Abstract:

This study investigates the dietary ecology of three sympatric Ursidae species— Ailuropoda melanoleuca baconi, Ursus thibetanus, and Ursus arctos — from two sites at Hualonglong (locality 1: ~300 ka; locality 3: late Middle Pleistocene to Late Pleistocene) in Anhui Province, southern China. Through stable carbon and oxygen isotope (δ¹³C, δ¹⁸O) analysis of tooth enamel, this study reveals distinct ecological strategies: at locality 1, U. arctos (n=3) occupied intermediate woodlands (δ¹³C_diet= −23.1‰±1.9‰), while A. melanoleuca baconi (n=5) and U. thibetanus (n=4) inhibited close-canopy forests (δ¹³C_diet values are −27.8‰±0.6‰ and −27.8‰±0.8‰, respectively). The latter exhibites more diverse dietary ecology, as reflected by their varied δ¹⁸O values (−6.9‰±0.3‰ and −8.3‰±1.1‰). By locality 3, U. arctos were absent, but A. melanoleuca baconi (n=5) and U. thibetanus (n=5) continue to inhabit close-canopy forests. The δ¹⁸O convergence between A. melanoleuca baconi (−7.0‰±0.4‰) and U. thibetanus (−7.2‰±0.8‰) suggests possible ecological shifts in U. thibetanus. Regional comparisons (Guangxi: Baxian Cave, Quzai Cave, and Yugong Cave from previous studies; Anhui: two localities at Hualongdong in this study) indicate that during the middle-late Pleistocene, both A. melanoleuca baconi (δ¹³C_diet values were −27.1‰±1.0‰ (n=20) in Guangxi and −27.8‰±0.6‰ (n=10) in Anhui) and U. thibetanus (δ¹³C_diet values were −27.7‰±1.7‰ (n=10) in Guangxi and −27.8‰±0.6‰ (n=9) in Anhui) consistently exploited close-canopy forests in Guangxi and Anhui, yet maintained niche partitioning at each sites. By integrating isotopic data from Pleistocene Ailuropoda, we observed a gradual shift towards more positive δ¹³C_diet values from the Early Pleistocene Ailuropoda microta (data from Gigantopithecus Cave and Yanliang Cave in Guangxi, δ¹³C_diet= −28.2‰±1.0‰, n=8) and A. melanoleuca wulingshanensis (data from Longgu Cave in Hubei, δ¹³C_diet= −27.7‰±0.7‰, n=4) to the middle-late Pleistocene A. melanoleuca baconi (all aforementioned specimens from Guangxi and Anhui, δ¹³C_diet= −27.3‰ ±0.9‰, n=30). Their δ¹⁸O values also varied by regions and periods. The spatiotemporal isotopic differences in Pleistocene Ailuropoda, linked to their specialized bamboo-diet, underscore the differences in regional paleoenvironments in southern China. In Guangxi, A. melanoleuca baconi exhibited slightly higher δ¹³C_diet values and a broader range of δ¹⁸O values compared to A. microta. This may suggest that, with the increase in body mass and food intake, A. melanoleuca baconi occupied more open habitats and utilized bamboo more diversely, as potentially evidenced by a wider variety of bamboo species, parts, and distribution ranges. This study provides the first isotopic evidence for sympatric Ursidae niche partitioning in southern China, offering critical paleoenvironmental context for understanding the coevolution between human and non-human animals in this region.

Key words: Hualongdong, Ailuropoda, Ursus thibetanus, Ursus arctos, Carbon and oxygen isotopes