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Estimate of the seed shadow created by the Asiatic black bear Ursus thibetanus and its characteristics as a seed disperser in Japanese cool-temperate forest


S. Koike, Tokyo Univ. of Agriculture and Technology, 3-5-8 Saiwai, JP–183-8509 Fuchu, Japan. E-mail:


We estimated the seed shadow created by the Asiatic black bear Ursus thibetanus in order to evaluate the bears effectiveness as a seed disperser. We combined data from bear movements, determined by GPS telemetry, with data from gut retention time (GRT). We estimated plant seed shadows in two ways: from direct movement data to give the actual seed shadow (ASS), and from cumulative movement data to give the potential seed shadow (PSS). The purpose of this study was to answer the following questions: (1) does GRT differ between seasons or in the size of contents? (2) Does seed shadow vary among sex, seasons, estimation method (ASS or PSS), and years? (3) Does the masting affect seed shadows? There were no differences in median GRT among seasons or seed dimensions. Combining these data, the seed shadows produced by long GRT (median; 15.2–19.7 hours, maximum; 44.0 hours) and large daily movements suggest that the bears effectively move 40% of the seeds they consume to a distance greater than 500 m from the parent tree and can potentially move the seeds up to a maximum distance of more than 22 000 m from the parent tree. The results also indicate that bears make complex seed shadows caused by multiple defecations and long periods of daily movement. In summary, PSS did not differ between sexes, but PSS can be expected to be larger in autumn than in summer of each year. ASS, however, can be expected to be larger in males than females, and to be larger in autumn than in summer. ASS may become especially large during a poor masting year as compared to good masting years. These results indicate that bears are potentially more effective seed dispersers during years of poor fruit production in autumn. The bears have longer seed shadows than other seed disperser and consequently may play a unique role in the maintenance and renewal of forest ecosystem.