Mayfly communities in a Laurentian watershed (Insecta; Ephemeroptera)

Mayfly communities were investigated in a series of four lakes, two beaver ponds, and 13 streams in a Laurentian watershed. Forty-five taxa were collected mostly through emergence trapping of adults (76 trap-years). Q and R analyses were used to show similarities between the stations and associations between the species. The middle reaches of the mainstream harbour the richest communities which are an assemblage of a few ubiquitous species (Baetis gr. pygmaeus, Stenonema modestum, Habrophlebia vibrans, and Paraleptophlebia volitans), lotic species (Baetis flavistriga, B. pluto, Stenonema vicarium, and Heptagenia pulla) some of which show a restricted distribution (Paraleptophlebia adoptiva, P. Ontario, Leucrocuta hebe, and Stenacron interpunctatum heterotarsale), and also lentic species (Eurylophella verisimilis, Leptophlebia cupida, Cloeon simplex, C. rubropictum, Centroptilum album, and Stenacron interpunctatum frontale). The headwater streams contain no distinct element, except perhaps Siphlonurus typicus, but rather the more resistant or dispersive species from the mainstream, mainly Ephemerellidae and Leptophlebiidae. The lower reaches of the mainstream are characterized by the addition of a few typical river species, Serratella sordida and Epeorus vitreus. Lacustrine communities are less diverse, comprising mostly the lentic species from the streams plus a distinctive element (Stenacron interpunctatum canadense, Callibaetis ferrugineus, and Hexagenia limbata occulta). Only Leptophlebia cupida colonizes the bog lake, and no species occur in the beaver ponds. Most congeneric species are either spatially or temporally segregated. The sections of the mainstream produce an average of some 1000 adult mayflies/m2 per year; other streams are less productive and the lakes even less so (less than 100/m2). The seasonal succession of the species and the emergence patterns of the dominant species are illustrated; a classification of emergence patterns is attempted on the basis of the present data and of other recent studies.