Dietary specialization depending on ecological context and sexual differences in Asiatic black bears

Abstract

The food habits of the Asiatic black bear (Ursus thibetanus) are well studied, but there is a little evidence of dietary specialization—that is, when individuals use a narrower set of resources compared to the population as a whole. To examine the dietary composition at the individual level, seasonal patterns of dietary specialization, and sex-based dietary differences in Asiatic black bears, we attached Global Positioning System (GPS) collars to 15 Asiatic black bears and collected their scats in Nagano Prefecture, Japan from 2017 to 2018. Our results showed that the dietary composition differed among individuals, although seasonal changes in dietary composition were observed at the population level. Dietary specialization was high in summer (resources less abundant) and low in spring and autumn (resources more abundant), indicating a relationship with general food abundance and the dietary diversity of bears. In spring, all bears consumed green vegetation and/or seed of Fagaceae family from previous autumn; in early- and late- summer, dietary composition, such as green vegetation, insects, and fruits, greatly differed among individuals. In autumn, most bears heavily depended on seeds of Fagaceae which is high-quality food for bears.Although we did not find statistical differences between sexes in terms of dietary specialization and diversity, we found variations in the timing of feeding on the Fagaceae family, being earlier in females compared with males. We also found considerable variation in dietary composition within sexes, suggesting that dietary specialization depends on multiple factors besides food abundance, food diversity, and sex.

Evolutionary transitions in diet influence the exceptional diversification of a lizard adaptive radiation

“…Plants often defend themselves with toxins, and associations with microbes or symbiotic nematodes are necessary to improve digestion [ 57 , 58 ]. Diet specialization depends on the degree of interactions between intrinsic traits of individuals and ecological contexts [ 67 ], and some clades with highly specialized diets will hardly transition to another type of diet. However, with our results we show that there is a certain degree of specialization that still has the possibility of transitioning to completely opposite diets through an intermediate step.…”

Temporal and individual variation in the feeding habits of Asiatic black bears (Ursus thibetanus)

“…Above 1600 m, the subalpine zone is dominated by Russian rock birch ( Betula ermanii ) and Maries' fir ( Abies mariesii ). Bears in this region sometimes supplement their diet with crops like corn ( Zea mays ) during the summer months (Mori et al., 2019 ). For this study, we divided the year into four categories based on the general phenological progression of plant phenology: spring (April to May; budding and flowering of many plant species), early summer (June to July; fruiting some fleshy fruits), late summer (August to September; fruiting of a variety of fleshy fruits), and autumn (October to November; maturing of acorns).…”

“…In spring, they consume green vegetation and/or Fagaceae hard masts, whereas green vegetation, fleshy fruits, and social insects are incorporated into their diets in summer, and fleshy fruits and hard masts are consumed in autumn (e.g., Hashimoto, 2002 ; Koike, 2010 ; Mori et al., 2018 ). The diets of Asiatic black bears also vary significantly at the individual level depending on the season (Mori et al., 2019 ; Naganuma et al., 2020 ). This highlights the potential for discrepancies in food habits at the population level, yielding erroneous conclusions regarding individual food habits.…”

“…To achieve this, we revisited the feeding habits of Asiatic black bears through a reanalysis and extension of previously published data by Mori et al. ( 2019 ). Mori et al.…”

Bed-site selection of Asiatic black bears in the Central Alps, Japan

“…(3) bed sites in broad-leaved forest environments during spring and autumn because these forests provide rich food for bears, including new tree buds and leaves in spring and acorn seeds in autumn (Mori et al 2019). We also hypothesized that (4) bed-site characteristics would differ between males and females because the microhabitat selection of bears differs according to social status, which is influenced by sex, age, and reproductive status (Skuban et al 2018).…”