Abundance and Distribution of Heterelmis cf. glabra (Coleoptera: Elmidae) within Dolan Falls Preserve and the Devils River State Natural Area, Texas, USA

Abstract

The Devils River watershed in south-central Texas has baseflows entirely attributable to groundwater primarily sourced from the Edwards-Trinity and Edwards Aquifers. The largest known populations of a species of riffle beetle, Heterelmis cf. glabra, are located in springs associated with the upper Devils River. The focus of this study was to 1) determine site-level abundances of H. cf. glabra using open system N-mixture models, 2) test mesohabitat associations of members in the riffle beetle family Elmidae and, 3) measure and examine abiotic and habitat associations for adult and larval beetles within the study area. We sampled 32 spring sources to determine occupancy and abundance of adult and larval riffle beetles (Elmidae) within the study area. Spring sources were mapped and categorized by type (orifice, upwelling, group of springs, or seep). Basic water chemistry and flow rate categorization were also performed at each site. Model results suggest that rainfall, flow and site are important for detection of H. cf. glabra. Based on our results, regular monitoring of these 32 sites using these methods, is recommended to conduct hypotheses tests on covariates influencing abundance. Such baseline information will be important in measuring impacts to this and other spring-associated species as the habitats of this region are impacted by natural or anthropogenic phenomena.