Spatial patterns and determinants of Moraceae richness in China

中国桑科植物物种多样性格局及其主导因子

Understanding large-scale patterns of biodiversity and their drivers remains central in ecology.Many hypotheses have been proposed,including hydrothermal dynamic hypothesis,tropical niche conservatism hypothesis,Janzen’s hypothesis and a combination model containing energy,water,seasonality and habitat heterogeneity.Yet,their relative contributions to groups with different lifeforms and range sizes remain controversial,which have limited our ability to understand the general mechanisms underlying species richness patterns.Here we evaluated how lifeforms and species range sizes influenced the relative contributions of these three hypotheses to species richness patterns of a tropical family Moraceae.The distribution data of Moraceae species at a spatial resolution of 50 km×50 km and their lifeforms(i.e.shrubs,small trees and large trees)were compiled.The species richness patterns were estimated for the entire family,different life forms and species with different range sizes separately.The effects of environmental variables on species richness were analyzed,and relative contributions of different hypotheses were evaluated across life forms and species range size groups.The species richness patterns were consistent across different species groups and the species richness was the highest in Sichuan,Guangzhou and Hainan provinces,making these provinces the hotspots of this family.Climate seasonality is the primary factor in determining richness variation of Moraceae.The best combination model gave the largest explanatory power for Moraceae species richness across each group of range size and life forms followed by the hydrothermal dynamic hypothesis,Janzen’s hypothesis and tropical niche conservatism hypothesis.All these models has a large shared effects but a low independent effect(<5%),except rare species.These findings suggest unique patterns and mechanisms underlying rare species richness and provide a theoretical basis for protection of the Moraceae species in China.

理解物种多样性大尺度格局及其驱动机制是生态学的核心议题之一。以往研究已提出了多种解释物种多样性格局的假说,其中包括水热动态假说、热带生态位保守假说、Janzen假说以及包含能量、水分、季节性和生境异质性的综合假说,但各假说对不同类别(如不同生活型、不同分布区大小的物种)植物物种多样性格局的相对贡献仍存在争议,这阻碍了我们理解驱动物种多样性格局形成的一般规律。本研究以桑科植物为对象,评估了以上假说对不同类别桑科植物物种多样性格局的相对影响。我们收集整理了中国164种桑科植物的物种分布图(空间分辨率50 km×50 km)及其生活型(即灌木、小乔木和大乔木)。在此基础上,估算了整个科、不同生活型以及不同分布区大小物种(广域种和狭域种)的物种多样性格局,分析了环境变量对物种多样性格局的影响,比较了不同假说对各类别桑科植物物种多样性格局的相对解释率。不同类别桑科植物的物种多样性格局高度一致,四川省、广州省和海南省的物种多样性较高,形成了该科物种多样性热点。气候季节性是桑科物种多样性格局的主导因素。在所有假说中,包含能量、水分、季节性和生境异质性的综合假说对不同生活型和不同分布区大小物种的多样性格局具有最高的解释率。需要指出的是,对除狭域种外的其他所有物种组的物种多样性格局来说,这些模型均具有较高的共享解释率,但较低的独立解释率(<5%)。这些结果说明,与其他物种组相比,狭域种物种多样性格局及其形成机制可能是不同的。本研究为保护桑科植物、特别是狭域桑科植物提供了理论依据。