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Epigenetic mechanisms are increasingly understood to have major impacts across ecology. However, one molecular epigenetic mechanism, DNA methylation, currently dominates the literature. A second mechanism, histone modification, is likely important to ecologically relevant phenotypes and thus warrants investigation, especially because molecular interplay between methylation and histone acetylation can strongly affect gene expression. There are a limited number of histone acetylation studies on non-model organisms, yet those that exist show that it can impact gene expression and phenotypic plasticity. Wild birds provide an excellent system to investigate histone acetylation, as free-living individuals must rapidly adjust to environmental change. Here, we screen histone acetylation in the house sparrow (Passer domesticus); we studied this species because DNA methylation was important in the spread of this bird globally. This species has one of the broadest geographic distributions in the world, and part of this success is related to the way that it uses methylation to regulate its gene expression. Here, we verify that a commercially available assay that was developed for mammals can be used in house sparrows. We detected high variance in histone acetylation among individuals in both liver and spleen tissue. Further, house sparrows with higher epigenetic potential in the Toll Like Receptor-4 (TLR-4) promoter (i.e., CpG content) had higher histone acetylation in liver. Also, there was a negative correlation between histone acetylation in spleen and TLR-4 expression. In addition to validating a method for measuring histone acetylation in wild songbirds, this study also shows that histone acetylation is related to epigenetic potential and gene expression, adding a new study option for ecological epigenetics.

The objective of this research was to delineate the trophic relationships among the nearshore salmonid complex and other nearshore predators within Lake Superior’s Western Arm to provide new insight into interactions among these potentially competing fishes. The focus of our study was to measure both trophic niche overlap and trophic position based on carbon and nitrogen stable isotope ratios. For the analysis, we used two main collections: angler-caught fish and MN DNR survey-captured fish. Among species, the nitrogen stable isotope ratio (15N) range was large, >5‰, indicating that our study species occupy ~2 trophic positions: omnivores (e.g., Steelhead Oncorhynchus mykiss, Coho Oncorhynchus kisutch) and piscivores (e.g., Siscowet Lake Trout Salvelinus namaycush). The carbon stable isotope ratio (13C) range among species was consistent with a mix of pelagic and benthic diet habits. Combined, the 13C and 15N values revealed some species have a relatively distinct trophic niche (e.g., Siscowet Lake Trout) whereas other species form an overlapping complex of species that occupy similar trophic niches (e.g., Walleye Sander vitreus and Lean Lake Trout or Steelhead and Chinook Salmon Oncorhynchus tshawytscha). A dual isotope mixing model revealed Siscowet Lake Trout, Lean Lake Trout, and Walleye all have the potential for diet competition since they all have a high energetic contribution from Rainbow Smelt, though Siscowet Lake Trout has a diverse diet whereas Lean Lake Trout and Walleye both heavily rely on Rainbow Smelt. Further, Chinook Salmon, Coho Salmon, and Pink Salmon exhibited high amounts of overlap with one another, largely relying on Diporeia spp. and other invertebrates. The management implications of this study are two-fold. First, introduced salmonids are in apparent existing resource competition for benthic invertebrates, which represents a long-term shift in trophic position. Second, given high niche overlap among introduced salmonids, routine monitoring of benthic invertebrates and supporting bioenergetic modeling to determine carrying capacity could help to further population targets for management actions.

Research has previously shown that Rumex (Polygonaceae) species introduced to New Zealand have multiple potential drivers behind their success, such as phenotypic plasticity, enemy release, and niche shift. However, it is not known whether these changes were caused by post-introduction evolution, or what other drivers could explain the success of these agricultural weeds. I combined demo-genetic traits and processes to assess how hybridisation and introgression, genetic differentiation, and breeding system contribute to the invasiveness of three introduced Rumex species. I compared plants from the species’ native (Europe, mainly the UK) and introduced (New Zealand) range and assessed whether the success is more likely due to prior adaptation or post-introduction evolution. Ploidy is associated with increased invasiveness, and if a species has multiple geo-cytotypes, higher ploidies are often found within the introduced range. Similarly, self-compatibility can help introduced populations to counter mate limitation and mixed mating can introduce new alleles to populations. I found no differences in genome sizes or chromosome numbers between plants from the two ranges using flow cytometry and manual chromosome counts. In addition, a comparison between bagged and unbagged Rumex conglomeratus plants showed no consequences from selfing, indicating mixed mating strategies. Surprisingly, the overall seed viability was lower for provenances from the introduced range compared to the native range. Hybridisation and introgression can increase genetic variation and help with adaptation to new environments. In a field survey, hybrid plants were found in New Zealand. However, the majority were likely first-generation hybrids, making introgression an unlikely driver behind the invasiveness. In addition, the parent species co-occurrence was lower in New Zealand compared to the UK. Lastly, genetic differentiation can indicate the origin of the introduction, as well as how likely a post-introduction evolution is a driver behind the invasiveness. A minimal differentiation was revealed by genotyping-by-sequencing both within but also between the native and introduced ranges. The population genetic analyses suggest that the UK is a likely origin for these species but admixture from elsewhere was also found. This would have likely helped the introduced populations to maintain comparable level of genetic variation to the native populations. As limited differences were found between the native and introduced populations, the investigated traits and processes are unlikely to explain the invasiveness in New Zealand. Rather, the success of these species is likely caused by prior adaptation. In addition, as these species are primarily agricultural weeds within both provenances, anthropogenically induced adaptation to invade is likely the main driver behind the success of these species. This method of adaptation, likely coupled with jack-of-all-trades genotypes, have allowed the species to thrive in manmade habitats, all around the globe. Thus, similar weeds within these habitats need to be carefully monitored to prevent further invasions in the future.

