Simulating selection and evolution at the community level using common garden data

A key issue in evolutionary biology is whether selection acting at levels higher than the individual can cause evolutionary change. If it can, then conceptual and empirical studies must consider how selection operates at multiple levels of biological organization. Here, we test the hypothesis that estimates of broad-sense community heritability, HC2, can be used to predict the evolutionary response by community-level phenotypes when community-level selection is imposed. Using an approach informed by classic quantitative genetics, we made three predictions. First, when we imposed community-level selection, we expected a significant change in the average phenotype of arthropod communities associated with individual tree genotypes [we imposed selection by favoring high and low NMDS (nonmetric multidimensional scaling) scores that reflected differences in arthropod species richness, abundance and composition]. Second, we expected HC2 to predict the magnitude of the community-level response. Third, we expected no significant change in average NMDS scores with community-level selection imposed at random. We tested these hypotheses using three years of common garden data for 102 species comprising the arthropod communities, associated with nine clonally replicated Populus angustifolia genotypes. Each of our predictions were met. We conclude that estimates of HC2 account for the resemblance among communities sharing common ancestry, the persistence of community composition over time, and the outcome of selection when it occurs at the community level. Our results provide a means for exploring how this process leads to large-scale community evolutionary change, and they identify the circumstances in which selection may routinely act at the community level.