The role of wetland habitat quality in evaluating functional connectivity for desert amphibians
In desert environments, amphibian reproduction is restricted to and limited by a dynamic and unpredictable network of small, isolated, ephemeral water sites. Desert amphibians appear to be somewhat plastic in their breeding site selection as long as the wetlands are within their seasonal migration distance. Further, these wetlands are important refugia for dispersing amphibians and support gene flow between isolated populations. Establishment of anthropogenic water sites for target species other than amphibians (e.g., game or federally listed) increases connectivity between potential breeding sites and populations. We explore how these anthropogenic water sites have improved structural connectivity of the landscape using graph theory for 117 water sites in southwestern Arizona, USA, and identify sites with the greatest connectivity potential. We then evaluate amphibian use of water sites using data from audio loggers (n = 13), game cameras (n = 22), and tadpole surveys (n = 26). Lastly, we merge this information to evaluate how our construction of artificial catchments is likely effecting desert amphibian populations.
The construction of water sites in the Sonoran Desert of southwestern Arizona has greatly increased the number of potential breeding sites and landscape-level connectivity between populations of amphibians such as Incilius alvarius, Scaphiopus couchii, and Anaxyrus punctatus. Within our study area, anthropogenic catchments and waters modified to extend hydroperiod played an important role in connectivity as five were included among the 10 most important stepping-stones, 10 most important hubs, and 2 cutpoints. Adult amphibians were recorded at the majority of sites sampled, both catchment and tinaja, using remote detection (game cameras and audio loggers). We found tadpoles at 87% of tinajas and 29% of the catchments sampled. Catchments with tadpoles were located < 5 km from natural waters. Structurally, natural waters and anthropogenic catchments were very different, which had drastic impacts on water quality. Ammonia concentrations in anthropogenic catchments were 10 times as high as the U.S. EPA's recommended criteria for freshwater life, based on pH and temperature ranges in the system, and well above toxic levels for other species. This work suggests that improved connectivity has attracted amphibians into breeding sites where tadpoles may not survive to become metamorphs. More research is needed to assess how land management practices for target wildlife may be creating ecological traps for non-target species.