GENETIC POPULATION-STRUCTURE OF THE WINTER MOTH (OPEROPHTERA-BRUMATA L.) (LEPIDOPTERA, GEOMETRIDAE) IN A FRAGMENTED LANDSCAPE

ks 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 diffe rentiation among habitat islands is expected to increase, whereas with in-area genetic diversity is expected to decrease. Indirect estimates from allozyme polymorphisms are used to investigate the effects of hab itat fragmentation in the winter moth on a very small geographical sca le. We demonstrated that genetic differentiation increased whereas gen etic diversity decreased with fragmentation, with habitat patches isol ated 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 gen e flow levels which prevent an equilibrium being reached between genet ic drift and gene flow. Consequently the effects of fragmentation prob ably remain limited.