New Zealand faces unique challenges with regards to invasive species due to a high number of endemic species and correspondingly high risk for the decline of indigenous species as a result of invasive introductions. Many of these introductions have been facilitated by human mediated transport, which promotes long range movement of plants and associated pests and pathogens. The transportation of these invasive species to new environments can negatively affect native plants, crops, and industries reliant on plant production. In particular, live plant trade networks represent effective mediums to disseminate invasive species such as pathogens, pests, and weeds. The movement of live plants through professional nurseries and private retailers in New Zealand is yet to be fully investigated. Performing an assessment of contact structures derived from live plant trades can be used to prevent the introduction and spread of invasive species, thereby safeguarding both businesses and the environment. Network analysis provides suitable tools to study live plant trade systems, such as the bilateral plant nursery network, as well as the itinerary online sales network. Fundamental characteristics related to geographic distribution of plant sales (such as location of origin and destination) and key metrics related to plant product movement within live plant trade networks need to be examined in order to better understand the nature of this structure. This thesis addresses gaps in knowledge related to live plant trade in New Zealand by generating networks that characterise human-mediated movement of horticultural products. Subsequently, developing network models of such systems was used to determine their vulnerability to invasive species acquisition and spread. This was accomplished via the assessment of three live plant trade systems of particular relevance to New Zealand biosecurity. These studies thusly characterise the forestry nursery transport network, the initial incursion of the invasive plant pathogen myrtle rust (Austropuccinia psidii) into New Zealand, and plant sales facilitated by the New Zealand-based online retailer Trade Me. Firstly, assessment of the forestry nursery transport network described the movement of product from seed orchards to nurseries to plantation forests and the biosecurity protocols in place at forestry nurseries. This study identifies seed orchards as the point of production most likely to facilitate widespread dispersal of a pathogen through the industry. The second study system, assessment of the initial incursion of myrtle rust into New Zealand, characterises the sale of nursery plants from myrtle rust positive nurseries during the first three months of the incursion. These networks identified a lack of comprehensive record keeping at ornamental nurseries as a risk for future invasions that are facilitated by contaminated nursery stock. Additionally, assessment of all myrtle rust positive locations during the first two years of the incursion identified delimiting surveys as a highly successful surveillance tool that would benefit from more research into optimisation of the survey radius depending on the nature of the invasive. The third and final study system, which characterised plant sales facilitated by Trade Me, employed the networking of plant sales based on their subcategorisation on the Trade Me site (into one of nine subcategories chosen by Trade Me) as well as the suburb of residence for both the seller and buyer of a product. Additionally, an assessment of the most common taxa sold on the site was conducted. The information derived from this study can be adopted for immediate use in biosecurity responses in the event of an introduction of an unwanted pest or pathogen vectored on ornamental plants, as well as identify the plant product classes at highest risk for long-distance dispersal.

Anthropogenic change causes landscape alteration and fragmentation, which leads to novel challenges for wildlife. Wildlife colonising anthropogenic habitats confront new conditions, such as air and noise pollution, limited space and food resources, higher levels of competition and predator pressures. Such colonists should display a wide spectrum of behavioural, phenotypic, physiological and genetic modifications. Adaptively responding to novel stimuli is a major challenge for urban and rural wildlife and is linked with their fitness. These responses will likely differ between urban and rural habitats as well. Populations will show behavioural and morphological variation along an urban-rural gradient in response to accompanying environmental changes. Certain behaviours, risk-taking, aggression and exploratory behaviour, will increase opportunities for populations to establish and maintain themselves in novel environments. I examined behavioural and morphological traits that allow blackbirds (Turdus merula merula Linnaeus, 1758) and thrushes (Turdus philomelos C. L. Brehm, 1831) to thrive in New Zealand anthropogenic landscapes. Urban blackbirds and thrushes were bolder, more aggressive and more exploratory compared to rural and peri-urban riverside individuals. I assessed the extent to which urban birds showed trends toward using more aggressive behaviour, increased flight duration around a speaker (rather than a signalling response), and decreased duration of singing over the speaker compared to the peri-urban river and rural individuals. The probability of responding with signalling behaviours toward conspecific songs increased in rural and peri-urban river birds. I identified variation in exploratory behaviour and approach response in the presence of a novel object to gather information. Urban birds approached closer to a novel object and had a higher rate of approach at the second attempt. There were inter-specific differences in exploratory behaviour between blackbirds and song thrushes. Blackbirds showed a faster approach response to a novel object compared to song thrushes. However, song thrushes approached closer to the novel object than blackbirds. Morphological traits changed in response to urban-rural landscapes, including increased body mass in rural blackbirds compared to urban individuals. There were morphological variations in response to different regions, including increased tail length for song thrushes and longer bill length for blackbirds in the Canterbury region compared to the Wellington region. Sex-specific traits, such as wing and tail length, varied between male and female blackbirds. There were also differences between the New Zealand populations, isolated for over a century, and their source English populations in tarsus and tail length. My findings can be used for future investigations into urban wildlife behaviours including risk-taking, aggression and novel avoidance behaviours and morphological variation between individuals. Before conducting conservation and reintroduction programs, we need to understand the behavioural variation between environmental sites and how birds cope with anthropogenic changes and perceive the human presence and potential predators in native and exotic populations. It also shows that morphological and behavioural variation in response to habitat change can occur in spatially adjacent areas, even for highly mobile species.

