Abstract
Top predators cause avoidance behaviours in competitors and prey, which can lead to niche partitioning and facilitate coexistence. We investigate changes in partitioning of the temporal niche in a mammalian community in response to both the rapid decline in abundance of a top predator and its rapid increase, produced by two concurrent natural experiments: 1) the severe decline of the Tasmanian devil due to a transmissible cancer, and 2) the introduction of Tasmanian devils to an island, with subsequent population increase. We focus on devils, two mesopredators and three prey species, allowing us to examine niche partitioning in the context of intra‐ and inter‐specific competition, and predator–prey interactions. The most consistent shift in temporal activity occurred in devils themselves, which were active earlier in the night at high densities, presumably because of heightened intraspecific competition. When devils were rare, their closest competitor, the spotted‐tailed quoll, increased activity in the early part of the night, resulting in increased overlap with the devil's temporal niche and suggesting release from interference competition. The invasive feral cat, another mesopredator, did not shift its temporal activity in response to either decreasing or increasing devil densities. Shifts in temporal activity of the major prey species of devils were stronger in response to rising than to falling devil densities. We infer that the costs associated with not avoiding predators when their density is rising (i.e. death) are higher than the costs of continuing to adopt avoidance behaviours as predator densities fall (i.e. loss of foraging opportunity), so rising predator densities may trigger more rapid shifts. The rapid changes in devil abundance provide a unique framework to test how the non‐lethal effects of top predators affect community‐wide partitioning of temporal niches, revealing that this top predator has an important but varied influence on the diel activity of other species.
Highlights
Top predators play important roles in structuring the behaviour of mesopredators and prey, sometimes leading to avoidance behaviours (Lima 1998, Laundré et al 2001)
We investigate changes in partitioning of the temporal niche in a mammalian community in response to both the rapid decline in abundance of a top predator and its rapid increase, produced by two concurrent natural experiments: 1) the severe decline of the Tasmanian devil due to a transmissible cancer, and 2) the introduction of Tasmanian devils to an island, with subsequent population increase
Two mesopredators and three prey species, allowing us to examine niche partitioning in the context of intra- and inter-specific competition, and predator–prey interactions
Summary
Top predators play important roles in structuring the behaviour of mesopredators and prey, sometimes leading to avoidance behaviours (Lima 1998, Laundré et al 2001). Prey species in South Africa, for example, are more diurnal when co-existing with nocturnal top predators (lion Panthera leo and spotted hyaena Crocuta crocuta), compared to a neighbouring area without these predators (Tambling et al 2015). Such niche partitioning can be a mechanism that facilitates coexistence (Carothers and Jaksić 1984). Some large carnivores are beginning to recover across parts of Europe (Chapron et al 2014), North America (Gompper et al 2015) and Asia (Athreya et al 2013), bringing hope that predators may once again exert control over the behaviour and abundance of other species
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