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large numbers of individuals and a large number of taxa with smaller numbers. <br />• Diversity is said to be directly related to stability (Odum 1971) on the premise that <br />higher diversity means longer food chains with greater numbers of taxa backing up <br />each step as well as greater opportunity for negative feedback control. Increased <br />stress generally eliminates some of the rare species, decreases The numbers of <br />intolerant species and leads to increased density of a few tolerant forms no longer <br />held in check by interspecific competition (Mathis 1968). Species diversity in Trout <br />Creek exhibited a slight decrease at the lower stations (Table 2.7-13). However, <br />values at all stations were typical of those found in clean water streams (Wilhm <br />1970). The diversity index D, did not vary significantly with season at any of the <br />stations. <br />A Total of 53 taxa were collected from The stations on Oak Creek with over <br />7096 occurring at both stations (Appendix 2.7-C -Table 3). Aquatic insects were <br />dominant members of the benthos at both sites, however non-insect invertebrates <br />(e.g. Oligochaeta) were more abundant aT Station I (Table 2.7-14) than Station 2. <br />There was a dramatic decrease in density and biomass from Station I to Station <br />2. This decrease was evident in all The abundant groups except Trichopiera (Table <br />2.7-14). Diptera (Athherix pachypus, Simulium and Chironomidae) Ephemeroptera <br />• (Baetis spp. Ephemerella infrequens and TricoryThodes) and Oligochaeta (tubificid <br />worms) exhibited the greatest decline in density (Table 2.7-14). Trichopiera <br />increased in both density and biomass at Station 2 due to increased density of <br />Hydropsyche, Cheumatopsyche and Helicopsyche. One notable trend was the greatly <br />increased density of Plecoptera at Station 2, since They were rare at Station I <br />(Appendix 2.7-C -Table 3). <br />Numbers of species and species diversity (D) for stations on Oak Creek are <br />presented in Table 2.7-14. These parameters exhibit the opposite trend of the <br />standing crop in Oak Creek with higher numbers of species and a higher species <br />diversity index at Station 2, due mainly to additional species of stoneflies and <br />caddisflies at the lower site. The observed increase in species diversity is due To the <br />combination of fewer organisms spread out among more species. <br />Along with changes in the structural aspects of the invertebrate community <br />(species composition, density and biomass), there were also changes in the functional <br />aspects of the invertebrate communities in both Trout Creek and Oak Creek. <br />Invertebrates can be assigned to one of five functional categories (Cummins and Klug <br />• 1979). Shredders ore animals which feed on large particles of dead plant matter, <br />such as leaf litter. Collectors-gatherers are animals that gather small particles of <br />2.7-50 <br />