Potential 'ecological traps' of restored landscapes: koalas Phascolarctos cinereus re-occupy a rehabilitated mine site
Cristescu, RH, Banks, PB, Carrick, FN & Frère, C 2013, PLoS ONE, vol. 8, no. 11, e80469.
The restoration of previously disturbed landscapes can provide suitable habitat for fauna. On North Stradbroke Island, koalas recolonised areas that were previously disturbed by mining activity in as little as six years post-rehabilitation. Rehabilitated sites possessed similar, if not better, vegetation quality and quantity to that of undisturbed areas. Most importantly, the fitness and reproductive output of the koalas residing within these rehabilitated areas were no different to those inhabiting undisturbed sites.
As pristine habitats become scarcer, the need to convert previously disturbed land into suitable habitat is becoming more pressing. There is increasing concern, however, about whether these restored areas may actually be population sinks and ecological traps for fauna, in which animals that recolonise and reside in these areas occur in lower abundance or have lower fitness than those occupying undisturbed areas. Using koalas on North Stradbroke Island as an indicator species, the current study compared vegetation characteristics, koalas’ conditions and diet, and predator index between areas that were rehabilitated in different years (pre-1997, 1997-1998, and post-1998) and undisturbed areas. It revealed that rehabilitated areas were neither population sinks, nor were they ecological traps for koalas. There was no evidence that rehabilitated areas were of lower quality on the basis of vegetation characteristics, the density of trees and tree species richness, than undisturbed areas. Furthermore, the younger rehabilitated sites contain more young, fast-growing trees, hence higher-quality foliage, which were preferred by koalas. A higher quantity and quality food trees also mean that koalas can satisfy their dietary requirements without expending too much energy on foraging. Koalas were found roosting and foraging in rehabilitated sites repeatedly throughout the study period and scat analysis revealed very little difference in their diets between rehabilitated sites and undisturbed sites. Regarding the fitness of koalas in rehabilitated sites, all koalas observed using the rehabilitated areas were of good health and breeding condition. Five of the six collared females were carrying young, one of which carried two young successively. It therefore appeared that inhabiting restored areas does not compromise the health and reproductive output of the koalas. Lastly, rehabilitated areas and undisturbed areas contained a similar amount of shelter (canopy cover) and had similar predation indices, which indicates that rehabilitated areas not only provide adequate amounts of predator avoidance features, but also did not pose as traps by attracting more predators.
To complement these findings, the authors suggested further research to investigate whether rehabilitated areas facilitate predator movements and increase risks to the koalas, as well as the long-term survival rates of koalas in restored areas, which will help validate the conclusions made in this study.
Summarised by Cherie Chan
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