espèces exotiques envahissantes étaient considérées comme une pollution ? Envisager cette hypothèse implique de procéder à une étude de fond tant des instruments de droit international, et de droit de la mer en particulier, que de la pollution marine. S’il est permis de reconnaître les espèces exotiques envahissantes comme étant une source de pollution, elle n’en reste pas moins une nouvelle forme de pollution encore jamais reconnue par les instruments de droit international : une pollution biologique. Cette pollution, autonome de celles déjà existant en droit international,impliquant la nécessité de repenser la définition de la pollution marine<br>Alien invasive species are a growing concern, but are they an object as any other in international law ? An invasive alien species is a living species which, by its mere presence in an ecosystem outside its natural range, causes deleterious effects which is not the case in its native ecosystem. Is the law of the sea equipped to meet this new threat ? The classification of its effects in international law, and more specifically the law of the sea, is as innovative as capital. The legal treatment of invasive alien species so far has been tied to the struggle for the conservation of biological diversity without wondering, in advance, what its classification is. What if alien invasive species are considered pollution ? Considering this hypothesis means studying instruments of international law, and more precisely those of the law of the sea, as well as marine pollution. If one can allow to identify invasive alien species as a source of pollution, it remains a new form of pollution that has never been recognized before by the instruments of international law : a biological pollution. This pollution, independent of those already existing in international law, implies the need to rethink the definition of marine pollution

Les groupements issus de l'enherbement au moyen de melanges de graines de varietes d'especes herbacees commercialisees (dont principalement festuca rubra, festuca ovina, phleum pratense, lolium perenne, trifolium repens, trifolium hybridum, lotus corniculatus) des zones terrassees lors de la construction des pistes de ski evoluent tres rapidement en fonction des configurations des milieux. Leur etude dans les domaines du montagnard superieur a l'alpin inferieur sur des terrains pauvres en calcium et a bon equilibre textural situes aux menuires et a val thorens en savoie fait ressortir: que jusqu'au subalpin moyen et sur des sols a bon potentiel edaphique (soit que les sols initialement en place ont ete faiblement decapes, soit que des apports importants en matiere organique et en elements mineraux ont ete realises ou que des dispositifs de piegeage des elements fins ont ete installes), ils constituent des formations fermees: ces groupements se stabilisent par modification dynamique: au cours d'une phase juvenile (pendant les trois premieres periodes de vegetation) ils sont composes par les especes introduites et quelques ruderales; au cours d'une phase de transition apparaissent des especes autochtones de premiere installation: au cours de la phase de maturation la contribution specifique et la richesse specifique des especes spontanees provenant pour partie des groupements vegetaux environnants augmentent fortement: pour les stations fortement terrassees et/ou a tres haute altitude, les recouvrements observes sont faibles

Dissertação de Mestrado em Ecologia apresentada à Faculdade de Ciências e Tecnologia<br>As invasões biológicas são um dos principais impulsionadores da perda de biodiversidade em todo o mundo, sendo particularmente perturbadora para as ilhas oceânicas. Essas extinções de espécies implicam a perda de funções do ecossistema, como a dispersão de sementes por animais. Trabalhando no hotspot de endemicidade da ilha de São Tomé, utilizamos análises complexas de rede de última geração para avaliar o impacto de grandes dispersores introduzidos nas redes de dispersão de sementes, formadas por pequenos dispersores endêmicos. As comunidades insulares evoluíram sob baixa pressão seletiva de grandes vertebrados, filtrados pela barreira oceânica para a dispersão. Portanto, a integração de grandes dispersores em São Tomé é susceptível de ter grandes implicações para a dispersão de plantas nativas e introduzidas, modelando o recrutamento de plantas e o futuro das florestas nativas.Durante um