Genetic population structure of the winter moth (Operophtera brumata L.) (Lepidoptera, Geometridae) in a fragmented landscape

As a result of human activities natural environments have been altered in many different ways. One important effect of human disturbance is the fragmentation of natural habitats. As a consequence, genetic differentiation among habitat islands is expected to increase, whereas within-area genetic diversity is expected to decrease. Indirect estimates from allozyme polymorphisms are used to investigate the effects of habitat fragmentation in the winter moth on a very small geographical scale. We demonstrated that genetic differentiation increased whereas genetic diversity decreased with fragmentation, with habitat patches isolated by only a few hundred metres up to 3 km. These results were even more striking considering that no genetic differentiation was detected at a larger scale (10–40 km). This pattern of distribution of genetic variation is in agreement with temporarily variable densities and gene flow levels which prevent an equilibrium being reached between genetic drift and gene flow. Consequently the effects of fragmentation probably remain limited.