Importance of behaviour to the re-establishment of drifting Ephemeroptera

Experiments with mayfly larvae in a laboratory stream revealed significant differences among settling capabilities of four species. Quantitative measures of overall settling capacity, contribution of morphology and that of behaviour were derived for comparative purposes. Importance of behaviour to re-establishment was greater in species which frequently show die1 drift periodicities than those which do not. Although morphological differences between species were large, mean size of nymphs was more important in determining rates of return of dead animals. Intraspecific vari-ations in the ability of drifting individuals to become re-estab-1ished may partially account for changes in the relative distri-bution of populations over time