A major goal of ecology is to understand the process of community assembly, and approaches to understanding community assembly often contain explicitly phylogenetic hypotheses. To the extent that phylogeny is a proxy for ecological similarity, it may be used as a predictive tool to understand community assembly, an objective of community ecology and especially community phylogenetics. We conducted two experiments to determine whether phylogeny predicts ecological similarity in a phylogenetically broad sample of angiosperms (Asteraceae, Fabaceae, Juncaceae, Polygonaceae, Rosaceae). First, we conducted a field experiment to determine the ability of phylogeny to predict the germination niche for 32 native plant species at Bodega Bay Marine Reserve (BMR). Species were planted into microhabitats belonging to conspecifics, congeners, confamilials, and more distant relatives. Then germination and early seedling survival were correlated with the phylogenetic distance between the focal species and species in the planting microhabitat, where phylogenetic distance was calculated using a molecular phylogeny based on four DNA regions. Second, we conducted a lathe house experiment with 12 native species from BMR to determine the relationships among soil environment (from soils collected from rhizospheres of each species in the field), phylogeny, and competitive response. Competitive response was then correlated with phylogenetic distance to the competitor.
Results/Conclusions
We provide the first experimental evidence that closely related plant species shared similar germination niches in the field; in other words, they germinated best at conspecific and close relatives' sites and less well at distant relatives' sites. The negative relationship between phylogenetic distance and germination and early seedling survival was consistent across the majority of the species studied (26/32 species for germination, 30/32 species for germination plus early seedling survival). Species also competed more strongly with close relatives than with distant relatives, consistent with assumptions of community phylogenetics, though the relationship between phylogenetic distance and competitive response was soil-dependent, and was strongest in the focal species' home soil (7/8 species that survived in the home soil exhibited a positive relationship between competitive response and phylogenetic distance). Overall, we found a strong signal of phylogeny on ecological similarity, lending support to efforts to make general predictions about ecological similarity and community assembly based on relatedness.
