Beefun: 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, is 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, using replicated data on three crops along Northeast USA I found that pollinator species traits do not predict either response to agricultural intensification or functional contribution, but that a few dominant species are responsible for most of the ecosystem services delivered. Hence, studying this species may be the most efficient way to make sound predictions. I expanded these 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, I already collected two years of data for measuring pollination stability in natural systems in southern Spain and I plan to collect two more years 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.

LINCX: Understanding biodiversity maintenance is central to ecology, especially on the face of human-induced environmental change and the alarming rates of biodiversity loss. Despite coexistence theory and complex networks theory have produced important theoretical advances on the mechanisms determining species persistence, information from both parallel fields have never been integrated. On one hand, coexistence theory has been useful to explain diversity for pairwise competitive interactions within one trophic level (e.g. plant-plant), but this theory has been difficult to scale up to a multitrophic community level. On the other hand, network theory works at the community level and has theoretically shown that the network structure of interspecific interactions (e.g. mutualism) is a key driver of species coexistence, but the theory still relies on important empirically untested assumptions. While the two theories aim to explain diversity maintenance, they do clash in their approaches. Here we propose to bring together researchers from both disciplines to develop a common framework that can potentially unify both theories. For that end, we choose a key simple question at the core of the controversy: what is a stronger factor determining community persistence, competitive processes or network topology? We will empirically address our question using a plant-pollinator system where plant species under different competition regimes are placed under two contrasting plant-pollinator network topologies. By properly perturbing the system, we can compare changes in species reproduction under different competition regimes and network topologies. The experiment will not only shed new light on the relative importance of competitive versus mutualistic interactions for diversity maintenance, but the measured parameters will directly feed the new theoretical models allowing us to start disentangling the actual conundrum of community persistence.