The Threatening of Australia's Marsupials

The Threatening of Australia's Marsupials

About fifty percent of all mammal species worldwide to have become extinct in the last 200 years have been from Australia, giving Australia the worst record for mammal conservation of any country or continent. Of a total 245 mammalian species, 59 are listed as extinct, threatened, or vulnerable (Short 1994). Most of these extinctions and declines come from two taxonomic groups--the rodents and the marsupials. Because marsupials are so abundant and diverse in Australia, I decided to research the endangerment and conservation efforts regarding marsupial species. Sixty percent of the extinct, endangered, and vulnerable Australian fauna are indeed marsupials; table 1 on the next page lists Australia's threatened marsupial species. Endangered is defined as a species in danger of extinction whose survival is unlikely if certain threats continue operating, vulnerable species are believed likely to move into the endangered category in the near future if threats continue, and to be considered extinct the species has definitely not been located in the wild during the last 50 years (ANPWS 1991).

Extinctions and declines have not uniformly affected marsupial species. Terrestrial, medium-sized marsupials in the weight range of 35.0 g to 5.5 kg have proven to be more vulnerable, and omnivores and herbivores have declined to a greater extent than carnivores. Arboreal species such as possums and gliders and species that use rock piles for shelter have been less affected. Most problems with extinction and endangerment occur in the southern arid zone and the wheat belt of Western Australia; while the tropical north of Australia, the mesic northeast and coast of New South Wales, Tasmania, and numerous offshore islands have remained relatively unaffected by local extinctions (Short 1994).

The problems

Seven main hypotheses have been put forward to explain why species have declined and/or disappeared from various parts of Australia, and they include: 1) clearing for agriculture, 2) draining and salination of wetlands, 3) grazing and browsing by introduce animals, 4) changed fire regimes, 5) introduced predators, 6) disease, and 7) overkill by hunters (Kennedy 1992). By studying the history of threatened fauna and patterns of decline, experts have come to the conclusion that some of these hypotheses can be dismissed as not being a primary cause of declining populations.

For instance, there is no direct evidence that disease has led to any mammal extinctions, though epidemics have been blamed for the decline of carnivorous marsupials in southeastern Australia and Tasmania at the turn of the century.