Predator-Dependent Functional Responses Alter the Coexistence and Indirect Effects among Prey that Share a Predator

Predator functional responses describe predator feeding rates as a function of prey abundance and are central to pred-ator–prey theory. Despite ample evidence that functional responses also depend on predator abundance, theory incor-porating predator-dependent functional responses has focused almost exclusively on specialist predator–prey pairs or linear food chains. This leaves a large gap in our knowledge as many predators feed on multiple prey, and in so doing, generate indirect effects among prey that can alter their coexistence. Here we investigate how predator-dependent functional responses in a one predator–two prey model alter the coexistence among prey and their net effects on one another. We use two different functional response forms (the Beddington–DeAngelis and Crowley–Martin functional responses) and consider situations in which the prey do not directly interact and in which they directly compete with one another. We find that predator dependence can facilitate, hinder, or have no effect on prey coexistence depending on whether prey compete directly and the role of predation in mediating coexistence among the prey in the absence of predator dependence. We also show that the negative net effects of prey on one another are generally weakened by predator dependence and can become positive under the Crowley–Martin functional response. Together, these results suggest that predator dependence may have widespread effects on ecological communities by altering the coexistence among prey species and the strength and signs of the interactions among them