Connectivity or isolation? Identifying reintroduction sites for multiple conservation objectives for wisents in Poland

Abstract

Large herbivores and carnivores today often only occupy small fractions of their former ranges, and restoring them is a conservation priority. Reintroductions may serve two critical goals in this context: (1) to expand and connect existing populations, or (2) to increase the number of separate populations as insurance in case individual populations are lost, for example, to disease. We developed an approach to identify reintroduction sites for both purposes, using an applied example of European bison or wisent (Bison bonasus) in Poland. Using a large occurrence dataset from all extant herds in Poland, we mapped suitable wisent habitats throughout Poland using a species distribution modelling approach. We identified 47 patches of suitable habitat, together covering 20,710 km2, and used graph theory tools to identify the top candidate reintroduction sites for (1) connecting existing herds into larger metapopulations or (2) establishing ‘reservoir’ herds that could serve as a backup in case of mass die-offs. The most well-connected habitat patches ranged between 203 and 728 km2 and occurred mainly in north-western and south-eastern Poland, in close vicinity to other free-ranging herds. In contrast, candidate sites for reservoir herds were smaller (204–410 km2) and occurred mainly in central Poland. Our approach provides a possible blueprint for wisent reintroductions in Poland. More broadly, our work also highlights how jointly planning for multiple conservation goals for wide-ranging species that depend on reintroductions or translocations can be achieved at the regional scale.