ABSTRACT
The uneven distributions of species over geography (e.g., tropical versus temperate regions) and phylogeny (e.g., rodents and bats versus the aardvark) are prominent biological patterns for which causal interconnections remain enigmatic. Here we investigate this central issue for living mammals using time-sliced clades sampled from a comprehensive recent phylogeny (N=5,911 species, ∼70% with DNA) to assess how different levels of unsampled extinction impact the inferred causes of species richness variation. Speciation rates are found to strongly exceed crown age as a predictor of clade species richness at every time slice, rejecting a clock-like model in which the oldest clades are the most speciose. Instead, mammals that are low-vagility or daytime-active show the fastest recent speciation and greatest extant richness. This suggests primary roles for dispersal limitation leading to geographic speciation (peripatric isolation) and diurnal adaptations leading to ecological speciation (time partitioning). Rates of speciation are also faster in temperate than tropical lineages, but only among older clades, consistent with the idea that many temperate lineages are ephemeral. These insights, enabled by our analytical framework, offer straightforward support for ecological effects on speciation-rate variation among clades as the primary cause of uneven phylogenetic richness patterns.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Statement of authorship: NSU and WJ conceived the study; NSU and JAE collected and curated the data; NSU performed all analyses and wrote the first draft of the manuscript, with contributions to revisions from WJ and JAE.
Data and material availability: All data and code are available in the manuscript and after publication on Zenodo (also to be available at github.com/n8upham/).
- Separated out the Fig. 2 analyses of diversification rates through time (BAMM, fossil speciation and extinction), lineages through time, and tip DR distributions -- all of which are now published in https://doi.org/10.1016/j.cub.2021.07.012 - Added new Fig. 1 and Fig. 2, Table 1 - Revised Fig. 4 - Re-wrote Results and Discussion sections to reflect new perspectives and organization