Uncovering the spatio-temporal drivers of species trait variances: A case study of Magnoliaceae in China

Abstract

Aim: Analyses of the relationships between evolutionary history, environmental constraints and associated trait variances can reveal how species distributions were shaped. Phylogenetic comparative models can be used to disentangle the relative roles of spatial and phylogenetic factors in explaining trait variances. Here, we analyse variances in plant traits and environmental variables of the widely distributed and early diverging Magnoliaceae within a phylogeographical context to test whether species distributions have been limited more by evolutionary or spatial constraints in this family. Location: China. Methods: The phylogenetic relatedness and geographical distributions of 183 Magnoliaceae species in China were analysed for phylogenetic clustering or over-dispersion. The phylogenetic signals of 15 plant traits and 12 environmental variables were determined, and the relative contributions of phylogeny and space to each quantitative trait were distinguished using four comparative models. Results: Species richness gradually decreased from south to north, with phylogenetic clustering along the southern coast, and in northern and central China. Strong phylogenetic signals were found in leaf form, flowering sequence, diameter at breast height, leaf length and width, mean and minimum mean annual temperature, and minimum mean annual precipitation. Variances of plant diameter, length and width of leaves and tepals, and fruit length were strongly associated with phylogenetic relatedness. In contrast, variances of plant height, flowering and fruiting time, and all of the 12 environmental variables (mean, minimum, maximum and range of altitude, temperature and precipitation) were associated with both spatial proximity and phylogenetic distance between species. Main conclusions: Phylogenetic niche conservatism was identified in most of the studied plant traits across the Magnoliaceae. In contrast, environmental variables showed weak phylogenetic signals, but strong spatial signals. These results suggest that the present tropical-temperate distributional pattern of the Magnoliaceae is driven by the ecophysiological adaptation of plant traits under both geographical separation and environmental constraints.