Mesohabitat associations of the threatened San Marcos salamander (Eurycea nana) across its geographic range

1. Habitat loss is one of the most critical factors affecting the loss of species. However, habitat conservation of many threatened species is performed with incomplete information on habitat requirements and trophic ecology, thus presenting a challenge to designing and implementing recovery plans. 2. The San Marcos salamander (Eurycea nana) is a federally threatened spring‐associated organism whose geographic distribution is limited to the headwaters of the San Marcos River in Texas, USA. Although its designated critical habitat includes the headwaters and the first 50 m of the river, little is known of its habitat requirements or co‐occurrence with benthic macroinvertebrates and macrophytes. 3. This study examined mesohabitat associations of the salamander and patterns of co‐occurrence with macrophytes and benthic invertebrates within its critical habitat. Surveys of mesohabitat characteristics were conducted during a one‐year period and data were analysed to assess mesohabitat associations of the San Marcos salamander and patterns of co‐occurrence with invertebrates and macrophytes. 4. Salamanders were distributed throughout the critical habitat, but were almost exclusively found in mesohabitats containing cobble and gravel with coverage of Amblystegium and filamentous algae. The salamander did not exhibit consistent co‐occurrence with specific invertebrates or macrophytes across the critical habitat, indicating that salamanders were probably selecting mesohabitats based on benthic substrate and not the biotic communities. 5. Protection of a specific mesohabitat type within the critical habitat of the San Marcos salamander is likely to be one of the most important conservation measures, given that i