title: A cautionary note on the use of Ornstein Uhlenbeck models in macroevolutionary studies.
abstract: Phylogenetic comparative methods are increasingly used to give new insights into the dynamics of trait evolution in deep time. For continuous traits the core of these methods is a suite of models that attempt to capture evolutionary patterns by extending the Brownian constant variance model. However, the properties of these models are often poorly understood, which can lead to the misinterpretation of results. Here we focus on one of these models - the Ornstein Uhlenbeck (OU) model. We show that the OU model is frequently incorrectly favoured over simpler models when using Likelihood ratio tests, and that many studies fitting this model use datasets that are small and prone to this problem. We also show that very small amounts of error in datasets can have profound effects on the inferences derived from OU models. Our results suggest that simulating fitted models and comparing with empirical results is critical when fitting OU and other extensions of the Brownian model. We conclude by making recommendations for best practice in fitting OU models in phylogenetic comparative analyses, and for interpreting the parameters of the OU model.
authors.affiliation: School of Natural SciencesTrinity College DublinDublin 2Ireland; Trinity Centre for Biodiversity ResearchTrinity College DublinDublin 2Ireland; Department of Life SciencesNatural History MuseumCromwell RoadLondonSW7 5BDUK.
authors.forename: Natalie
authors.identifier: 0000-0003-4919-8655
authors.initials: N
authors.lastname: Cooper
authors.affiliation: Department of Animal and Plant Sciences University of Sheffield Sheffield S10 2TN UK.
authors.forename: Gavin H
authors.initials: GH
authors.lastname: Thomas
authors.affiliation: School of Biological Sciences University of Reading Reading Berkshire RG6 6BX UK.
authors.forename: Chris
authors.initials: C
authors.lastname: Venditti
authors.affiliation: School of Biological Sciences University of Reading Reading Berkshire RG6 6BX UK.
authors.forename: Andrew
authors.initials: A
authors.lastname: Meade
authors.affiliation: Department of Animal and Plant Sciences University of Sheffield Sheffield S10 2TN UK.
authors.forename: Rob P
authors.identifier: 0000-0002-8338-864X
authors.initials: RP
authors.lastname: Freckleton
keywords: OU; comparative methods; macroevolutionary models; phylogeny; stabilizing selection