Data for: Climatic-niche breadth, niche position, and speciation in lizards and snakes

Aim: The climatic niche is associated with diversification in many groups of animals and plants. However, the relationships between climatic-niche breadth evolution, climatic-niche position evolution, and speciation remain underexplored. It is particularly unclear whether changes in climatic-niche breadth are related to diversification. We tested two hypotheses relating niche breadth, niche position, and speciation using climatic data in Squamata (lizards and snakes), one of the largest radiations of tetrapods. These hypotheses were: (1) the oscillation hypothesis (niche breadth changes along with niche position and speciation); and (2) the musical chairs hypothesis (niche breadth remains relatively constant when niche position changes during speciation).

Location: Global.

Taxon: Squamata (lizards and snakes).

Methods: We estimated rates of speciation and evolutionary rates for both climatic-niche position and climatic-niche breadth for 5,320 squamate species. We tested relationships among these rates using Bayesian phylogenetic generalized linear-mixed models.

Results: Higher speciation rates were associated with higher rates of evolution in niche position and in niche breadth. Faster rates of change in niche breadth were related to narrower niches and faster rates of change in niche position.

Main Conclusions: Our results support the oscillation hypothesis to explain the relationships between speciation and changes in climatic niche position and climatic niche breadth. We found that species that changed climatic-niche breadths more rapidly: (1) speciated faster; (2) evolved towards narrower niche breadths; and (3) changed climatic-niche positions more rapidly. These results suggest that the oscillation between wider and narrower niches is coupled with climatic-niche divergence and speciation. These conclusions may apply to many other groups of plants and animals in which speciation is often related to climatic-niche divergence.

Methods
Climatic-niche data

We obtained historic climatic data and distribution maps for 5,320 squamate species. We calculated two characteristics of the realized climatic niche for each species: niche position and niche breadth. For niche position, we performed a phylogenetic principal component analysis (pPCA) and focused on the first two axes: PC1 and PC2. For niche breadth we calculated two distinct but complementary metrics: species niche breadth for temperature (SNBT) and species niche breadth for precipitation (SNBP).

Speciation rates

We estimated species-specific speciation rates (and rates of climatic-niche evolution) for all 5,320 species of Squamata included in the tree. We estimated speciation rates (λ) using the ClaDS approach.

Rates of climatic-niche evolution

We used BAMM to infer the evolutionary rates (r) for changes in species’ climatic-niche position (PC1 and PC2) and climatic-niche breadth (SNBT and SNBP) on the final tree. We then calculated pathwise rates of evolution (∑r) for each climatic-niche variable using the mean trait rates per-branch obtained from BAMM. The pathwise rate for a given species is the sum of the mean rates per branch from the root of the tree to that species’ terminal branch, and quantifies the amount of changes in rates that a trait has experienced along the evolutionary path leading from the root to each individual species.

Statistical analyses

We tested the oscillation and musical chairs hypotheses using Phylogenetic Generalized Linear Mixed Models (PGLMM). Specifically, we used PGLMM to estimate regression coefficients for the relationships between speciation rates and rates of climatic-niche evolution. First, we tested for a relationship between speciation rates and rates of climatic-niche change. Second, we tested whether species evolved towards narrower niches (oscillation hypothesis) or maintained relatively constant niche breadths (musical chairs hypothesis). Finally, we tested if rates of change in climatic-niche breadth were correlated with rates of change in climatic-niche position.