Summary
Patterns of food use and food availability were analysed in a species rich summer weedbed community of juvenile lake fish to elucidate ontogenetic and ecological adaptations facilitating species co-existence and rapid growth. It was found that: (a) the community was based on the period of high seasonal invertebrate abundance linked to the spring-summer proliferation of macrophytes: food was not limiting; (b) diet separations of individual fish species were high. In mid-July when nine species were present, Schoener diet overlap values exceeded 0.25 in only ten of 36 pairs of combinations. This contrasted with findings from a preceding May-June community of larval fish (Keast 1980); (c) mouth size helped channel the species towards different diets; and (d) diets of the early juveniles were distinct from those of the larvae, and late juveniles and adults of their species. At both the species and community level, ontogenetic and ecological developments have evolved in response to the opportunities created by an annually repetitive resource base.
Methodology
Lake Opinicon, Leeds County, Ontario (7.7 x 0.6 km), is part of the Rideau Canal system. The macrophyte/fish community studied was located in water 0.7-1.5 m deep at the head of Cow Island Bay.
Seasonal development of the plant community was documented by removing the vegetation from ten 1 m2 plots in mid-May, ahead of plant growth, and mid-June, mid-July, and August. Divers, equipped with SCUBA, gathered the material which was placed in plastic bags for transport to the surface. The material was dried in an oven at 60° C for 12 h to obtain mean dry weight biomass data.