Shifting metacommunity assembly rules: How do invasive fishes influence the assembly of an ephemeral metacommunity?

Background/Question/Methods: The question of how communities assemble has been a central theme in ecology for nearly as long as the field has existed. In recent decades metacommunity ecologists have begun to investigate the role of spatial processes on assembly rules, leading to an improved understanding of independent local and regional influences. However, the influence of non-natives on the assembly process in metacommunities is still largely unknown. Within the Rocky Glades, a karst shallow marsh within the greater Everglades National Park, solution holes serve as long hydroperiod areas where fish communities must assemble when water seasonally recedes from the marsh surface, establishing an ephemeral metacommunity. As this is among the most highly invaded areas in the Everglades, with nearly 50% non-native fish diversity, it provides the opportunity for addressing this poorly understood question. We began with a meta-analysis of available data and literature to determine if recent fish introductions have corresponded to shifts in the assembly process. We then sampled 63 solution holes in two consecutive years, via electrofishing, to directly address what factors may be driving modern assembly.

Results/Conclusions: Previous work in this region noted the fish metacommunity assembly was a random process, with no significant deviation from a null distribution; however, our meta-analysis indicates that this has shifted toward determinism in the form of aggregation in 2003. Interestingly, this corresponded with the expansion of the African Jewelfish, a non-native micro-piscivore, in to the marsh. This species is now the second most abundant fish in the marsh, and is a significant predictor of species diversity at the local scale (P<0.001, R²=0.368), while regional scale is better predicted by dispersal distance (P<0.001, R²=0.409). We note a similar shift, increased aggregation, following the 2014 expansion of Asian Swamp Eels through this habitat, but not following the introductions of several other fishes. These results, as well as a limited but growing body of literature, suggest that the introduction of an invasive species shifts metacommunity assembly patterns to be aggregative. The mechanism behind this shift however is still unknown, and is the subject of our continuing research.