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, this theory assumes that consumers have a linear, resource-dependent functional response, ignoring well-documented effects of resource handling times and consumer dependence. Second, this theory assumes that the trait under selection only influences the percapita 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 that have multiple simultaneous ecological effects) influence the strength 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 cause a decrease in the strength of disruptive selection while the effects of interference depend on the mechanism through which interference occurs. The effects of handling times and interference, however, are dependent on whether and how ecological pleiotropy causes correlations between handling times or interference rates and attack rates. Overall, my results suggest that features defining the 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 composed of individual diet specialists who experience lower handling times and interference rates on the resources for which their attack rates are highest.