Linking Taxonomic Diversity and Trophic Function: A Graph-Based Theoretical Approach

Abstract

The purpose of this study is to develop a novel, visual method in analyzing complex functional trait data in freshwater ecology. We focus on macroinvertebrates in stream ecosystems under a gradient of habitat degradation and employ a combination of taxonomic and functional trait diversity analyses. Then we use graph theory to link changes in functional trait diversity to taxonomic richness and habitat degradation. We test the hypotheses that: 1) taxonomic diversity and trophic functional trait diversity both decrease with increased habitat degradation; 2) loss of taxa leads to a decrease in trophic function as visualized using a bipartite graph; and 3) loss of taxa will result in loss of redundancy. The first hypothesis was supported by the similarity of Shannon-Wiener diversity values for taxa and trophic function, correlated at r = 81%. The bipartite graph theoretic approach we developed clearly was effective in showing the linkages between taxonomic diversity and trophic functional traits related to habitat condition. In the most impaired site, loss of taxa led to the complete loss of some trophic functions and significantly less overall redundancy, supporting the third hypothesis. The implications are that taxa loss directly affects trophic function and that loss of taxonomic diversity may affect ecosystem function.