Dataset preparation
A data matrix comprised by all sample sites reported in allstudies was built from the database described above. For each
study captured in our database, sites where sampled populations occurred
were logged in the data matrix as 0’s. Sites located between sampled
populations where genetic discontinuities were recorded, and hence
putative BGF existed, were logged as 1’s. Thus, for each study, whenever
panmixia were detected, geographic ranges between genetically
homogeneous populations were marked as a string of zeros between sample
sites. From this data matrix, we built a frequency data matrix by
summing all putative BGF occurrences across logged studies, normalized
by the total number of studies that included each site (Table S1).
A large normalized BGF frequency value in a given site indicates that a
large number of studies identified that particular site as either a BGF
or a location of high probability of occurrence of BGF. Consequently,
those sites can be considered locations of high BGF concordance.
Conversely, a small value means either absence of BGF in a particular
site (= area of high genetic connectivity) or that a small number of
articles and studies included those sites within the range of their
sampling designs. A distribution of the frequencies of occurrence of
putative BGF along a latitudinal gradient (which is the case for most of
the Brazilian coast) can be easily applied to comparative
phylogeography, because this distribution represents the likelihood for
which a phylogeographic break exists in a given location given by
multiple empirical studies. Thus, the frequency of occurrence of
putative BGF not only quantifies but also describes how one of the most
important concepts in comparative phylogeography is distributed in
space: concordance in the spatial distribution of phylogenetic breaks
across co-occurring species (type III concordance in Avise, 2000).