Massey Documents by Type

Permanent URI for this communityhttps://mro.massey.ac.nz/handle/10179/294

Browse

Subject: search.filters.subject.Dispersal

Search Results

Now showing 1 - 7 of 7
  • Thumbnail Image
    Item
    Population genetics and genomics of a marsupial species : analysis of native and invasive brushtail possum populations (Trichosurus vulpecula) : a dissertation presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Conservation Biology, Massey University, Manawatū Campus, New Zealand
    (Masey University, 2024-04-15) Pattabiraman, Nimeshika
    One of the leading causes of global biodiversity decline is the introduction of invasive pest species that destroy native flora and compete with native fauna for food and other resources. Aotearoa New Zealand is one of the foremost countries in the world that has focussed on eradicating pest species and in particular exotic mammals from the archipelago, which lacks native, terrestrial mammals. The New Zealand Government recently set in train the ambitious task of removing all mustelids, rats, and possums from the terrestrial landscape by the year 2050. Brushtail possums (Trichosurus vulpecula) were introduced to Aotearoa New Zealand from Australia in the mid-1800s, after which they were translocated across the country and have become widespread, destroying indigenous habitat, eating native birds and invertebrates, and spreading bovine TB. Control efforts have seen possum numbers decline in the last two decades from close to 75 million in 2002 to 40 million in 2020. There is, however, a gap in the scientific understanding of possum populations with respect to their genetic composition and population structure across the country, and this knowledge could help us develop effective and dynamic management strategies to eradicate possums on a nationwide scale. In this thesis, I focus on three aspects of population structure and diversity of brushtail possums. First, I investigated a small geographical study area - The Kenepuru Peninsula - where I sought evidence of genetic correlations with geography, time and fur colour. I used two types of genetic markers that target the nuclear and mitochondrial regions of possum DNA with large population samples. In every case, it was determined that the possums comprised one freely interbreeding population at this scale. In particular I demonstrated that colour morphs associated with distinct subspecies in Australia, freely interbreed in New Zealand. I then increased the scale of sampling to include representation of populations across New Zealand and Australia, with the same genetic markers. This threw light on the heterogenous nature of possum diversity in New Zealand, and showed that even after ~110 generations, possums retained genetic separation among spatial groups. Additionally, the data showed evidence of multiple possum lineages across New Zealand that are derived from several Australian populations. High haplotype diversity in New Zealand suggests that the rapidly expanding population has retained novel haplotypes and the data thus far indicated a non-homogenous (metapopulation) distribution of possums without geographical concordance. As the project progressed, I was able to apply high-throughput genotyping-by-sequencing to generate a large genomic dataset. This dataset provided much more detail of the genotypic distribution of possums in Australia and among invasive metapopulations in New Zealand, as well as informing us of the relationship between them. This large, robust database of possum population structure and genetic diversity throughout Aotearoa New Zealand will support future studies in providing informed management decisions to eradicate brushtail possums.
  • Thumbnail Image
    Item
    Life history strategies of Tetranychus ludeni Zacher (Acari: Tetranychidae) with special reference to biological invasion : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Entomology at Massey University, Manawatū, New Zealand
    (Massey University, 2022) Zhou, Peng
    With the increase of worldwide trade and travel in recent decades, increasingly more arthropod species have become established outside their natural range of distribution, causing substantial ecological and economic impacts in novel habitats. Successful invaders may bear certain life history traits that can overcome various barriers such as mate and food shortage and inbreeding depression. Here, I investigated the life history strategies of a haplodiploid pest, Tetranychus ludeni Zacher (Acari: Tetranychidae), with special reference to its invasion success. It is native to Europe but now cosmopolitan. Virgin females laid larger eggs than mated females, giving rise to larger adults, and sons from virgin females produced more daughters at a higher rate than sons from mated females in their lifetime. Virgin females produced maximum number of sons in their early life to ensure subsequent mother-son mating but later saved resources to prolong longevity for potential future mating. Females maximised their resource allocation to egg production immediately after mating regardless of whether mating delay occurred to secure production of maximum number of both daughters and sons as early as possible. Mated females with mating delay increased proportion of daughters in offspring produced to compensate the loss of production of daughters during their virgin life. Neither mother-son mating nor sibling mating affected female reproductive output and longevity in any of the 11 successive inbred generations and neither sex showed inbreeding avoidance behaviour, suggesting that inbreeding has no negative impact on its invasion success at any points or generations. Mated females did not trade off their survival and lifetime reproductive output with dispersal. Long-distance dispersers invested more in dispersal in their early life while resident mites and short-distance dispersers invested more in reproduction during their early life, which may allow long-distance dispersers to explore the novel environment more effectively without compromising lifetime reproductive fitness. Older females with more mature eggs were more likely to disperse and move longer distances than younger ones with fewer eggs. Females increased dispersal probability and distance with the increase of population density. The synchronization of dispersal and reproduction and the positive density-dependent dispersal strategy may facilitate habitat colonization and invasion speed of T. ludeni. Findings from this study improve our understanding of the invasion mechanisms of T. ludeni and other haplodiploid species, providing knowledge for development of programmes for prediction and management of biological invasions.