An important goal in the research of introduced organisms is the understanding of the traits and mechanisms that contribute to the long-term ecological success of non-native plants. The evolution of increased competitive ability (EICA) hypothesis states that introduced plants escape natural coevolved enemies (pests, pathogens and herbivores) in their new environment, allowing them to reallocate resources from producing expensive chemical defences towards a higher growth rate and competitive ability. To date numerous studies have tested the predictions of EICA, but empirical support is mixed. This lack of consensus may exist because studies usually only assess competitive ability and do not examine all the predictions of EICA. Furthermore, most studies assess competitive ability against a heterospecific, which could confound competitive effects with species-specific interactive effects. This thesis addresses the shortcomings of previous studies by conducting the most comprehensive EICA test to date. To do this, I use three Rumex species (R. conglomeratus, R. crispus and R. obtusifolius), which have their native range in the United Kingdom and Europe and were introduced to New Zealand. I conducted field surveys in both the native (United Kingdom) and introduced (New Zealand) ranges of the study plants with the aim of assessing the abundance and diversity of insect herbivores, as well as the damage they cause. I found that in the introduced range specialist insect herbivores are absent, there are fewer chewing insects and less herbivore damage on the leaves and roots of plants. These findings show that Rumex plants in the introduced range have all the necessary conditions for the evolution of increased competitive ability and the resulting shifts in defences. To test for increased competitive ability, I conducted an intraspecific greenhouse competition experiment in New Zealand to see if plants from the introduced provenance have evolved to be better competitors. However, contrary to expectations, this experiment did not show any evidence of greater competitive ability in introduced provenance plants. In order to assess any evidence for shifts in chemical defences, I investigated if the quantitative chemical defences of plants arising from seeds from the introduced range are different from plants grown from seed from the native range when grown under similar glasshouse conditions. Here it was found that R. conglomeratus plants from the introduced provenance had lower levels of percentage ellagitannins, but no differences between ranges were detected for any of the other quantitative defences measured. For the other two study species, the quantitative defences measured did not differ between ranges. The results of this thesis provide convincing evidence that EICA is not a key mechanism for explaining the success of Rumex species in New Zealand, although all three study species experience less herbivory in the introduced range. The results also suggest that EICA should be considered on a case-by-case basis and cannot be generalized across species. This thesis also shows that an accurate assessment of EICA requires a comprehensive test of all its predictions, which is something that future studies should take into consideration.

Riparian zones are important hotspots of biogeochemical cycling, yet these systems are stressed by the compounding pressures of altered hydrology, nitrogen-rich agricultural runoff, and opportunistic introduced species. Changes in environmental conditions can favor opportunistic species and disadvantage native woody species. Once established, grasses’ litter inputs and subsequent decomposition may in turn alter watershed biogeochemical cycling through differences in leaf chemistry. However, these outcomes are species- and environment-specific. A shift in the plant community from woody species toward grasses can enhance, reduce, or maintain carbon and nitrogen cycles; further, these cycles may play out differently in riparian soils and in the streams they are adjacent to. I evaluated the biogeochemical interactions of one such species that is now prolific in watersheds throughout the U.S. southwest: giant reed Arundo donax. In experimental settings Arundo inhibited the growth of Salix lasiolepis (willow) under conditions with high N amendments characteristic of intensive upland agricultural runoff. However, Arundo did not reduce willow’s growth in low N amendments or without N amendments (levels representative of upland runoff associated with sustainable farming practices or no agriculture). Arundo was able to reduce willow’s growth under high N conditions by taking up more N and maintaining high photosynthetic N use efficiency as well as decreasing investment in root biomass—perhaps enabling it to allocate excess N to compete for another resource. Once established, collecting field litter and soils showed that Arundo contributed less litter C and N than woody species, but soils beneath Arundo accumulated dissolved organic C (DOC) and N (DON). These soils also hosted a relatively small microbial community and had higher silicate content, suggesting that EOC is stabilized following microbial transformations and/or in silicate complexes. In an aquatic incubation, leachates of Arundo foliage contributed less dissolved DOC and more DON than willow, but this DOC was in fact more extensively decomposed by aquatic microbes during a two-week incubation. High resolution mass spectrometry revealed that Arundo foliage’s low DOC:DON, high aliphatics and peptides and low aromaticity and oxidation state contributed to its bioavailable fraction, yet over longer-term stages of decomposition Arundo foliage required more DON to break down, perhaps to create exoenzymes. Overall, Arundo material contributes a lower quantity of bioavailable DOC than willow. These results indicate that plant community shift towards Arundo could reduce soil and stream respiration, but also reduce bioavailable DOC at the base of these foodwebs.

