What Is The Role Of Isolation And Disturbance On The Diversity Of Aquatic Invertebrates In Former Ranchlands Of The Northern Chihuahuan Desert?

The Chihuahuan Desert is considered one of the most diverse deserts in the world and its aquatic systems have been identified as unique and of global importance. Despite this, the Chihuahuan Desert has remained relatively unstudied, especially concerning its aquatic systems and how the extreme desert environment has shaped the diversity of the organisms within them. In this study we examined the effects of isolation and disturbance on macroinvertebrate diversity in both temporary and permanent desert ponds. To examine the effects of isolation and desiccation, macroinvertebrates were collected from a permanent spring (Squaw Spring) and six nearby temporary ponds (tanks) over a five-month period following the summer monsoon. Macroinvertebrate diversity in the tanks was found to become more similar to the Spring as hydroperiod increased and tanks with shorter hydroperiods were found to contain higher numbers of passive dispersers, such as Diplostraca and Anostraca, who utilize diapausing eggs to survive desiccation. A drop in species richness, experienced by tanks in the month prior to their total desiccation, was attributed to taxa, such as Ephemeroptera, emerging from the tanks in search of more ideal habitat, such as the Spring. Decreasing depth and increasing total phosphorus, ammonia, and dissolved organic carbon were all identified as possible cues for dispersal from drying tanks. To understand the impact of disturbance, such as drought and flooding, on desert water bodies, macroinvertebrate diversity was examined at Squaw Spring in four years between 2002-2011, including two years with average annual rainfall, one dry year, and one wet year. Long-term changes in macroinvertebrate community composition were found to be driven by the interactions between both drought and flooding with specific taxa being associated with either wet, dry, or average years. We conclude that more research is needed to understand the patterns of diversity in these unique ecosystems