Do ecosystems need top predators? A review of native predator-prey imbalances in south-east Australia
Yugovic, J 2014, The Victorian Naturalist, vol. 132, no. 1, pp. 4-11.
This review assesses the capacity of top predators in south-east Australia to control mesopredators and herbivores and in turn, manage local terrestrial ecosystems. In particular, the ecological imbalances associated with Eucalyptus over-browsing by koalas is examined. With the large-scale loss of top native predators, namely the dingo (Canis lupus dingo), introduced mesopredators such as the red fox and cat have overtaken this apex ecological function, regulating herbivore populations in local areas.
Top predators play an integral role in managing mesopredator and herbivore populations, preventing the overexploitation of resources that are relied upon by multiple species. Original top predators of south-east Australia include the Dingo, Thylacine, Powerful owl and Lace monitor; however, such species are now either extinct or occur in highly fragmented populations. In their absence, mesopredators including the Red Fox and Cat have become surrogate top predators, yet neither display aerial or arboreal predatory behaviours. Consequently, with reduced predator pressure, a number of herbivorous mammals have become overabundant. This is evident in south-eastern koala populations, where overabundance has resulted in the decimation of key food trees by over-browsing. The Coast Manna Gum is especially vulnerable, as well as the Swamp Gum, Southern Blue Gum and River Red Gum. In response to overpopulation, translocation of individuals was initially utilised as a management technique; however, in situ sterilisation has become increasingly common. There exists evidence to suggest that, prior to European settlement, both Indigenous Australians and dingoes suppressed koala population growth. Current low predation rates have ultimately resulted from a combination of predator inefficiency and control of introduced species, whereby some areas have become devoid of mesopredators.
Introduced mesopredators have become prolific in south-east Australia due to the decline of the dingo – a native top predator. With the ecological release of cats and red foxes, a number of sensitive fauna species have been over-predated and consequently, are vulnerable. However, while these predators are efficient at controlling ground-based herbivores, their management of koala populations is significantly limited.
Summarised by Julian Radford-Smith
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