Habitat Selection by the Stream Mayfly Paraleptophlebia guttata

The causes and consequences of habitat distribution of larvae of the mayfly Paraleptophlebia guttata were analyzed in a 2nd-order stream in west-central Kentucky. Among macrohabitats, larvae were typically significantly more dense in runs and riffles than in pools. Densities were positively related to the percentage of coarse substrata in macrohabitats, but were not correlated with current velocity, predatory fish densities, or the quantity of fine particulate organic matter (food) in macrohabitats. This relationship between density and substratum coarseness was further evidenced in an in-situ colonization experiment in which larvae selected gravel and pebble substrata over sand. Among microhabitats, larvae were more abundant in leaf litter and in gravel/pebble than in silt/sand. Laboratory manipulations showed that predation rates by fish were significantly lower on mayflies in leaf litter and gravel than in fine substrata. The combined effects of substratum particle size and fish predation determine habitat distributions of larvae. Larger larvae were more abundant in runs than in riffles, but larval growth rates in artificial stream channels were similar between current velocities simulating those in riffles and runs. These results, coupled with data from drift samples, suggest that larvae shifted macrohabitats with size. Size-related differences in macrohabitat use may reflect size-related changes in microhabitat use; larvae were significantly larger in leaf litter than in other microhabitats, and leaf litter amounts were greater in runs than in riffles.