ENVIRONMENTAL AND BIOLOGICAL FACTORS INFLUENCING ANCIENT AND CONTEMPORARY AQUATIC LIFE IN SOUTHERN GREAT BASIN SPRING SYSTEMS’

Springs provide much of the aquatic environment in arid lands and a substantial portion of regional aquatic and riparian biodiversity. The region between Las Vegas, Nevada and the Sierra Nevada Mountains is characterized by a series of north-south oriented ranges and intervening valleys and includes some of the most arid parts of North America where most of the surface water is limited to spring systems. The geological evolution, ancient climates, aquatic connectivity with adjacent basins, and evolution of crenophilic species (obligatory spring-dwelling organisms) in this area have been active fields of research for decades. However, the complex web of interactions between these fields and the distribution of aquatic organisms within springs across the landscape remains unknown and a significant research challenge. Multiple parameters were found to have a significant relationship on crenobiontic distribution. However, geochemistry and water quality parameters played a larger role in crenobiontic distribution then physical habitat characteristics. Current benthic macroinvertebrate community structure within springs also had a significant relationship with crenobiontic species distribution. Although community structure has been traditionally described using species richness, such approaches present important limitations, since it assumes that all species contribute equally to biodiversity. In our study area, there was a negative relationship with species richness, spring water residence time, and crenophilic abundance, indicating that in older springs crenophilic species influenced the available niche space and therefore the community structure of the spring and reduced overall richness. Our data highlights the role of certain environmental processes not considered before in the distribution and composition of crenophilic species in spring environments.