CiteWeb id: 20150000109

CiteWeb score: 1391

The question is often raised whether it is statistically necessary to control for phylogenetic associations in comparative studies. To investigate this question, we explore the use of a measure of phylogenetic correlation, l, introduced by Pagel (1999), that nor- mally varies between 0 (phylogenetic independence) and 1 (species' traits covary in direct proportion to their shared evolutionary his- tory). Simulations show l to be a statistically powerful index for measuring whether data exhibit phylogenetic dependence or not and whether it has low rates of Type I error. Moreover, l is robust to incomplete phylogenetic information, which demonstrates that even partial information on phylogeny will improve the accuracy of phy- logenetic analyses. To assess whether traits generally show phyloge- netic associations, we present a quantitative review of 26 published phylogenetic comparative data sets. The data sets include 103 traits and were chosen from the ecological literature in which debate about the need for phylogenetic correction has been most acute. Eighty- eight percent of data sets contained at least one character that dis- played significant phylogenetic dependence, and 60% of characters overall (pooled across studies) showed significant evidence of phy- logenetic association. In 16% of tests, phylogenetic correlation could be neither supported nor rejected. However, most of these equivocal results were found in small phylogenies and probably reflect a lack of power. We suggest that the parameter l be routinely estimated when analyzing comparative data, since it can also be used simul- taneously to adjust the phylogenetic correction in a manner that is optimal for the data set, and we present an example of how this may be done.