Interactive Segregation between the Stream Fishes Etheostoma simoterum and E. rufilineatum

The habitat associations, density and behavior of two stream fishes, Etheostoma simoterum and E. rufilineatum, were studied in the Little River of eastern Tennessee, USA. Density manipulations conducted in the field indicated that interactive segregation occurred between these species in runs. Laboratory experiments showed that E. simoterum reduced its shelter utilization by 50% when in the presence of E. rufilineatum, whereas E. rufilineatum reduced its utilization by 29% when E. simoterum was present. The field experiments suggested that an interplay between interactive segregation and physical factors influenced the distribution of E. simoterum. In a year characterized by high temperature and low discharge, E. simoterum's distribution shifted away from shore after E. rufilineatum was removed from the river. In contrast, during a period of low temperature and high discharge no habitat shift was observed. These data indicate that the intensity of biotic interactions in streams varies over time and is altered by a dynamic physical environment.