Predators can impact their prey via consumptive effects that occur through direct killing, and via non-consumptive effects that arise when the behaviour and phenotypes of prey shift in response to the risk of predation. Although predators' consumptive effects can have cascading population-level effects on species at lower trophic levels there is less evidence that predators' non-consumptive effects propagate through ecosystems. Here we provide evidence that suppression of abundance and activity of a mesopredator (the feral cat) by an apex predator (the dingo) has positive effects on both abundance and foraging efficiency of a desert rodent. Then by manipulating predators' access to food patches we further the idea that apex predators provide small prey with refuge from predation by showing that rodents increased their habitat breadth and use of 'risky 0 food patches where an apex predator was common but mesopredators rare. Our study suggests that apex predators' suppressive effects on mesopredators extend to alleviate both mesopredators' consumptive and non-consumptive effects on prey.

The mesopredator release hypothesis (MRH) predicts that the removal of apex predators should lead to increased abundance of smaller predators through relaxation of suppressive, top-down effects. However, apex predators' effects on mesopredators are also likely to be modulated by interactions with human activities and ecosystem productivity. The exploitation ecosystems hypothesis (EEH) predicts that biomass of apex predators will scale with primary productivity but herbivore and mesopredator biomass will remain constant due to top-down control. Here, we take advantage of the manipulation of dingo abundance across Australia's Dingo Fence to explore the primacy of top-down and bottom-up effects as drivers of feral cat abundance. Using field data collected across the Dingo Fence, we test the predictions generated by MRH and EEH that cat populations should be bottom-up controlled by prey abundance (a proxy for primary productivity) where top-down control exerted by dingoes was weak but not where it was strong. We examined dingo and cat scats to provide mechanistic support for the idea that dingoes control cats through killing and exploitative competition. Overall, cats were more abundant where dingoes were rare. Cat abundance was correlated positively with prey abundance where dingoes were rare but was not correlated with prey abundance where dingoes were common. Cat remains were present in 1% of dingo scats, and dietary overlap between cats and dingoes was high (0.75-0.82). Our study provides evidence that top-down control exerted by apex predators can decouple population dynamics between mesopredators and their prey and thus have primacy over bottom-up effects.

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The 5500 km long dingo barrier fence (DBF) is a boundary at which the goal of dingo control programs shifts from management to elimination. Since 1980 ecologists have used the discrepancies in dingo densities across the DBF to study the ecological role of Australia’s largest terrestrial predator. We used drone imagery, ground based shrub and tree counts, and camera trap footage to test our hypothesis that there are alternate states in plant, bird and mammal assemblages on either side of the DBF. We found that shrubs and trees were twice as dense where dingoes were rare, and 28 % of shrub and tree species, 78 % of mammal species, and 14 % of bird species recorded were significantly more likely to occur on one side of the DBF than the other. We provide the first comprehensive snapshot of how flora and fauna assemblages differ across the DBF. This study adds to literature demonstrating that the removal of the dingo has led to profound shifts in the shrub, mammal and bird assemblages in arid Australia. Any expansion of dingo control in arid Australia must be considered against the far-reaching consequences for ecosystem assembly associated with the removal of a top predator.