Food and Space as Regulators of Salmonid Populations in Streams

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Abstract
Unique characteristics of streams, food as a social convention, food-space interactions, exploitation of resources, visual isolation, and predators and parasites are reviewed and discussed as they bear upon population regulation. A speculative summary is derived, suggesting that in summer stream-dwelling salmonids are regulated in density by a space-food, sometimes by a space-shelter, mechanism. In the former case competition for space has been substituted for conventional competition for food but the substitution is incomplete, permitting populations to make use of temporarily super-abundant food. Aminimal spatial requirement appears to be present regardless of food supply and perhaps has beenfixedover the evolutionary time scale by minimalfood supply. If density is regulated in winter, it probably is related to space necessary to escaped own stream displacement or damge by current.