To understand how fish density and food availability affect habitat selection and growth of juvenile coho salmon (Oncorhynchus kisutch), we manipulated fish density (2–12 fish·m–2) and natural invertebrate drift (0.047–0.99 mg·m–3) in 12 experimental stream channels constructed in a side-channel of Chapman Creek, British Columbia. Increased food resulted in increased growth of both dominant and subdominant fish and a shift to higher average focal velocities (from 6.5 to 8.4 cm·s–1) with maximum growth in the range of 10–12 cm·s–1. Increased food appears to permit juvenile coho to exploit higher velocity microhabitats that might otherwise be bioenergetically unsuitable at lower food levels. Increased fish density resulted in lower growth of subdominant but not of dominant fish and a general displacement of fish to both higher and lower focal velocities. The shapes of habitat suitability curves were sensitive to food abundance, implying that differences in food availability may affect transferability of habitat suitability curves between streams of different productivity. While habitat suitability curves captured the change in extent of available habitat following prey enrichment, actual increases in growth rate with enrichment (i.e., changes in habitat quality) were poorly represented by habitat suitability values and better represented by bioenergetic model predictions.

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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.Abstract. In small-scale field and related laboratory experiments, I examined the immediate and delayed effects of nuclear polyhedrosis virus (NPV) introduction and density on the performance of Malacosoma californicum pluviale. In a factorial experiment, larvae at high density showed increased feeding and development rates and decreased reproductive potential. The introduction of NPV significantly increased per capita mortality of the host, particularly at high density, and generally reduced host reproductive potential. Adults from this experiment were mated and their offspring reared in the laboratory. Pupal mass of female offspring was influenced by treatments in the parental generation, whereas egg viability, larval development time and mortality, and pupal mass of male offspring were not. M. c. pluviale introduced to host trees the year following the factorial experiment showed no effects of previous caterpillar density on mortality or reproductive potential, as would be predicted by host-plant induction theory. An interactive effect of previous virus introduction and density on mortality was observed due to the persistence of NPV in the environment. Results are discussed in light of population dynamics and observed changes in fecundity in tent caterpillar populations.

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