Restoration of permanently invaded ecosystems: The key role of large predators

Background/Question/Methods

Ecosystems containing mixed assemblages of native and introduced species are now widespread, and many are degraded and simplified. In Australia, introduced species have been the major drivers of mammalian extinction in the past two hundred years. Efforts to suppress introduced species and recover native species have been unsuccessful, and in many cases such attempts have made matters worse. Although introduced species exert profound pressures within some ecological communities, others appear to be more resilient. One fundamental component may spell the difference: the presence or absence of large predators.

Top-order predators play a critically important role in maintaining ecosystem structure by regulating herbivores and mesopredators. Where they are lost this inhibiting factor is removed resulting in shifts to bottom-up driven states that facilitate population eruptions of opportunistic species. The preservation of diverse biological communities therefore depends on the predation force exerted by top-order predators.

Results/Conclusions

Australia’s top-order predator is the dingo. Since European settlement, dingoes have been persecuted across much of the continent. The consequent loss of top-down regulation has been closely followed by uncontrollable outbreaks of introduced mammals such as foxes, cats and rabbits. Where predator control has been relaxed, dingo packs successfully suppress introduced species to levels that enable native and introduced species to coexist.

This suggests that introduced species may not be a problem in their own right, and that native communities are potentially more resilient than previously believed.  Rather than attempting to force ecosystems back into purely native conditions, we could promote large predators whose influence enables mixed ecosystems to function. In essence, our contribution to the process of ecosystem restoration would be best concentrated on identifying and cooperating with the inherent mechanisms that enable ecosystems to adapt to change.