Trait-driven vs. syndrome-driven diversification in the Mediterranean woody flora

In the woody flora from the Mediterranean basin there are two character syndromes which differ in diversification rate : the sclerophyll and the nonsclerophyll syndrome ; the latter has the highest diversification rate mainly due to rampant speciation. The cause of this increased diversification rate in nonsclerophylls could be the overall and complex interaction between their syndrome traits (conspicuous flowers, dry fruits, small seeds, non-animal dispersal, fireinduced germination) and environmental pressures (pollinator competition, summer drought, poor soils, frequent fires). Alternatively, one or very few of the syndrome traits could be responsible of most of the difference in diversification rate (trait-driven diversification). This work examines the relative role of syndrome traits on nonsclerophyll diversification using ANCOVA analyses for the flora of Western Andalusia (Spain). The results point that the increased diversification rate typical of the nonsclerophyll syndrome is largely caused by one single trait : the obligate seeder strategy (that is, fireinduced germination in fire-killed shrubs). This is the only trait whose consideration erases the difference in diversification rate between both syndromes. This result cannot be explained as the effect of altitudinal range as a potentially confounding variable. Furthermore, obligate seeder genera show a much higher diversification rate than the other genera and account for most of the species richness here considered. Thus the origin of this Mediterranean flora can be better understood as the outcome of traitdriven (seeder strategy) instead of syndromedriven diversification. The role of fire in the evolution of this regional flora stands out over the other possible factors here considered.