. Critical trends in Illinois ecosystems. Ecological assessment (Biology); Environmental impact analysis; Nature; Pollution; Conservation of natural resources; Environmental quality. 34 Critical Trends in Illinois Ecosystems. I ^. I I J 1 is S g Figure 26. Distribution of average native fish species richness statewide and for 10 ISIS basins Note: squares indicate the mean, the horizontal line in the bixx indicates the median, the bar denotes 25-75 percentiles, while vertical lines denote 10-90 percentiles. Number of observations are indicated above category labels. Fish Species Dominance: Stre
. Critical trends in Illinois ecosystems. Ecological assessment (Biology); Environmental impact analysis; Nature; Pollution; Conservation of natural resources; Environmental quality. 34 Critical Trends in Illinois Ecosystems. I ^. I I J 1 is S g Figure 26. Distribution of average native fish species richness statewide and for 10 ISIS basins Note: squares indicate the mean, the horizontal line in the bixx indicates the median, the bar denotes 25-75 percentiles, while vertical lines denote 10-90 percentiles. Number of observations are indicated above category labels. Fish Species Dominance: Streams that support large numbers of a relatively few species, as opposed to those with low-to-moderate numbers of many species, are generally thought of as being degraded. Moreover, in cases where one or a few species are abnormally dominant, those species are usually disturbance-tolerant. When the number and quality of microhabitats (pools, riffles, undercut banks, stable sand bars) are reduced it tends to eliminate habitat specialists, leaving behind mostly habitat generalists. For instance, when sedimenta- tion becomes severe the variability of pool depth decreases while the expanse of shifting sand bottom with shallow water overhead increases. Species such as the sand shiner and bluntnose minnow, habitat generalists, often become dominant in this situation. Of the seven IDNR basins surveyed. Salt Creek — a large tributary of the Sangamon River — has the largest percentage of the three most abundant fish species (Fig. 27). This basin receives tremen- dous quantities of water because much of the watershed is tiled. The increased runoff has eaten away at banks, making the streambed wider, and deposited tremendous quantities of s:md and silt, promoting extremely high numbers of red and sand. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfe
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