Fig 1. Graphical representation of phylogeographic models.

In this study we consider three phylogeographic methods: the structured coalescent, DTA, and BASTA. This figure shows some of the differences in these models, in particular in the modelled events and time intervals. Coloured dots show different subpopulations (one orange subpopulation and one turquoise for both sampled and internal nodes in the genealogy. a) In the structured coalescent eight events are considered, delimiting seven time intervals of lengths τ ₁…τ ₇. Three of these events are sampling events (denoted by the grey horizontal lines), one is a migration event (represented by an arrow between two coloured dots), and four are coalescence events. b) In DTA, migration events are not explicitly parameterized, so we have a total of seven sampling or coalescence events, delimiting six time intervals of lengths τ ₁…τ ₆. While locations for internal nodes are depicted in the figure, the method effectively integrates over all possible ancestral locations at each MCMC step. c) As in DTA, BASTA does not consider migration events, and therefore has seven events and six time intervals. Yet, each of these intervals is split exactly in half (blue horizontal dotted lines), and the two halves are considered separately. Again, as in DTA, at each MCMC step BASTA integrates over all possible internal nodes locations.