Species and functional diversity accumulate differently in mammals

Abstract

Aim Whether the gradients of global diversity conform to equilibrium or non‐equilibrium dynamics remains an unresolved question in ecology and evolution. Here, we evaluate four prominent hypotheses which invoke either equilibrium (more individuals, niche diversity) or non‐equilibrium dynamics (diversification rate, evolutionary time) to explain species richness and functional diversity of mammals worldwide. Location Global. Methods We combine structural equation modelling with simulations to examine whether species richness and functional diversity are in equilibrium with environmental conditions (climate, productivity) or whether they vary with non‐equilibrium factors (diversification rates, evolutionary time). We use the newest and most inclusive phylogenetic, distributional and trait data for mammals. Results We find that species richness and functional diversity are decoupled across multiple regions of the world. While species richness correlates closely with environmental conditions, functional diversity depends mostly on non‐equilibrium factors (evolutionary time to overcome niche conservatism). Moreover, functional diversity plateaus with species richness, such that species‐rich regions (especially the Neotropics) host many species that are apparently functionally redundant. Main conclusions We conclude that species richness depends on environmental factors while functional diversity depends on the evolutionary history of the region. Our work further challenges the classic notion that highly productive regions host more species because they offer a great diversity of ecological niches. Instead, they suggest that productive regions offer more resources, which allow more individuals, populations and species to coexist within a region, even when the species are apparently functionally redundant (the more individuals hypothesis). Together these findings demonstrate how ecological (the total amount of resources) and evolutionary factors (time to overcome niche conservatism) might have interacted to generate the striking diversity of mammals and their life histories.

Spatial variation of mammal richness, functional and phylogenetic diversity in the Mexican transition zone

“…According to Oliveira et al (2016) we would expect that the old colonized areas had the highest phylogenetic diversity (Nearctic zone in our study area), nonetheless, our results are congruent with expecta- Table 2. Slope of abiotic variables related with richness (S), phylogenetic diversity (PD) and functional diversity (FD), taking in account for S and PD effects.…”

“…In a global study, Oliveira et al (2016) found evidence showing that mammal species richness and functional diversity are decoupled in America, with species richness being explained by environmental factors (equilibrium processes), whilst functional diversity is related to evolutionary time (non-equilibrium processes). Our results agree with these findings, and also with the general pattern of species richness increase towards the tropics (Rosenzweig 1995, Brown 2014.…”

Ecological controls of mammalian diversification vary with phylogenetic scale

“…Climatic data were taken from the WorldClim database of Hijmans, Cameron, Parra, Jones, and Jarvis () and resampled to the resolution of our distributional maps (1° × 1°), using bilinear interpolation. We selected mean annual temperature (BIO1) and annual precipitation (BIO12) for our analyses because they seem most relevant to mammalian macroecology and macroevolution (e.g., Buckley et al, ; Oliveira et al, ). In addition, we combined all climatic variables (BIO1–BIO19) into a single composite variable (PC1) using principal component analysis (PCA).…”

“…Finally, we calculated multiple measures of regional coexistence. These measures were based on the geographical overlaps between species distributions, capturing the degree of resource sharing and partitioning across the species that coexist within a region (Machac et al, ; Oliveira et al, ; Rabosky, ; Rabosky & Hurlbert, ). Specifically, we calculated geographical overlaps between the distributions of mutually related species (i.e., all species within a given clade) but also distributional overlaps with unrelated species (species outside the clade) and with all mammals (species both within and outside the clade).…”

Plant species richness across the Himalaya driven by evolutionary history and current climate

“…This index is derived from the average distance between all pairs of species in an assemblage (the mean phylogenetic distance), which Oliveira et al (2016) showed by simulation to be relatively invariant to species richness. We focus on the net relatedness index (NRI).…”