METAPOPULATION PERSISTENCE OF AN ENDANGERED BUTTERFLY IN A FRAGMENTED LANDSCAPE

We describe an extensive metapopulation study on the Glanville fritillary Melitaea cinxia, in a network of 1502 discrete habitat patches, comprising the entire distribution of this butterfly species in Finland. A thorough survey of the easily detected larval groups revealed a local population in 536 patches (dry meadows). We demonstrate that this system satisfies the four necessary conditions for a species to persist in a balance between stochastic local extinctions and recolonizations. Patterns of patch occupancy support several qualitative and quantitative model predictions. With decreasing regional density and average area of habitat patches, the butterfly occurs in a diminishing fraction of suitable habitat. To our knowledge. this is the first conclusive demonstration, based on a comparison of many conspecific metapopulations, of declining habitat occupancy and hence of increasing threat to survival caused by increasing habitat fragmentation.