Our research focuses on the population dynamics of plants and how they are influenced by impacts of natural disturbances and global environmental change. We are particularly interested in the interactive effects of fire, grazing and drought in grasslands and woodlands in southern Australia, and how climate change, fragmentation and shrub encroachment affect ecosystems.

Tuesday, 3 May 2011

Is conservation science informing conservation?

As a plant ecologist with a strong interest in conservation, I'm often looking at the sort of science and actions that we are undertaking to deal with the great challenges that face native biota of southern Australia. Something recently caught my eye.

A few weeks ago, I read in The Age that Eastern-Barred Bandicoots are being released into a predator proof exclosure at Woodlands Historic Park near the Melbourne Airport (bandicoots head back to the wild). Re-introductions are critical for the persistence of many species that have had their habitat transformed by agriculture (as has happened to the grassland and woodland habitats of the EBB), or where feral predators have obliterated the last of the wild populations.

The introduction of bandicoots into the grassy woodlands (itself an endangered ecosystem) at Woodlands is not new - there have been various attempts to establish a population at this site since the 1980s - and as far as I am aware, there has been only limited success. The causes for failure, unfortunately, have not been well understood, but it would appear that failure has not always been due to predation by feral animals such as foxes. Weight-loss after release (Long et al) and drought (Winnard & Coulsen) have contributed to the failure observed, yet in 2011, more animals are being released behind an expensive (to build and maintain) fence.

Predator-proof fencing at the Arid Recovery Centre
On further investigation, I found that the exclosure erected  is 300 ha in size, yet the home range of the EBB varies between 13 to 20 hectares for males and 2 to 3 hectares for females. I'm not sure how much overlap there is in home ranges of the males, but it is possible that the exclosure might only permit a maximum of 50 or so males, and 100 females perhaps. Is this going to be enough to maintain a viable population in the long-term, as well as maintain the habitat (in this case, grassy vegetation cover) that is necessary for this species? If we are going to invest in the conservation of threatened species to ensure their survival in the wild in the long-term, I'd argue that we are obliged to do it properly so that repeated failures are not the 'norm' of these activities.

There's lots of literature on minimum viable population size and island biogeography that would suggest that small, island populations are at most risk of local extinction due to stochastic, demographic and genetic processes. I note that the predator exclosure at Arid Recovery Centre in Roxy Downs is 60 km2, an area much more likely to maintain wild populations of threatened animals.  Larger fenced areas protect larger (more viable) populations, but are harder to maintain, and more expensive to build and this is the difficult trade-off facing all conservation actions. But, if we want to achieve the outcomes we want (species survival), then we have to factor this into our decision making.

Native grasslands on the Werribee Plains likely
to become  part of the new Western Grassland Reserve
(Photo: John Morgan)
I suggest that there is much to be learnt about optimal exclusion fence size. The new Western Grassland Reserve to be created between Werribee and the You Yangs (as part of the offsets for loss of native grasslands due to urban expansion) provide an ideal opportunity to test the importance of (a) the need for predator proof fencing and (b) the size of exclosures. 

Imagine a large fenced area (say ten times bigger than that at Woodlands) in which animals could be released and their population dynamics followed over the coming years (as well as that of the habitat). This could be compared to areas outside the fence where 'normal' fox control activities are undertaken - indeed, in East Gippsland, the Southern Ark project doesn't rely on fences to preserve native animals but rather, intensive feral animal control. And at Mooramong in western Victoria, EBB released there in the 1990s survive (perhaps in the largest numbers in Victoria) without the need for an exclosure (Winnard & Coulsen). After 5 or 10 years, a comparison of the 'state' of the population in large fenced areas, small fenced areas, and areas where traditional control strategies were undertaken would put us in a much better place to understand how to do this optimally in future. This is the essence of the adapative management approach - the 'learning-by-doing' strategy - it's often emphasised and here's an opportunity to put it into practice. At best, we can learn from our failures - something that I am not sure has always happened in the past with EBBs.

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