VARIABILITY AND ADAPTIVE-BEHAVIOR - IMPLICATIONS FOR INTERACTIONS BETWEEN STREAM ORGANISMS

A central set of questions in ecology asks how population densities re spond to changes in environmental variables. Two general features of e cological communities, adaptive behavior and temporal variability, hav e major effects on the way that this class of questions should be appr oached. A review of recent theory suggests that leaving out either ada ptive 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 implicat ions of these 2 features for some simple models with 4 or fewer specie s. It also reviews evidence suggesting that both features are likely t o be important for stream communities: 1) streams are often highly var iable in time; and 2) many of the ecologically important organisms in streams exhibit adaptive behavior that is likely to create and/or modi fy interspecific interactions. The article Ends with a brief discussio n of the additional work, both empirical and theoretical, that is need ed if we are to understand the implications of variability and adaptat ion in stream communities. The actual roles of these 2 factors in dete rmining interspecific interactions in both multi-species models and na tural systems remains largely unknown. However, the preliminary theore tical results presented here challenge the commonly-held views that: 1 ) adaptation may influence the values of ecological rate constants, bu t does not greatly alter the framework for describing or modeling comm unities, and 2) the main impact of variability is to weaken interspeci fic interactions.