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 5320 squamate species. We tested relationships among these rates using Bayesian phylogenetic generalised 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 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.