Intraspecific diversity poorly predicts invasibility and invasiveness: A meta-analysis of experimental invasions

Identifying the biotic factors underlying invasion success is critical to understand the dynamics of biological invasions; and while some studies suggest that intraspecific diversity may play an important role, there has not been a systematic evaluation of the evidence. We performed a meta-analysis on 35 experimental studies and 107 effect sizes to test two hypotheses: (1) higher intraspecific diversity in a resident population decreases the likelihood of it being successfully invaded by other species, and (2) higher intraspecific diversity in an invading population increases its ability to invade another species or community. We found heterogeneous effects among studies and that overall resident genetic diversity has a very small, non-significant negative effect on invasion success, while invader genetic diversity has a small but significant positive effect. The minimal impact of intraspecific diversity is somewhat unexpected, given the well-understood mechanisms analogous to those offered for interspecific diversity. These include sampling effects and complementarity, in which diversity is expected to maximize resource use and increase density, thereby reducing niche availability and subsequent invasibility. We recommend that future research focus on a wider diversity of organisms, include longer term experiments, and measure genetic dissimilarity to better understand the role of intraspecific diversity.