Can Predators Regulate Small Mammal Populations? Evidence from House Mouse Outbreaks in Australia

House mouse Mus domesticus populations in Australia can occur at either low or very high densities. During a 2-yr study mice increased from rarity to abundance in two phases: in phase A mice reached medium densities and declined, in phase B they reached very high densities before declining to near extinction. We hypothesise that mice were regulated by predators in phase A, but escaped from regulation to form plagues in phase B. We measured directly the mortality imposed by raptors and mammalian predators. Two predictions were tested: (1) if predators regulate prey populations then the predator total response shoud be density-dependent within the range of low densities (phase A); (2) when a prey outbreak occurs (phase B) predator total response should be inversely density-dependent