The equilibrium theory of island biogeography has become a conceptual pillar of conservation biology. However, empirical data on species diversity in agricultural and seminatural areas and in fragmented forests often do not match the expectations of island biogeography. The mosaic concept is an alternative approach to explain species numbers in habitat patches of cultural landscapes.
lt is based on the assumptions !hat species numbers increase with habitat diversity (number of habitat types per unit area) and with habitat heterogeneity (number of mosaic patches per uni! area). In metacommunities (communities of metapopulations) of cultural landscapes, where habitat suitability rather than immigration is the limiting factor for most species, fragmentation may increase survival time for a majority of species. Metapopulation dynamics allow for temporary local extinctions, which enables other, less competitive species to occupy vacant habitats. Furthermore, a mosaic landscape offers a variety of ecotone structures between habitat patches, which are inhabited by ecotone specialists. Habitat diversity and heterogeneity also favor species which depend on habitat changes during development, for hibernation, or even for their daily activities.