Environmental filtering and biotic interactions jointly shape medium-to-large vertebrate community assembly along a subtropical montane gradient

Understanding how environmental filtering and biotic interactions jointly structure ecological communities remains a major challenge in ecology, particularly in ecosystems where apex predators have been lost. In many subtropical montane forests of China, historical extirpation of large carnivores has produced vertebrate communities dominated by mesopredators, ungulates, and ground-dwelling birds, yet the relative importance of environmental and biotic assembly processes in such systems remains unclear. Using multi-year camera-trap data collected from 206 stations between 2017 and 2024, we applied Joint Species Distribution Models to investigate assembly patterns of medium- and large-bodied vertebrates in the Daxiangling Mountains of Giant Panda National Park, southwestern China. Environmental covariates explained most variation in community composition (64.14%), with climate, terrain, vegetation, and resource-related variables jointly forming the primary template of species distributions. However, substantial residual covariance (35.86%) indicated additional community structure beyond measured environmental effects alone. Residual associations were functionally structured: ungulates exhibited predominantly negative associations suggestive of niche partitioning or competition, whereas mesopredators showed positive associations with smaller prey-associated taxa and other carnivores. Temporal trends further revealed increasing relative abundance for many taxa alongside declining human disturbance, consistent with ongoing faunal recovery under changing trophic conditions. Nevertheless, species responses were heterogeneous, with some disturbance-sensitive taxa showing weak or negative trends. Together, these findings indicate that vertebrate community assembly in predator-depleted montane forests is shaped primarily by environmental filtering, while biotic interactions and latent ecological processes further refine local coexistence patterns. Our study highlights the value of joint species approaches for disentangling assembly mechanisms and provides conservation insights for Giant Panda National Park and other recovering forest ecosystems experiencing long-term apex predator loss.