Variability and dynamics of a desert stream community

Communities can be highly variable over a few years, but remain fairly constant over the long term. Evaluating measures and examining the variability associated with long-term change is useful because it increases our understanding of and our ability to predict responses to disturbances. We used long-term fish community data from Aravaipa Creek, Arizona, USA, a Sonoran Desert stream, to determine whether there had been long-term changes in the community composition, what measures best describe these shifts, and what environmental factors are correlated with the changes. Aravaipa Creek is an intrinsically variable system and one of the few remaining desert streams to support its complete historical assemblage of native fishes. Multivariate analyses illustrated important, changes in composition of the native fish community that were not described by traditional measures of persistence and stability. In the early 1980s, changes in community composition were correlated with alterations in base flow, while more recent changes are likely associated with the presence of exotic species. Changes in stream morphology, hydrology, and climate have decreased flow variability, thereby increasing the likelihood of exotic establishment, and may have increased the downstream connection between Aravaipa Creek and the San Pedro River thus increasing the likelihood of repeated invasions by normative species. These results support previous research in intrinsically variable desert systems, which conclude that retention of high flow variability is important to conservation of the native fish community. In addition, although connectivity in aquatic lotic systems is important, isolation from large river systems teaming with exotics may be important in preserving these remnant native fish assemblages.