Dynamic and temporal structure of the troglobitic beetle Speonomus hydrophilus (Coleoptera: Bathyscimae)

The population ecology of the beetle Speonomus hydrophilus , occurring both in caves (reduced fluctuations in many abiotic parameters) and under the deepest layer of soil in mountains (MSS, more exposed to climatic variations), was studied in four habitats in the French central Pyrenees We have assessed some of the characteristics of the environment where these populations occur c g physical data (altitude and exposure), geologic data (nature of the parent-rock) and abiotic parameters (temperature with its seasonal fluctuations) and we investigated the relative importance of environmental structure and ecological characteristics on the temporal organization of S hydrophilus and the troglobitic fauna which cohabits The climatic study shows the existence of an annual thermal cycle which is regular and well marked for the MSS habitats but slightly out of phase with the surface cycle These periodic variations however slight may be stressful for troglobitic species In the MSS populations, the phenology of the entire community is reflected in the pattern seen in Speonomus The analysis of faunal profiles shows that samples follow the same seasonal succession during the annual cycle A potential seasonal rhythm of emergence may reflect a seasonal rhythm of vitellogenesis which produces a rhythm of egg-laying