Print PageGlobally, climate-driven productivity (abundant rainfall and/or solar energy) is the strongest predictor of regional-scale plant and animal diversity. A little understood aspect of this pattern is that productivity is also associated with higher beta diversity, i.e., greater differentiation of species composition among communities within regions. A possible explanation for the productivity-beta diversity relationship is that higher productivity leads, via more intense competition, to greater niche specialization. We test this hypothesis by analyzing the productivity-beta diversity relationship in the California flora, asking whether the dissimilarity of plant communities on adjacent serpentine and nonserpentine soils increases with productivity, both at the level of species and at higher taxonomic scales.
We surveyed 95 paired serpentine and nonserpentine plots over a 1200-km latitudinal and rainfall gradient in California, including >1000 species. For each plot pair, we calculated beta diversity and phylogenetic beta diversity. We used 30-year mean annual precipitation as a correlate of productivity and created a phylogeny using Phylocom, adding phylogenetic resolution when possible.
Results/Conclusions
Beta diversity was significantly, positively correlated with productivity. Phylogenetic beta diversity also increased with productivity, even after controlling for species-level dissimilarity. On-going work suggests that high phylogenetic betadiversity in productive regions is related to high turnover of functional traits, which are phylogenetically conserved. Our results are consistent with the hypothesis that more competition in productive regions causes more niche specialization. The results help explain the causes of regional-scale plant diversity gradients in California, and, globally, have implications for why specialization has promoted plant diversity hotspots in productive regions of the world, but not in unproductive regions where the same soils occur.
