Experimental Tests of Optimal Habitat Use in Fish: The Role of Relative Habitat Profitability

Abstract

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.Abstract. Utilizing optimal foraging theory and laboratory estimates of foraging costs, we predict the choice of foods and use of habitats by fish in the field. These predictions are tested with the bluegill sunfish (Lepomis macrochirus) foraging in three habitats (open water, sediments, and vegetation) in a pond. Relations describing prey encounter rates in each habitat as a function of prey size, prey density, and fish size were derived from laboratory experiments. These relations permitted us to estimate prey encounter rates based on weekly prey samples in each habitat of the pond. We then determined the optimal diet and profitability (net energy return) for each habitat through time.Predictions of optimal diet exhibited good qualitative correspondence to the actual diet of the fish in the open water and vegetation, although we consistently predicted a slightly narrower diet than the fish were choosing. The model correctly predicted the magnitude of the change in size selection on Daphnia pulex with fish size and with decline in prey density. Predictions of optimal diet in the sediments were considerably in error apparently due to a tendency for late-instar midges to burrow deep in the sediments, thereby becoming unavailable to the fish. In this case habitat profitabilities were computed simply on the basis of the actual observed diet.Predictions of optimal habitat use, i.e., when the fish should switch habitats to maximize feeding rates, showed striking correspondence to the actual habitat use of the fish; the bluegills switched from feeding in the open water column to feeding from the sediments within a few days of our predictions. The actual habitat use pattern differs dramatically from a null model of random habitat use. We indicate how this approach may be useful in studying intra-and interspecific exploitative interactions. All use subject to JSTOR Terms and Conditions 1526 EARL E. WERNER ET AL. Ecology, Vol. 64, No. 6itats. Net energy return rates for the different habitat types are then calculated, which enable us to quantify habitat profitability and predict optimal habitat use. Finally, we show that temporal habitat switches by the fish conform to our predictions based on the premise that they maximize energetic gain. These tests of optimal habitat use were performed in the context of a larger experiment evaluating the influence of foraging profitability and predation risk on habitat use by three size-classes of the bluegill. A companion paper (Werner et al. 1983) examines the bluegills' behavior under predation risk. The current paper concerns the foraging relations of the bluegill, with respect to changing resource levels. EXPERIMENTAL DESIGN AND METHODS The experime...

Habitat use by the fish assemblages of two chalk streams

“…This indicates that from an evolutionary point of view, these species have developed few habitat adaptations and display an opportunistic behaviour in habitat selection as in other life-history aspects, such as fecundity or lifespan (Maitland, 1965;Mann et al, 1985, Angermeier, 1987. However, this does not exclude the possibility that in specific sites each species selects those microhabitat patches where the cost-benefit relationship is minimized, from an energetic point of view (Werner et al, 1984).…”

Habitat use by the fish assemblages of two chalk streams

“…This indicates that from an evolutionary point of view, these species have developed few habitat adaptations and display an opportunistic behaviour in habitat selection as in other life-history aspects, such as fecundity or lifespan (Maitland, 1965;Mann et al, 1985, Angermeier, 1987. However, this does not exclude the possibility that in specific sites each species selects those microhabitat patches where the cost-benefit relationship is minimized, from an energetic point of view (Werner et al, 1984). Angermeier (1987) found inconsistent patterns of habitat selection by widespread fish species between sites and dates in some North American streams.…”

Why do juvenile fish utilise mangrove habitats?

“…Similarly, in high densities of seagrass (Syringodium), pursuit and capture of invertebrates by pinfish is inhibited in larger size classes due to restriction of movement of the pectoral fin, while the same habitat is apparently no barrier to locomotion in small pinfish (Stoner, 1982). Habitat shifts are likely to be a mechanism to reduce intraspecific competition between size classes, and have been demonstrated for sunfish (Werner et al, 1983b), grey snapper (Thayer et al, 1987) and several other species of fish (Butner and Brattstrom, 1960;Laegdsgaard, 1996).…”