Population viability analysis of European bison populations in Polish and Belarusian parts of Białowieża Forest with and without gene exchange

European bison (Bison bonasus) became extinct in the wild at the beginning of the 20th century. The contemporary Lowland line of bison was founded by seven individuals that survived in captivity. The largest population of Lowland bison live in the Białowieża Forest, but the forest and the population are divided by a border fence between Poland and Belarus. This fence is a barrier to the movement of ungulates. In this study, we used population genetic models to predict the future viability of the Polish and Belarusian bison populations. We determined the founder contribution, founder equivalent, mean inbreeding coefficient, mean kinship, and the proportion of genetic diversity retained in the Belarusian bison population. Although the founding group of the Belarusian population was larger than that of the Polish population, the latter had more favourable genetic parameters. We assessed inbreeding depression for fecundity in free-ranging European bison compared to captive individuals. Using population viability analysis (PVA) we modelled both bison populations with or without gene exchange, and with or without incorporating the kinship of the founders. When founder kinship was included, in both populations the mean number of alleles and the gene diversity retained within extant populations decreased substantially compared to PVA models in which founders were not related. The worst genetic parameters were obtained for the Belarusian population under a scenario in which the founders are related and gene exchange is lacking, which is the closest to the real situation. Creation of passages for animals by partial removal of the border fence would have a favourable effect on the genetic variation and viability of both bison populations, especially the Belarusian.