| Southwestern desert anurans live in extreme habitats predicted to experience increased drought and precipitation variability. Desert anurans utilize temporary pools for breeding during annual monsoon seasons. How desert anurans relate to habitat features and respond to changes in water quality are not well understood. I surveyed five desert anuran species to determine occurrence, how anurans relate to environmental gradients, and elucidated responses of Spea multiplicata and Scaphiopus couchii eggs and tadpoles to combinations of pH levels with and without UV-B exposure.;This dissertation includes four chapters. Chapter one is an overview of the subsequent research. In chapter two, I determined occurrence accounting for imperfect detection using repeated surveys and covariates hypothesized to influence detectability. Occupancy models confirmed detection varies among species. Spea multiplicata, S. bombifrons, and Sc. couchii were more detectable on the first night following a rain event, Anaxyrus cognatus were more detectable during warm nights, and A. debilis detection was constant. Spea multiplicata and A. debilis had the highest occurrence across sites, followed by A. cognatus, S. bombifrons, and Sc. couchii. In chapter three, I related anuran community structure to environmental gradients. Spea bombifrons associated with tall grasses/forbs, shrubs/trees, and elevated dissolved oxygen; Sc. couchii related to tall grasses/forbs and warmer water; A. cognatus associated with warmer air temperature and larger breeding sites, while S. multiplicata and A. debilis had general affinities to environmental gradients. In chapter four, I assessed effects of pH (5.25-9.25), UV [filtered (UVF) and transmitted (UV-B)], and interactive effects on egg hatching success, tadpole growth, and survival on S. multiplicata and Sc. couchii. Spea multiplicata eggs tended to have reduced hatching in UV-B treatments, and survival was reduced in low pH with UV-B. Spea multiplicata growth response favored low pH (5.25), but survival improved with increasing pH. For Sc. couchii, no eggs hatched in pH 5.25, while growth and survival improved in pH 8.25. My research confirms the complexity of southwestern deserts regarding their species-specific habitat preferences and responses to an extreme pH gradient with and without UV-B. Further shrub encroachment or climate change in the southwest could cause significant shifts in anuran composition. |
