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Abstract
We manipulated food inputs among patches within experimental streams to determine how variation in foraging behavior influenced demographic and phenotypic responses of juvenile steelhead trout (
Oncorhynchus mykiss) to the spatial predictability of food resources. Demographic responses included compensatory adjustments in fish abundance, mean fish size, and size inequality. These responses paralleled shifts in individual foraging behavior, which increased the strength of exploitative competition relative to interference competition in streams with lower spatial predictability of food resources. Variation in the spatial predictability of food resources also favored different physiological phenotypes, as inferred from selection on an index of standard metabolic rate (SMR) based on fish otolith size. We observed positive directional selection on SMR in streams with spatially predictable food resources, disruptive selection for SMR at intermediate levels of spatial predictability, and negative directional selection for SMR in streams with the lowest level of spatial predictability of food resources. Thus, variation in the spatial predictability of food resources resulted in changes in individual behavior and modes of population regulation, and produced physiologically divergent cohorts of stream salmonids.
Keywords
competition,
exploitation,
interference,
emigration,
growth depensation,
intraspecific competition,
Oncorhynchus mykiss,
phenotypic selection,
population dynamics,
regulation,
spatial predictability,
standard metabolic rate,
steelhead trout
Citation
Sloat, Matthew R.; Reeves, Gordon H. 2014. Demographic and phenotypic responses of juvenile steelhead trout to spatial predictability of food resources. Ecology. 95(9): 2423-2433.
