Reconciling diversification: random pulse models of speciation and extinction.

Abstract

Inferring the underlying speciation-extinction dynamics of a clade from the phylogenetic relationships of contemporary species has proven difficult, primarily because the record of extinction is absent. Moreover, models of diversification tend to emphasize either time homogeneity or gradual trends in speciation and extinction rates. In contrast, the fossil records of many groups exhibit repeated increase and decrease of species richness within clades. Modeling this dynamic in the structure of phylogenetic trees has had limited application. Here, I consider the idea that pulses of diversification followed by declines in clade size-such pulses having short life spans in evolutionary time-occur frequently and more or less randomly among lineages. I suggest that this model might characterize diversification quite generally. Analyses of a recent phylogeny of the ovenbirds and treecreepers (Aves: Furnariidae) supports the random pulse model in that ancestral lineages at 15, 10, and 5 Ma exhibit diversification rate heterogeneity, but the sizes of ancestral and descendant lineages are uncorrelated. Simulations of such a process and its manifestations in reconstructed phylogenies would help to characterize diversification pulses in an abstract sense and draw attention to the underlying biological processes that produce them.