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Pollinator responses to global change and its implications for ecosystem function

Final Report Summary - BEEFUN (Pollinator responses to global change and its implications for ecosystem function)

As of the year 2000, 40% of Earth’s ice-free land area is being directly used by humans, and an additional 37% is surrounded by human-modified areas. Land-use change, along with other human-induced global change drivers, are accelerating the rates of extinction of most taxa. Researchers are beginning to experimentally investigate how these changes in biodiversity affect ecosystem services, such as water purification, climate regulation, and food production, but do not yet understand the effects of species loss in real ecosystems. Pollination is a critical ecosystem service and relies upon multiple species of pollinators. This project aims to understand the threats to the pollinator species that provide this critical ecosystem function and assess the consequences of their decline in real ecosystems. Research about the functional consequences of biodiversity is dominated by small-scale experimental studies. These experiments have manipulated diversity by assembling random subsets of species drawn from a common pool of taxa. This approach is useful for understanding the theoretical consequences of diversity loss but is unrealistic in the sense that it assumes species can go extinct in any sequence over time. Extinction, however, is generally a nonrandom process with risk determined by life- history traits such as rarity, body size, and sensitivity to environmental stressors. The importance of biodiversity loss on the production and stability of ecosystem services will depend, then, on which bee species are lost, and which species are well-adapted to anthropogenic habitats. I investigated this relationship by developing a framework that goes beyond aggregate biodiversity measures and takes into account trait functional diversity, species specific responses, and community structure. So far, I found that pollinator species traits do not predict either response to agricultural intensification or its functional contribution, but that a few dominant species are responsible for most of the ecosystem services delivered. In some cases, this species can be exotic species well adapted to disturbed environments. I expanded this ideas in a global synthesis including more than 40 different crops around the globe to show that these dominant species depend on the crop studied, and hence a diversity of pollinators is needed for securing food production. Moreover, during the project we collected four years of data for measuring pollination stability in natural systems in southern Spain in order to answer longer term stability questions. This data will allow me to validate some of the trends observed in larger scale analysis and infer more direct mechanisms on how pollinators respond to global change drivers and its implications for the ecosystem functioning.