Differences among latitudinal regions (Q2)
Adding the factor latitudinal region to models with the four life
history traits notably increased fit to the data (models 5–7,
AIC=–488.6 to –503.9, Table 1). This is particularly evident when
comparing the best-fit models for each instance (models 4 vs. 6,
ΔAIC=21.6). Model performance was indistinguishable for models 6 vs. 7
(ΔAIC=1), which only differed in the addition of seed dispersal mode.
Finally, in models 5 and 7 the factor seed dispersal mode was no longer
a significant predictor of FST (Table 1 and 2). Below we
focus on results from model 7, as it is the most inclusive model of the
factors we tested with the best fit to the data.
Figure 1 shows how the levels of each factor affect population
differentiation as measured by FST values (after
transformation). The effect of each factor is depicted after accounting
for the effect of the other independent variables in model 7. For mating
system, outcrossers tend to have lower population differentiation than
mixed-mating plants (Fig. 1a). Trees tend to have significantly lower
population differentiation relative to non-woody plants and shrubs,
while the latter two growth forms did not differ between each other
(Fig. 1b). Pollination by small insects leads to significantly greater
differentiation compared to large insect, vertebrate and wind
pollination, while the latter three pollination modes did not differ
between each other (Fig. 1c). Temperate zones have significantly lower
FST values than tropics and subtropics, and the latter
two regions did not differ from each other (Fig. 1e). Finally, seed
dispersal mode was not a significant predictor of population genetic
differentiation. FST values associated with gravity
dispersal were highly variable, and although gravity dispersal results
in higher FST values compared to wind dispersal, this
difference was not significant. Animal dispersal also resulted in highly
variable FST values that did not differ from other
dispersal modes (Fig. 1d).