Ideal free distributions of stream fish: A model and test with minnows, Rhinicthys atratulus
- Oak Ridge National Lab., TN (United States)
- North Carolina State Univ., Raliegh, NC (United States)
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 cost of maintaining position while foraging in moving water, and (2) a decrease in the proportion of drift food items they capture as current speed increases. These costs differ between patches, and the cost of position maintenance is unaffected by changes in the number of fish foraging in a patch. An Ideal Free Distribution (IFD) model (IFD With Costs) is used to describe forager distributions in a habitat composed of patches in which foragers compete for food and incur an energetic cost when foraging unaffected by the number of competitors in the patch. The ability of two versions of the IFD With Costs as well as two alternative IFD models to predict the distribution of minnows (Rhinicthys atratulus) foraging in a laboratory flow-tank with two side-by-side patches was tested. In all trials the patches differed in their supply of drift food, and in some trials the patches had different water velocities. When the water velocities differed, the fish distributions (1) changed as the total supply of food increased while the ratio of food supply in the patches remained constant; (2) did not match relative food availabilities; 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. 62 refs., 6 figs., 9 tabs.
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-84OR21400
- OSTI ID:
- 50823
- Journal Information:
- Ecology, Vol. 76, Issue 2; Other Information: PBD: Mar 1995
- Country of Publication:
- United States
- Language:
- English
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