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

Abstract

We estimated the seed shadow created by the Asiatic black bear Ursus thibetanus in order to evaluate the bears eff ectiveness 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). Th e purpose of this study was to answer the following questions: (1) does GRT diff er 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 aff ect seed shadows? Th ere were no diff erences 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 eff ectively 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. Th e results also indicate that bears make complex seed shadows caused by multiple defecations and long periods of daily movement. In summary, PSS did not diff er 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. Th ese results indicate that bears are potentially more eff ective seed dispersers during years of poor fruit production in autumn. Th e bears have longer seed shadows than other seed disperser and consequently may play a unique role in the maintenance and renewal of forest ecosystem.

Prior reproduction and weather affect berry crops in central Ontario, Canada

“…However, recent work from Spain suggests that mammals, particularly carnivores, opportunistically exploit large fruit crops and can be important dispersers of endozoochorous seeds (Martínez et al 2008;Fedriani and Delibes 2009;Guitiàn and Munilla 2010;Matías et al 2010). Among North American carnivores, American black bears (Ursus americanus), brown bears (U. arctos), raccoons (Procyon lotor), coyotes (Canis latrans), red foxes (Vulpes vulpes), gray foxes (Urocyon cinereoargenteus), and American martens (Martes americana) are highly frugivorous and can be effective dispersers because they harvest fruits effectively, carry many seeds, may move several kilometers before depositing seeds, and deposit viable seeds (Willson 1993;Borchert and Tyler 2010; also see Koike et al 2010).…”

Exploring the potential of brown bear (Ursus arctos arctos) as a long-distance seed disperser: a pilot study in South-Western Europe

“…Like in Koike et al (2011), we simply estimated dispersal distances as the straight distances between two locations. However, taking into account animal activity and behaviour (Westcott et al 2005, Russo et al 2006) would help us better predict effective dispersal distances.…”

“…Traveset and Willson (1997) conclude their study on seed germination of fleshy-fruited shrubs by bears and birds by stating that "the advantages of animal seed dispersal lie more in seed movement away from the parent plant than in seed treatment within the disperser's guts". Koike et al (2011) estimated the seed shadow created by Asiatic black bear and did not check for seed germination rate in relation to GRT. Yet, we argue that future research should also focus on the germination rate of the seeds dispersed.…”

“…We used the median gut retention time (GRT min , GRT 50% and GRT max ) experimental assessments from Elfström et al (2013), who measured GRT on captive brown bears fed two contrasted seasonal diets, namely, carcasses or berries (Table 2). We then coupled the distances covered by our three selected individuals with the corresponding median GRT to assess potential seed dispersal distances (Koike et al 2011). …”

Fleshy fruit characteristics in a temperate deciduous forest of Japan: how unique are they?

“…Seeds dispersed by vertebrates are often transported long distances, likely enabling the population to expand distribution (Dennis and Westcott 2007;Jordano et al 2007;Koike et al 2010;Kamitani 2003, 2004). Dispersal by vertebrates is common not only in tropics with abundant frugivorous birds and primates, but also in temperate regions.…”