Abstract
Despite the numerous studies on the large-scale patterns of species richness, the spatial variation and determinants of species richness for alpine plant are still an outstanding question and critical to future biodiversity conservation. The genus Saxifraga is a typical alpine plant group with high species richness in the Himalaya-Hengduan mountain regions, China. We performed simple regression models and variance partitioning to assess the importance of different factors, especially soil-related ones, in driving Saxifraga richness patterns. The results showed that environmental energy, habitat heterogeneity, and soil heterogeneity together dominated the spatial variation of species richness. The coarse fragments volume of soil, elevation range, and soil heterogeneity, are positively related to Saxifraga richness. Soil slightly outperforms habitat heterogeneity in predicting the spatial variation of Saxifraga species richness with an explanatory power of 39.3% and 36.6%, respectively. Environmental energy, such as the maximum temperature of the warmest quarter, is negatively correlated with species richness and explains 44.8% of spatial variation of Saxifraga richness. Multiple regression models, including three variables, each representing energy, soil, and habitat heterogeneity, can only explain 53.1% variation of species richness. Variance partitioning outscored 26% of the shared effects of the three variables, while the independent effect of each variable is less than 10%. These results indicated the energy, soil, and habitat heterogeneity together are primary determinants of the spatial variation of Saxifraga species richness. However, there are probably other hidden factors predicting species richness variation due to the low explanatory power of the multiple regression models. Our study emphasizes the significance of soil properties in determining species richness patterns in China, especially for the alpine plant groups. The negative association of species richness with temperature suggests a potential threat of alpine biodiversity loss in HHM from future warming.
Highlights
The mechanisms of large-scale patterns of species richness are one of the central and controversial issues in macroecology and biogeography (Gaston et al, 1995; Brown et al, 2004)
The species richness patterns of Saxifraga were highly consistent with the topographical structure of China with a high striking species richness in the Himalaya-Hengduan Mountain (HHM) regions (Figure 1)
The Qinghai-Tibetan Plateau harbors high species richness, whereas Saxifraga species were rarely distributed in the eastern part of China
Summary
The mechanisms of large-scale patterns of species richness are one of the central and controversial issues in macroecology and biogeography (Gaston et al, 1995; Brown et al, 2004). Previous studies in large-scale species richness patterns focus on the effects of contemporary climate, habitat heterogeneity, and evolutionary history and have proposed productivity hypothesis, water– energy dynamic hypothesis, and niche conservatism hypothesis (Rosenzweig, 1995; O’Brien et al, 2000; Currie and Francis, 2004; Wiens and Donoghue, 2004; Wiens and Graham, 2005). Southwestern China, especially the Himalaya-Hengduan Mountain (HHM) regions, holds the highest species richness and an extraordinary diversity in alpine plants. It was regarded as one of the global biodiversity hotspots (Myers et al, 2000). Despite the numerous studies on the patterns and determinants of species richness in China (Wang et al, 2009, 2011a,b; Shrestha et al, 2018a), the largescale patterns, and determinants of alpine plant richness are still poorly understood
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