IMPACTS OF ANTHROPOGENIC ENVIRONMENTAL CHANGES ON BIODIVERSITY, ECOSYSTEM PROCESSES, AND TROPHIC INTERACTIONS

Abstract

Habitat loss, climate change, invasive species, nitrogen deposition, and over-exploitation are all contributing to a global biodiversity crisis. Yet, there is high uncertainty in regards to which drivers exert the largest influence on local biodiversity and ecosystem processes, and how the magnitude, direction, and consistency of responses compares across drivers, habitats, and trophic groups. In this thesis, I generated worldwide databases of empirically derived ecosystem responses to global change and evaluated general trends in local biodiversity and ecosystem responses to several human-induced environmental changes. I then used projections of future environmental change across the Earth’s biomes to assess biases in the spatial distribution of local biodiversity change studies. Lastly, My results revealed widespread decline in local species richness from human-induced environmental changes by an average 18%. Species loss was greatest following land-use change and species invasions. In contrast, species invasions had little consistent impact on several ecosystem processes, and instead warming was the major driver of ecosystem function change. I also observed strong, yet opposite, trends in the predictability of biodiversity responses for species invasions and removals, suggesting that accuracy in forecasting community change is dependent on habitat and trophic role. My analyses emphasized that the biodiversity data used in current biodiversity change syntheses is not geographically representative and I provide recommendations for where future studies should be conducted. Finally, my experiments revealed a strong impact of warming on top predators that cascaded to lower trophic levels. This demonstrates how ecosystem responses to global change are influenced by trophic structure and shows that indirect effects mediated by species interactions can be equally important as direct effects of global change drivers in restructuring ecological communities. My thesis represents a comprehensive empirical evaluation of how contemporary ecosystems respond to human-induced environmental changes. I have illustrated several general trends of local biodiversity and ecosystem process responses across drivers, habitats, biomes, and trophic groups that may inform future predictive analyses of how global change impacts ecosystems around the globe.