Effects of forest fragmentation and local habitat structure on densities of winter moth (Operophtera brumata L.)

We study the effects of habitat fragmentation (habitat area, isolation, distance from forest edge) and local habitat structure (size and phenology of host tree and density of herb cover) on winter moth densities in oak forests near Antwerp, N. Belgium, focussing on both effects simultaneously and comparing males and females. In this way, we can study how adult dispersal strategies - active male flight vs. flightless females - affect the distribution of individuals. The analyses show that both the degree of fragmentation and local habitat structure affect moth densities and that the effects differ between males and females. Failing to correct for sex-differences and for various aspects of local habitat structure would have lead to the conclusion that there were no effects of fragmentation on winter moth densities. Thus, structured populations in which dispersal rates vary between individuals need careful evaluation of the effects of fragmentation, separately for the different groups of individuals.