Abstract 236 – Population sex structure and recolonization in the Norwegian brown bear

Pierre Dupont, Cyril Milleret, Richard Bischof

1.Population recovery can be a drawn-out process, characterized not only by growing
abundance and expanding range, but also changes in demographic structure. Due to sex
differences in vital rates and dispersal propensity, we expect significant changes in the
population sex structure during population recovery.

2.In Scandinavia, intensive persecution brought the brown bear population to the brink of
extinction in the 1920s. Since then, protective measures and sustainable management have
allowed the brown bear to reclaim much of its former range. In Norway, recolonization started
around the 1970s from areas with higher bear densities in neighboring Sweden, Finland, and
Russia.

3.Using an extensive long-term monitoring dataset and a spatially-explicit population dynamic
model, we estimate and map sex-specific brown bear densities in Norway over the last 11
years. We show how sex ratio evolved over time and demonstrate the decades-long delay in
recovery of this important demographic variable.

4.Due to female philopatry and primarily male-driven dispersal, male-biased sex-ratio
characterized the early stages of the recovery, which was followed by an increase in female
abundance. The speed by which balanced sex-ratio was reached depended strongly on the
distance from the population source.

5.Our findings reveal the important role that of sex differences dispersal and life history play in
shaping the demographic structure and spatio-temporal dynamics of recovering wildlife
populations.