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expected to heighten.the growth of the algal components of the aufwuchs, thus enhancing the proliferation of these taxa. As these taxa increase in abundance, an overall reduction would be expected in the number of species present. The pattern shown in Figure 8 can be interpreted as reflecting environmental degradation, with cluster 1 being most impacted and 5 the ieast? -However, --all -but -two -samples in cluster 1 had a low sample size (less than 75 individuals per sample). Low sample size can indicate low populations or inadequate sampling. Some resampling of selected stations in cluster 1 is needed to confirm if cluster 1 sites are more degraded than sites in other clusters. Many species of chironomids have a high habitat specificity: (1) Cricotopus (Nostococladius) nostocicola Wirth occurs only in Nostoc colonies; (2) species of Lopescladius, Saetheria, Bed dia, C}phomella, Paratendipes and Robad a occur only on sandy substrata (psammophilic); (3) Xestochironomus and some species of Brillia are found solely in submerged, partially decomposed wood (xylophagous), while some species of the latter feed on decomposing leaves; (4) Apedilum, Endochironomus and some species of Polypedilum and Cricotopus are found predominantly on aquatic vegetation (phytophagous); (5) Chironomus, Harnischia and Dmdcryptochironomus only occurs on soft silty substrata; (6) CardioclaXus and Rheotanytarsus are obligate rheobionts, with the former feeding on simuliid larvae and the latter constructing miniature nets to strain the water for microscopic organic particles (FPOM); Heleniella and Rheocricotopus are also obligate rheophiles, but are probably aufwuchs scrapers. Habitat specificity of individual species and high habitat heterogeneity, in the absence of extraliminal stressors, are necessary for high chironomid species diversity. Thus, a stream with a predominantly boulder-gravel-sand substratum, with cold, clear water,- and with thigh ratio of riffles and cascades to pools supports the highest species diversity. The turbid, warm, low velocity streams at lower elevations in New Mexico with sand-silt substrata will appear, in contrast, to have a depauperate fauna. Benthie Maerninvertebrates Benthic macroinvertebrate taxa produced clusters similar to those obtained for chironomid species. The most distinct assemblage of benthic macroinvertebrate taxa was a group of widespread taxa. This assemblage included taxa with an intermediate tolerance to environmental degradation and a general high relative abundance at many sites. The two remaining faunal regions were indicative of low to middle elevation and middle to high elevation, , respectively. Both of these assemblages had subgroups of taxa that varied in their tolerance to environmental degradation. Fuh Presence/absence data provided better broad scale assemblages of fish species than did relative abundance data. Within the upper Rio Grande drainage of New Mexico, five fish associations were identified with cluster analysis, three were identified with DCCA. The predominant association of fish species is the "trout stream assemblage." With expansion into a wider geographic range of 41 ^ I