ano, compilámos interações entre plantas e os dispersores das suas sementes, através de cinco métodos complementares de amostragem: observações diretas, revisão literária, questionários, análise de excrementos e conteúdos estomacais. Após a reconstrução da rede de dispersão, avaliámos se a origem dos dispersores (nativos vs. introduzidos) ou a largura da sua garganta afeta o seu papel enquanto dispersores de sementes, nomeadamente: número de plantas dispersadas, grau de seletividade (d'), “species strenght” e tamanho das sementes dispersadas. A rede de São Tomé revelou 419 interações entre 22 espécies de dispersores (12 aves, 2 morcegos, 1 cobra e 7 mamíferos não voadores) e 150 espécies de plantas. Duas das plantas mais frequentemente dispersadas, Cecropia peltata e Rubus rosifolius são espécies altamente invasoras. Cada método de amostragem revelou-se principalmente útil para um pequeno grupo de dispersores, fornecendo por isso informação altamente complementar. Os questionários provaram ser o método de amostragem que contribuiu com mais interações, seguido da análise de excrementos e de conteúdos estomacais. Os dispersores nativos e introduzidos não diferiram significativamente em nenhum dos três descritores topológicos analisados, no entanto os dispersores introduzidos tenderam a dispersar espécies com sementes maiores. Esta diferença deve-se especificamente à maior largura da garganta dos dispersores introduzidos. No seu conjunto, estes resultados apontam para um importante potencial perturbador dos dispersores introduzidos, ao alterarem a pressão seletiva em favor de espécies com sementes grandes. Estas diferenças no tamanho das sementes dispersadas não se refletiu contudo em diferenças na topologia das interações estabelecidas, alertando para a necessidade de considerar simultaneamente características biológicas na interpretação das redes de interações.<br>Biological invasions are a key driver of biodiversity loss worldwide being particularly disruptive on oceanic islands. Such species extinctions entail the loss of ecosystem functions such as seed dispersal by animals. Working in the endemicity hotspot of São Tomé Island, we used state-of-the art complex network analysis to evaluate the impact of large introduced dispersers on seed-dispersal networks formed by small endemic dispersers. Island communities have evolved under low selective pressure from large vertebrates, filtered by the oceanic barrier to dispersal. Therefore, the integration of large dispersers into São Tomé is likely to have large implications for the dispersal of native and introduced plants, shaping plant recruitment and the future of the native forests. During one year, we compiled interactions between plants and seed dispersers through five complementary sampling methods: direct observations, literary review, questionnaires, excrement analysis and stomach contents. After rebuilding the dispersion network, we evaluated whether the origin of the dispersers (natives vs. introduced) or the width of their throat affects their role as seed dispersers, namely: number of plants dispersed, degree of selectivity (d '), "Species strength" and seed size dispersed. The São Tomé network revealed 419 interactions between 22 dispersers species (12 birds, 2 bats, 1 snake and 7 non-flying mammals) and 150 plant species. Two of the most frequently dispersed plants, Cecropia peltata and Rubus rosifolius are highly invasive species. Each sampling method proved to be particularly informative for a small group of dispersers, and therefore their results are largely complementary. The questionnaires proved to be the sampling method that contributed with more interactions, followed by fecal and stomach content analysis. Native and introduced dispersers did not differ significantly in any of the three topological descriptors analyzed, however introduced dispersers tended to disperse species with larger seeds. This difference is largely explained by the larger gape width of the introduced dispersers. Altogether, these results point to an important disruptive potential of introduced dispersers, by altering the selective pressure in favor of species with larger seeds. However, these differences in the size of the dispersed seeds were not reflected in differences in the topological patterns of the interactions, highlighting the need to simultaneously consider biological traits while interpreting interactions networks.

