DIVERSE EFFECTS OF FOREST FRAGMENTATION ON A NUMBER OF ANIMAL SPECIES

Since 1990 we have initiated a number of studies on the population eco logy, population genetics and social organization of several animal sp ecies in forest fragments of varying sizes. Study species include squi rrels, small passerines and butterflies. Study sites are forest fragme nts between 1 and 40 ha, and study plots in ''continuous'' forest of 1 00 to 1500 ha. Our results so far suggest that forest fragmentation ha s more profound effects on dispersal patterns and population structure than on reproductive output and survival. Effects on dispersal includ e at least two aspects, which are not necessarily found in the same sp ecies. First, immigration deficits may be caused by low disperser succ ess and/or source-sink effects. Second, reduced gene flow among local populations may result in genetic differentiation and/or loss of genet ic variation. Negative consequences of the latter are not obvious, but indirect effects may be important e.g. for local adaptation. We concl ude that studies on population structure in fragmented habitats should include quantitative (dispersal distance, immi/emigration, genetic st ructure) as well as qualitative aspects (timing of dispersal, habitat selection).