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

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. 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 behavior and associated effects on desert wetlands. Focusing on a feral donkey population in Death Valley National Park, we compared donkey activity patterns and impacts between wetlands with and without cougar predation. Donkeys were primarily diurnal at wetlands with cougar predation, thereby avoiding cougars. However, donkeys were active throughout the day and night at sites witho...