Document: CHR-3-78-3

Recruitment, density thresholds, and interannual variability in interaction strength.

HARLEY, C.D.G.*

University of Washington, Seattle, WA 98195, USA. ¹

Abstract:
In order to make generalizations beyond the typically limited scope of ecological experiments, we need to understand the ways in which the results are context dependent. I measured the per capita interaction strength of an intertidal predator (Pisaster ochraceus) on its invertebrate prey in the same location in two different years. Although Pisaster densities were similar between years, the recruitment of prey species was much heavier in 1998 than in 1999. Because Pisaster cannot suppress a dominant prey item (Balanus glandula) below a certain density, the weak recruitment year resulted in little difference between exclosures and controls, and low measured interaction strengths. In the heavy recruitment year, Pisaster exclusion resulted in rapid community changes, and identified Pisaster as a much stronger interactor. Spatial and temporal variation in Pisaster's effects can therefore be determined, at least in part, by variability in the recruitment of its resource base.

Keywords: interaction strength; interannual variability; predation; recruitment

This abstract is being presented at: 10:15 AM in session:
Oral Session #7: Aquatic Ecology: Shellfish to Snails.