Though there has been much focus on honey bee (Apis mellifera L.) decline, wild bees, which are essential to both ecosystem functioning and crop pollination, are also facing declines across Europe and North America. Potential drivers of theses declines include competition with non-native species, landscape simplification, increased pesticide risk, and reduced diet diversity. Here, I ask 1. how an introduced wild bee impacts a closely related, native congener at a regional scale, 2. how landscape simplification, diet diversity, and pesticide risk interact to impact wild bee populations in apple agroecosystems, and 3. how pesticide risk levels compare between wild bees and honey bees in the same apple orchards during bloom. To assess the impact of non-native Osmia cornifrons on the decline of native O. lignaria across the Eastern Seaboard, Ie used historical specimen records from 36 insect collections over 120 years. I found no evidence that O. cornifrons influenced O. lignaria decline; instead, their abundance (relative to other bees) has been decreasing since 1890, long before the 1977 introduction of O. cornifrons. Next, I was interested in exploring the drivers of Osmia performance in agroecosystems. Due to limited availability of O. lignaria, I assessed the response of nesting female O. cornifrons to landscape simplification, pesticide risk, and floral diet diversity in 17 NY apple orchards in 2015. In simplified landscapes, O. cornifrons produced fewer female offspring that weighed less, via reduced diet diversity and increased fungicide risk levels from Rosaceae (likely apple) pollen. Reductions in female offspring number and weight could lead to O. cornifrons population decline over time, as smaller-bodied bees produce fewer offspring and have shorter life-spans, suggesting that further studies of wild bee declines should focus on landscape simplification, pesticide risk, and floral diet diversity as potential drivers. To assess whether the historic use of honey bees as models for wild bee decline is adequate, I directly compared one driver of bee decline, pesticide risk levels, in O. cornifrons and A. mellifera pollen in 14 apple orchards during bloom in 2015. For O. cornifrons, increasing apple land cover resulted in increased pesticide risk levels in their pollen provisions, via increased Malus (crop) pollen collected. However, these relationships were not significant for honey bees, suggesting that their use as a model for all bee species may lead to inaccurate assessments of pesticide risk to some wild bee populations in agroecosystems. My results show that Osmia lignaria decline is not necessarily exacerbated by Osmia cornifrons at the regional scale. At the local scale, I show that landscape simplification, increased pesticide risk, and reduced diet diversity could potentially lead to O. cornifrons population decline, via reduced offspring number and size. Finally, I show that it is essential to continue studying the drivers of wild bee decline, as honey bees do not provide an adequate model with which to assess health of all bee species. By continuing to research the underlying causes of wild bee decline at both the regional and local scales, we can better preserve these important pollinators.

Abstract: Salmonids are stocked around the world to create and enhance fishing opportunities. Most research into the effects of trout on lake ecosystems has occurred in alpine and other oligotrophic systems, often naturally fishless, where negative impacts are likely. In contrast, I investigated effects of stocked Rainbow Trout (Oncorhynchus mykiss) on native fishes, invertebrates and food webs in productive lakes in the boreal foothills of Alberta and examined mechanisms that may act to limit trout impacts. I used a variety of approaches, including whole-lake comparisons, Before-After-Control-Impact (BACI) analyses, and mesocosm experiments. Unlike results from alpine lakes, I found few negative effects of trout on native species. In Chapter 2, I showed that stocked trout were dietary generalists and consumed a variety of prey taxa across multiple trophic levels, not dissimilar to the native fishes, and the structure of food webs in stocked lakes was generally unaffected by trout relative to unstocked lakes. Stable isotope analysis revealed that many native organisms primarily inhabit littoral areas and may therefore benefit—passively or actively—from the predation refuge provided by dense aquatic macrophytes. In whole-lake comparisons, trout did not affect the abundance or lengths of forage fishes, but both adult and young-of-year dace (Chrosomus spp.) were captured more frequently in vegetated habitats in stocked lakes relative to unstocked lakes (Chapter 3). BACI analyses revealed that invertebrate assemblages were likely affected by trout the first year after stocking; however, by the second year, assemblages in a focal stocked lake were similar to those in unstocked controls (Chapter 4). My mesocosm experiment demonstrated that native fishes will adjust their use of macrophyte beds in the presence of trout to avoid open water habitat (Chapter 2) and that macrophyte stands and occasionally small-bodied fishes can shape the community composition and taxon-level abundance of invertebrates (Chapter 5). Indeed, the “pre-structuring” effects of forage fishes and macrophytes may limit the negative impacts of trout in my lakes compared to lakes that lack these features. My results demonstrate that stocked trout do not always negatively affect native fauna and suggest that native forage fishes and/or dense beds of macrophytes buffer against impacts of trout. Although the precautionary principle should be applied before introducing a species into a novel ecosystem, some systems, such as these isolated productive lakes, appear to have the capacity to support introduced trout with few effects on native forage fishes and invertebrates.