An improved understanding of how ecosystems function is important for effective natural resource management and biodiversity conservation. Recent research suggests that top-order predators have important ecological roles in many ecosystems through controlling populations of smaller predators. This thesis examined how the management of Australia's apex predator, the dingo (Canis lupus dingo), influenced the activity and behaviour of two introduced mesopredators, the red fox (Vulpes vulpes) and feral cat (Felis catus) and select prey species. The aim was to increase our understanding of the role dingoes may play in the conservation of endangered fauna through the trophic regulation of exotic mesopredators. The study monitored the activity and behaviour of dingoes, foxes, feral cats and select prey species at five sites in arid Australia. Dingo management varied between the study sites. Sites included areas where dingoes remained uncontrolled, where dingoes were controlled through exclusion fencing and where 1080 poison baiting was conducted. At each site the activity of predators and prey, including macropods, rabbits and small vertebrates was monitored over two summers. Sampling times included prior to, three months post and one year post a significant rainfall event. Transects and scent stations were used to measure activity while behaviour was monitored through direct observation and the use of a thermal imaging camera attached to a remote recording system. Results showed the management of dingoes to be a key determinant of the activity of foxes and select prey, including macropods, rabbits and small mammals. Feral cat activity showed a positive response to both dingo and fox control through poison baiting. Dingo management also affected the activity of mesopredators around shared resources, particularly in proximity to water resources. Both feral cats and foxes showed an avoidance response to the presence of dingoes around water points, and again feral cats displayed an increased response to the removal of both canids. Habitat use by mesopredators did not appear to be affected by dingo management, and while foxes showed a behavioural avoidance response, limited data was collected on the response of feral cats to dingoes at shared food and water resources so results were inconclusive. The results of this study supported the presence of top-down regulation occurring in the arid ecosystems under some conditions and that behavioural mechanisms, such as avoidance, are important in the ability of dingoes to regulate smaller predator populations. While arid ecosystems are traditionally viewed as "bottom-up" or productivity driven, evidence from this research showed that while the strength of trophic regulation by dingoes may fluctuate, top-down effects occurred both prior to and post significant rainfall events at the study sites. In particular, strong relationships were found between dingo management, fox activity and fox behaviour at the study sites regardless of rainfall. In conclusion, it may be that dingoes provide a net benefit to prey populations, particularly medium-sized and small mammals, through reducing predatory impacts of foxes and under some conditions, feral cats. Thus retaining dingo populations in some ecosystems may assist in the management of biodiversity over the long term, including the conservation of native fauna populations susceptible to fox and feral cat predation. While further research into the trophic effects of dingoes in other bioregions is recommended, through improving our understanding of such trophic interactions, results from this research could assist managers in making more ecologically informed decisions about control of top-order carnivores in arid areas.

"August 2003."<br>Includes bibliographical references (leaves 294-333)<br>2 v. (xxxi, 333 leaves) ; ill. (some col.) ; 30 cm.<br>Title page, contents and abstract only. The complete thesis in print form is available from the University Library.<br>Thesis (Ph.D.)--University of Adelaide, School of Agriculture and Wine, Discipline of Plant and Pest Science, 2005

Tese de mestrado, Biologia da Conservação, Universidade de Lisboa, Faculdade de Ciências, 2016<br>Com a população mundial a aumentar, os impactos antropogénicos nos ecossistemas naturais vão sendo cada vez mais evidentes. Assistimos actualmente a uma elevada taxa de extinção de espécies, e com elas se perdem as funções e os serviços ecossistémicos que prestam, deixando os ecossistemas mais vulneráveis às pressões humanas. Uma dessas funções, essencial à manutenção da dinâmica florestal, é a dispersão de sementes, que nos trópicos é feita essencialmente através de relações mutualistas entre plantas e animais. A eficácia da dispersão pode variar substancialmente em função da espécie dispersora e depende não só da quantidade de sementes que os animais transportam, mas também da qualidade do tratamento que estes proporcionam às sementes. A perda de um