Indirect interactions shape selection in a multi-species foodweb

Species do not live, interact, or evolve in isolation, but are instead members of complex ecological communities. In ecological terms, complex multi-species interactions can be understood by considering indirect effects that are mediated by changes in traits and abundances of intermediate species. Interestingly, traits and abundances are also central to our understanding of phenotypic selection, suggesting that indirect effects may be extended to understand evolution in complex communities. Here, we explore indirect ecological effects and their evolutionary corollary in a well-understood foodweb comprising a plant, its herbivores, and enemies that select for opposite defensive phenotypes in one of the herbivores. We show that ecological indirect interactions are mediated by changes to both the traits and abundances of intermediate species, and that these changes ultimately reduce enemy attack and weaken selection. We discuss the generality of the link between indirect effects and select...