Eucalyptus trees were introduced to Kenya a little over a century ago. European colonization along with the development of a railway system increased the demand for a fast growing wood source. The expansion of the tree across the fertile lands in Kenya raises concerns about the environmental impact on ecosystems where it has been introduced. These concerns include degraded soils, loss of water resources, co-introduction of ectomycorrhizal species, and allelopathy. Economic benefits to local landowners were also explored as well as the potential for large Eucalyptus woodlots to maximize the sequestration of CO₂ from the atmosphere. This was examined through farmer interviews and the collection of data from both Eucalyptus and indigenous forests. The results indicate that the density of Eucalyptus varied by age and species and managed harvest rates could be utilized to maximize carbon content in Eucalyptus to increase carbon sequestration potential of woodlots. In the greenhouse study of allelopathy, Eucalyptus did inhibit the growth and germination of the test plants. The indigenous plants were the most strongly affected. The soil analyses indicate that overall, Eucalyptus may not have a strong effect on the soils but do have a significant effect on soil moisture and diversity found within the woodlots. Ectomycorrhizal fungi were molecularly identified as some of the same species associating with Eucalyptus in Australia, indicating co-introduction. Farmers indicated that they were aware of the environmental concerns associated with cultivating Eucalyptus but the economic benefits were greater than the environmental issues.

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

Genetic approaches, along with ecological and natural history data, can help address the status of non-native species, particularly in taxonomically problematic introductions to clarify their identities and geographic origins. We used these approaches to investigate non-native softshell turtles (family: Trionychidae) in the Hawaiian Islands: Palea steindachneri and Pelodiscus sinensis. In light of multiple knowledge gaps surrounding these introduced populations and native range conservation concerns, we clarified their range and distribution as well as their genetic status in Hawaii. Field surveys indicate that the current range of P. steindachneri is limited to Kauai whereas Pelodiscus is limited to Oahu. Our genetic study revealed two species of the Pelodiscus complex present (P. sinensis sensu stricto and P. maackii) and low genetic diversity within P. steindachneri. Historical and genetic data indicate that Hawaiian populations of P. sinensis and P. steindachneri originate from China and P. maackii originates from Japan.

The barnacle Megabalanus coccopoma is a recent invader of the southeastern U.S.A. from the tropical eastern Pacific. In Georgia, M. coccopoma populations along the immediate coastline often suffer extensive mortality during the winter, but population rebuilding is common after these events suggesting that there may be nearby larval sources. I investigated the hypothesis that artificial structures (i.e., buoys, towers), occurring far enough offshore of Georgia for water temperatures to be moderated by the Gulf Stream, provide refuges for breeding adults of M. coccopoma and can serve as the larval source. I investigated this hypothesis by first developing thirteen microsatellite primer pairs specific to M. coccopoma. I also developed the polymerase chain reaction (PCR) and sequencing protocols for use with the primers. These 13 primer pairs were tested on 42 individuals from two populations of M. coccopoma. The results indicated high allelic diversity in all of the loci making these primers useful in evaluating population genetics questions related to M. coccopoma. To further evaluate the role of artificial structures in the range expansion of M. coccopoma, I collected demographic information on existing populations, monitored temperature and salinity both on and offshore, and assessed genetic diversity and structure at 8 research sites ranging from the shoreline to ~50km offshore in the southeast. Demographic information and abiotic parameter monitoring indicated that offshore artificial structures are suitable habitats for M. coccopoma adults and these structures also house M. coccopoma populations that are composed of stable, mature individuals that can serve as an abundant source of larvae. The genetic assessment revealed high allelic diversity and significant deviations from Hardy-Weinberg Equilibrium (HWE) in all subpopulations. The analysis of genetic structure indicated that the M. coccopoma population in the Georgia Bight is panmictic and suggested that a Wahlund Effect is acting to increase allelic diversity and causing HWE deviations. The combined results support my hypothesis that offshore structures in the Georgia Bight can act as refuges for breeding adults, however there are likely additional larval sources from beyond the region examined that are facilitating the range expansion of M. coccopoma in the southeastern U.S.A.

