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, H2C, 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 H2C 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
H2C 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.