BIGGER MAY NOT BE BETTER: VOID SIZE OF HABITAT FOR TROGLOBITIC KARST INVERTEBRATES

Consistent and correct identification of karst invertebrate habitat is needed for protection of endangered species and ecological conservation, yet few studies have evaluated the effectiveness of the current habitat parameter guidelines. This analysis tested the relevancy of void size as a criterion for identification of troglobitic karst invertebrate habitat using logistic regression. Data were obtained from technical reports documenting habitat assessments and karst invertebrate detections by USFWS-permitted scientists performing surveys on construction sites in northern San Antonio, Texas. Void size was approximated by calculating a volume estimate for each karst void, and successful habitat identification was defined as detection of a common troglobitic karst invertebrate, the silverfish Texoreddelia sp. No statistically significant relationship was found between void size and troglobite occupancy. This indicates that surveyors should not rely on a minimum void size to define habitat, and that even very small void spaces should be evaluated for potential habitat.

It is intuitive that karst invertebrates whose bodies are only a few mm in width and length need voids only a few mm in diameter to travel. These species probably need interconnected cavities to forage and reproduce. Interconnected cavities are also important as conduits for water and nutrients to make their way from the surface to underground habitats. Current conservation strategies focus on cave entrances and cave passages that are large enough for humans to traverse, yet protection of smaller interconnected voids may be important for tiny species. Habitat conservation may be the best strategy for protecting karst invertebrates, and a successful strategy would rely on an effective protocol for identifying and delineating habitat. Nine karst invertebrate species are listed as endangered in San Antonio, and this discussion is relevant to USFWS protocols, field scientists, and interested citizens.