The community effects of phenotypic and genetic variation within a predator population

Background/Question/Methods . Natural populations are heterogeneous mixtures of individuals differing in physiology, morphology, and behavior. Despite the ubiquity of phenotypic variation within natural populations, its effects on the dynamics of ecological communities are not well understood. Here, we use a quantitative genetics framework to examine how phenotypic variation in a predator affects the outcomes in the community modules of apparent competition and intraguild predation.

Results/Conclusions . 1) Classical apparent competition theory predicts that prey have reciprocally negative effects on each other. The addition of phenotypic trait variation in predation can marginalize these negative effects, mediate coexistence, or generate positive indirect effects between the prey species. Long-term coexistence or facilitation, however, can be preceded by long transients of extinction risk whenever the heritability of phenotypic variation is low. Greater heritability can circumvent these ecological transients, but also can generate oscillatory and chaotic dynamics. 2) Classical intraguild predation theory predicts that coexistence of the intraguild predator and intraguild prey requires the intraguild prey is superior at resource competition. Preliminary results suggests that heritable phenotypic trait variation permits contingent coexistence even if the intraguild prey is inferior at resource competition. Alternatively, phenotypic trait variation in the intraguild predator can generate rock-paper-scissor dynamics: intraguild prey displace intraguild predators specializing on  the common resource, intraguild predators specializing on the intraguild prey displace the intraguild prey, and the cycle restarts due to selection for intraguild predators specializing on the common resource. 3) These dramatic changes in ecological outcomes, in the sign of indirect effects, and in stability suggest that studies which ignore intraspecific trait variation may reach fundamentally incorrect conclusions regarding ecological dynamics.