A novel trophic cascade between cougars and feral donkeys shapes desert wetlands

Abstract

1. Introduced large herbivores have partly filled ecological gaps formed in the late Pleistocene, when many of the Earth's megafauna were driven extinct. However, extant predators are generally considered incapable of exerting top-down influences on introduced megafauna, leading to unusually strong disturbance and herbivory relative to native herbivores.2. We report on the first documented predation of juvenile feral donkeys Equus africanus asinus by cougars Puma concolor in the Mojave and Sonoran Deserts of North America. We then investigated how cougar predation corresponds with differences in feral donkey behaviour and associated effects on desert wetlands.3. Focusing on a feral donkey population in the Death Valley National Park, we used camera traps and vegetation surveys to compare donkey activity patterns and impacts between wetlands with and without cougar predation. 4. Donkeys were primarily diurnal at wetlands with cougar predation, thereby avoiding cougars. However, donkeys were active throughout the day and night at sites without predation. Donkeys were ~87% less active (measured as hours of activity a day) at wetlands with predation (p < 0.0001). Sites with predation had reduced donkey disturbance and herbivory, including ~46% fewer access trails, 43% less trampled bare ground and 192% more canopy cover (PERMANOVA, R 2 = 0.22, p = 0.0003). 5. Our study is the first to reveal a trophic cascade involving cougars, feral equids and vegetation. Cougar predation appears to rewire an ancient food web, with diverse implications for modern ecosystems. Our results suggest that protecting apex predators could have important implications for the ecological effects of introduced megafauna.

How cougars and feral donkeys change desert wetlands: Novel interactions between native predators and non‐native megaherbivores shape trophic cascades in the Anthropocene

“…In addition, intense human activity in those areas is likely to repel cougars and act as shields for synanthropic prey species, such as donkeys (Berger, 2007;Lundgren et al, 2022;Suraci et al, 2019). Lundgren et al (2022) corroborate that fearful grazers can trigger trophic cascades, as previously reported in different terrestrial and aquatic ecosystems (e.g. Beschta & Ripple, 2007;Madin et al, 2011).…”

“…Lundgren et al (2022) corroborate that fearful grazers can trigger trophic cascades, as previously reported in different terrestrial and aquatic ecosystems (e.g. Beschta & Ripple, 2007; Madin et al, 2011).…”

“…Lundgren et al (2022) report a natural experiment enlightening how a novel interaction between a non‐native megaherbivore and a native predator triggered a trophic cascade in the desert wetlands of Death Valley National Park. These are the first documented records showing predation of the African wild donkey, Equs africanus asinus , a megaherbivore with up to 275 kg, by one of the most widespread predators of the Americas, the cougar Puma concolor .…”

“…Indeed, cougars actively select sites with less horizontal F I G U R E 1 Novel trophic cascade involving a native predator and a non-native megaherbivore emerging at Death Valley National Park, United States. Text and icons in black provide a schematic view of how a behaviourally mediated novel trophic cascade emerges from the predation of feral donkeys, Equs africanus asinus, by cougars, Puma concolor, as reported by Lundgren et al (2022). Text and icons in grey refer to questions their work raises about the outcomes of this emerging trophic cascade.…”

Predator protection dampens the landscape of fear

“…We also corrected for potential bias in estimates pooled from sites with different sampling effort and fox detections by resampling our data over 1000 bootstraps, sampling equally between each context and site. Following Lundgren et al (2022), we then selected 25% of detections within our contextual categories (human treatment of predators or vegetative cover) with the least detections, using this quantity to sample equally from each category. Within these subsets, we calculated fox and dingo temporal activity patterns with a circular von Mises density distribution kernel (Ridout and Linkie 2009) and calculated 95% confidence intervals (CIs), enabling significance testing of activity patterns of foxes between sites.…”