Macroevolutionary diversification rates show time dependency

Abstract

For centuries, biologists have been captivated by the vast disparity in species richness between different groups of organisms. Variation in diversity is widely attributed to differences between groups in how fast they speciate or go extinct. Such macroevolutionary rates have been estimated for thousands of groups and have been correlated with an incredible variety of organismal traits. Here we analyze a large collection of phylogenetic trees and fossil time series and describe a hidden generality among these seemingly idiosyncratic results: speciation and extinction rates follow a scaling law in which both depend on the age of the group in which they are measured, with the fastest rates in the youngest clades. Using a series of simulations and sensitivity analyses, we demonstrate that the time dependency is unlikely to be a result of simple statistical artifacts. As such, this time scaling is likely a genuine feature of the tree of life, hinting that the dynamics of biodiversity over deep time may be driven in part by surprisingly simple and general principles.

A Laurasian origin for a pantropical bird radiation is supported by genomic and fossil data (Aves: Coraciiformes)

“…This result is not particularly surprising due to the fact that rate shifts for Ceyx were not as consistently supported as those for Todiramphus. Similarly, we found a lower diversification rate for Todiramphus kingfishers than reported by Andersen et al [39], the inferred core shift and elevated diversification rates for Todiramphus are consistent with a recent study that suggested that diversification rates are timedependent and that younger clades speciate and go extinct faster than older clades [124]. Regardless, our study corroborates that Todiramphus has elevated diversification rates compared to background coraciiform rates, irrespective of this study's older divergence dates.…”

Phylogenies of extant species are consistent with an infinite array of diversification histories

“…In such situations, the tree can always be decomposed into a set of sub-trees with distinct LTT curves, each of which is subject to the same identifiability issues as described here. Our findings thus shed doubts over a lot of previous work on diversification dynamics, including some of the conclusions from our own work (14, 17).…”

“…By analogy, studies that test whether diversification dynamics are influenced by some environmental or geological variable X (e.g., temperature), either by testing for correlations between X and the estimated λ or µ (16, 17) or by fitting models in which λ or µ are explicit functions of X (18, 19, 20), will generally lead to unreliable conclusions. Indeed, specifying λ or µ as functions of X (e.g., assuming µ = αX + β and fitting the coefficients α and β ) is essentially equivalent to choosing particular functional forms for λ or µ .…”

“…A central challenge in evolutionary biology is to explain why some taxonomic groups and some time periods have so many species while others have so few; ultimately this means estimating and explaining variation in rates of speciation and extinction (13). Estimating these rates is crucial to investigating fundamental questions such as the role of biotic and abiotic processes in shaping patterns of species richness (7), how Earth’s biota recover after mass extinction events (15, 16) and whether there are general dynamics that govern how biodiversity accumulates (17). Measuring such rates has taken on a new urgency as we try to understand how anthropogenically induced extinctions compare to “background” rates (18, 19).…”

“…Even the common methodological decision to estimating net diversification ( r = λ − µ ) rather than λ and µ separately (8, 11), is no longer meaningful in light of our results; the shape of r is not conserved across a congruence class. Likewise, the models in a congruence class will not share “average” (however defined) rates; hence absolute rate estimates (1), which have been used to estimate broad macroevolutionary patterns (17) and background rates of extinction (19), are also unlikely to be accurately reconstructed. These issues are likely also present in more complex models with additional free parameters, for example where some clades exhibit distinct diversification regimes (42, 47).…”