dispersor chave num ecossistema pode portanto comprometer a viabilidade das populações de plantas e alterar a dinâmica da vegetação. Os efeitos da perda da biodiversidade são particularmente graves nas ilhas, onde se concentra grande parte das espécies, sobretudo endémicas. Aqui, as espécies evoluíram em isolamento, existindo naturalmente uma menor diversidade de espécies e possivelmente uma menor redundância funcional entre espécies. Estas características fazem com que estes ecossistemas sejam mais frágeis, e é nas ilhas que se tem verificado a maioria das extinções de espécies. Uma das principais ameaças identificadas é a introdução de espécies invasoras, que competem com as espécies nativas, acabando por as excluír. São Tomé é uma pequena ilha oceânica de clima tropical, situada no sistema insular do Golfo da Guiné. Com uma das maiores concentrações de endemismos de todo o mundo, São Tomé está a sofrer as consequências dos impactos humanos, estando a sua biodiversidade bastante ameaçada. Este trabalho tem então como objectivo perceber de que forma as aves estão a contribuir para a dispersão de sementes, uma função ecossistémica essencial para as florestas ricas em endemismos de São Tomé. Para tal, foram definidos três objectivos específicos: (1) avaliar a rede de dispersão de sementes por aves do sub-bosque em floresta de montanha, através da análise dos excrementos de aves capturadas com redes verticais; (2) avaliar a contribuição específica dos pombos como potenciais dispersores de sementes em São Tomé, através da análise de conteúdos de papos de pombos caçados; (3) caracterizar a dispersão de sementes na floresta de montanha, unindo os dados provenientes dos pontos anteriores, ponderados com a abundância relativa das aves. As redes de dispersão de sementes foram construídas analisando as matrizes de interação com o ‘package’ bipartite do programa R. A frequência de interação foi quantificada como o número de excrementos ou papos de cada espécie de ave contendo pelo menos uma semente intacta de cada espécie de planta. Foram capturadas 15 espécies de aves com redes verticais no sub-bosque em floresta de montanha, todas elas endémicas. Confirmámos dispersão de sementes por seis destas espécies, de destacar a contribuição do Olho-grosso (Speirops lugubris), responsável por 88% da frequência de interação. As espécies de plantas nativas dominam esta rede (14 espécies, 70% das espécies identificadas), incluindo algumas espécies endémicas ameaçadas, enquanto que poucas são as espécies introduzidas incorporadas na rede de dispersão (seis espécies, 20% das espécies identificadas). Através de curvas de acumulação de espécies, é possível afirmar que o esforço de captura foi bastante elevado, tendo-se conseguido capturar 71% das espécies de aves que ocorrem na área de estudo e 65% das plantas a serem dispersas. A comparação entre as redes de dispersão de sementes da floresta primária (obô) e da floresta secundária (capoeira) revelou poucas diferenças, o que pode estar relacionado com a proximidade geográfica das áreas de amostragem. Estes resultados sugerem ainda que os dispersores se movem entre os dois tipos de floresta, contribuindo para a disseminação das sementes entre habitats, o que vai facilitar tanto a invasão por espécies introduzidas, como a regeneração de espécies nativas em zonas de floresta degradada. A análise da rede de dispersão de sementes por pombos em São Tomé permitiu verificar a importância das três espécies endémicas caçadas como potenciais dispersores de sementes. Em especial a Rola (Columba malherbii) e o Cécia (Treron sanctithomae), tanto por serem as mais abundantes, como por serem as que mais frequentemente continham sementes no papo. Esta rede é dominada por sementes nativas (53 % da frequência de ocorrência) e apenas uma pequena percentagem de introduzidas (21% da frequência de ocorrência), sendo que uma destas (Cecropia peltata) está incluída na lista das 100 piores espécies invasoras do mundo. Já o Pombo-do-mato (Columba thomensis) é uma espécie mais rara, tendo a sua população vindo a decrescer maioritariamente devido à pressão de caça. É necessária alguma cautela ao analisar estes resultados, uma vez que as sementes nos papos dos pombos teriam ainda de passar por todo o processo de digestão, podendo levar à sua destruição antes de serem depositadas. No entanto, mesmo que poucas sementes resistam à passagem pelo trato digestivo da ave, a probabilidade destas serem dispersas a longa distância é elevada, dada a grande capacidade de voo dos pombos quando comparada com as das restantes aves existentes na ilha. A dispersão de sementes nas florestas de montanha de São Tomé é suportada exclusivamente por aves endémicas, um resultado surpreendente mesmo no contexto de ilhas oceânicas. A grande importância do Olho-grosso como dispersor de sementes resulta não só da frequência com que as dispersa, mas também da sua elevada abundância nestas florestas. Apesar do método utilizado