Effects of intraspecific genetic diversity on ecological communities are context-dependent

Background/Question/Methods

Increased genetic diversity in a population can have strong, often positive effects on both that population (e.g., increased average survival, growth rate or fecundity), and on the ecological community (e.g., diversity of other species) containing that population.  However, most experimental studies of this problem manipulate genetic diversity in only one environmental context.  The ubiquity of environmental variation in nature raises the question as to whether the ecological effects of increased genetic variation are (1) constant across different environments, and (2) similar in magnitude to the effects of environmental variation.  To answer these questions, we conducted a mesocosm experiment in which we manipulated genetic diversity of groups of 100 wood frog (Rana sylvatica) tadpoles.  High and low genetic diversity groups were replicated across four different environments:  high or low resources crossed with the presence or absence of predatory dragonfly larvae.   We measured variables related to the tadpole populations (tadpole behavior, survival, growth and development rates) and the ecological community (chlorophyll a, copepod and cladoceran abundances, and microbial community diversity).

Results/Conclusions

Two variables (i.e., tadpole survival, chlorophyll a) were affected only by the environment, while tadpole behavior was affected only by the level of tadpole genetic diversity.  However, there were also significant tadpole genetic diversity X environment interactions for wood frog growth rate and the ecological community (copepod abundance, cladoceran abundance and microbial species richness).   The significant interaction effect indicated that the ecological consequences of genetic diversity were not constant across different environments, thus obscuring our ability to make clear predictions about the ecological consequences of genetic variation.  We also compared the standardized effect sizes for the genetic variation treatments and the environmental variation treatments.  Standardized effect sizes were similar for the tadpole genetic diversity treatment and the environment treatment.  This indicates that the amount of genetic diversity in amphibian populations can have as strong an effect as variation in resources or predation risk.