  • Thumbnail Image
    Item
    Amphibian disease risks and the anthropogenic dispersal of invasive Litoria species : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Albany, New Zealand
    (Massey University, 2021) Laycock, Jennifer
    The scope of this research is to provide a broad outline of the interaction between anthropogenic disease spread, risk of an invasive amphibian species establishing into the New Zealand environs, and prevalence of amphibian chytrid in wild introduced amphibian populations. The objective of this overview is to identify risk pathways that could threaten New Zealand’s four endemic Leiopelma species of frogs. Worldwide amphibian populations are in decline with an estimated 32.5% of amphibians globally threatened (IUCN 2008). New Zealand’s four endemic amphibians Leiopelma spp. are high on the ICUN list of critically endangered animals, further, two of the three introduced tree frogs (Litoria spp..) are listed endangered and vulnerable in their native home. Disease has been one factor implicated in the worldwide amphibian decline in particular the two diseases Chytridiomycosis and Ranavirus. Although Chytridiomycosis has had the most profound effect on the decline of amphibian species. The spread of such diseases is, at least in part, human-mediated through media such as the bait trade, food industry, and possibly the pet trade. To date, there have been no reports of Ranavirus in New Zealand amphibians. Conversely, amphibians chytrid fungus is widespread and has been implicated in the decline of the endemic Leiopelma archeyi. This makes amphibian chytrid an ideal disease to model disease transmission with particular reference to the anthropogenic movement of amphibians. The two main goals of this Ph.D. were to investigate specific anthropogenic mediated risks of spreading disease using the pathogen Batrachochytrium dendrobatidis (Bd), which is responsible for amphibian chytrid fungus, as a modality to model this. Included in this will be the enquiry into how Bd entered New Zealand and how it spread so quickly via the movement of Litoria spp.. Furthermore, to look at invasive amphibian species incursion risks by evaluating previous border seizures. Currently, it is unknown how the amphibian chytrid entered New Zealand and whether New Zealand’s borders are a high-risk entry pathway for amphibian disease. Examining the anthropogenic dispersal of Litoria in New Zealand and developing systems that reduce the risk of introducing disease into naive populations is an important role in ensuring the long-term survival of New Zealand’s endangered Leiopelma spp. frogs. The presence of Bd in New Zealand has been recorded but the prevalence of the pathogen in populations is unknown. Identifying the prevalence of infection within populations will provide insight into how populations of Litoria spp. are surviving Bd infection. Furthermore, this Ph.D. project will assess the risk of invasive exotic amphibians entering New Zealand and becoming naturalised. Education is one of the important areas that will greatly help the plight of New Zealand’s frogs. For education to be successful it needs to be targeted, therefore assessing risk areas of amphibian disease is imperative. Furthermore, understanding the public’s knowledge of frogs in New Zealand will further help in the development of resource material and targeting the main groups where education is needed. Key findings of this research are that the three species of Litoria frogs are moved around New Zealand in large numbers via the pet trade. The spread of amphibian chytrid has most likely been so rapid due to the frequency and volume of tadpoles and frogs being bought and sold. The pet trade thereby effectively and inadvertently is a major means of the unregulated translocation of Litoria amphibians throughout New Zealand. Results of this research also show there is a gap in the knowledge about amphibians in areas of husbandry, disease, species identification, and legal responsibilities in the ownership and containment of amphibians in New Zealand. Additionally, the introduction of a new disease is more likely to occur than the risk of an invasive species becoming established. Finally, the wild populations of Litoria frogs were surviving with a high prevalence of amphibian chytrid fungus in two of the three study sites in this research, the third site which had the presence of a reservoir species had low numbers of frogs present.
