SYSTEMATICS AND THE SYNECOLOGY OF AQUATIC INSECTS, PHENOLOGY AND TEMPORAL STRUCTURE OF TEMPERATE LAKE ASSEMBLAGES

Four emergence series were collected from a small mesotrophic-dystroph ic lake in the southern Laurentians of Quebec: near shore (station A, 0.3 m, shrubs and heaths), in the littoral zone (B, 0.6 m, and C, 1 m, aquatic vegetation), and in open water (D, 6 m, no vegetation). A gra dient of species richness (121-34), of numbers (4622-1120/m2), of dive rsity (5.62-2.42 bits), and of equitability (0.81-0.48) extended from the shore to the open water. Also recognized was a seasonal succession of early synchronized species, many of which completed a second gener ation by late summer, and of more dispersed summer species. This patte rn was best exemplified in the shore station, whereas in deeper sites, the assemblages were increasingly less structured and dominated by fe wer species. Chaoborus punctipennis. a benthic insect feeding in the w ater column at night, tended to predominate in the outer stations and to impose its particular seasonal dynamics on the assemblage there. Ch ronological clustering revealed distinctive early- and late-season ass emblages in all sites. A succession of distinct and temporally structu red mid-season assemblages was evident at the shore station, but this pattern was obscured in other stations because of the recurrence and d ominance of the same species throughout. Though these particular patte rns may be restricted to the one lake studied, this approach based on a taxonomical and temporal analysis offers promise for generalizations once it has been applied to a variety of lake systems.