Metapopulation dynamics of the bog fritillary butterfly: comparison of demographic parameters and dispersal between a continuous and a highly fragmented landscape

We investigated the effects of habitat loss and fragmentation on population functioning. We compared demography ( daily and total population sizes) and dispersal ( dispersal rate and dispersal kernels) of the bog fritillary butterfly in two 6-km(2) landscapes differing in their degree of fragmentation. In 2000, we conducted a Capture-Mark-Recapture experiment in a highly fragmented system in the marginal part of the species distribution ( Belgium) and in a more continuous system in the central part of its distribution ( Finland). A total of 293 and 947 butterflies were marked with 286 and 190 recapture events recorded in the fragmented and the continuous system respectively. Our results suggest that habitat loss and fragmentation affect dispersal more than demography. Although density was lower in the continuous system, it remains in the yearly range of variation observed on 10 generations in the fragmented system. However, in the fragmented system, the dispersal rate dropped drastically (39 vs. 64%) and females moved longer distances. Patch area had a significant effect on migration in the fragmented system only. From our results, we propose the definition of a new parameter, the minimal patch area (MPA) needed to establish a local population in highly fragmented landscapes.