Ongoing recovery of a brown bear population from a century-old severe bottleneck: insights from population genetic and spatially explicit analyses

Abstract

By the beginning of the twentieth century, many brown bear populations in Europe were on the brink of extinction due to relentless hunting pressure and habitat loss. The situation was critical also in Estonia, where in the 1920s the population went through a severe demographic bottleneck. Thanks to the protective measures implemented in the 1930s, the population started to recover. However, the process has been slow, especially in the western and southern areas of the country. To study the effects of the demographic bottleneck, we analysed 216 brown bear samples from throughout their main range in Estonia. In combination with widely used methods of population genetics, a recently developed spatially explicit analysis (distribution of residual dissimilarity, DResD) was also applied. Three genetic clusters were revealed, of which two were most likely founded by the survivors of the bottleneck. The DResD analysis revealed several contact zones near the Estonian-Russian border, suggesting that the third cluster was influenced by gene flow from the neighbouring population in Russia. The DResD analysis revealed also a male biased movement corridor along the forested south-north axis in the central part of Estonia. In comparison to other European populations, the genetic diversity of the Estonian population is relatively low and is comparable with other populations that have gone through a severe bottleneck. This work has important implications for brown bear conservation and highlights once again the dangers of excessive hunting.