Community Ecology of Stream Fishes: Concepts, Approaches, and Techniques

<em>Abstract</em>.—Timing of reproduction differs among fish species in nearly all rivers, and reproductive phenology is predicted to strongly influence freshwater fish community structure in some systems. Despite its potential importance, few long-term studies of reproductive phenology in river fishes have been conducted in a community context. Here, we evaluated timing and sequence of reproduction of fishes in the Rio Grande, New Mexico over 9 years. Dates and rank order of first appearance of larvae varied among species and years, but three consistent spawning guilds were evident: early season, late season, and species that were intermediate in rank order of spawning. We hypothesized that appropriate reproductive timing enhanced recruitment to the extent that spawning cues predicted future availability of critical resources for larvae. Analysis of historical discharge records indicated that present and future discharge exhibited positive autocorrelation for up to 90 d. Likewise, larval fish densities were highest at moderate flows and coincident with high food resource abundance. However, stable isotope data for larval and adult fishes indicated considerable overlap in food resource use among larvae and adult fishes. There may be pressure for spawning time to converge among species to match the appearance of seasonal resources, but to diverge to lessen competition among young-of-year fishes in a classical trade-off scenario. More long-term studies are needed, and we propose that an integrated research program that combines detailed analysis of reproductive phenology, food web dynamics, and comparative genomic analyses could forge connections between environmental variation in spawning cues, recruitment success, and community assembly in river fishes. Such an integrated program could lead to better predictions about fish community responses to global warming, especially in vulnerable arid-land systems like the Rio Grande.