Invertebrate community structure and habitat associations in the arid Davis Mountains region of West Texas
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In arid regions, springs often represent ecologically important aquatic habitats which are patchily distributed across the landscape. This separation can lead to localized endemic populations of organisms that exhibit small species distributions and are adapted to local environmental conditions. Desert spring aquatic organisms are also frequently of high conservation priority and are listed as imperiled and in need of protection. This study examined invertebrate community structure and habitat associations at seven sites in and around the Davis Mountains in the Trans Pecos region of west Texas. The overall purpose of this study was to determine mesohabitat associations and estimate population sizes of three endangered aquatic invertebrates found in the region: the Phantom springsnail (Pyrgulopsis texana), the Phantom tryonia (Tryonia cheatumi), and the diminutive amphipod (Gammarus hyalleloides). I conducted stratified random sampling at all sites quarterly for a year starting in March of 2017. Results indicate that the abundance of most of the endangered species was most strongly influenced by site (the particular location that was sampled) and that mesohabitat conditions were substantially less important in influencing the density of species. In addition, I found that two species of non-native and invasive snails (Melanoides tuberculata and Tarebia granifera) were found at most of the study sites sometimes at densities higher than populations of native invertebrates. These results suggest that regionally distributed invertebrates with low dispersal potential (such as snails and amphipods with no desiccation-resistant life stages) exhibit high site-specific occurrence. In addition, these results indicate that conservation of these populations in the wild should focus on site-specific objectives to preserve water quality and habitat conditions. However, this management strategy is complicated by the fact that these spring systems are interconnected by a larger regional groundwater pool. With agricultural demands and oil and gas development increasing in the Trans-Pecos region, the risk for groundwater over-pumping and contamination place individual and collective regional populations at risk.