|dc.description.abstract||Invasive species are a major threat to global biodiversity due to the competitive and predatory pressures they exert on indigenous species, and the alterations they cause to native ecosystems. Within New Zealand, introduced mammalian species have had significant impacts on native fauna and flora, and are responsible for population declines and extinctions. One of the most devastating invasive species in New Zealand is the Australian common brushtail possum (Trichosurus vulpecula Kerr). The behavioural flexibility and generalist lifestyle of this species enables it to exploit a wide range of food sources and habitats, including urban areas. For an invasive species to be effectively managed, knowledge regarding its spatial ecology and population genetics is essential. Possums have not been studied within urban New Zealand environments, but it is well documented that urban-based populations of animals can behave and use resources differently than in their native habitats. This study aimed to investigate the distribution, habitat use, and genetic population structure of possums within an urban environment in New Zealand and provided new insights to inform control operations.
Within invaded environments, the distribution and availability of key resources required by a species for survival will partly determine species distribution and habitat use. WaxTags® were deployed in five urban habitats to collect presence/absence data which were analysed using the software PRESENCE. Occupancy models revealed that the probability of possum occupancy within the urban environment was influenced by the type of habitat, supplementary food resources, and proximity to forest fragments. These results indicate that possums do not use the urban habitat evenly at a broad scale.
Lightweight GPS collars were used to investigate the spatial ecology of urban possums. The accuracy and performance of these collars were assessed through stationary field tests within three residential habitat types. Fix rates and error around collected locations were influenced by sky availability, vegetation complexity, distance to buildings, and satellite configuration. Estimated error values were incorporated into subsequent spatial analyses to generate more robust conclusions regarding habitat selection.
GPS collars were deployed on 24 brushtail possums trapped within residential gardens. Home ranges estimated using minimum convex polygons and Brownian bridges revealed that sizes of home ranges varied considerably between individuals within the urban landscape and in relation to possums in other environments, with males having larger home ranges than females. Resource utilisation functions were used to assess resource selection at a finer scale within the urban environment. The strongest selection was consistently for forest fragments and residential areas composed of structurally-complex vegetation, and areas in closer proximity to forest fragments. For urban possum management to be effective, control needs to target these habitat types concurrently to minimise reinvasion potential.
Recently, molecular genetics have been incorporated into the management of invasive species to identify potential reinvasion pathways, allowing the identification of ‘eradication units’. An attempt to eradicate possums from the Otago Peninsula is currently underway. Potential reinvasion sources were investigated by determining the population structure of possums from seven locations around Dunedin and within the rural environment on the Otago Peninsula using twelve microsatellites. Population clustering determined by STRUCTURE and TESS, coupled with differences in genetic variation between populations, revealed a potential reinvasion pathway onto the Otago Peninsula from residential suburbs at the base of the Peninsula. This implies that if an urban buffer zone is well managed based on the fine-scale GPS information, the Otago Peninsula should remain possum-free.||