Relationships between ecological interaction modifications and diffuse coevolution: similarities, differences, and causal links

A major empirical approach in community ecology is to describe the dynamics of a community by examining small subsets of species. Unfortunately, inter action modifications, which cause pair-wise interaction coefficients to dep end on the presence or absence of additional species, can make it difficult to predict the overall dynamics of species within a community from experim ents with pairs of species. In a similar fashion, one of the major approach es in evolutionary ecology has been to describe the likely evolutionary dyn amics of a single species by focusing on the selection imposed by a limited number of other species within the community. However, recent work on diff use coevolution indicates that selection pressures due to one species can c hange in the presence of other species. The magnitude of the difficulty tha t interaction modifications and diffuse coevolution present for predicting ecological and evolutionary dynamics is an unresolved question. Here we out line the similarities and differences between the two topics, discuss exper imental and statistical approaches to studying them, and make predictions a bout when ecological interaction modifications are likely to cause diffuse coevolution. Since the currencies for interaction modifications are usually fitness components such as growth, fecundity, or survival, is it likely th at these will translate into corresponding differences in the relative fitn ess of individuals or genotypes, and thus in general these two phenomena wi ll occur together. We argue that community ecologists and evolutionary ecol ogists will both benefit from experiments that test for the effects of inte raction modifications, and that studies of the mechanisms driving interacti on modifications and diffuse coevolution (e.g., changes in behavior, nonlin ear effects on shared resources, genetic covariances) will aid our progress in understanding the ecological and evolutionary dynamics of communities.