High plant endemism in China is partially linked to reduced glacial-interglacial climate change

Aim Endemic species are hypothesized to particularly occur in areas with relatively stable climates during the Quaternary glacial-interglacial oscillations (orbitally forced species' range dynamics hypothesis). This hypothesis has received support in global studies and studies from regions highly affected by glaciations. Here, we test its applicability to Chinese endemic species, thereby testing it in a region that was relatively mildly affected by glaciations. Location China. Methods We tested for associations between endemic species richness and Quaternary climate change, current climate and topography. Changes in mean annual temperature (MAT) and annual precipitation (MAP) between the Last Glacial Maximum and present were used to describe Quaternary climate change. We used simultaneous autoregressive (SAR) models to account for spatial autocorrelation in predictors, and Random Forest modelling to deal with non-linear relationships and better handle multicollinearity among predictor variables. To get a deeper understanding of the mechanisms involved we also performed analyses based on growth-form (woody versus herbaceous plants) and species age (palaeo- and neoendemics). Results Single-predictor SAR models showed that glacial-interglacial MAT velocity always has higher explanatory power than current climate (with a pseudo r(2) difference of 0.581-0.604 between the best palaeoclimate and current climate predictors for models for all endemic plants). Model selection on multivariate SAR models (based on Akaike weights) and Random Forest modelling (based on correlations between predicted and observed species richness) always included at least one variable representing Quaternary climate change as well as one or more current climate variables. Quaternary climate-change variables were generally of similar strength to the current climate predictors. Notably, the summed Akaike weight across all models in the relevant model set was always 1 for glacial-interglacial MAT velocity. There were no clear differences with respect to growth forms or species age in the estimated importance of Quaternary climate change. Main conclusions The consistent association between long-term climatic stability and high plant endemism in China provides strong evidence for the importance of Quaternary glacial-interglacial climate changes in shaping the distribution of endemic species, even in regions relatively mildly affected by glaciations. Hence, even moderate climate changes may have strong, long-term effects on species diversity patterns.