Tempo of trophic evolution and its impact on mammalian diversification

Abstract

Mammals are characterized by the complex adaptations of their dentition, which are an indication that diet has played a critical role in their evolutionary history. Although much attention has focused on diet and the adaptations of specific taxa, the role of diet in large-scale diversification patterns remains unresolved. Contradictory hypotheses have been proposed, making prediction of the expected relationship difficult. We show that net diversification rate (the cumulative effect of speciation and extinction), differs significantly among living mammals, depending upon trophic strategy. Herbivores diversify fastest, carnivores are intermediate, and omnivores are slowest. The tempo of transitions between the trophic strategies is also highly biased: the fastest rates occur into omnivory from herbivory and carnivory and the lowest transition rates are between herbivory and carnivory. Extant herbivore and carnivore diversity arose primarily through diversification within lineages, whereas omnivore diversity evolved by transitions into the strategy. The ability to specialize and subdivide the trophic niche allowed herbivores and carnivores to evolve greater diversity than omnivores.

Fig. 1.

Phylogeny of all 1,530 mammalian species for which we have dietary data; branch color is a rough guide to diet: herbivores, green; carnivores, blue; and omnivores, purple. The tree shown here represents one of the 100 trees used in the analysis and just one of the many possible character histories used within our analyses. This mapping of diet onto the tree, unlike the reconstructions used internally by diversitree (19), was made for the purposes of illustration without regard to diversification rates. The topology and branch lengths are from ref. .

Fig. 2.

Plot of the posterior probability density of the parameter estimates of the all rates-free model (which was the best-fitting model from the maximum-likelihood analysis) analyzed using Bayesian MCMC methods on 10 of the 100 replicate phylogenies. (A) Depiction of the net diversification rate (speciation minus extinction) for all three trophic strategies and (B) the rate of transition between the trophic strategies.