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

Identifying the biotic factors underlying invasion success into existing
communities 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 37 experimental studies and 109
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,
non-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.