  • Thumbnail Image
    Item
    Landscape genetics for conservation management : brushtail possums (Trichosurus vulpecula) in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Conservation Biology at Massey University, New Zealand
    (Massey University, 2019) Pattabiraman, Nimeshika
    The negative impact of brushtail possums (Trichosurus vulpecula) on New Zealand ecosystems became apparent soon after their introduction from Australia in 1858. Possums not only denude native vegetation but prey on native birds and invertebrates. They also carry bovine tuberculosis (TB) impacting the dairy industry and consequently the New Zealand economy. New Zealand possum populations have spread from several introduction sites and densities have increased. The resulting complex patterns of gene flow influences regional diversity, and potentially the effectiveness of control measures. Currently, ~100 million dollars are spent on 1080 management per year, mostly in response to Tb risk, but there is little information about the migration rates associated with resulting population density fluctuations. To determine whether the potential for intermixing between populations since their introductions could have caused a homogenizing effect on the genetic diversity across New Zealand, I began a detailed population genetic analysis by genotyping possums from 19 locations using nuclear microsatellites and mitochondrial DNA haplotyping from across the country to estimate population structure. Initial introductions of possums from multiple locations resulted in genetic and fur colour diversity but, in comparison to natural Australian populations, it appears that only a subset of genetic variants was brought to New Zealand from Australia. Mitochondrial sequence variation analyses showed overall high haplotype diversity with substantial differences among samples in haplotype frequencies, but with relatively low nucleotide diversity. Similarly, analysis of nuclear markers (microsatellite genotypes with Naïve Bayesian clustering) reveals that while there has been admixture between populations in various locations, indicated by shared genotypes, there are genetically distinct regional populations. Concordance of genetic and geographically distant sampling shows a well-developed population structure of possums across New Zealand. These results are also supported by pairwise Fst comparisons between all pairs of populations; although nearly all populations showed significant differences, there was no signature of isolation by distance as expected from their history of introductions. This study provides a foundation for further research into spatial structure of brushtail possums which will enable the effective targeting of management and is essential for modelling population recovery, disease spread, and potentially the emergence of toxin resistance. Predator-free 2050 is an ambitious objective considering current circumstances. In order to achieve its goals, even for the targeted species, we need to efficiently manage our resources and improve the accuracy of control measures to maintain long-term effects.
  • Thumbnail Image
    Item
    Spatial dynamics of anthropogenically altered dispersal patterns : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Albany, New Zealand
    (Massey University, 2017) Bütikofer, Luca
    The thesis put forward in this study is that anthropogenic disruption of natural dispersal is of central importance for the conservation of biodiversity. The main rationale being that dispersal, as a fundamental life history trait, is directly linked to, and affected by three of the main threats to biodiversity: Invasive species, habitat fragmentation and climate change. In terms of biological invasions, the introduction of exotic taxa into a foreign habitat is performed by people, and the spread of these species within the invasion range is often a result of human aided dispersal. Surprisingly though, not much emphasis is put on anthropogenic dispersal when modelling biological invasions. Habitat fragmentation is the direct consequence of habitat destruction. In a fragmented landscape, remnant natural patches host populations with varying degrees of inter-connectivity. Dispersal through degraded habitat is the key to maintaining viable meta-populations in a fragmented landscape. To facilitate dispersal in highly fragmented landscapes such as cities, a clear knowledge of the roles played by different land cover features (e.g. density of trees or traffic) is the starting point to make informed urban planning decisions. The main issue with climate change is not that climate conditions are disappearing, but that they are moving. As a consequence of this, organisms also need to move along with the climatic conditions they are adapted to. This process, named range shift, is being observed worldwide on several taxa. Researchers, however, put very little attention to the problems arising when “climate migrants” encounter dispersal barriers (e.g. anthropogenic land cover) on their path. The main body of work presented here consists in both the practical analysis of specific systems and the development of conceptual and methodological frameworks to address general issues. Among the former, I used population and landscape genetics approaches to analyse the case of Copper skinks (Oligosoma aeneum) in Auckland (New Zealand) as a recent and intensive habitat fragmentation scenario, with the goal of detecting the land cover types that allow the highest dispersal in urban settings. I also analysed the case of the Australian Litoria frogs (L. aurea, L. raniformis and L. ewingii) in New Zealand with the intent of quantifying the anthropogenic dispersal component of their invasion. As per the latter, I developed a novel method for estimating the anthropogenic component of biological invasions, infer their natural dispersal parameters, and forecast future developments of biological invasions. I also developed the novel concept of C-trap, whereby the shape and spatial orientation of the interface between natural and anthropogenic land cover types may originate traps for climate migrants, and used it to determine where, on a global scale, their high densities can further threaten endangered, endemic animal species. My results identified an early stage fragmentation scenario for urban Copper skinks in Auckland. Relatively high population genetic structure formed as a result of segregation by a motorway. However, the roles of other land cover types in controlling population connectivity could not be determined. Of all Litoria frog populations recorded in New Zealand, about 30% were found to be of anthropogenic origin. Even though the borders of the distribution range occupied so far are unlikely to expand, the density of populations within the range is expected to rise with new, suitable patches being found. Tests on virtual species with the novel methodology for the modelling of biological invasions showed good performance (accuracy in estimating natural dispersal kernel and anthropogenic contribution), also in the presence of challenging limitations in the input dataset. Finally, the global scale application of the C-traps concept to endangered, terrestrial species highlighted the high potential for conservation issues among climate migrants in Eastern Europe and Southern Asia. Although it is challenging to quantify the consequences for biodiversity conservation of anthropogenic alterations to natural dispersal, results from the applied studies confirm the initial thesis on their critical role as biodiversity threats; while the novel concepts and methodologies provide a valuable tool for better incorporating these aspects in ecological studies and conservation management.
