Seasonal dynamics and micro-climatic preference of two Alpine endemic hypogean beetles

Hypogean beetles generally live in stable environments, characterized by constant temperature and high relative humidity. Changes in the underground microclimatic conditions generally induce local migrations of the beetles through the hypogean environment in search of suitable microhabitats. We studied the seasonal dynamics and the micro-climatic preference of two Alpine endemic hypogean beetles - Sphodropsis ghilianii (Coleoptera, Carabidae) and Dellabeffaella roccae (Coleoptera, Cholevidae) - in the hypogean complex of Pugnetto (Graian Alps, Italy). We surveyed the two species for one year, using baited pitfall traps and measuring temperature and humidity along the two main caves. We used logistic mixed regressions models (GLMMs) to relate the presence of the two species to several environment variables, namely microclimatic variables (seasonality, temperature and humidity) and different cave features (subjacency, cave length). In addition, we tested the attractive power of the bait on the two species. The thermic optimum for S. ghilianii was found to be around 7°C, with an increasing probability of finding the species in the vicinity of the cave entrance during summer, autumn and spring. The species migrates inside the cave in winter, in response to the drop in the mean daily temperature and in the relative humidity occurring in the outer parts of the cave. On the contrary, D. roccae showed a significant preference for the deeper sections of the cave, characterized by an almost constant temperature of 9°C in air saturated with water vapour. Males and females individuals of both species were found to be equally affected by the environmental variables included in the analysis. We also provided information on the life history of the two species and methodological insights about the use of the bait in the traps.