METAPOPULATION PERSISTENCE OF AN ENDANGERED BUTTERFLY IN A FRAGMENTEDLANDSCAPE

We describe an extensive metapopulation study on the Glanville fritill ary Melitaea cinxia, in a network of 1502 discrete habitat patches, co mprising the entire distribution of this butterfly species in Finland. A thorough survey of the easily detected larval groups revealed a loc al population in 536 patches (dry meadows). We demonstrate that this s ystem 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 quantita tive model predictions. With decreasing regional density and average a rea of habitat patches, the butterfly occurs in a diminishing fraction of suitable habitat. To our knowledge. this is the first conclusive d emonstration, based on a comparison of many conspecific metapopulation s, of declining habitat occupancy and hence of increasing threat to su rvival caused by increasing habitat fragmentation.