Collaborative Research: Linking carbon preferences and competition to predict and test patterns of functional diversity in soil microbial communities

This project will develop theory to understand the connections between biodiversity and competition for limiting resources. Competition is an important interaction among all living organisms. For example, plants compete with other plants for light and nutrient resources, while animals compete for food and territories. Because resources are limited, competition is unavoidable. This limitation constrains the ability of species to coexist together, so scientists seeking to understand biodiversity must also understand competition. Competition theory suggests that competing species can only coexist by specializing on different resources. However, this cannot explain the existence of diverse communities where species outnumber the resources. This project will explore the theoretical possibility that species in diverse communities may successfully share resources. The project will develop theory to test if coexistence occurs when communities contain clusters of species with highly similar traits but high dissimilarity among clusters. The focus will be on soil microbial communities, which are among the most diverse on Earth. Soil microbes compete for carbon molecules, which are their main source of energy and biomass. The research will quantify how these interactions affect those microbes’ ability to coexist. Given the important role that microbes play in nutrient cycling and the likely impacts that temperature changes have on competitive relationships, this research will allow ecologists to predict the consequences of accelerated environmental change. Additionally, this project will train and mentor graduate and undergraduate students and produce an interactive online app where students will learn how competition among individuals creates patterns of biodiversity at the community scale. The research builds on existing consumer-resource microbial models to develop a trait-based multispecies competition model for soil bacteria. The model will assume that carbon sources have natural inflow and degradation rates while microbe populations grow from immigration and temperature-dependent resource uptake and have a fixed mortality rate. Each species will have its own repertoire of usable carbon sources and, as it uptakes those resources, produces byproducts which may be part of other species’ repertoires (cross-feeding). The approaches include computer simulations, statistical inference, and clustering analysis in high-dimensional spaces. The central hypotheses that will be tested are a) competitive dynamics coupled with dispersal leads to the spontaneous emergence of several co-occurring consortia of species, such that species in the same cluster have high overlap in carbon preferences, whereas species in different clusters have low overlap in carbon preferences; b) environmental conditions and dispersal regimes determine the number and species composition of the clusters. These hypotheses are supported by results showing that competition is an important process in microbial communities and by the observation of analogous clustering patterns in competition-driven communities of animals, plants, and phytoplankton. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.