Global change drives opposing shifts in phylogenetic and functional diversity in grasslands worldwide

Background/Question/Methods

Ecologists are tasked with forecasting community responses to global change drivers (GCDs), and community assembly theory can inform our understanding of these responses. Commonly invoked niche-based mechanisms driving community assembly such as environmental filtering (local environmental conditions selects for species with similar traits) and limiting similarity (biotic processes limits overlap of species with similar traits, as well as their feedbacks can inform our ability to predict community responses to GCDs. A combination of approaches has been proposed to better generalize and increase predictability of how communities respond to GCDs by examining both (1) community-level functional trait expression and (2) phylogenetic diversity within communities. We are examining how changes in plant species composition with global change shift phylogenetic and functional diversity within a database of more than 145 global change experiments from around the world utilizing a causal modeling approach.

Results/Conclusions

Results indicate opposing shifts in phylogenetic vs functional diversity for each global change driver. For example, with nitrogen addition treatments, phylogenetic diversity increases while functional trait diversity decreases. In contrast, with water addition phylogenetic diversity declines while functional trait diversity increases. These opposing shifts indicate that (1) communities are converging on a trait space under some global change treatments but not others, and (2) that these traits are not conserved across the phylogeny. Together, our results indicate that community-level functional trait expression and phylogenetic diversity are both being affected by GCDs in different ways, and together can be used to inform how communities assemble.