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

Abstract

Global declines of large carnivores have reduced the ‘landscape of fear’ that constrains the behaviour of other species. In recent years, active and passive trophic rewilding have potentially begun restoring these lost top–down controls. The Tasmanian devil Sarcophilus harrisii has declined severely due to a novel transmissible cancer. In response to extinction fears, devils were introduced to the devil‐free Maria Island, where their abundance rapidly increased. We tested how this introduction influenced risk‐sensitive foraging in the common brushtail possum Trichosurus vulpecula, a major prey species for devils, using giving‐up densities (GUDs). Before the introduction of devils, possum GUDs on Maria Island were indistinguishable from the long‐diseased region of Tasmania, where devils have been rare since ~2000. Three years after devil introduction, GUDs were 64% higher on Maria Island than the control region, demonstrating that after an initial period of high mortality, possums quickly adopted risk‐sensitive foraging behaviours. Devil activity across Maria Island was variable, leading to a heterogeneous landscape of fear and highlighting that top predators must be at functional densities to elicit behavioural responses from prey. Our study provides strong evidence that top predators modify the behaviour of prey by instilling fear, causing rapid ecological change following recoveries.

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

“…While there is much evidence of the cascading effects that often follow toppredator removal, there is less evidence about the reversal of effects following predator recovery (Alston et al 2019). Our study provides valuable evidence that top predator recoveries can reinstate anti-predator behaviours in other species (Berger et al 2001, Estes et al 2011, Cunningham et al 2019b). The effects we show are distinct from the direct demographic impacts of predation on population size or distribution, but they may compound those direct impacts.…”

Prey availability and ambient temperature influence carrion persistence in the boreal forest

“…We then excluded candidate models that contained uninformative parameters (Leroux, 2019), which were identified when the addition of a parameter to a simpler nested model had no improvement on model fit (i.e. log-likelihood), and increased AICc by approximately the penalty of two (as in Cunningham, Johnson, Hollings, Kreger, & Jones, 2019). We then calculated model-averaged coefficients and included models with ∆AIC < 4 to retain the most information (Burnham, Anderson, & Huyvaert, 2011).…”

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

“…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 ). 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 ; Cunningham et al ).…”

“…The greater abundance of possums in long‐diseased areas agrees with other research that shows declining devil abundance has released possums from top‐down control. For example, possums relaxed their risk‐sensitive foraging behaviours following devil population declines (Hollings et al ), and reinstated these behaviours following the introduction of devils to the previously devil‐free Maria Island (Cunningham et al ). 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 ).…”