A consistent species richness–climate relationship for oaks across the Northern Hemisphere

Xiaoting Xu,Nawal Shrestha,Zhiheng Wang,Dimitar Dimitrov,Carsten Rahbek,Greg Jordan

doi:10.1111/geb.12913

Abstract

AbstractAimAlthough the effects of climate on species richness are known, regional processes may lead to different species richness–climate relationships across continents resulting in species richness anomalies, especially for tropical groups. Phylogenetic niche conservatism may also influence species richness–climate relationships of different lineages. Here, we tested whether regional effects also exist for temperate lineages using the genus Quercus.LocationNorthern Hemisphere.Time periodPresent day.Major taxa studiedQuercus (Fagaceae).MethodsWe used a dated phylogeny and distribution data for Quercus to evaluate its global species richness patterns and phylogenetic niche conservatism. To evaluate the consistency in species richness–climate relationships across continents of the genus Quercus as a whole and the temperate subgenus Quercus, we conducted analyses of covariance with continent as the categorical variable and climate variables as the covariate. We calibrated four widely used models using the global data or data from each continent separately and evaluated the predictive power of each model for different continents using the root mean squared error.ResultsThe relationships between species richness and climate were not significantly different among continents for both the genus Quercus as a whole and the subgenus Quercus. Unlike the models based on European data, those based on North American and eastern Asian data predicted both the global species richness and the richness in other continents. The species richness of a subtropical subgenus Cyclobalanopsis was most influenced by water availability, while that of a temperate subgenus Quercus was most influenced by environmental temperature.Main conclusionsIn contrast to the subtropical subgenus Cyclobalanopsis, our results showed a consistent richness–climate relationship and absence of regional effects on species richness across continents for the temperate subgenus Quercus, likely suggesting that the species richness of temperate lineages, for example subgenus Quercus, may have reached equilibrium with the contemporary climate in the Northern Hemisphere.

Highlights

Large‐scale species richness patterns have intrigued ecologists for more than two centuries (Lomolino, Riddle, Whittaker, & Brown, 2010)
When we used EU models to predict eastern Asia, North America and global Quercus species richness, we found that the models built by Xu et al (2016), O’Brien et al (2000) and Francis and Currie (2003) showed larger root mean squared error (RMSE) values than did the Wang et al (2011b) model (Figure 4)
Our results showed that Quercus species richness was a func‐ tion of energy, water and their interaction (Table 4), which conforms with the tree species richness–climate models proposed in previous studies (Field et al, 2005; Francis & Currie, 2003; Hawkins et al, 2003; O’Brien, 1998; O’Brien et al, 2000; Whittaker, Nogues‐Bravo, & Araujo, 2007; Xu et al, 2016)

Summary

| INTRODUCTION

Large‐scale species richness patterns have intrigued ecologists for more than two centuries (Lomolino, Riddle, Whittaker, & Brown, 2010). When we used EU models (the model built with European data) to predict eastern Asia, North America and global Quercus species richness, we found that the models built by Xu et al (2016), O’Brien et al (2000) and Francis and Currie (2003) showed larger RMSE values than did the Wang et al (2011b) model (Figure 4) This difference is probably due to the nar‐ rower range of climate regimes in Europe, which limits the extrapo‐ lative power of nonlinear regression models based on the European data alone (Figure 5)

| DISCUSSION

Findings

| CONCLUSIONS