ser dirigido a aves do sub-bosque, foi possível capturar também alguns indivíduos de espécies mais associadas à copa das árvores, como o Neto-de-olho-grosso (Zosterops feae). Foi também possível comprovar que o Pardal (Serinus rufobrunneus) é sobretudo um predador de sementes, já que apenas uma reduzida proporção dos dejectos continha sementes intactas. Os pombos parecem ser quantitativamente pouco relevantes, sobretudo devido à sua abundância reduzida, mas podem constituir importantes dispersores a longa distância e de sementes de maiores dimensões. Foi ainda detetada alguma complementariedade entre os vários dispersores, já que apenas o Tordo (Turdus olivaceofuscus) e o Papafigos (Oriolus crassirostris) foram encontrados a dispersar as sementes maiores (8-10mm). Estes dois dispersores, de maiores dimensões, possuem uma garganta mais larga que lhes permite engolir sementes maiores. A elevada ‘species strength’ destes dispersores reflete isso mesmo: uma grande dependência deles por parte das plantas com sementes maiores, já que estas aves são as únicas capazes de dispersar as suas sementes. O Tchin-tchin-txoló (Ploceus sanctithomae), a Camussela (Ploceus grandis) e o Pastro (Onycognathus fulgidus) já foram observados a consumir frutos e sementes, mas permanecem indicados apenas como potenciais dispersores, pois não foi possível comprovar que desempenhem esta função. Dos nove dispersores de sementes encontrados neste estudo, seis estão ameaçados de extinção, segundo os critérios da IUCN. Este é um facto preocupante, uma vez que a extinção de qualquer um destes dispersores irá ter um impacto negativo na dispersão de sementes, com consequências desconhecidas para a estabilidade do ecossistema. Apesar da importância da dispersão de sementes para a dinâmica florestal, muito pouco se sabe sobre esta função do ecossistema em São Tomé. Este é um trabalho pioneiro nesta área, na medida em que foram dados os primeiros passos para compreender como funciona esta importante função do ecossistema nesta ilha. No entanto ainda há muito por perceber. É preciso uniformizar a metodologia de amostragem e aplicá-la a todos os dispersores e também potenciais dispersores, estendendo a amostragem no espaço e no tempo. É ainda necessário compreender a qualidade do tratamento que cada dispersor dá a cada espécie de planta, inibindo ou aumentando a sua taxa e velocidade de germinação. Para além das aves, focadas neste trabalho, outros grupos de animais terão certamente um papel relevante na dispersão de sementes, nomeadamente os invertebrados, os morcegos frugívoros e alguns dos mamíferos introduzidos, como a Lagaia (Civettictis civetta) e o Macaco (Cercopithecus mona). É também necessário avaliar até que ponto as espécies de plantas introduzidas se comportam como invasoras e de que forma competem com as nativas, diminuindo as suas probabilidades de recrutamento. Finalmente, o transporte das sementes, mesmo que viáveis, não se traduz necessariamente no recrutamento de novos indivíduos: a qualidade do local de deposição é um factor crucial no contributo das aves para a dinâmica populacional dessa planta, e no conjunto, para a dinâmica florestal. Em resumo, esta tese fornece a primeira caracterização da rede de dispersão de sementes de São Tomé, abrindo as portas para um conhecimento mais detalhado e abrangente das interacções biológicas que sustêm as comunidades biológicas nestes ecossistemas.<br>The island of São Tomé, in the Gulf of Guinea, is a biodiversity hotspot with a remarkable number of endemic species and unique forest ecosystems. Much of its biodiversity is currently threatened by the increasing human population and associated habitat change, which is simultaneously threatening ecosystem functions and services. Seed dispersal is one of such key ecosystem services, essential for forest regeneration. The goal of this work is to understand how forest birds are contributing to the dispersal of both native and introduced seeds in São Tomé, providing the first community-level assessment of species interactions in maintaining ecosystem functions in the island. We collected droppings from mist netted birds and analysed the crop contents of hunted pigeons. All 18 sampled bird species were endemic and nine of them were dispersing seeds. The São Tomé Speirops played a central role as seed disperser. The seed dispersal network is dominated by native plant species, with only a few introduced species being dispersed in the forest. We corrected the frequency of occurrence of seeds in the droppings with independent estimates of bird abundance, and showed that this correction is key to understand disperser contribution to the overall network. Birds are therefore playing a double role, facilitating the dispersal of introduced species but also spreading the native flora. These results highlight a difficult conservation dilemma, since birds might be simultaneously contributing to forest regeneration and to biological invasion.