The Evolutionary Role of Indirect Effects in Communities

Indirect effects occurring through chains of direct species interactions have been shown to be important in many communities. If indirect effects have strong ecological effects, then they must also have strong evolutionary effects through natural selection. We consider how indirect effects, both positive and negative, combine with positive and negative direct effects to influence evolution between interacting species. Any one species can evolve in response to direct interactions with other species by changing its “response” to the presence of the other species or changing its “effect” on the species. We argue that the direction (positive or negative) of the direct and indirect effects will determine whether traits related to “response” or “effect” are most likely to be subject to natural selection. Further, covariance patterns of species in the same community should increase when direct and indirect effects between species act in the same direction, resulting in greater compartmentalization of such communities.