Nonlinear functional responses and ecological pleiotropy alter the strength and likelihood of disruptive selection in consumers

Abstract Much of the theory on disruptive selection has focused on selection in generalist consumers caused by ecological opportunity through the availability of alternative resources and intraspecific competition for those resources. This theory, however, makes several ecologically unrealistic assumptions. First, it assumes consumers have a linear, resource-dependent functional response, ignoring well-documented effects of resource handling times and consumer dependence. Second, it assumes the trait under selection only influences the per-capita attack rates of the consumer, ignoring other effects of the trait that may influence feeding rates and hence, fitness. Here, I develop a one consumer-two resource model to investigate how nonlinear functional responses and ecological pleiotropy (traits with multiple simultaneous ecological effects) influence the strength and likelihood of disruptive selection. I find that handling times and interference among consumers are capable of altering disruptive selection by changing feeding rates differentially across consumer phenotypes. In particular, handling times decrease the strength and likelihood of disruptive selection while the effects of interference depend on the mechanism through which interference occurs. The effects of handling times and interference, however, depend on whether and how ecological pleiotropy causes correlations between handling times or interference rates and attack rates. Overall, my results suggest that features underlying functional responses of consumers and the relationships among those features determine the likelihood and strength of disruptive selection. In particular, disruptive selection should be strongest in generalist populations with individuals who experience lower handling times and interference rates on the resources for which their attack rates are highest.