Population biology and conservation of beetles and pseudoscorpions associated with hollow oaks

Sammanfattning: Many species associated with old trees are threatened, as this habitat has decreased severely in Europe during the last 200 years. In old oaks, hollows with wood mould often form in the trunks and these harbour a specialized fauna mainly consisting of beetles, flies and pseudoscorpions. This thesis contains the first quantitative examination of the habitat requirements and population ecology of species belonging to this fauna. The occurrence of many species were found to be correlated with tree characteristics related to the microclimate and the successional stage of the tree hollows. The species richness of beetles per oak was higher in plots that were originally open and were still grazed. Many species were harmed by forest regrowth and, thus, to preserve the rarer fauna in old oaks it is important to continue the management of pasture woodlands. The population dynamics were investigated on a certain species, Osmoderma eremita (Coleoptera: Scarabaeidae), within the framework set by metapopulation ecology. In O. eremita, the occupancy/tree was higher in larger stands than in smaller stands, but there was no correlation between occupancy/stand and isolation of stands. This suggests dispersal is important in the population processes within stands, but not between stands. O. eremita occurred in most of the larger stands and this probably mirrors the fact that the density of hollow oaks has been much higher in the area than today. A mark-release-recapture experiment on O. eremita was performed over five years. The population size in each tree varied moderately between years, whereas the population size variability in all trees combined was not larger than expected from sampling errors alone in a constant population. This indicates that the populations in each tree fluctuate independently of each other. The dispersals observed with mark-release-recapture occurred between trees situated 30–190 m from each other. As only a minor part of all dispersals are observed by mark-release-recapture, a simulation model was constructed to reveal the dispersal rate per individual. The model results suggest that 85% of the adults remain in the same tree throughout their entire life. This suggests that each hollow tree sustain a local population with limited connection with the populations in surrounding trees. Thus, the individuals of each tree could be seen as a local population, and the populations in all occupied trees in a stand together form a metapopulation. A study on the genetic structure was carried out on Allochernes wideri (Pseudoscorpionida: Chernetidae) and Larca lata (Pseudoscorpionida: Garypidae). Both occur in hollow trees, but L. lata is a rarer and more specialized species than A. wideri. Among trees within a stand, the genetic differentiation was low but significant in A. wideri, whereas in L. lata, it was not deviating significantly from zero. This suggests the migration rate between neighbouring trees is high, in particular in L. lata, and thus we can reject the hypothesis that the low habitat occupancy observed in L. lata would be an effect of a low dispersal rate.