Roles of climate niche conservatism and range dynamics in woody plant diversity patterns through the Cenozoic

Abstract

Aim Large‐scale biodiversity patterns are often discussed in the context of ‘out of the tropics’ (OTT) dynamics and/or tropical niche conservatism (TNC), but empirical evidence of these processes remains very limited. The aim of this study was to infer diversification processes and mechanisms of Cenozoic diversity dynamics using woody angiosperms. Location East Asian continental islands and global. Time period Cenozoic. Major taxa studied Woody plants. Methods We compiled Cenozoic fossil and modern records for woody angiosperm genera to reconstruct biodiversity patterns. To evaluate the relative importance of TNC and OTT, we investigated extinction/survival patterns and latitudinal range dynamics for each genus, in combination with their clade age (mean family age), cold tolerance and per‐genus species richness. Results We found diversity decreasing with latitude in modern‐day flora, but not in the warmer periods of the Neogene and Palaeogene. The percentage of genera surviving decreased with latitude through the Cenozoic. Older genera with less cold tolerance and/or species‐poor genera went extinct locally at high latitudes in response to post‐Pliocene global cooling. Evolutionarily younger temperate genera dispersed from the extratropics to lower latitudes and the Southern Hemisphere after the Neogene. Main conclusions The latitudinal diversity gradient (LDG) has rapidly steepened post‐Pliocene through: (a) selective extinction in higher latitudes of old, less‐diversified tropical genera with low freezing tolerance, and (b) equatorward distributional shift of temperate genera. Both these processes were driven by the high‐latitude cooling. Such major roles of TNC and OTT, wherein temperate genera in the Northern Hemisphere expanded through the tropics into higher latitudes of the Southern Hemisphere across climatic boundaries without losing their temperate presence, are in contrast to OTT processes in marine systems. Cenozoic patterns of terrestrial woody angiosperm biodiversity indicate the importance of TNC and high‐latitude processes, including the extinction of tropical genera and range contraction or shift of temperate genera.

Global biogeographic synthesis and priority conservation regions of the relict tree family Juglandaceae

“…The long‐term stability of favourable climate and topographically diverse landscapes in the mountains of Eastern Asia, provided advantageous conditions for relict species survival (Shiono et al, ; Tang et al, ). In this region, the highest species and generic diversity of Juglandaceae are located in Southwest China (Figure ; Figure S5); where the species prefer to occupy high elevations (Figure ).…”

Biases in assessing the evolutionary history of the angiosperm flora of China

“…are younger than the Early Miocene (<11.63 million years ago) but reliable Oligocene or older fossils were well documented in the literature (e.g. Xing et al., ; Shiono et al., ; Appendix S1 in Supporting Information). Each pair of dots represents one genus [Colour figure can be viewed at wileyonlinelibrary.com]…”

“…In general, this discrepancy is not due to the use of different taxonomies or misidentification of fossils. For example, Sassafras , Ulmus and Zelkova are taxonomically stable and have abundant reliable fossils in the deposits of the Eocene (56–33.9 Mya; Shiono, Kusumoto, Yasuhara, & Kubota, ); however, stem ages of these genera are younger than 10 million years (in the Late Miocene) in Lu et al. 's phylogeny.…”

“…for the proportion of the angiosperm genera in China that did not originate until early in the Miocene is biased. However, because the vast majority of the Japanese angiosperm genera also occur in China, the recently published fossil database for Japanese plants (Shiono et al., ) can be used to estimate the proportion of the genera in China that originated before the Miocene but were assigned to an age of the Miocene or younger in Lu et al. Of the 300 angiosperm genera that were included in Lu et al.…”

“…Of the 300 angiosperm genera that were included in Lu et al. and have well‐documented fossil records in the Japanese plant fossil database (252 genera; Shiono et al., ) and the global database of Cenozoic plant fossils (Xing et al., ), 181 genera were considered as originating in the Miocene or later in Lu et al. However, 139 (76.8%) of these 181 genera have fossil records before the Miocene.…”