No evidence of nonlinear effects of predator density, refuge availability, or body size of prey on prey mortality rates

Abstract

Predator density, refuge availability, and body size of prey can all affect the mortality rate of prey. We assume that more predators will lead to an increase in prey mortality rate, but behavioral interactions between predators and prey, and availability of refuge, may lead to nonlinear effects of increased number of predators on prey mortality rates. We tested for nonlinear effects in prey mortality rates in a mesocosm experiment with different size classes of western mosquitofish (Gambusia affinis) as the prey, different numbers of green sunfish (Lepomis cyanellus) as the predators, and different levels of refuge. Predator number and size class of prey, but not refuge availability, had significant effects on the mortality rate of prey. Change in mortality rate of prey was linear and equal across the range of predator numbers. Each new predator increased the mortality rate by about 10% overall, and mortality rates were higher for smaller size classes. Predator–prey interactions at the individual level may not scale up to create nonlinearity in prey mortality rates with increasing predator density at the population level.

Failed predator attacks have detrimental effects on antipredatory capabilities through developmental plasticity in Pelobates cultripes toads

“…A final consideration of overwhelming importance in Evolutionary Biology is regarding the potential benefit for the predators in subsequent encounters. Whether this detrimental effect on the antipredatory capabilities of metamorphs enhances the forthcoming hunting success of the same or another different individual predator will depend on the density of predators in that population, and may hence connect with predator fitness through individual or even group selection (Pruitt et al, ; Simkins & Belk, ).…”