Density-Dependent Mortality Caused by Physical Stress Interacting with Biotic History

Abstract

The long-standing debate among ecologists as to whether physical factors act in a density-dependent or density-independent fashion may be partially resolved by recognizing that a history of crowding alters an organism''s susceptibility to stress. Mortality following sedimentation for sand-flat bivalves is shown to be density-dependent solely because of the historical influence of crowding. Consequently, the density dependence is actually caused by the interaction between the stress of sedimentation and the density history of the organisms. The demonstrated importance of interactions with biotic history raises questions about the interpretation of bioassays, pollutant impacts, responses to weather, paleoecological changes, and results in experimental ecology and physiology whenever the equivalence of organisms is assumed without a knowledge of historical conditioning.