Abstract:
Statistical model comparison has become common in historical biogeography, enabled by the R package BioGeoBEARS, which implements several models in a common framework, allowing models to be compared with standard likelihood-based methods of statistical model comparison. Ree and Sanmartín (2018) critiqued the comparison of Dispersal-Extinction-Cladogenesis (DEC) and a modification of it, DEC+J, which adds the process of jump dispersal at speciation. DEC+J provides highly significant improvements in model fit on most (although not all) datasets. They claim that the comparison is statistically invalid for a variety of reasons. However, analysis of the critique demonstrates a number of problems, ranging from mistakes in the example likelihood calculations through to misunderstanding the true causes of the likelihood advantage of DEC+J on typical datasets. I show that DEC+J fits better on datasets because the DEC model is statistically inadequate in the common situation when most species have geographic ranges of single areas; the DEC model requires long residence times of multi-area ranges, and when these are not observed, a model that does produce such data patterns, such as DEC+J, prevails. More fundamentally, I demonstrate that statistical comparison of DEC and DEC+J produces identical log-likelihood differences to statistical comparison of two submodels of ClaSSE where extinction rates are fixed to 0. As Ree and Sanmartín recommend ClaSSE models as valid for comparison, the comparison of DEC and DEC+J is statistically valid according to their own criteria.
