ENVIRONMENTAL VARIATION, LIFE-HISTORY ATTRIBUTES, AND COMMUNITY STRUCTURE IN STREAM FISHES - IMPLICATIONS FOR ENVIRONMENTAL-MANAGEMENT AND ASSESSMENT

Fishes in midwestern streams of the United States experience strong upstream-downstream gradients in natural environmental variability. Upstream fishes experience greater temporal variability in physical-chemical conditions than downstream fishes, particularly in intermittent streams. Associated with these changes in environmental variability, basic changes occur in life history attributes and temporal variation in community structure of stream fishes. As a whole, upstream species have a shorter life-span, smaller body size, and earlier sexual maturity than downstream species. Descriptive studies also suggest upstream species exhibit more rapid recolonization after severe physical disturbance than downstream species, and fish community structure is temporally more variable in upstream than downstream areas. These longitudinal differences in life history characteristics suggest that upstream fish communities will exhibit more rapid recovery from severe anthropogenic disturbances than downstream fish communities. The greater temporal variability of fish community structure in upstream areas also suggests it will be more difficult in upstream than downstream areas to use fish-based indices to distinguish whether subtle changes in environmental quality are due to natural or anthropogenic disturbances. Long-term monitoring of fishes throughout drainage basins is critically needed to establish more precisely the natural range of variation in community structure. Such monitoring will allow regulatory agencies to distinguish, with greater confidence, the influence of anthropogenic disturbances on stream fishes from the influence of natural environmental variation. © 1990 Springer-Verlag New York Inc.