Global mean sea levels are expected to rise up to 1.9m by 2100 and will change the distribution and community structure of low-lying coastal ecosystems due to flooding, erosion, and salt-water intrusion. Although habitats will be inundated, ecosystems have the potential to shift inland and endemic species may persist if conditions are favorable. Multiple-stressors including invasive species and destructive land-use practices have caused widespread coastal aquatic ecosystem degradation over the last century. Predictions of ecosystem migration due to sea level rise need to account for these stressors, which, even at low levels, may reduce the resilience of these ecosystems. The goal of this dissertation was to predict potential consequences of future sea level rise on groundwater-fed anchialine pool ecosystems in Hawaii by comparing scenarios of inundation with current patterns of habitat, introduced species, and land use. First, high resolution sea level rise models that incorporate groundwater were developed for the west coast of the island of Hawaii. Ecological surveys were also conducted to identify habitat condition and the occurrence of native and non-native species at 398 pools located along 280 km of the coastal corridor. Statistical models were used to determine the current relationship between native and non-native species occurrence and various physical and biological parameters. Stable isotope analysis was used to examine food web relationships within pools. Geospatial analyses were used to predict future pool inundation, pool creation, and non-native species dispersal under various sea level rise scenarios. Results showed that sea level models incorporating groundwater levels were up to 37% better at detecting known anchialine pools than corresponding models without groundwater levels (Chapter 1). Pool surveys showed that two dominant endemic shrimp Halocaridina rubra and Metabetaeus lohena were located across the region in a wide range of habitats, but that introduced fishes (tilapia, poeciliids) were present in ~ 25 % of pools. Statistical models showed that introduced fishes had a strong negative effect on the occurrence of H. rubra and M. lohena, while benthic silt cover and adjacent development also had significant negative relationships with shrimp occurrence (Chapter 2). Geospatial models indicate that current habitats will be increasingly inundated by marine waters, but that new habitat will emerge in the landscape in low lying open space (Chapter 3). Because of high subsurface hydrologic connectivity, many endemic species are likely to populate these new habitats by moving through the coastal aquifer. However, in some areas, rising sea levels will provide surface connectivity between pools currently infested with introduced fishes (Chapter 3). Additionally, results suggest that tilapia are a bigger threat to endemic anchialine species and ecosystem health and should be targeted for removal before poeciliids (Chapter 4). This study demonstrates an interdisciplinary approach to examining ecosystem risk due to sea level rise. Successful conservation of coastal aquatic biodiversity will continue to require current restoration efforts along with protection of potential habitat sites under future climate conditions.

The brushtail possum, Trichosurus vulpecula is an introduced nocturnal marsupial no larger than a house cat. First arriving in 1848, it was intended to bring a profitable fur industry to New Zealand. This proved unsuccessful and many trappers, not understanding the consequences of their actions, released them into surrounding forests. Possum were highly successful in the New Zealand landscape and have become a major vertebrate pest species. Possum not only threaten the native plants and animals (through direct predation) of New Zealand, but also the agricultural industry, as they are vectors of bovine tuberculosis (Tb). The Department of Conservation (DOC), Animal Health Board (AHB) and various regional and district councils spend an estimated $72 million annually on possum control. This clearly highlights the significant threat they pose and the need for an effective and well thought-out control program. Being mindful of periods during the month when possum activity is highest can aid in the assurance of successful trapping and poisoning efforts. There are limited studies on possum ecology and even fewer on how they respond to lunar illumination and seasonal changes. Prior to the current study, no published information existed that studied the effects of lunar phase on the activity patterns of the possum during winter months. Monitoring new-and-full moon phases over a four-month period included the use of WaxTags® and camera traps, which measured activity at three different habitat types including 1) exotic-and-native scrub, 2) pine plantation and 3) mixed-hardwood-andbroadleaf forest. It was predicted that possum foraging behaviour would vary during the moon phases. According to previous research on small nocturnal mammals, they substantially reduce their activity under moonlit nights, exhibiting a behaviour known as lunar phobia. This includes reducing use of open space, spending less time foraging and reducing vocalizations and movement. This anti-predator tactic is a common behaviour amongst small mammals. The results of the current study show that possum foraging behaviour does in fact vary during the moon phases however, they are more active during the full moon, exhibiting lunar philia, an uncommon behaviour among potential prey species. This could be due to lack of the possum’s natural predators in New Zealand. Another interesting result from the current study is that possum activity significantly decreased during the new moon (less illuminated) phase in forested sites (with canopy) compared to scrubland habitats. Less exposure from daily ambient light coupled with canopy cover provided unfavourable conditions for possum during this study. My results indicate that the behaviour of common brushtail possum in New Zealand is influenced by changing lunar phases and as such, timing must be considered when carrying out future possum control operations.

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

This dissertation focuses on the little studied topic of seed saver groups in New Zealand assessing the context within which they operate in order to describe their current state of activity. It finds that seed savers can make a significant contribution to the conservation of biological diversity, namely crop genetic diversity. Twenty groups were contacted, with nine useful replies documented to provide a picture of Seed Saving Group activity in 2010. Seed Saver groups are found to exhibit similarities and distinct differences on a range of measures including group size, socioeconomic status of members, means of organising, mission and objectives, resources and values. Significantly, the focus of seed saving groups is to act as a hub or centre of a network to promote seed saving and seed exchange. As primarily voluntary organisations, their biggest challenge is to have enough people carry out their work.