  • Thumbnail Image
    Item
    Dispersal : the effects of phenotype and habitat selection in reintroduced populations : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Conservation Biology at Massey University, Manawatū, New Zealand
    (Massey University, 2015) Richardson, Kate Mackinnon
    Dispersal is a complex behaviour, recognised as the primary mechanism by which gene flow occurs. In the field of reintroduction biology, dispersal can influence reintroduction success both positively and negatively, yet the mechanisms underpinning dispersal in reintroduced populations are not well understood. Extensive literature is now available on the proximate forces driving natal dispersal, and in this thesis I draw on this field to inform our understanding of dispersal processes in reintroduced populations. It is widely accepted that both internal state (phenotype) and the external environment have multi-causal effects on natal dispersal patterns across three recognised phases of movement (departure, exploration, settlement), but the relationship to post-release dispersal is less well understood. I use reintroduced populations of an endangered passerine, the hihi (stitchbird, Notiomystis cincta), to answer specific research questions regarding the proximate factors driving both postrelease and natal dispersal in this species. I first examine phenotypic variation in behavioural traits (personality) in my study species, in particular the effects of early natal nutrition on the expression of personality, and the influences on subsequent survival and dispersal. I find complex relationships between natal nutrition and personality that are sex-specific, and that “bold” individuals have higher survival probabilities. I find evidence for a relationship between personality and natal dispersal patterns in one study population, but not in another. I then examine the influence of internal state (personality, early natal nutrition and degree of inbreeding) on post-release dispersal of newly translocated hihi at two sites, and find that all these factors affect dispersal behaviour in the initial post-release and exploration phases. I then examine the role of the external environment on both natal and post-release dispersal using species distribution models. There is a strong social effect in habitat selection of natal dispersers, but no detectable social effect in habitat selection of post-release dispersers, and evidence for use of physical characteristics of the environment in habitat selection at both stages. Finally, I discuss the wider implications of dispersal to reintroduction biology. I advocate for careful consideration of proposed release sites, and an integrated landscape approach within reintroduction planning.
  • Thumbnail Image
    Item
    A decade of seascape genetics: Contributions to basic and applied marine connectivity
    (28/07/2016) Selkoe KA; D'Aloia CC; Crandall ED; Iacchei M; Liggins L; Puritz JB; Von Der Heyden S; Toonen RJ
    Seascape genetics, a term coined in 2006, is a fast growing area of population genetics that draws on ecology, oceanography and geography to address challenges in basic understanding of marine connectivity and applications to management. We provide an accessible overview of the latest developments in seascape genetics that merge exciting new ideas from the field of marine population connectivity with statistical and technical advances in population genetics. After summarizing the historical context leading to the emergence of seascape genetics, we detail questions and methodological approaches that are evolving the discipline, highlight applications to conservation and management, and conclude with a summary of the field's transition to seascape genomics. From 100 seascape genetic studies, we assess trends in taxonomic and geographic coverage, sampling and statistical design, and dominant seascape drivers. Notably, temperature, oceanography and geography show equal prevalence of influence on spatial genetic patterns, and tests of over 20 other seascape factors suggest that a variety of forces impact connectivity at distinct spatio-temporal scales. A new level of rigor in statistical analysis is critical for disentangling multiple drivers and spurious effects. Coupled with GIS data and genomic scale sequencing methods, this rigor is taking seascape genetics beyond an initial focus on identifying correlations to hypothesis-driven insights into patterns and processes of population connectivity and adaptation. The latest studies are illuminating differences between demographic, functional and neutral genetic connectivity, and informing applications to marine reserve design, fisheries science and strategies to assess resilience to climate change and other anthropogenic impacts.