Phylogenetic conservatism and biogeographic affinity influence woody plant species richness–climate relationships in eastern Eurasia

Xiangyan Su,Dimitar Dimitrov,Nawal Shrestha,Denis Sandanov,Siyang Wang,Zhiheng Wang,Xiaoting Xu,Qinggang Wang

doi:10.1111/ecog.04839

Abstract

Mechanisms underlying species richness patterns remain a central yet controversial issue in biology. Climate has been regarded as a major determinant of species richness. However, the relative influences of different evolutionary processes, (i.e. niche conservatism, diversification rate and time for speciation) on species richness–climate relationships remain to be tested. Here, using newly compiled distribution maps for 11 422 woody plant species in eastern Eurasia, we estimated species richness patterns for all species and for families with tropical and temperate affinities separately, and explored the phylogenetic signals in species richness patterns of different families and their relationships with contemporary climate and climate change since the Last Glacial Maximum (LGM). We further compared the effects of niche conservatism (represented by contemporary‐ancestral climatic niches differences), diversification rate and time for speciation (represented by family age) on variation in the slopes of species richness–climate relationships. We found that winter coldness was the best predictor for species richness patterns of most tropical families while Quaternary climate change was the best predictor for those of most temperate families. Species richness patterns of closely‐related families were more similar than those of distantly‐related families within eudicots, and significant phylogenetic signals characterized the slopes of species richness–climate relationships across all angiosperm families. Contemporary‐ancestral climatic niche differences dominated variation in the relationships between family‐level species richness and most climate variables. Our results indicate significant phylogenetic conservatism in family‐level species richness patterns and their relationships with contemporary climate within eudicots. These findings shed light on the mechanisms underlying large‐scale species richness patterns and suggest that ancestral climatic niche may influence the evolution of species richness–climate relationships in plants through niche conservatism.

Highlights

IntroductionUnderstanding the latitudinal gradient in species richness (i.e. the decrease in species richness with latitude) has been a central question in biology for two centuries, and yet it remains a major challenge to biologists (Hawkins 2001)
Understanding the latitudinal gradient in species richness has been a central question in biology for two centuries, and yet it remains a major challenge to biologists (Hawkins 2001)
Our results indicated that species richness of most tropical families was dominated by winter coldness (MTCQ), while that of most temperate families was dominated by temperature anomaly since the Last Glacial Maximum (LGM) (MATano) rather than by winter coldness

Summary

Introduction

Understanding the latitudinal gradient in species richness (i.e. the decrease in species richness with latitude) has been a central question in biology for two centuries, and yet it remains a major challenge to biologists (Hawkins 2001). Niche conservatism likely leads to more similar species richness patterns and species richness–climate relationships among more closely related clades (Ricklefs 2006), and leads to lower species richness and flatter species richness–climate relationships of clades with larger differences between ancestral and contemporary climatic niches. Both predictions of niche conservatism hypothesis remain to be fully understood. Most studies testing the effect of niche conservatism on species richness–climate relationships are usually based on tetrapods (Hawkins et al 2006, Weir and Schluter 2007, Buckley et al 2010, Pyron and Wiens 2013, Duchêne and Cardillo 2015) but rarely for plants (but see Kerkhoff et al 2014, Folk et al 2019)

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