Metapopulation theory considers that the populations of many species are fragmented
into patches connected by the migration of individuals through an interterritorial matrix. We applied
fuzzy set theory and environmental favorability (F) functions to reveal the metapopulational
structure of the 222 butterfly species in the Iberian Peninsula. We used the sets of contiguous grid
cells with high favorability (F ≥ 0.8), to identify the favorable patches for each species. We superimposed
the known occurrence data to reveal the occupied and empty favorable patches, as unoccupied
patches are functional in a metapopulation dynamics analysis. We analyzed the connectivity
between patches of each metapopulation by focusing on the territory of intermediate and low
favorability for the species (F < 0.8). The friction that each cell opposes to the passage of individuals
was computed as 1‐F. We used the r.cost function of QGIS to calculate the cost of reaching each cell
from a favorable patch. The inverse of the cost was computed as connectivity. Only 126 species can
be considered to have a metapopulation structure. These metapopulation structures are part of the
dark biodiversity of butterflies because their identification is not evident from the observation of
the occurrence data but was revealed using favorability functions