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

Invasive aquatic species are becoming increasingly problematic for aquatic ecologists and resource managers, as the ecological and economic impacts of introductions become better known. The flathead catfish Pylodictis olivaris is a large piscivorous fish native to most of the interior basin of the United States. Via legal and illegal introductions, they have been introduced into at least 13 U.S. states and one Canadian province primarily along the Atlantic slope. I used a variety of capture-recapture models to estimate flathead catfish population parameters in three North Carolina coastal plain rivers (Contentnea Creek, Northeast Cape Fear River, and Lumber River). My estimates using a Jolly-Seber model were hindered by low capture probabilities and high temporary emigration. Reasonable estimates were possible using a robust-design framework to estimate population size and temporary emigration with supplemental information from a radio-telemetry study to examine model assumptions. Population size estimates using a robust design model including temporary emigration ranged from 4 to 31 fish/km (>125-mm total length, TL) of sampling reach. Additional analyses showed high rates of temporary emigration (>90%), independently supported by radio-telemetry results. I also examined flathead catfish diet in these rivers and found that flathead catfish fed on a wide variety of freshwater fish and invertebrates, anadromous fish, and occasionally estuarine fish and invertebrates. Fish or crayfish comprised more than 50% of the stomach contents by percent occurrence, percent-by-number, and percent-by-weight in all rivers and years. A significant difference in the diet composition percent-by-number was found between Contentnea Creek and the Northeast Cape Fear River. Significant differences were not detected between years within Contentnea Creek but were found within the Northeast Cape Fear River. Feeding intensity (as measured by stomach fullness) was highest in the Northeast Cape Fear River associated with a lower mean size of feeding flathead catfish in this river than of those in Contentnea Creek or the Lumber River. A significant correlation between diet item length and flathead catfish total length was found for Contentnea Creek in 2001. This relationship was not significant in the Northeast Cape Fear River in either year. Based on the diet composition data collected in this study and those published on native and introduced flathead catfish populations, I am not able to support or refute the hypothesis that flathead catfish are preferentially feeding on specific species or families. However, the flathead catfish populations examined here are well established, and the greatest impact from selective predation may have occurred immediately following introduction. Based on my findings, flathead catfish could restructure or suppress native fish communities in coastal rivers through direct predation because of their primarily piscivorous food habits. To evaluate the potential ecosystem impact of this invasive species on the native fish community, I developed an ecosystem simulation model (including flathead catfish) based on empirical data collected for a North Carolina coastal river. Model results suggest that flathead catfish suppress native fish community biomass by 5-50% through both predatory and competitive interactions. However, these reductions could be mitigated through sustained exploitation of flathead catfish by recreational or commercial fishers at levels equivalent to those for native flathead catfish populations (6-25% annual exploitation). These findings demonstrate the potential for using directed harvest of an invasive species to mitigate the negative impacts to native species.

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

Concern has been raised regarding the effects of invasive fishes, among them white perch (Morone americana), in a variety of freshwater systems. Previous research on white perch as an invasive species has examined landlocked white perch in ponds, lakes and reservoirs throughout much of its geographic range. However, research has been lacking regarding the role of invasive white perch in southern reservoirs. A long-term data set of the Jordan Lake fish community indexed via gill nets was evaluated to assess the expansion of white perch in Jordan Lake, as well as concurrent declines in other fishes found in Jordan Lake from 1987 through 1998. White perch catch rates increased from zero fish per net night in 1987 to 16.1 fish per net night in 1994, surpassing catch rates for all other fish captured in gill nets. White perch were found to live to age 7 in Jordan Lake where they shift food habits seasonally from zooplankton and diptera larvae in the spring to young shad in the fall. Relative weights and mean calculated total lengths at annulus formation suggest that the Jordan Lake white perch population is in good condition, comparable to other landlocked white perch populations in North Carolina and surpassing white perch populations found in their native estuarine environs throughout the eastern seaboard. Young white perch were found to prefer cover-free primary points featuring hard sand and clay substrates, minimizing the likelihood that Jordan Lake white perch will impact centrarchids as has been suggested by research in other freshwater systems outside of the southeastern United States.

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 distribution of the rare endemic shrub Teucridium parvifolium was investigated throughout New Zealand to determine the geographic distribution of the species, and specifically on Banks Peninsula. T. parvifolium is spread discontinuously throughout New Zealand and occurs in widely scattered, generally small populations. Aspects of the community ecology, including floristic composition, and community/physical site relationships, were studied to determine the habitat requirements of T. parvifolium on Banks Peninsula. T. parvifolium occurred in two plant communities that differed in species composition. The healthiest populations occurred in the marginal community characterised by Hoheria angustifolia and Urtica ferox rather than the community characterised by Macropiper excelsum and Melicope simplex. Data was gathered on the size and structure of populations, plant size, seed production and viability, seedbank, plant growth and the extent of browsing. Population structures were characterised by a large number of seedlings, fewer saplings, and very few adult plants. Adult plants were capable of producing large numbers of seeds and many of these entered the soil to form a seedbank. Seedlings were capable of rapid growth under ideal conditions but growth was restricted in the wild by introduced herbaceous weeds. Agents of decline were identified as browsing animals, competitive introduced plant species, and habitat disruption. The continued decline in suitable habitat, the effects of introduced weeds, severe browsing, and the severely fragmented nature of the populations warrants the IUCN threat classification of Vulnerable. Management options include managed browsing to control introduced plant species, provision of suitable habitat, and active management to increase the size and frequency of small populations.

