Climate, human disturbance and geometric constraints drive the elevational richness pattern of birds in a biodiversity hotspot in southwest China

Human Disturbance and Geometric Constraints Drive Small Mammal Diversity and Community Structure along an Elevational Gradient in Eastern China

Simple Summary

Biodiversity patterns and mechanisms along elevational gradients have long been the focus of conservation research. However, few studies have been conducted in mountainous areas of eastern China, especially for small mammals. In this study, we used a standard sampling method to survey small mammals along the gradient of Qingliang Mountain in eastern China and analyzed the patterns and mechanisms of diversity and community structure. We found inconsistencies between different diversity dimensions. Functional and phylogenetic structures were mainly clustered but showed opposite elevation patterns. Human disturbance and MDE were the main drivers of the diversity patterns, but with contrasting effects on different dimensions. These findings emphasize the importance of a multiple dimensions approach to biodiversity conservation and call for increased conservation efforts in the low and middle elevation regions.

Abstract

Understanding the mechanisms influencing patterns and processes of biological diversity is critical to protecting biodiversity, particularly in species-rich ecosystems such as mountains. Even so, there is limited knowledge of biodiversity patterns and processes in the mountains of eastern China, especially about small mammals. In this study, we examined the taxonomic, functional, and phylogenetic diversity of small mammal distribution and community structure along the elevational gradient of Qingliang Mountain, eastern China. We then evaluated how they are influenced by space (area and mid-domain effect (MDE)), environment (temperature, precipitation, and normalized difference vegetation index (NDVI)), and human disturbance. The results showed hump-shaped patterns of taxonomic and phylogenetic diversity along elevation gradients, peaking at 1000 m, unlike functional diversity, which peaked at lower elevations (600 m). The mean pairwise distance and mean nearest taxon distance of functional and phylogenetic variance (MFD and MPD, respectively) were also incongruent. The MFD and MPD showed hump-shaped patterns along elevations; however, unlike MFD, which peaked at lower elevations (600 m), MPD peaked at higher elevations (1200 m). The mean nearest functional taxon distance (MNFD) decreased, while the mean nearest phylogenetic taxon distance (MNTD) increased along the elevation gradient. The higher elevations were functionally more clustered, while the lower elevations were phylogenetically more clustered, suggesting that environmental filtering for traits was stronger at higher elevations. In comparison, phylogenetic conservatism of ecological niches had a stronger influence at lower elevations. The diversity and community structure indices were inconsistently explained, with human disturbance and MDE accounting for the biggest proportions of the model-explained variances. Overall, the results confirm that environmental filtering and human disturbance significantly influence small mammals’ diversity and community structure. These findings also emphasize the need for increased conservation efforts in the middle and lower elevation regions of Qingliang Mountain.

Positive abundance-elevational range size relationship weakened from temperate to subtropical ecosystems

Describing the patterns and revealing the underlying mechanisms responsible for variations in community structure remain a central focus in ecology. However, important gaps remain, including our understanding of species abundance. Most studies on abundance-based relationships are from either temperate ecosystems or tropical ecosystems, and few have explicitly tested abundance-based relationships across a temperate to tropical ecotone. Here, we use a comprehensive dataset of breeding birds across elevation spanning a temperate to subtropical gradient in the Himalayas-Hengduan Mountains of China to examine the relationship between species abundance and (a) elevational range size, (b) body size, (c) elevational range centre and (d) endemicity. We tested a priori predictions for abundance-elevational range size relationship, abundance-body size relationship and abundance-elevational range centre relationship, and explored how these relationships change along this temperate to subtropical mountain ecosystem. We found that species abundance was significantly positively correlated with elevational range size across the study sites, demonstrating the key importance of elevational range size towards species abundance. Body size and elevational range centre are weakly correlated with abundance. A novel finding of our study is that the abundance-elevational range size relationship gradually weakened from temperate to subtropical ecosystems, adding to a growing body of evidence suggesting that abundance-elevational range size tracks a temperate to tropical ecotone. Our study demonstrates that abundance range-size relationship can transition across ecotones where faunas of different evolutionary origins converge. Furthermore, measuring abundance relationships across different environmental variables at the same spatial scale with comparable biogeography is a key strategy that can reveal the underlying mechanisms behind abundance patterns.

Elevation patterns and critical environmental drivers of the taxonomic, functional, and phylogenetic diversity of small mammals in a karst mountain area

Understanding how biodiversity components are related under different environmental factors is a fundamental challenge for ecology studies, yet there is little knowledge of this interplay among the biotas, especially small mammals, in karst mountain areas. Here, we examine the elevation patterns of the taxonomic diversity (TD), phylogenetic diversity (PD), and functional diversity (FD) of small mammals in a karst mountain area, the Wuling Mountains, Southwest China, and compare these patterns between taxa (Rodentia and Eulipotyphla) and scales (broad‐ and narrow‐range species). We also disentangle the impacts of the human influence index, net primary productivity (NPP), normalized difference vegetation index (NDVI), annual precipitation (AP), and annual mean temperature (AMT) on these three facets of biodiversity by using structural equation modeling. We recorded a total of 39 small mammal species, including 26 rodents and 13 species of the order Eulipotyphla. Our study shows that the facets of biodiversity are spatially incongruent. Net primary productivity has a positive effect on the three facets for most groups, while the effect of the NDVI is negative for TD and PD in most groups. AMT temperature and AP have negative effects on FD and PD, whereas TD is dependent on the species range scale. The human influence index effect on TD and PD also depends on the species range scale. These findings provide robust evidence that the ecological drivers of biodiversity differ among different biotas and different range scales, and future research should use multifacet approach to determine biodiversity conservation strategies.