Additive and substitutable prey responses to feral and native predator combinations

Abstract

In captive experiments of Negev Desert granivores, we investigated the ways in which combinations of feral mesocarnivores and native predators alter wild prey behavior. We hypothesized that feral mesocarnivores would have a greater impact on prey energy acquisition, reflected in foraging dynamics, than native predators. Allenby's gerbils (Gerbillus andersoni allenbyi) and greater Egyptian gerbils (Gerbillus pyramidum) were used as prey species, with feral dogs (Canis lupus familiaris), feral cats (Felis catus), barn owls (Tyto alba), and horned vipers (Cerastes gasperetti) as predators. Gerbil perceived risk was measured using optimal patch-use theory, with exposures to tethered predators occurring hourly throughout the night. Some nights, two predators were alternated every other hour. We found that human-commensal predators, particularly feral cats, induced stronger foraging than native predators, such as barn owls. Combined predators caused gerbils to decrease foraging only when a higher-risk predator was introduced, as indicated by higher giving-up densities (GUDs) for the dog and cat combination compared to the dog alone, and a nonsignificant increase compared to the cat alone. The impact of feral cats especially appears to outweigh that of native predators. This highlights the conservation challenges to arid environments where feral cats have become ubiquitous.