US-IALE 2018

AUTHORS: Gabriela Nunez-Mir*, Songlin Fei – Purdue University

ABSTRACT: Empirical and theoretical studies have shown that the association between native diversity and invasion (e.g., usually exotic richness) is inconsistent, varying across scales and ecosystems of study. To explain the different patterns, ecologists have proposed a number of underlying processes, focusing mostly on the role of local or regional native species richness. Yet, there are other aspects of native diversity involved in influencing a community’s invasibility that may be contributing to the inconsistencies observed. Although abiotic environmental heterogeneity has been extensively explored as a driver of these patterns, little is known about the role of biotic heterogeneity. Here, we seek to understand how beta diversity, the heterogeneity of species composition among assemblages, influences the observed relationship between native and exotic species richness. In addition, we sought to understand how this influence changes across scales. To do this, we obtained native and exotic richness data for the entire continental United States from the USGS nonindigenous aquatic species and NatureServe databases. We took advantage of the nested properties of these databases (HUC levels) to incorporate the influence of scale in these relationships. Because beta diversity is likely to be a good indicator for spatial heterogeneity, we hypothesized that high beta diversity enhances coexistence and supersedes processes that decrease invasibility. Therefore, we expected that areas with higher levels of beta diversity would display more positive relationships. Our results seem to indicate a scale-dependent effect of beta diversity on invasibility. Contrary to our hypothesis, we found beta diversity to have, not a negative effect, but a positive effect on invasibility, and only at scales with the largest spatial extent. Ultimately, our study contributes to our understanding of these invasion patterns and their relationship with scale, as well as to our ability to evaluate the vulnerability of communities to invasion.