Temporal partitioning of activity: rising and falling top‐predator abundance triggers community‐wide shifts in diel activity

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.

Trophic rewilding establishes a landscape of fear: Tasmanian devil introduction increases risk‐sensitive foraging in a key prey species

“…In addition to predation pressure, energetic state influences an animal's GUD (Brown 1992, Bedoya-Perez et al 2013. Other research shows that devils modify the behaviour of mesopredators and prey; for example, spotted-tailed quolls Dasyurus maculatus temporally partition activity to avoid devils at high density (Cunningham et al 2019a), and feral cats Felis catus willingly feed on carcasses in areas where devils are rare, but less so in areas where devils are abundant, possibly a response to increased risk of encountering a devil at a carcass (Cunningham et al 2018). Maria Island and the control region were both exposed to similarly low rainfall preceding the 'after' period, yet the control region saw a significantly larger drop in GUDs, and the two regions had significantly different slopes.…”

“…We demonstrate that top predators modify the behaviour of prey by instilling fear, and that behavioural change can occur rapidly following top predator introductions, far more rapidly than demographic change. Other research shows that devils modify the behaviour of mesopredators and prey; for example, spotted-tailed quolls Dasyurus maculatus temporally partition activity to avoid devils at high density (Cunningham et al 2019a), and feral cats Felis catus willingly feed on carcasses in areas where devils are rare, but less so in areas where devils are abundant, possibly a response to increased risk of encountering a devil at a carcass (Cunningham et al 2018). The next important step is to quantify how these behavioural changes affect fitness, demography and the flow-on effects to vegetation.…”

A native apex predator limits an invasive mesopredator and protects native prey: Tasmanian devils protecting bandicoots from cats

“…Other research shows that devil declines have resulted in the behavioural release of quolls. For instance, where devils are rare, quolls consume more carrion (Cunningham et al ) and increase their activity during the period of the day preferred by devils (Cunningham et al ). Despite this behavioural release, no study has found evidence for increased abundance of quolls following devil declines (Hollings et al ; Troy ; Hollings et al ), and our study further supports those findings.…”

“…For example, possums relaxed their risk-sensitive foraging behaviours following devil population declines (Hollings et al 2015), and reinstated these behaviours following the introduction of devils to the previously devil-free Maria Island (Cunningham et al 2019a). Wallabies also responded to the introduction of devils to Maria Island by increasing activity at periods of the day when devils are inactive (Cunningham et al 2019c). Because possums are typically arboreal but often forage on the ground, the trends we show here could reflect changes in abundance or increased ground-based activity by possums in response to a relaxed landscape of fear (Hollings et al 2015;Cunningham et al 2019a).…”

Space use and temporal partitioning of sympatric Tasmanian devils and spotted‐tailed quolls

“…In quolls, home range size varies from several hundred to several thousand hectares, and while male home ranges overlap females are intrasexually territorial but tolerate the presence of female young (Belcher & Darrant 2004; Claridge et al 2005; Glen & Dickman 2006b). A recent camera study revealed temporal shifts in quolls in response to progressive decline in devil populations across the width of Tasmania, suggesting temporal avoidance by quolls of devils (Cunningham et al 2019).…”