An ecological regime shift resulting from disrupted predator-prey interactions in Holocene Australia.

The mass extinction events during human prehistory are striking examples of ecological regime shifts, the causes of which are still hotly debated. In Australia, human arrival approximately 50 thousand years ago was associated with the continental-scale extinction of numerous marsupial megafauna species and a permanent change in vegetation structure. An alternative stable state persisted until a second regime shift occurred during the late Holocene, when the largest two remaining marsupial carnivores, the thylacine and devil, disappeared from mainland Australia. These extinctions have been widely attributed to the human-assisted invasion of a competing predator, the dingo. In this unusual case, the simultaneous effects of human "intensification" (population growth and technological advances) and climate change (particularly increased ENSO variability) have been largely overlooked. We developed a dynamic model system capable of simulating the complex interactions between the main predators (humans, thylacines, devils, dingoes) and their marsupial prey (macropods), which we coupled with reconstructions of human population growth and climate change for late-Holocene Australia. Because the strength of important interspecific interactions cannot be estimated directly, we used detailed scenario testing and sensitivity analysis to identify robust model outcomes and investigate competing explanations for the Holocene regime shift. This approach identified human intensification as the most probable cause, while also demonstrating the potential importance of synergies with the effects of climate change. Our models indicate that the prehistoric impact of humans on Australian mammals was not limited to the late Pleistocene (i.e., the megafaunal extinctions) but extended into the late Holocene.