Environmental variation is a major predictor of global trait turnover in mammals

Ben G. Holt, Gabriel C. Costa, Caterina Penone, Jean-Philippe Lessard, Thomas M. Brooks, Ana D. Davidson, S. Blair Hedges, Volker C. Radeloff, Carsten Rahbek, Carlo Rondinini, Catherine H. Graham

To evaluate how environment and evolutionary history interact to influence global patterns of mammal trait diversity (a combination of 14 morphological and life-history traits). We calculated patterns of spatial turnover for mammalian traits and phylogenetic lineages using the mean nearest taxon distance. We then used a variance partitioning approach to establish the relative contribution of trait conservatism, ecological adaptation and clade specific ecological preferences on global trait turnover.

Global patterns of (a) phylogenetic turnover and (b) trait turnover across mammalian assemblages within 2° grid cells, as well as
(c) environmental conditions across the same grid cells. “Turnover” refers to differences in species assemblages due to changes in composition
(i.e. composition of phylogenetic lineages or phenotypic traits). Plots on the right of turnover maps show the results of NMDS ordinations on
matrices of pairwise turnover comparisons between global grid cell assemblages for each of the two biodiversity dimensions, which attempt to
show variation within these matrices as accurately as possible within two-dimensional space. Stress values for the NMDS ordinations are 0.20
and 0.24 for phylogenetic turnover and trait turnover, respectively; which reflect the amount of error in the correlation between pairwise
distances in the original distance matrix and those calculated from the NMDS plot. The environmental data ordination is based on the first two
principal components (associated with 55.2% and 23.8% of the total environmental variation, respectively) produced by a principal component
analysis. All ordination points are plotted within the HCL colour space shown in the bottom left inset, and these colours are then transposed
onto the maps. Therefore, locations on the maps with similar colours are similar with regard to the focal variable (i.e. phylogenetic turnover,
trait turnover or environmental conditions) and the locations with more distinct colours are more distinct in respect of this variable

We provide a global scale analysis of trait turnover across mammalian terrestrial assemblages, which demonstrates that phylogenetic turnover by itself does not predict trait turnover better than random expectations. Conversely, trait turnover is consistently more strongly associated with environmental variation than predicted by our null models. The influence of clade-specific ecological preferences, reflected by the shared component of phylogenetic turnover and environmental variation, was considerably higher than expectations. Although global patterns of trait turnover are dependent on the trait under consideration, there is a consistent association between trait turnover and environmental predictive variables, regardless of the trait considered.

Our results suggest that changes in phylogenetic composition are not always coupled with changes in trait composition on a global scale and that environmental conditions are strongly associated with patterns of trait composition across species assemblages, both within and across phylogenetic clades.

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