Impacts of drivers of global change on community structure and ecosystem functioning

Abstract

One of the greatest challenges in ecology today is to predict the impact of global changes on the future of our ecosystems. Natural ecosystems not only provide vital functions but also harbor a vast amount of biological diversity. Global changes act as drivers that alter many of the fundamental factors which directly determines species success, community structure, and ecosystem functioning. In addition to this direct effect, ecosystem functioning can be indirectly altered via changes in community structure. Thus, to fully understand the consequences of global changes, it is necessary to quantify how they impact multiple aspects of ecosystem structure and those ties to ecosystem functioning. Without a holistic view of the ecosystem, it is likely that predictions will be inaccurate and that management strategies could tackle the wrong things. Here, I utilize both theoretical and experimental approaches to quantify how multiple global change drivers impact several different aspects of community structure. I then link these community-level changes to changes in ecosystem functioning through time. Specifically, in chapter 1, I model how multiple persistent drivers impact the extinction probability of a species. In chapter 2, I quantify how chronic irrigation and fertilization push several aspects of community structure away from ambient trajectories. In chapter 3, I determine how chronic nitrogen enrichment shifts species richness and soil pH leading to diminishing returns of fertilization on productivity through time. My results show that (1) current extinction rates may be underestimated by not considering multiple concurrent and interacting drivers., (2) communities are becoming increasingly dissimilar from ambient conditions, and (3) losses in richness under N-enrichment not only indirectly impact productivity but may also lead to soil acidification, further limiting productivity. This dissertation begins to untangle some of the complex relationships between multiple global changes and the fate of ecosystems, and demonstrates the importance of such approaches for accurate predictions and pertinent, proactive management strategies.