Latitudinal Diversity Gradients and Rapoport Effects in Chinese Endemic Woody Seed Plants

Abstract

The distribution of plant species diversity has long been a major focus on biogeography. Yet, the universality of the popular Rapoport’s rule remains controversial for endemic plants, as previous studies have focused more on broad-ranged species. Here, we collected data for 4418 endemic woody seed plant species across China, including trees, shrubs, and lianas, to explore the latitudinal patterns of species range size and richness, and test the relevant biogeographic law. The species range size distribution was examined for conformity with Rapoport’s rule using four methods (i.e., Steven’s, Pagel’s, the mid-point, and the across-species method). Spatial patterns of species richness along latitudinal gradient were also investigated by parabolic regression. Results showed that species range size increased with latitude for all species as well as by trees, shrubs and lianas, especially assessed by Pagel’s method. Species richness was highest at low latitude, where species range size was smallest, and decreased with increasing latitude. The species range size and richness of shrubs were maximum, followed by trees then lianas. These findings prove that Rapoport’s rule is strongly supported by latitudinal patterns of species distribution in Chinese endemic woody seed plants.

Latitudinal Diversity Gradient in the Changing World: Retrospectives and Perspectives

“…A global species density map for liverworts showed a significant pattern of LDG in species richness [28]. And latitudinal gradients of the richness of shrub and liana showed the same trends, i.e., the latitudes occupied by shrubs ranged nearly from 18-50 • N, a greater range than that occupied by shrubs (18-45 • N) and lianas (18-40 • N) of latitude in species range size [29]. However, not all plants conform to the obvious LDG, i.e., the latitudinal trend in species richness is weakly negative in some liverworts and woody plants [22].…”

“…That is, the effects of species distribution on different species reflect different climatic tolerance among them. Thus, the explanations of the climatic variability hypothesis for variation along the latitudinal gradient favor the evolution of broader climatic tolerance of species at high latitudes [29,30].…”

“…For precipitation seasonality and availability, the spatial precipitation heterogeneity in mosses is considered an important predictor of species richness, but the temperature variables generally have higher explanatory power than water variables in woody plants [22]. Also, hierarchical partitioning in the species richness of liverworts and mosses indicated that the independent effects of temperature variables are higher than those of water variables and that water variables have more variation in these families than in woody plants [29]. This is consistent with the evolution of terrestrial plants, which involves their ability to adapt to water deficiencies [89].…”

Thermal tolerance of tropical and temperate alpine plants suggests that ‘mountain passes are not higher in the tropics’

“…Realized rather than fundamental thermal niches may better correspond to distribution of species (Braschler et al, 2020; Bush et al, 2017). In plants, an elevational variant of Rapoport's rule (e.g., Feng et al, 2016; Macek et al, 2021; Mumladze et al, 2017) has been studied more commonly than the original latitudinal one (Lane, 2007; Liu et al, 2020; Weiser et al, 2007). The studies examined the correlative nature of distribution patterns using latitude and elevation as proxies of species thermal niches (McCain, 2009; McCain & Bracy Knight, 2013), arriving at ambiguous results.…”