Abstract 58 – Males disperse, females remain: revealing the dispersal patterns of Asian black bears through genetic analysis

Naoki Ohnishi, Kahoko Tochigi, Tomoko Naganuma, Shinsuke Koike, Koji Yamazaki,
Takeshi Osawa

It is commonly believed that about 95% of mammal species exhibit male-biased dispersal and
females' philopatry, but few species have been studied to confirm this difference in dispersal
systems, especially in large species where it is difficult to track their movements or obtain
sufficient sample sizes. This presentation introduces our genetic studies that used genetic
methods to elucidate the dispersal patterns and seasonal movements of Asian black bears
(Ursus thibetanus).
We estimated parentage using DNA from 550 captured individuals and found that there was a
3.6-fold difference in mean dispersal distance between males and females. Also, 96% of males
dispersed from their natal area, while half of females remained in their mother's home range.
Furthermore, we found that the timing of male dispersal was at 3 years of age.
The female's site fidelity results in a geographic cluster of matrilines, which disappears
temporarily during autumn when there is a shortage of acorns but re-establishes the same
structure the following spring.
As Asian black bears breed during the summer, any temporary autumnal movements are not
expected to affect the genetic structure of the next generation. Female site fidelity is also
suggested by landscape genetic analysis. Not only anthropogenic environments such as
farmland and residential areas, but also natural open areas such as wetlands and bare land,
impede female movement and create a "landscape of fear" for female bears.