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

Calum X Cunningham,Tracey Hollings,Christopher N Johnson,Kaely Kreger,Menna E Jones

doi:10.1111/ecog.04635

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.

Highlights

Large carnivores have declined severely across much of the earth (Ripple et al 2014), leading to weakened landscapes of fear (Ritchie and Johnson 2009)
Possum giving-up densities (GUDs) were initially indistinguishable between Maria Island and the long-diseased region, but following the introduction of devils to Maria Island, possum GUDs were 64% higher on Maria Island than the control region (Fig. 2a)
The interaction between region and period was present in the topperforming linear mixed-effects models (LMM), which carried 95% model weight, and the interaction term had a relative importance of 0.98 (Table 1), clearly demonstrating that the foraging behaviour of possums became more risk-sensitive on Maria Island following the introduction of devils, relative to the control site

Summary

Introduction

Large carnivores have declined severely across much of the earth (Ripple et al 2014), leading to weakened landscapes of fear (Ritchie and Johnson 2009). Racoons Procyon lotor exposed to large-carnivore vocalisations reduced their foraging, which led to an increase in their prey, and a decrease in the prey of racoons’ prey (Suraci et al 2016). Trophic rewilding has gained recent popularity and aims to restore natural top–down processes to promote self-regulating, biodiverse ecosystems (Svenning et al 2016, Derham et al 2018). Passive rewilding has occurred too, as top predators have begun recovering. Rewilding is popular, empirical research on its effects are rare, with the literature dominated by opinion pieces and essays (Svenning et al 2016)

Methods

Results

Conclusion