A species with a strong influence in one ecological community may have a limited influence under other environmental conditions, but the factors determining the strength of species interactions are often unclear. Fish control important characteristics of many stream systems. Native fishes of the American southwest are ideal for testing the influence of abiotic and biotic factors on species interactions because single species are broadly distributed throughout a heterogeneous landscape of hot deserts and cool mountains. Native fishes are declining in these streams; thus, understanding the effects of their loss is vital.
To assess how environmental context affects species interactions in Southwestern streams, this study will investigate the influence of two related, but functionally different fish species, Catostomus insignis and Catostomus clarki, on ecosystem processes along an elevational gradient. This gradient will enable examination of the effects of these species on critical stream processes such as primary production and organic matter generation under conditions ranging from warm water, low desert streams to cool water, high mountain streams. Using large-scale enclosures controlling fish identity in a single stream combined with small-scale fish exclosures in multiple streams, this study will estimate the effects of fish on ecosystem properties, and assess how environmental context modifies them. The project also will track fish habitat use to understand if effects on ecosystem processes are heterogeneous within the stream. Understanding the factors modifying species importance in ecosystems will provide information particularly valuable for management agencies, which must develop sustainable practices to use and protect these ecological resources.
