The impact of propagule pressure and genetic diversity on non-native establishment into plant communities

Background/Question/Methods

A non-native species’ ability to establish into a novel habitat is dependent on many abiotic and biotic conditions, yet the factors contributing to the success or failure of these invasions are still largely unknown. Some of the most important components considered have been propagule pressure (the number of individuals introduced), the number of separate introductions, and the availability of suitable habitat. Past studies have indicated that seed limitation can reduce non-native establishment. However, in addition to seed availability, the specific phenotypic traits of the propagules may also be important. In particular, the match between introduced phenotypes and the new environment may influence the colonization success and fitness of introduced propagules. Thus, genetic (and phenotypic) diversity has the potential to increase establishment success by increasing the likelihood that some of the introduced genotypes will be compatible with the available habitat. In this experiment, we explored how propagule pressure and genetic diversity independently and interactively influence the establishment of a non-native species (Arabidopsis thaliana) into a new community. The widespread availability of molecular markers for A. thaliana provides us with the opportunity to identify which genotypes successfully establish. We applied three levels of propagule pressure (16, 120, or 1200 seeds) crossed with three levels of genetic diversity (1, 4, or 8 genotypes) to 10cm diameter plots in an old field. Genotypes were chosen from twelve different population accessions across the native range of A. thaliana.

Results/Conclusions

We found that increasing propagule numbers significantly increased seedling establishment, p<0.001. Additionally, at high propagule pressure, preliminary data indicates that genetic diversity increases seedling establishment; the eight genotype mixtures had higher establishment success than the single or four genotype treatments in the 120 and 1200 propagule treatments, but not in the low seed addition treatment. We also found significant correlations between percent bare ground and seedling establishment, p<0.001. Interestingly, the effect of available space (bare ground) is more important for establishment in lower genetic diversity treatments, while seedlings established across all levels of habitat quality in the highest diversity plots. This suggests that genetic diversity provides an increased ability for populations to respond to poor quality sites or heterogeneous habitats due to more available phenotypic variation. Taken together, our results indicate that during the early stages of establishment in a novel habitat, both propagule pressure and the amount of genetic diversity in the invading population can impact invasion success.