Summary
Analysis of the fish faunas of Lake Opinicon and other small, cold temperate Ontario water bodies shows that the component species differ in body size, morphology, abundances, habitats, diurnal and seasonal habitat utilization patterns, diets, dietary changes with age, reproductive strategies, and population turnover rates. These differences are detailed. The number of species occurring in a lake is partly due to historic factors, the number of habitats available, and morphological, behavioral and ecological adaptations that, by channelling their owners towards alternative resources, permit species to co-occur. Diet overlap values between most species are low except for the congeneric bluegill and pump kinseed sunfishes, where values are moderate. These are the two commonest species in the lake and other parameters must increase the ecological differences between these two species. Lake Opinicon is a highly variable ecosystem. Part of this variability stems from the seasonal nature of the environment and the fact that different resources reach their peak abundance at different times of the year. Ecological overlap levels between fish species fluctuate greatly in the course of the season as species switch from, or move on to, different resources. Population levels in different habitats also vary seasonally. Species adaptations and interaction patterns were presumably evolved over a long period; most of these adaptations undoubtedly developed before the component species colonized the lake. Introduction The present review, dealing with the fish faunas of small cold temperate Ontario waterbodies and specifiReceived 20.6.1 977 Accepted 31.5.1977 * This paper forms part of the proceedings of a mini-symposium convened at Cornell University, Ithaca, N.Y., 18-19 May 1976, entitled 'Patterns of Community Structure in Fishes' (G.S. Helfman, ed.). cally Lake Opinicon, is directed at determining: (i) how the component species use space and food resources, (ii) patterns of interaction between the species and their age classes and (iii) what controls the ecological roles and types of species that co-occur. Attention is given to the relationship between morphology and ecology, food specializations, resource division, habitat specializations, community groupings, and quantification of ecological overlap values between species. In association with the present review attention is drawn to studies of space utilization in waterways to the south of the Great Lakes where whole assemblages of congeneric species occur and where species richness is higher (Mendelson 1975, Werner et al. 1977). An experimental approach to the analysis of species relationships in lake fishes has been introduced by Werner & Ha11 (1976) and Werner (1977).
Methodology
Lake Opinicon is broadly typical of a large number of small lakes in northeastern North America. It has an area of 890 ha, maximum depth of 11 m, is structurally diverse, and is ice-covered from December to April. It has been the focus of fish investigations since 1961. Published studies on its fauna and those of nearby water bodies include: resource division in a small bay community (Keast 1965) and in a stream (Keast 1966); body morphology relative to way of life (Keast & Webb 1966); feeding periodicity (Keast & Welsh 1968); feeding at low temperatures (Keast 1968a); and successional spawning (Amundrud et al. 1974). See also the work of Harker (1976) and Brown (1977) comparing the feeding and diets of common species in habitats within a lake and between different lakes, reviews of the comparative feeding ecology of age groups within species (Keast 1977a-d), and studies of habitat utilization and cornmunity patterns (Keast & Harker 1977a,b, Keast et al. 1977).