Timing and distance of natal dispersal in Asian black bears

Abstract

Dispersal has important implications for population ecology and genetics of a species through redistribution of individuals. In most mammals, males leave their natal area before they reach sexual maturity, whereas females are commonly philopatric. Here, we investigate the patterns of natal dispersal in the Asian black bear (Ursus thibetanus) based on data from 550 bears (378 males, 172 females) captured or removed in Gunma and Tochigi prefectures on central Honshu Island, Japan in 2003–2018. We used genetic data and parentage analysis to investigate sex-biased differences in the distance of natal dispersal. We further investigated the age of dispersal using spatial autocorrelation analysis, that is, the change in the correlation between genetic and geographic distances in each sex and age group. Our results revealed that male dispersal distances (mean ± SE = 17.4 ± 3.5 km) were significantly farther than female distances (4.8 ± 1.7 km), and the results were not affected by years of mast failures, a prominent forage source for this population. Based on an average adult female home range radius of 1.8 km, 96% of the males and 50% of the females dispersed. In the spatial autocorrelation analysis, the changes in the relationship between genetic and geographic distances were more pronounced in males compared to females. Males seem to mostly disperse at age 3 regardless of mast productivity, and they gradually disperse far from their home range, but young and inexperienced males may return to their natal home range in years with poor food conditions. The results suggest that factors driving the dispersal process seem to be population structure-based instead of forage availability-based. In females, a significant genetic relationship was observed among all individuals in the group with a minimum age of 6 years within a distance of 2 km, which resulted in the formation of matrilineal assemblages.

Maternal den site fidelity of polar bears in western Hudson Bay

“…This observed fidelity may be due to philopatry, on-ice spatial fidelity, and a tendency to travel a similar distance in-land once returning to shore. Spatial fidelity of female ursids to the general area of their birth site is in part associated with higher levels of philopatry in females than in males (Manchi & Swenson, 2005; Roy et al ., 2012; Takayama et al ., 2023). Similarly, philopatry in polar bears appears common across both sexes (Derocher & Stirling, 1990; Paetkau et al ., 1999; Zeyl et al ., 2010) but may be lower in males that move across subpopulations more often (McGeachy et al ., in press).…”

Demographic Parameters of Asian Black Bears in Central Japan

“…Photographically captured bears were identified based on the information obtained from GPS collars, ear tags, chest mark patterns, and DNA sequence data from hair-snare traps that were placed with the camera traps. Details on the methods used for identifying individuals based on DNA can be found in Takayama et al (2023). For identified female bears, we recorded whether they were accompanied by cubs-of-the-year.…”