The role of community assembly processes in the biodiversity-production relationship: tests of theory on real gradients

Understanding spatiotemporal variation in net primary productivity (NPP) continues to be of fundamental importance to basic ecology and to applied conservation and management efforts for human well-being. Diversity is an important driver of NPP variation, but its effect is variable depending on ecosystem context and spatial scale as well as more closely linked to functional traits. Explicitly considering processes of trait-based community assembly and maintenance at relevant scales at which they occur can potentially resolve some of this variation. In my thesis, I address this gap by considering various processes that structure and maintain diversity in communities and analyze NPP as an outcome of these processes. I examine processes in high diversity tropical forests, relatively less explored in the context of biodiversity-ecosystem functioning. In Chapter 1, through a manipulated experiment, I show that diversity effect on biomass gain in seedling communities is modulated by light. This interactive effect holds across different functional groups that are known to respond uniquely to light. In Chapter 2, I expand the spatial scale of inquiry to community assembly processes that maintain diversity at regional spatial scales – dispersal and competition, akin to island biogeographic contexts. Through simulations, I show that dispersal and competition acting on correlated traits explain a range of variation in BEF curves observed in nature. Finally, in Chapter 3, expanding the focus of inquiry to include human aspects, I consider the impact of a biodiversity-driven human intervention, protected areas, in maintaining NPP. I show that at the landscape scale, mean annual NPP and temporal stability are both influenced by protection status, but the effectiveness of protection is contingent on environmental factors. Taken together, my thesis suggests that understanding the combined drivers of diversity and NPP can improve predictions for spatiotemporal variation of this ecosystem function. Further inquiry integrating diversity-gradients at multiple scales can improve process-based understanding of the effect of biodiversity on ecosystem functioning

Trophic complexity alters the diversity–multifunctionality relationship in experimental grassland mesocosms

Plant diversity has a positive influence on the number of ecosystem functions maintained simultaneously by a community, or multifunctionality. While the presence of multiple trophic levels beyond plants, or trophic complexity, affects individual functions, the effect of trophic complexity on the diversity–multifunctionality relationship is less well known. To address this issue, we tested whether the independent or simultaneous manipulation of both plant diversity and trophic complexity impacted multifunctionality using a mesocosm experiment from Cedar Creek, Minnesota, USA. Our analyses revealed that neither plant diversity nor trophic complexity had significant effects on single functions, but trophic complexity altered the diversity–multifunctionality relationship in two key ways: It lowered the maximum strength of the diversity–multifunctionality effect, and it shifted the relationship between increasing diversity and multifunctionality from positive to negative at lower function thresholds. Our findings highlight the importance to account for interactions with higher trophic levels, as they can alter the biodiversity effect on multifunctionality.We used a manipulated grassland mesocosm experiment to test the effects of higher trophic levels on ecosystem multifunctionality. We find that the number and identity of trophic levels affect the jack‐of‐all‐trades relationship between biodiversity and ecosystem multifunctionality. Our findings have implications in refining predictions for ecosystem multifunctionality in the face of ongoing biodiversity loss.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/168308/1/ece37498.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/168308/2/ece37498_am.pd

Trophic complexity alters the diversity–multifunctionality relationship in experimental grassland mesocosms

Plant diversity has a positive influence on the number of ecosystem functions maintained simultaneously by a community, or multifunctionality. While the presence of multiple trophic levels beyond plants, or trophic complexity, affects individual functions, the effect of trophic complexity on the diversity–multifunctionality relationship is less well known. To address this issue, we tested whether the independent or simultaneous manipulation of both plant diversity and trophic complexity impacted multifunctionality using a mesocosm experiment from Cedar Creek, Minnesota, USA. Our analyses revealed that neither plant diversity nor trophic complexity had significant effects on single functions, but trophic complexity altered the diversity–multifunctionality relationship in two key ways: It lowered the maximum strength of the diversity–multifunctionality effect, and it shifted the relationship between increasing diversity and multifunctionality from positive to negative at lower function thresholds. Our findings highlight the importance to account for interactions with higher trophic levels, as they can alter the biodiversity effect on multifunctionality