Patch size important for possum populations


A Sugar Glider, Petaurus breviceps.

Habitat loss associated with native vegetation clearance can have major implications for the survival of native animal populations. It can reduce a species’ ability to disperse through the landscape and compromise the genetic integrity of populations over time. Populations can become inbred, making them vulnerable to disease and extinction. Also, catastrophic events like bushfires could potentially wipe out entire populations that would not be replaced by migration.

A collaborative research project between the Museum, Monash University and the University of Adelaide is examining a range of marsupials including bandicoots, sugar gliders and possums, to help inform conservation priorities.

In the south-east of South Australia, approximately 87 per cent of native Eucalyptus forests have been replaced by plantations of exotic pine species (Pinus radiata) or pastoral land. Common ringtail possums (Pseudocheirus peregrinus) persist in the remaining fragmented patches of native forest in the region. Despite evidence of their ability to nest and forage in pine plantations, recent research has shown their extinction risk is high due to a loss of genetic diversity caused by isolation.

Dr Melanie Lancaster (formerly of the University of Adelaide) and colleagues trapped 312 possums in seven native Eucalyptus forests surrounded by pine plantations. The forests ranged in size from 4 to 490 hectares and had been separated for at least 26 years. A large continuous forest (5000 hectares) was also sampled to compare dispersal within larger native patches. Possums were weighed, aged, tagged and had a small sliver of skin collected for genetic analysis.

Professor Steve Cooper from the Museum’s Evolutionary Biology Unit analysed the skin samples using microstatellite DNA markers. This next generation genetic method is the same as that used in forensic science to distinguish between individual people. As each individual possum has a unique profile, the researchers were able to get an indication of genetic diversity within a population and determine whether possums were moving around the landscape between the isolated native forest patches.

The genetic analysis indicated that pine plantations severely restricted possum movement between native forest patches and therefore gene flow. Possum populations in small, isolated patches of native forest were more genetically similar to each other than populations in large patches. Eighty seven per cent of possums sampled in small patches were born in that patch or dispersed only a short distance into neighbouring remnant forest. In contrast, possums in large patches had equivalent genetic diversity to those in the continuous forest. Continuous forest was only an important source of immigrants for patches close by (within 2.5km). This emphasises the need to conserve large proximate native forest remnants (> 200ha) where populations maintain the higher levels of genetic diversity that are critical to minimising extinction risk.

The research has highlighted the value of genetic tools in understanding the long-term biological consequences of habitat fragmentation. Conservation strategies can then be designed to reduce isolation of populations and improve gene flow. Plans are underway for building habitat corridors that enable possums and potentially other marsupials to move between native forest patches to reduce the genetic isolation and extinction risk.


Lancaster, M. L., Taylor, A. C., Cooper, S. J. B., and Carthew, S. M. (2011). Limited ecological connectivity of an arboreal marsupial across a forest/plantation landscape despite apparent resilience to fragmentation. Molecular Ecology 20: 2258–2271.