Local hot spots and their edge effects: small mammals in oak-hazel woodland

Much recent work on biodiversity conservation has focused on concentrations of species and individuals. Little understanding has yet emerged for important structures and processes at such diversity hot spots. Here I examine small mammal distributions in relation to local food surplus in order to reveal factors that affect community composition and to pose relevant questions for exploring more general relationships governing species abundances in and around various types of hot spots. Small mammal species and numbers in small groves of mast seeding deciduous trees depended on occurrences in the poorer surrounding matrix. One specialist and one generalist granivore as well as an insectivore showed peak numbers simultaneously, one year after peak food supply. Other congeneric granivores and insectivores were attracted by the seed surplus area but showed inverse habitat distributions at the border towards the matrix. The edges of the groves functioned as refugia rather than as eliminators of the animal surplus in situations of food decline. A species with limited movement ranges demonstrated pronounced edge effects in distribution and survival while a far-ranging species moved fairly evenly over the surplus site and large areas of adjoining matrix. Only immature individuals of the latter species showed a clear edge effect. Habitat composition at the edge affected survival or dispersal more than reproduction. I finally present some general questions regarding patch-matrix interactions, on distributions of specialist and generalist species, of more and less mobile species, and on the refugial character of hot spots to be examined in other contexts, and for other species, in order to arrive at more definite generalizations.