USE OF GRAPH THEORY TO DETERMINE EFFECT OF TAXONOMIC DIVERSITY LOSS ON TROPHIC FUNCTION

Does loss of taxa affect trophic function? Taxonomic diversity and trophic function for aquatic insects were estimated across streams exhibiting a habitat degradation gradient. Data were obtained for use from streams across Iowa, Nebraska, and Kansas with permission from Central Plains Center for Bio-assessment. Two hypotheses were tested: 1) habitat degradation impacts diversity and 2) loss of taxa leads to loss of trophic function. Shannon-Wiener diversity values for taxa and trophic function were similar, correlated at r = .8, and both decreased as habitat degradation increased, supporting the first hypothesis. Three sites were explored with Graph Theory: a habitat-degraded site, and moderate site, and a habitat-healthy site. Edges linked taxonomic and trophic groups. Affinities between taxa and trophic function were denoted by edge color. Vertices were weighted by abundance. In the most impaired site, loss of taxa led to the complete loss of some trophic functions and the compression of others, supporting the second hypothesis. The implications are taxa loss directly affects trophic function and that loss of taxonomic diversity directly affects ecosystem function.