The metacommunity concept invokes the role of species dispersal among local communities in altering species diversity at multiple spatial scales. Theoretical and empirical work in metacommunities structured by competition demonstrates that the frequency of species dispersal can alter local species richness, with diversity maximized at moderate (intermediate) levels of dispersal. The consequences of local dispersal-diversity relationships to community invasibility remain largely untested, however. Insights from invasion biology suggest that changes in species diversity and composition should alter the biotic resistance of native communities to invasion. Communities with moderate levels of native species dispersal should therefore be more resistant to invasion by non-native species according to local diversity-invasibility relationships. Here, I tested these predictions in a microcosm experiment with planktonic communities by manipulating native species immigration frequency (none, low, moderate) and invasion of a non-native species (Daphnia lumholtzi) represented by populations originating from different regions of the introduced range (core, middle, peripheral). Native communities were invaded after dispersal-driven divergence in community composition. Invasion success of the non-native species was evaluated in response to native species dispersal and intraspecific (inter-region) variation of the invader.
Results/Conclusions
Prior to invasion, and as predicted by theory, immigration frequency altered local species richness and ecosystem properties. Moderate dispersal communities supported higher levels of native zooplankton species richness and lower levels of phytoplankton biomass than either low dispersal or no dispersal communities. After invasion, the non-native species had 100% establishment success in the absence of dispersal, 75% establishment success at low dispersal, and 8% establishment success at moderate dispersal. There was no influence of intraspecific variation (source region) of the non-native species on establishment success or native community composition. Thus, native community connectivity was more important in determining invasion success of the non-native species than intraspecific variation in ecological traits associated with invasion history. The results indicate that dispersal-diversity relationships can influence diversity-invasibility relationships in metacommunities. The strength of community connectivity in the landscape can therefore alter local biotic resistance to species invasions. In landscapes experiencing anthropogenic alteration, particularly biotic homogenization and habitat fragmentation, critical thresholds of connectivity may be required to maintain the ecological integrity of native communities.