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The altitudinal distribution of biodiversity in alpine ecosystems has captured academic attention, especially in streams because of their sensitivity to climate change. In the past years, research mainly focused on understanding the role played by alpine streams' internal factors such as aquatic environmental variables, as well as physical and hydrological conditions, on the shaping of benthic macroinvertebrate communities. More recently, external factors such as terrestrial environments were included in analyses worldwide. In particular, the inherent properties constituting the ecological niche of specific species were considered as factors regulating dispersal and influencing community construction. The objective of this study was to reveal the distribution pattern and the driving factors regulating aquatic biodiversity in alpine streams. We hypothesized that the altitudinal distribution of aquatic macroinvertebrates could be explained by the interaction of the aquatic environment with both species' ecological niche and the terrestrial environment surrounding their habitat, and that rare species display a more pronounced pattern than widespread dominant species. To test these hypotheses, samples were collected from two alpine streams situated on opposite slopes of Biluo Snow Mountain in Yunnan Province, China. Results of statistical analyses showed poor explanatory power from aquatic environmental factors, while the differences in vegetation type and the ecological niche of the species played an important role in determining the distribution pattern of aquatic biodiversity. Furthermore, we found that the altitudinal distribution pattern of aquatic biodiversity exhibits a bimodal type, with rare species fitting the bimodal peaks. These findings call for a better inclusion and further investigation on the effects of the terrestrial environment on aquatic ecosystems., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021. Published by Elsevier B.V.)

Environmental factors that affect spatiotemporal distribution patterns of animals usually include resource availability, temperature, and the risk of predation. However, they do not explain the counterintuitive preference of high elevation range in winter by the black-and-white snub-nosed monkey (Rhinopithecus bieti). We asked whether variation of sunshine along with elevations is the key driving force. To test this hypothesis, we conducted field surveys to demonstrate that there was a statistically significant pattern of high elevation use during winter. We then asked whether this pattern can be explained by certain environmental factors, namely temperature, sunshine duration and solar radiation. Finally, we concluded with a possible ecological mechanism for this pattern. In this study, we employed GIS technology to quantify solar radiation and sunshine duration across the monkey's range. Our results showed that: 1) R. bieti used the high altitude range between 4100-4400 m in winter although the yearly home range spanned from 3500-4500 m; 2) both solar radiation and sunshine duration increased with elevation while temperature decreased with elevation; 3) within the winter range, the use of range was significantly correlated with solar radiation and sunshine duration; 4) monkeys moved to the areas with high solar radiation and duration following a snowfall, where the snow melts faster and food is exposed earlier. We concluded that sunshine was the main factor that influences selection of high elevation habitat for R. bieti in winter. Since some other endotherms in the area exhibit similar winter distributional patterns, we developed a sunshine hypothesis to explain this phenomenon. In addition, our work also represented a new method of integrating GIS models into traditional field ecology research to study spatiotemporal distribution pattern of wildlife. We suggest that further theoretical and empirical studies are necessary for better understanding of sunshine influence on wildlife range use.