Identifying national responsibility species based on spatial conservation prioritization

The concept of National responsibility species (NRS) was developed to coordinate the conservation efforts of species occurring in multiple countries. Calculated as the fraction of the global species' distribution within a country, it measures the contribution of a local population to global survival of the species. However, there may be more co-occurring species in one region than another, making the conservation of a species more cost-efficient in the first than the latter. If cost-efficient resource allocation is the goal, then identifying NRS should also be based on spatial priorities. We propose that a species is considered NRS when a large part of its distribution falls within high priority areas in a country. We identify NRS from spatial conservation prioritization outputs to (1) maximize the overall cost-efficiency of allocation of conservation resources and (2) to provide information about which species the spatial priorities are based on. We analyzed data on vertebrates in the Birds and Habitats directives in the EU28 countries and compared the traditional NRS measure to three alternative strategies. While the majority of species maintained their NRS status in most countries regardless of the approach, differences occurred, with varying numbers and identities of responsibility species in a country, or responsibilities for species shifting between countries. The differences were largest in geographically marginal countries and for species that were distributed across a few countries. Other NRS approaches may also be useful, and the choice of approach should ultimately depend on the purpose and complement information on conservation status in decision-making.