Abundance Patterns and Community Attributes of Fishes Relative to Environmental Gradients

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Abstract
Seventy-five lakes of the Canadian boreal forest were examined for patterns of fish species abundance and community structure in relation to gradients of four environmental variables: (1) lake area, (2) mean depth, (3) Secchi disk transparency, and (4) morphoedaphic index (MEI). Mean depth appeared to exert the greatest control on the relative abundance of the species considered. The remaining variables influenced abundance in unique ways, although, as with mean depth, this influence was mainly a consequence of changes in thermal and nutrient regimes. An examination of lower trophic components indicated that these regimes appear to structure food webs, with distinctly different patterns in food webs occurring in dimictic and polymictic lakes. Major shifts in aquatic biota occur in the transition region between lake types. Lakes with these characteristics are at a lower successional state due to environmental unpredictability, as demonstrated by an increasing importance of r- over K-strategists.