Variability and adaptive behavior: Implications for interactions between stream organisms

A central set of questions in ecology asks how population densities respond to changes in environmental variables. Two general features of ecological communities, adaptive behavior and temporal variability, have major effects on the way that this class of questions should be approached. A review of recent theory suggests that leaving out either adaptive behavior or environmental variability can result in predictions about changes in population density that are qualitatively as well as quantitatively incorrect. This article summarizes the general implications of these 2 features for some simple models with 4 or fewer species. It also reviews evidence suggesting that both features are likely to be important for stream communities: 1) streams are often highly variable in time; and 2) many of the ecologically important organisms in streams exhibit adaptive behavior that is likely to create and/or modify interspecific interactions. The article Ends with a brief discussion of the additional work, both empirical and theoretical, that is needed if we are to understand the implications of variability and adaptation in stream communities. The actual roles of these 2 factors in determining interspecific interactions in both multi-species models and natural systems remains largely unknown. However, the preliminary theoretical results presented here challenge the commonly-held views that: 1) adaptation may influence the values of ecological rate constants, but does not greatly alter the framework for describing or modeling communities, and 2) the main impact of variability is to weaken interspecific interactions.