Trophic filters in community phylogenetics: An analysis of fish predation on two aquatic midge metacommunities from the Swiss Alps and Sierra Nevada Mountain Range

Background/Question/Methods

Species do not exist in isolation and their patterns of co-existence and interactions across the landscape are not random with respect to phylogeny.  Our empirical study focuses on what affect predation has on driving local co-existence of chironomid midges in alpine lakes. Midges provide an incredible model system because they are the most diverse aquatic macroinvertebrate, water bodies have many co-existing species, and are linked as metacommunities because they fly as adults.  These characteristics of midge communities allowed us to measure the affect of predation from introduced fish on local community’s phylogenetic diversity in 18 lakes in two metacommunities (10 in the Sierra Nevada and 8 in the Alps).  We hypothesized presence of fish in lakes would correlate with a decrease in phylogenetic diversity in midges due to non-random predation of fish.  We tested this by comparing the mean phylogenetic distance (MPD) measured from phylogenies generated with sequences from the cytochrome oxidase I mitochondrial gene.  We compared the gene diversity in midges from fish and fishless lakes to that of the regional gene tree phylogeny to test whether phylogenetic diversity was significantly different from random expectations.

Results/Conclusions

Preliminary analysis suggest that in lakes with fish, midges are more phylogenetically similar (SES_mpd=2.10; p<0.05) and lakes that are fishless have no significantly different pattern compared to that from the regional phylogenetic diversity (SES_mpd=-0.72; p>0.05).  This pattern likely resulted from larger and predatory taxa being lost from lakes with fish.  The finding that fish predation is correlated with loss of phylogenetic diversity in midges sheds new light on the effects of introduced species on phylogenetic diversity of whole communities.  Furthermore, patterns in community phylogenetic diversity have rarely been evaluated both in aquatic systems and for consumer resource interactions.  Our empirical study shows that predation may have a strong control on aquatic systems creating a trophic filter on local species co-existence and that it is non-random with respect to phylogenic diversity.