Using the Directional Comparative Method in Macroecology: The body size – latitudinal range relationship in the Sebastes genus (Pisces: Scorpaeniformes)

Background/Question/Methods

While many researchers have begun to evaluate the effect of ancestor-descendent relationships on observed patterns using the Phylogenetic Comparative Method, most macroecological studies only utilize the Cross-sectional Comparative Method to “remove the phylogenetic history”, without considering the option of evaluating its effect without removing it. We illustrate the usefulness of the Directional Comparative Method in a Bayesian framework using the phylogeny of the Sebastes genus (Pisces: Scorpaeniformes), together with data on the body size – latitudinal range relationship, in order to estimate the effect of phylogenetic history on the observed macroecological pattern without “removing the phylogenetic history”. We explicitly evaluate the two fundamental evolutionary assumptions of the Comparative Method in macroecology: 1.- that the phylogeny is constructed without error; 2.- that the model of evolution of the characters effectively recapitulates their history.

Results/Conclusions

The macroecological pattern of the Sebastes genus indicated a positive relationship between body size and range of distribution, with a significant lower limit to geographic range, describing a triangular polygon. The directional comparative method results showed that the best predictor of body size evolution was a directional change model with a negative trend, while a random-walk model provided better fit for the evolution of range of distribution. Both characters were significantly influenced by phylogeny, but body size has been more influenced by the phylogenetic relationships. The correlated evolution analysis showed that both traits evolve positively correlated along the phylogeny, indicating that a significant historical relationship between the characters exists. The observed macroecological pattern is greatly influences by the phylogenetic history, probably because both traits increased or decreased together during the species’ divergence. Finally we propose that macroecological studies will benefit from use of the directional comparative method to assess the effect of phylogenetic history, without removing this effect. In addition, explicit evaluations of the assumptions of Comparative Methods using Bayesian approaches will allow researchers to quantify the uncertainty of specific evolutionary hypotheses accounting for observed macroecological patterns.

FONDECYT 11080110