Document: MAR-3-72-4

Habitat partitioning in size-structured fish populations.

OLSON, M.H.* ¹ and B.P.YOUNG ²

Franklin and Marshall College, Lancaster, PA 17604 U.S.A. ¹
Cornell Biological Field Station, Bridgeport, NY 13030 U.S.A. ²

Abstract:
Habitat partitioning is often observed among potential interspecific competitors. For many organisms, however, size-dependent changes in foraging ability and predation risk force a convergence in habitat use among small individuals of different species. Consequently, two species may compete when small even if larger individuals partition habitats. Previous studies of co-occurring largemouth bass (Micropterus salmoides) and smallmouth bass (M. dolomieui) have documented strong habitat partitioning among adults, with largemouth bass occupying vegetated habitats and smallmouth bass occupying rocky habitats. Visual observations of habitat use in three New York lakes indicated that juvenile bass exhibited the same pattern of partitioning as adults, despite the fact that both species fed on similar prey and were vulnerable to predation. To examine mechanisms underlying these patterns of habitat use, we conducted a pair of laboratory experiments. The first experiment compared habitat-specific foraging abilities of juvenile largemouth and smallmouth bass. The second experiment compared habitat-specific predation risk. Results of the first experiment indicated that smallmouth bass fed much more effectively in rocks than vegetation, whereas largemouth bass fed equally well in both habitats. In the second experiment, smallmouth bass were at similar risk to predation in the two types of habitats. In contrast, largemouth bass were more vulnerable to predation in rocks than vegetation. These results suggest that habitat partitioning among juvenile bass is maintained by a combination of mechanisms.

Keywords: specialization, foraging ability, predation-risk

This abstract is being presented at: 3:30 PM in session:
Oral Session #62: Freshwater Fish Ecology.