Ecology of the hermit beetie (Osmoderma eremita) in Mediterranean woodlands

Abstract

One of the most endangered assemblage of species in Europe is represented by saproxylic beetles associated with old trees, as this habitat has decreased severely in Europe during the last 200 years. This thesis contains the first quantitative studies of the population status, the habitat characteristics and the dispersal patterns of Osmoderma eremita in Mediterranean woodlands, at the southernmost limit of its distribution range, i.e. central Italy. Pitfall traps, associated with visual encounter surveys, resulted to be the optimal method to assess the species presence and to obtain reliable population size estimates. Differently from northern Europe, where the demographic structure of this species has been explained by the metapopulation approach, at the southernmost limit of its distribution range a single hollow tree may host only a reduced number of individuals, which do not represent a population in itself, and a single population is widespread on the landscape. The frequency of presence was higher in cavities with more than 4 l of wood mould, in cavities with dry or half-moist wood mould rather than wet wood mould, and with a low soil contamination. A comparison with northern regions indicated that the warmer macroclimatic conditions in the south made the species independent on sun exposure. As most of the hollow trees contained only a small amount of wood mould (< 4 l), the habitat quality was generally poorer than in the oak pastures studied in northern Europe. Telemetered beetles spent their life time not only inside hollow trees but also in other habitats, such as on the ground surface and under the ground level. Beetles were more active at the beginning of the season. Even though 81% of the males and 69% of the females conducted dispersals during their life-time, the dispersal distance over individuals’ life-time did not differ between sexes. The longest dispersal was conducted by a female that moved 1504 m, and power function predicts that 9.7% of beetles move distances farther than 1600 m. Both dispersal rate and range are higher than what has been found in northern Europe. Since the population size per tree is low, the habitat quality is generally poor and a high predation rate (at least 28%) was observed in dispersing beetles, conservation efforts for this species should not focus on preserving few and isolated monumental hollow trees, but should be extended to large stands.