Mechanisms of plant diversity-productivity relationships in complex ecological networks

The importance of biodiversity for providing ecosystem functions and services crucial to human well-being is well documented. However, the mechanisms underlying biodiversity-ecosystem functioning (BEF) relationships are insufficiently understood. I address this issue by zooming in on plant diversity-productivity relationships and their potential drivers. Specifically, I combine theoretical and empirical approaches focusing on resource- and animal-based processes, as well as their joint effect on plant community composition and productivity. Additionally, I consider spatial aspects of resource-based, animal-based, and generalized empirical interactions. My findings show that plant diversity only affects productivity positively when plants have complementarity resource requirements and spatially overlap in their resource access, thereby risking negative effects from competition. This includes the competitive exclusion of inferior competitors. However, in complex food webs, competitive exclusion of plant species is largely mitigated. This aligns with my empirical findings that suggest coexistence mechanisms playing a central role in driving plant diversity-productivity relationships. Despite positive effects on plant coexistence, animal-based processes induce strong variation on plant diversity-productivity relationships. Specifically, unconstrained animal movement can lead to negative relationships, whereas movement scaled with animal body masses turns them positive. My findings further suggest considerable interactive effects between resource- and animal-based mechanisms. However, clear differences in how either mechanism assembles plant communities could serve as a tool to disentangle them. This opens a way to focus conservation and restoration efforts that counteract the global biodiversity crisis, ensuring the provisioning of ecosystem service that are crucial to human society.

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