Importance of functional group dominance and colonizer genetic diversity on invasive success

Background/Question/Methods

Colonization success is crucial for the establishment of introduced invasive species. Increased genetic diversity may cause immediate benefits to the population either due to the increased probability of including good genotypes (sampling effect) or specific combinations of genotypes that perform well together (complementarity effect). Although much is known about the relationship between invasibility and species diversity in plant communities, data on the effects of community dominance and evenness are sparse and confounded with species identity. We address the following questions: 1) How does invasibility change across communities dominated by different functional groups? 2) Does increased population genetic diversity enhance invading species’ colonization success? 3) How important are these factors, relative to each other?  We conducted a greenhouse experiment using a model invasive species, the weedy Arabidopsis thaliana. We varied population genetic diversity of A. thaliana by sowing seeds of 1, 4 or 8 genotypes (selected from a global pool of 30 natural accessions) into experimental communities dominated by legumes, grasses or forbs or with equal relative abundances of the three.  For each functional group, species were randomly selected from a large pool common in southeast Texas to draw inferences about invasibility across a wide range of plant communities.

Results/Conclusions

Contrary to our predictions, increased population genetic diversity of the colonizer A. thaliana did not increase the total number of emergents, nor did it decrease seedling mortality within the first three months of the experiment.  Communities dominated by forbs and those with all functional groups equally represented had higher seedling mortality than communities dominated by legumes or grasses, although these patterns were strongly influenced by species identity.  However, this abundance-based evenness measure masks substantial variation that can be more precisely quantified using biomass-based evenness metrics once the experiment is complete.  To date, our results suggest that immediate effects of genetic diversity in colonizing populations may be fairly weak, particularly when compared to effects of community composition.