Additive, substitutable, and antagonistic prey responses to feral and native predator combinations

Question: Do combinations of human commensal mesocarnivores with native predators alter wild prey behavior in additive or substitutable responses? Hypothesis: Feral mesocarnivores will have a greater impact on prey energy acquisition than native predators. Organisms: Allenbys gerbils (Gerbillus andersoni allebyi) and Greater Egyptian Gerbils (Gerbillus pyramidum) as prey and feral dogs (Canis lupus familliaris), feral cats (Felis catus), barn owls (Tyto alba) horned vipers (Cerastes gasperetti) as predators. Field Site: A 17x34 meter semi natural arena mimicking sand dune environments in Sde Boker, Israel. Methods: Gerbil perceived risk was measured using optimal patch-use, predator exposures were conducted with guided (leashed) predators on an hourly basis throughout the night. Viper musk was used in lieu of live vipers. On nights with combined predators, two predators were exposed, rotating between the predators every hour. Conclusions: Human-commensal predators induced a stronger foraging aversion from the gerbils than the owl. When combining predators, the gerbils significantly decrease their foraging only when a predator perceived to be of greater risk is introduced. This was exemplified by a significantly higher GUD for dog and cat combination over dog alone, but insignificant increase, compared to the cat alone. The impact of human commensals, especially feral cats, appears to outweigh the ecological impacts of native predators.