Herbivores and pathogens mediate grassland responses to global changes

Abstract

Human wellbeing depends on the functioning of Earth’s ecosystems which provide invaluable provisioning services (e.g., food and fuel production) and regulating services (e.g., water purification, carbon storage, and climate regulation) (Cardinale et al. 2012). However, human activities (e.g., changes in land use and resource extraction) and associated climate change are impacting ecosystem functioning by changing biodiversity through species extinctions and introductions (e.g., spread of invasive species or grazing by domestic livestock) and changing the availability and cycling of resources that drive ecosystems including water, carbon, nitrogen, phosphorous and potassium (C, N, P and K) (Rockstrom et al. 2009). Over the last few decades, research has examined the impacts of human activities on biodiversity and resource supplies (Rockstrom et al. 2009; Ceballos et al. 2015), biodiversity on ecosystem functioning (Cardinale et al. 2012; Tilman et al. 2014), and more recently, changes in climate and resources on biodiversity (Harley 2011; Malcolm et al. 2006; Harpole et al. 2016). Much of this research has focused on plant diversity; however, human-induced ecosystem changes simultaneously affect a whole host of organisms and their interactions (Harley 2011), while also impacting resource supplies. A full understanding of human impacts on the Earth’s ecosystems requires research that includes a wide range of organisms from microbes to mammals (Soliveres et al. 2016), and examines their impacts on ecosystem functioning in relation to the changing availability of resources due to climate change and other human activities. The broad goal of this dissertation research is to examine the impacts of concurrent loss of a broad range of biodiversity and changes in resource supply (water, N, P, K) on ecosystem functions. More specifically, my goal has been to advance our understanding of how various plant consumers and pathogens, from soil fungi to large herbivores, influence the effects of global changes on plant communities, ecosystem functions and stability. To do this, I used a combination of new and ongoing experiments conducted across grasslands of the world to examine how grassland ecosystems respond to changes in plant diversity, presence of consumers and pathogens, resource supply (N, P & K), and climate (temperature and precipitation).