Intraspecific genetic variation for phenotypic traits within populations can have wide-ranging effects on the patterns and dynamics of multispecies communities, but the influence of evolution on the ecological dynamics of communities is not well understood.  I examined the hypothesis that evolution by natural selection within plant populations can cause temporal changes in the abundance, composition and diversity of arthropods associated with plants.  I conducted an ecological genetics field experiment using the native herbaceous plant, common evening primrose (Oenothera biennis).  I followed plants from germination until death, during which time I measured multiple morphological, phenological, physiological, and chemical plant traits, including lifetime fecundity.  I also quantified the abundance of over 120 species of arthropods that naturally colonized each plant during its lifetime and assessed whether genetic variation in specific plant traits explained variation in the arthropod community. 

Results/Conclusions

I detected significant heritable variation in 32 of 33 plant traits and variation in two life-history traits (plant biomass and flowering strategy) accounted for more than 70% of the variation in the abundance and richness of arthropods on O. biennis plants.  Using phenotypic and genotypic selection analyses, I found that directional selection favored larger plants with longer lifespans (i.e. higher fitness of biennial genotypes than annual genotypes).  This selection on O. biennis resulted in correlated selection on the abundance, composition and richness of arthropods, measured as the covariance between the relative fitness of O. biennis genotypes and variation in the arthropod community.  After partitioning out variation due to selection on plant traits, the covariance between plant fitness and arthropod community variables became non-significant, providing further evidence that selection acting directly on plant traits can have correlated community-level effects on arthropod communities.  This natural selection is predicted to lead to an evolutionary response within plant populations that is sufficient to drive rapid changes in the ecological characteristics of arthropod communities over time.