Demographic and behavioural responses of brushtail possums (Trichosurus vulpecula) to population manipulations

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dc.contributor.advisor Clout, Mick en
dc.contributor.advisor Craig, John en
dc.contributor.advisor Sarre, Steve en Ji, Weihong en 2007-12-06T07:04:46Z en 2007-12-06T07:04:46Z en 2000 en
dc.identifier THESIS 01-294 en
dc.identifier.citation Thesis (PhD--School of Environmental and Marine Sciences)--University of Auckland, 2000 en
dc.identifier.uri en
dc.description Full text is available to authenticated members of The University of Auckland only. en
dc.description.abstract Introduced from Australia, the common brushtail possum (Trichosurus vulpecula) is now a major marsupial pest damaging native flora and fauna by browsing and predation, and the farming industry by acting as a reservoir of bovine tuberculosis. Effective control of possums requires knowledge of population recovery after control operations, and knowledge of possible effects of proposed biological control methods on possum populations. In this study, the responses of brushtail possums to conventional control and to female sterilisation, (simulating the outcome of a biological fertility control), were investigated in two native forest remnants, Coatesville and Huapai, near Auckland, New Zealand. Half of the females from each study site were surgically sterilised to simulate a biological control targeting possum fertility, such as immunocontraception. The body condition of males was significantly poorer in the presence of sterilised females in the winter post-mating period following the treatment. In contrast, the body condition of females showed no change following the sterilisation treatment, either during the autumn mating period or in the winter post-mating period. More adult male possums were recorded at both study sites after the sterilisation treatment, changing the originally female-biased sex ratio. This may have been caused by the prolonged presence of oestrous females attracting males from surrounding areas. The attraction of males from surrounding areas to areas containing sterilised females might facilitate the local spread of an immunocontraceptive agent. The populations at both study sites were removed after a two-year study on the preremoval populations. The populations had recovered to about half the original density at coatesville, and to one-third at Huapai two years after the depopulation. Initial recolonisation was mainly a result of surrounding animals moving into the depopulated areas. The recovering populations responded to depopulation with a higher proportion of breeding females, higher survival rates of young and smaller fluctuations in seasonal body condition. The dispersal pattern and body sizes of recovering possums did not differ significantly from those of the original populations. Males in the post-removal populations had significantly larger mean home ranges (8.7 ± 1.53 ha) and range spans (602 ± 55.7 m) per tracking session than females (5.3 ± 0.65 ha and 452 ± 33.1 m). The range area overlapped extensively between and within sexes. There was no evidence that the range sizes of the possums in the recovering populations varied seasonally. For denning, possums prefer trees of larger diameter which are more likely to bear larger clumps of perching epiphytes. Some tree species which had been used as den sites by pre-removal populations were not used by possums in the recovering populations. Individual possums in the recovering populations used more den sites. Simultaneous den sharing was uncommon in both pre-removal and recovering populations. However, sequential den sharing was common and occurred mostly between females and males. Den sharing patterns, both simultaneous and sequential, were not affected by population reduction. The genetic similarity within the pre-removal populations, revealed by minisatellite DNA profiling, was lower between males than between females. Conversely, the genetic similarities between males and females in the two recovering populations were not significantly different, while relatedness among males was significantly higher in the recovering populations compared with than in the pre-removal populations. These data indicate two important characteristics of dispersal in possums: (1) that dispersal in established populations is male-biased, and (2) that within the first three years following population control, range shift is the most important factor in the recolonisation process. There is no evidence that the mating system, which is not monogamous, varied when density was markedly reduced. These results suggest that the rate of spread of biological control agents that rely on sexual transmission for dissemination is unlikely to be greatly affected by drastic population reductions. en
dc.language.iso en en
dc.publisher ResearchSpace@Auckland en
dc.relation.ispartof PhD Thesis - University of Auckland en
dc.relation.isreferencedby UoA9997430914002091 en
dc.rights Restricted Item. Available to authenticated members of The University of Auckland. en
dc.rights Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. en
dc.rights.uri en
dc.title Demographic and behavioural responses of brushtail possums (Trichosurus vulpecula) to population manipulations en
dc.type Thesis en Environmental and Marine Sciences en The University of Auckland en Doctoral en PhD en
dc.rights.holder Copyright: The author en

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