Conservation biology of greater bilby (Macrotis lagotis) populations translocated to the temperate zone of South Australia
Date
2024
Authors
Berris, Karleah Kyrene
Editors
Advisors
Cooper, Steven
Breed, William
Carthew , Susan (Charles Darwin University)
Breed, William
Carthew , Susan (Charles Darwin University)
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Thesis
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Abstract
Many threatened Australian marsupial species had distributions that encompassed large parts of the Australian continent prior to European occupation. However, as their remnant populations are now confined to relatively small parts of Australia, our knowledge on their ecology is limited to their extant range or captive populations. This thesis aimed to explore whether aspects of the biology of the greater bilby (Macrotis lagotis) differed in a temperate environment from what has been recorded in arid zone populations, and sought to gather information that will aid in the future establishment and management of translocated temperate zone populations. This study used a comparative approach to investigate the population dynamics, breeding biology, and behaviour of greater bilby populations translocated to two sites in temperate South Australia, Venus Bay Conservation Park and Thistle Island. Regular field surveys were conducted between August 2007 and April 2010. Mark-recapture and spatially explicit capture-recapture analyses indicated a high density, stable bilby population occupied Thistle Island, which had a previous history of clearance and grazing, but was free of exotic predators. In contrast, the Venus Bay Conservation Park population declined over the study period. Adult survival rates were similar in both populations; however, the Venus Bay population had low recruitment rates and low numbers of subadults despite high adult female fecundity, likely due to high levels of predation by feral cats after pouch emergence. Births of pouch young in both populations were seasonal (June to January) with a cessation of breeding in autumn, which differed from what has been recorded in arid zone populations. Females produced up to three litters per annum, and the mean head length of females that successfully raised twins was significantly larger than that of females who raised a single pouch young. Spool-and-line tracking of bilbies at Venus Bay Conservation Park revealed individuals used multiple burrows and regularly moved between diurnal burrows. Spatial analysis using burrow locations revealed males had significantly larger burrow ranges than females, and that burrow range sizes in this temperate zone population were similar to those recorded in an arid zone population. Active burrow density at the site was at least 2.75 to 5 times the density of bilbies at the site. Parentage analysis using 10 microsatellite loci concluded that a small number of males in the two populations dominated the breeding in the areas they were captured. In both populations, nearly all females bred within a breeding season, whereas only a maximum of 20% of the males that we captured had sired pouch young we sampled in the area. Body mass and relative testes size of males were poor predictors of reproductive success. However, genetic relatedness values of breeding pairs were lower than expected by chance in the Venus Bay population. The thesis suggests a previously widespread species such as the greater bilby can adapt its reproductive strategy to suit local conditions. However, burrow use behaviour and the mating system operating at the sites were similar to what has been recorded in arid zone populations. Given female body size influenced fecundity in the study, releasing large females at the start of the breeding season in temperate areas may maximise the initial rate of increase of a translocated greater bilby population. Female-biased founder groups may also be appropriate given that only a small proportion of males were found to breed in a breeding season. This thesis suggests that greater bilbies and their burrows were once a common part of the southern Australian landscape prior to their local extinction. Therefore, greater bilbies should be considered as part of any ecosystem restoration projects within southern temperate areas of their former range.
School/Discipline
School of Biological Sciences
Dissertation Note
Thesis (Ph.D.) -- University of Adelaide, School of Biological Sciences, 2024
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