Extrapolating from individual behavior to populations and communities in streams

Biological processes, such as predator-prey or competitive interactions, occur at multiple spatial and temporal scales, but their impacts on the distribution, abundance and fitness of organisms may only be detectable at some scales. This is because 1) small scale (local) processes may be constrained by large-scale (regional) processes, 2) the influence of organism movement changes with spatial scale, and 3) multiple small-scale processes may interact and produce variation that obscures large-scale patterns. Most ecologists would like to know the relevance of small-scale observations and experiments for large-scale patterns and processes acting over long time periods. In this paper we consider whether patterns of individual behavior translate in a straightforward way to patterns in population dynamics, community structure or individual fitness at larger spatial and longer temporal scales. We illustrate our discussion with data from communities living in high altitude streams in western Colorado, coastal streams in southern California, and streams on the South Island of New Zealand. We describe patterns of individual behavior including selective predation, predator-avoidance behavior, and competitive interactions. Our examples indicate that large scale patterns of distribution and abundance of organisms sometimes deviate from those expected from patterns of individual behavior. We hypothesize that such discrepancies are often due to multiple confounding factors, including abiotic disturbances, that have effects on populations and communities at larger scales. Similarly, our data illustrate that present behaviors may not have measurable fitness consequences over longer time scales. We emphasize that only by studying all life history stages of organisms with complex life cycles can we interpret the long-term fitness consequences of individual behaviors. We conclude that our ability to extrapolate from individual behaviors to populations and communities in streams will improve when we consider the repercussions of individual behaviors and environmental factors over broader spatial and temporal scales.