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

Abstract

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. 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. 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. 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. 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 it accounts for ~7% of the total area within the designated critical habitat. These results also emphasize that habitat conservation plans for species at risk should consider that contemporary spatial distribution of species within habitats may be influenced not only by their evolutionary history but also by past and current human pressures. Copyright © 2015 John Wiley & Sons, Ltd.

Movement, demographics, and occupancy dynamics of a federally threatened salamander: evaluating the adequacy of critical habitat

“…While movement was frequent throughout the stream channel, overall abundances were highest near the spring outlet. This is consistent with previous observations for this and similar species ( Tupa & Davis, 1976 ; Sweet, 1982 ; Bowles, Sanders & Hansen, 2006 ; Pierce et al, 2010 ; Bendik et al, 2014 ; Diaz et al, 2015 ). However, the largest proportion of small juveniles was found 80 m downstream, at the limits of our study area and the subsequently updated critical habitat buffer ( US Fish and Wildlife Service, 2013 ).…”

“…Site occupancy within these stream reaches may also be predicted by other aspects of their habitat. Rock cover (RC) is an important habitat characteristic that is often correlated with presence and abundance of Eurycea ( Bowles, Sanders & Hansen, 2006 ; Pierce et al, 2010 ; Diaz et al, 2015 ). RC was measured as the mean of three visual estimates of the percentage of rocks available (i.e., unembedded) for cover (>8 mm) at the substrate surface.…”

“…Although a few collections of epigean (surface-dwelling) populations of Texas Eurycea have been from stream localities (e.g., Bishop & Wright, 1937 ; Milstead, 1951 ; Bruce, 1976 ), the predominant view has generally been that epigean populations are restricted to the vicinity of springs ( Sweet, 1982 ). This view may persist for several of the following reasons: (1) several high profile, single-site endemic Eurycea species do not occur far beyond their large, highly modified spring habitats (e.g., E. sosorum : Chippindale, Price & Hillis, 1993 ; E. nana : Diaz et al, 2015 ; E. waterlooensis : Hillis et al, 2001 ); (2) ease of collection and high abundances around springs make these areas obvious locations for ecological studies ( Sweet, 1982 ; Bowles, Sanders & Hansen, 2006 ; Pierce et al, 2010 ; Bendik et al, 2014 ); or (3) physiological, morphological, or behavioral adaptations indicate the importance of groundwater-associated habitats to their evolutionary history ( Stejneger, 1896 ; Sweet, 1978 ; Sweet, 1984 ; Chippindale et al, 2000 ; Bendik et al, 2013a ). This habitat restriction is in contrast to most other Eurycea species that occupy headwater streams (in addition to seeps and springs) as aquatic larvae and paedomorphs ( Petranka, 1998 ; Tumlison & Cline, 1997 ; Martin et al, 2012 ; Steffen et al, 2014 ).…”

Evaluating the impacts of small impoundments on stream salamanders

“…Therefore, these data suggest that small impoundments may play an important role in maintenance of stream salamander populations in an ecoregion characterized by ephemeral streams. This supports conclusions by others that habitat protection for salamanders is complex and requires attention to important habitats that are infrequently located and represent a small proportion of available habitat (Romano et al , ; Diaz et al , ).…”

The aquatic annelid fauna of the San Marcos River headsprings, Hays County, Texas

“…Despite its low taxonomic resolution, findings from this study suggested a remarkable amount of diversity, with twelve separate orders reported from the gut contents of this one species of fish. This diversity was verified by a subsequent diet study of the San Marcos salamander, Eurycea nana Bishop whereby numerous taxa (also largely hard-bodied forms), were reported from the SMR for the first time (Diaz 2010). …”