Corkum, L. D. and J. H. Ciborowski (eds.) 1995. Current directions in research on Ephemeroptera. Canadian Scholars’ Press, Toronto. pp. 225-236

STREAM SIZE AND THE DISTRIBUTION OF SELECTED EPHEMEROPTERA

S. P. Yanoviak and W. P. McCafferty

Department of Entomology, Purdue University, West Lafayette, IN 47907

Information on stream size and mayfly distribution has been largely anecdotal. We studied relationships of stream length (as distance of occurrence from headwaters) and distributions of 57 recently revised and well‑documented species of North American Anthopotamus, Baetisca, Caenis, Isonychia, Pseudiron, and Stenonema. Our data provide a numerical basis for predicting potential occurrences of these mayflies in different sized streams or regions of streams. Species are categorized as having high stream‑size specificity (7%), moderate (81%), or low (12%). Those inhabiting long streams show the least relative variability. Certain species, however, are apparently restricted to short streams. Our stream‑length regions proved to be highly compatible with stream order concepts.