Determinants of difference in genetic diversity between
populations
The log response ratio values for the genetic diversity measures
included in our analysis ranged from 0, indicating cases with no
difference between populations, to 4.32, which corresponds to a ratio
difference of approximately 75:1 between measures of genetic diversity
between two populations. In the main model we found no evidence for a
strong effect of geographic or macroclimatic distance, system type or
kingdom on the log ratio of mean genetic diversity measures between
populations, as the posterior distributions of all parameters overlapped
with zero (Table 1b, Table S6.2a). Of all variables, geographic distance
had a weak, positive influence on the difference in mean genetic
diversity between populations, with the posterior distribution for all
100 combined models slightly overlapping zero, and an increasingly
larger range of inter-population differences in neutral genetic
diversity observed at higher geographic distances (Table 1b, Table
S6.2a, Fig. S6.2b). Across the random terms included in the model, most
of the variation was associated with the residual terms, less variation
was associated with the response type, and very little effect was
attributed towards the phylogenetic term, study and species (Table 1b).
In the model that did not include geographic distance, we detected
higher differences in genetic diversity between islands than between
mainland populations (Table S6.6b), but this effect did not persist in
the model that included geographic distance (Table S6.5b). The zero
adjusted model (TableS6.3b), the reduced model of heterozygosity (Table
S6.4b) and the models which excluded environmental distance (Table
S6.5b) produced qualitatively similar results to the main genetic
diversity model.