The natural biodiversity of New Zealand is being threatened by habitat loss, fragmentation, lack of formal protection of representative, viable ecosystems and predation and competition from introduced animals and plants. It is the latter concern that is concentrated on in this project, and it is recognised that despite the over-riding importance of biodiversity conservation, there are limited funds available to the Department of Conservation to control pests that are degrading biodiversity. A more cost-effective system of pest control that is ecologically and economically more sustainable is evaluated for the practicality of introducing into the status quo. This is a system that creates tradeable property rights in pest control, where hunters competitively tender for the right to control pests within an area for which the maximum tolerable density of pests has been set by the agency paying for the control. Property right owners are paid on attainment of the conservation goal, thus incentives to pest controllers are related the values at stake. West Coast conservancy is chosen as a focus for investigating the model, and the theoretical assumptions within the model are investigated as to whether they are borne out in practice. Tradeable property rights are found to be impractical to implement at the present time, and a similar system called periodic tendering is proposed, that has the same benefits of efficiency and accountability, but is less problematic to set up at the present time. These two approaches are compared with the current system of pest control and recommendations for further research are made.

The Argentine stem weevil, Listronotus bonariensis (Kuschel) (Coleoptera: Curculionidae), is an important introduced pasture pest in New Zealand and causes hundreds of millions of dollars in damage annually to pasture and livestock health. Adult L. bonariensis were collected from 9 diverse locations in South America (the species' native habitat), 5 locations in New Zealand and 1 location in Australia (where the species is also an introduced pest). The 15 populations were studied by 2 DNA-based techniques, RAPD and mitochondrial analysis, in an effort to determine the geographical origin of the pest populations in New Zealand. RAPD revealed similarities between populations sampled within New Zealand, as well as polymorphisms between the South American populations. Mitochondrial restriction fragment length analysis revealed the unusually large mitochondrial genome size of approximately 32 kilobases in this species but negligible variation within or between populations. Based on the RAPD results, the Rio de la Plata region on the east coast of South America is thought to be the geographical source for the Listronotus bonariensis (Kuschel) populations in New Zealand. The discrepancy between the levels of genetic variation revealed by RAPD and mitochondrial analysis in the native populations is discussed and hypotheses are presented to reconcile this difference.

The patterns of extinction were examined among species of passeriforms introduced to three oceanic islands (Oahu, Tahiti, and Bermuda). Survival was significantly greater for plumage monomorphic than plumage dimorphic species on Oahu and Tahiti. Bermuda did not show this pattern, possibly due to introduced species pool size. Previous studies have documented morphological overdispersion among surviving species and have shown that species introduced earlier are more likely to persist. Yet, neither morphological similarity nor introduction order differed significantly between plumage monomorphic and dimorphic species introduced on Oahu and Tahiti. Also the abundance data were examined on Oahu in order to determine if monomorphic species had larger population sizes than the population sizes of dimorphic species. The abundance of the monomorphic species was not significantly different than the dimorphic species. I suggest that plumage dimorphic species have experienced more intense sexual selection pressures, and that response to sexual selection in these species has contrained response to natural selection pressures, thereby, increasing the risk of extinction.

During the 1860s and 1870s the early settlers in New Zealand experienced insect plagues, especially armies of caterpillars, which created havoc amongst their crops (Drummond, 1907). Although some native birds were regarded as insectivorous, the clearance of native bush and settlement of land had restricted the distribution of these birds and the numbers remaining in crop areas were considered insufficient to control the insect numbers. Attention therefore turned to know insectivorous birds from other countries. Acclimatisation societies were formed and various birds were imported. Australian magpies (Gymnorhina spp.) and starlings (Sturnus vulgaris) were introduced during this period in the hope that they would help control the insect pests. Now, approximately 100 years later, both these birds are strongly associated with pastoral farming and are still commonly regarded as beneficial in keeping down insect numbers. However, with the restricted use of DDT insecticides for pasture pest control in recent years, the development of DDT resistant populations of grass grubs (Costelytra zealandica) and the resulting resurgence of grass grubs and porina (Wiseana spp.) as pests in certain areas, there is a need to evaluate the actual roles birds play in agriculture and especially as biologically controlling agents of insects. Very few detailed studies covering most aspects of the ecology of introduced birds have been carried out in New Zealand. Marples (1942) is the only worker so far to have made a systematic study on the food of an introduced bird. The objective of this thesis was to study the biology of magpies in New Zealand. The most important aspect of this was an investigation of the food to ascertain what magpies actually eat and to discover if any of these items were of any agricultural interest. Other aspects studied included possible interbreeding between the two, Gymnorhina hypoleuca Gould and G. Tibicen Latham, present in New Zealand and consequently their taxonomic classification: distribution of both species; taxonomic measurements and identification of sex and age classes; breeding biology; territorial behaviour and mortality factors. A subsidiary objective was to review and if possible obtain fresh evidence on the aggressive behaviour shown by magpies towards other birds and mammals (including man).