Prey diversity constrains the adaptive potential of predator foraging traits

Predators are generally under selective pressure to get better at foraging, leading to steeper functional responses and stronger predator-prey interactions. Yet strong interactions can de-stabilize food webs, and most interactions across ecological communities are thought to be weak. This conflict between evolutionary and community expectations for the strength of predator-prey interactions represents a fundamental gap in our understanding of how the evolution of foraging plays out in food webs. Here we help to resolve the conflict by showing analytically that the expectation for the evolution of steeper functional responses is relaxed in communities with diverse prey types. We simulate communities with varying prey richness and show that increasing prey richness can indeed constrain the adaptive potential of predator foraging traits, but that at low prey richness predators can evolve to have a stronger interaction with prey that have high net energy yields. Our results also indicate that handling time plays a role in determining whether predators may evolve to have a stronger interaction with abundant prey, suggesting that the evolution of keystone predator modules in food webs is most likely when handling times are negligible. Our results also provide a new mechanism predicting more diffuse interactions in diverse tropical communities relative to more species-poor communities at higher latitudes.