Phylogenetic distance was calculated as the mean pairwise phylogenetic distance (MPD, a, c, e) and difference between observed MPD and expected MPD (ΔMPD, b, d, f). Positive values of ΔMPD support Darwin’s naturalization hypothesis, whereas negative values support the preadaptation hypothesis. a, b show the global distribution of MPD and ΔMPD. The ΔMPD values in b, f, as well as the gray circles in d, were generated using the null model based on the global naturalized alien species pool. The colors in a and b correspond to different MPD and ΔMPD. We used bins with equal intervals, with the exception of the bins for the lowest and highest values, as there were relatively few observations for those extreme values. Gray areas represent regions without data.
