Abstract |
The recently proposed index of biotic integrity (IBI) was evaluated for several watersheds throughout the midwestern United States. Five of the community metrics comprising the IBI depend on the number of fish species present and must be adjusted for changes in expected species richness with stream size or zoogeography. The authors use basic relationships of fish species richness versus stream size, calculated from historical fish community data for seven watersheds, to define lines of maximum species richness. These lines are used to predict attributes of 'excellent' fish communities, the basis of comparisons for assigning scores to 5 of 12 IBI metrics. When zoogeographic and stream-size factors were accounted for in assigning scores, the IBI accurately reflected watershed and stream conditions. As partial tests of the IBI, the authors found that the index conforms to knowledge of biologists familiar with several watersheds, is independent of stream order in homogeneous watersheds, and isn't biased upwards in generally degraded watersheds. (Copyright (c) by the American Fisheries Society 1984.) |