Ideal Free Distributions of Stream Fish: A Model and Test with Minnows, Rhinicthys Atratulus

Abstract

Ideal Free theory has furthered our understanding of the processes determining the distribution of mobile foragers in a spatially heterogeneous (patchy) habitat. The Input Matching rule derived from Ideal Free theory has been used to predict forager distributions, but does not account for unshared environmentally induced costs that individuals may incur. Drift—feeding stream fish typically contend with such costs in the form of (1) an energetic costs of maintaining position while foraging in moving water, and (2) a decrease in the proportion of drift food items they can capture as current speed increases. These costs often differ between patches, and the cost of position maintenance is unaffected by changes in the number of fish foraging in a patch. Here, we developed an Ideal Free Distribution (IFD) model (IFD With Costs) to describe forager distributions in a habitat composed of patches in which foragers compete for food and incur an energetic cost when foraging that is unaffected by the number of competitors in the patch. We tested the ability of two versions of the IFD With Costs as well as two alternative IFD models to predict the distribution of minnows (Rinichtys atratulus) foraging in a laboratory flow—tank with two side—by—side patches. In all trials the patches differed in their supply of drift food, and in some trials the patches had different water velocities. When the patches' water velocities differed, the fish distributions (1) changed as the total supply of food in the two patches increased while the ratio of food supply in the patches remained constant, (2) did not match relative food availabilities in the patches, and (3) favored the slow water velocity patch. One version of the IFD With Costs predicted each of these results while none of the alternative models could account for these findings. The results support the hypothesis that fish quantitatively integrate energetic gains and costs in a manner similar to that described by the IFD With Costs when making patch selections.

Trade-Offs in Daphnia Habitat Selection

“…Larsson (1997) and Lampert et al (2003) showed with a horizontal and vertical food gradient, respectively, only weak evidence that Daphnia used population density in choosing their position in the patch. Moreover, Lampert et al (2003) suggested that Daphnia distribute at night according to the ideal free distribution (IFD) with costs model (Tyler and Gilliam 1995). This model describes the distribution of species in a food gradient associated with environmental costs (e.g., temperature).…”

Annual variation in temperature selection by Atlantic cod Gadus mortiua in the southern Gulf of St. Lawrence, Canada, and its relation to population size

“…Abrahams & Dill (1989) developed a model to predict the effects of food availability (the density-dependent resource) and predation risk (assumed to be a density-independent cost) on the distribution of guppies Poecilia reticulata between 2 feeders, one with and the other without a risk of predation. Tyler (1994) developed a similar model to predict the distribution of minnows Rhinichfhyes atratulus between 2 sides of a stream tank differing in food supply and current speed. Finally, a similar model was developed by Kramer (unpubl.…”

Density-dependent habitat selection in marine flatfish: the dynamic role of ontogeny and temperature

“…The inconsistent trends among species may be more a consequence of scale rather than behavioural differences. In the laboratory, movement between habitats is unrestricted, but may be restricted in the field if (1) distances separating those habitats are too large and/or the costs of movement are too high (Tyler & Gilliam 1995), (2) physical barriers or predators separate those habitats (Kennedy & Gray 1997) or knowledge of alternative, more 'ideal' habitats is absent (Milinski 1994). Shepherd & Litvak (2004) also note that patterns resembling DDHS can emerge in large scale studies of marine fish populations through spatially autocorrelated changes in density-independent factors (see Gaston et al 1997 for review).…”