Species Richness Patterns and Water-Energy Dynamics in the Drylands of Northwest China

Dryland ecosystems are highly vulnerable to climatic and land-use changes, while the mechanisms underlying patterns of dryland species richness are still elusive. With distributions of 3637 native vascular plants, 154 mammals, and 425 birds in Xinjiang, China, we tested the water-energy dynamics hypothesis for species richness patterns in Central Asian drylands. Our results supported the water-energy dynamics hypothesis. We found that species richness of all three groups was a hump-shaped function of energy availability, but a linear function of water availability. We further found that water availability had stronger effects on plant richness, but weaker effects on vertebrate richness than energy availability. We conducted piecewise linear regressions to detect the breakpoints in the relationship between species richness and potential evapotranspiration which divided Xinjiang into low and high energy regions. The concordance between mammal and plant richness was stronger in high than in low energy regions, which was opposite to that between birds and plants. Plant richness had stronger effects than climate on mammal richness regardless of energy levels, but on bird richness only in high energy regions. The changes in the concordance between vertebrate and plant richness along the climatic gradient suggest that cautions are needed when using concordance between taxa in conservation planning.

干旱生态系统极易受到气候变化与土地利用变化的影响，而干旱区物种丰富度格局背后的调控机制仍未明晰。本研究依托中国新疆地区3637种本土维管植物（vascular plant）、154种哺乳类以及425种鸟类的分布数据，检验了中亚干旱区物种丰富度格局的水热动态假说。研究结果证实了该假说：三大类群的物种丰富度均与能量可获得性呈驼峰型函数关系，而与水分可获得性呈线性函数关系。进一步分析表明，相较于能量可获得性，水分可获得性对植物物种丰富度的影响更强，而对脊椎动物物种丰富度的影响更弱。本研究通过分段线性回归（piecewise linear regression）识别了物种丰富度与潜在蒸散量（potential evapotranspiration）之间关系的拐点，据此将新疆划分为低能量区域与高能量区域。在高能量区域内，哺乳类与植物物种丰富度的一致性强于低能量区域，这与鸟类和植物间的一致性变化趋势恰好相反。无论能量水平高低，植物物种丰富度对哺乳类物种丰富度的解释力均强于气候因子，但仅在高能量区域内，植物物种丰富度对鸟类物种丰富度的解释力才强于气候因子。脊椎动物与植物物种丰富度的一致性随气候梯度发生的变化提示，在生物多样性保护规划中利用类群间的一致性进行推演时需谨慎行事。