An experimental test of eco-evolutionary dynamics on rocky shores

A growing body of theoretical studies and laboratory experiments has focused attention on reciprocal feedbacks between ecological and evolutionary processes. However, uncertainty remains about whether such eco-evolutionary feedbacks have an important or negligible influence on natural communities. Thus, recent discussions call for field experiments that explore whether selection on phenotypic variation within populations leads to contemporaneous effects on community dynamics. To help fill this gap, in this study, we test the hypothesis that selection on consumer traits in a population of predatory drilling snails can drive eco-evolutionary dynamics in a rocky intertidal community in California, USA. We first conducted a laboratory selection experiment to raise newly hatched dogwhelks (Nucella canaliculata) on four diet treatments encompassing a range of prey species and shell thicknesses. Snails that survived to adulthood under these diet treatments differed in their capacity to drill thick-shelled mussels. Dogwhelks from these treatment groups were then outplanted to intertidal field cages for 1 year to test whether groups experiencing selection differed in their effects on mussel bed succession. As expected, succession proceeded most rapidly in the reference treatment with dogwhelks excluded. However, successional patterns differed minimally among dogwhelks raised under the different diet treatments. Thus, although our laboratory results suggest that prey can impose selection that leads to rapid adaptation and divergent consumer traits, these feedbacks were not strong enough to result in clear community effects in the field. We propose that a limited range of variation in functional traits within populations, moderate strengths of selection, and a background of substantial abiotic and biotic variation may all act to dampen the potential for strong eco-evolutionary dynamics in this and many other natural communities.