Ecological Implications of Reptile Mesopredator Release in Arid South Australia
Few examples of mesopredator release, whereby subordinate predators increase in abundance in response to a reduction in dominant predators, have been demonstrated from reptile communities despite the important ecological role of large varanids and snakes. We tested the hypothesis that trophic cascades attributable to mesopredator release of varanids could explain the apparently perverse decline of some small reptiles following removal of exotic mammalian predators in a landscape-scale reserve in arid South Australia. We used counts of Sand Goanna (Varanus gouldii) tracks and diggings as a surrogate activity index in paddock-scale treatments with different assemblages of feral predators and reintroduced mammals. Varanus gouldii activity was five times higher in regions where cats and foxes were removed than where they were present. We hypothesize that the suppression of mammalian predators can have complex effects that extend to reptile communities and should inform conservation management decisions in environments with large reptile predators.Abstract
Reintroduced mammals, control, and exotics treatments within and outside the 8,600-ha Arid Recovery Reserve in northern South Australia. Location of reserve indicated on map of Australia.
Mean (± SE) Varanus gouldii tracks counted along 12 500-m transects in each of the treatments of exotics, reintroduced mammals, and control, at the Arid Recovery Reserve.
Box-and-whisker plots showing the middle 50% of the count of Varanus gouldii digs in the box, bisected by the median line of V. gouldii digs counted in a 20-m radius (N = 8) in the Arid Recovery treatments of exotics, reintroduced mammals, and control. Vertical whisker lines indicate the range of typical data values, and the stars denote possible outliers.
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