Patterns of seed dispersal syndromes on serpentine soils: examining the roles of habitat patchiness, soil infertility and correlated functional traits

<b><i>Background:</i></b> It is critical to understand the ecological factors shaping seed dispersal in plant communities in order to predict their fate in the face of global change. Communities restricted to patchy habitats may contain more species with ‘directed’ dispersal syndromes that facilitate successful seed dispersal to other patches; however, habitat quality may constrain the presence of and efficiency of dispersal syndromes found within those habitats.<b><i>Aims:</i></b> The aim of this study was to hypothesise that if habitat patchiness is an important filter on dispersal syndromes, ‘directed’ vertebrate dispersal should be more prevalent in serpentine habitats because of their patchiness. Alternatively, if habitat quality is more important, wind dispersal should be more prevalent in serpentine habitats because of their low fertility.<b><i>Methods:</i></b> Using three datasets representing grassland, chaparral and forest vegetation types, we analysed differences in the composition of dispersal syndromes (vertebrate, wind, passive, water and ant) between communities on patchy infertile serpentine soils and on continuous, fertile non-serpentine soils. Our analyses also accounted for correlated functional traits and phylogenetic relatedness.<b><i>Results:</i></b> Across and within all three vegetation types, serpentine communities had significantly higher proportions of wind dispersed and lower proportions of vertebrate-dispersed species. These patterns were not independent of functional traits. Proportions of the other dispersal syndromes did not differ.<b><i>Conclusions:</i></b> Our results suggest that on low-fertility soils, habitat quality may outweigh habitat patchiness as a filter on the availability of dispersal syndromes, potentially adding to the vulnerability of such communities to stochastic extinctions and global change.