UAlberta Math Biology Seminar: Bo Zhang

A large body of theory predicts that populations dispersing in heterogeneous environments reach higher total size than if non-diffusing, and, paradoxically, higher size than in a corresponding homogeneous environment. However, this theory and its assumptions have not been rigorously tested. We first extended previous theory to include exploitable resources, proving qualitatively novel results, which we tested experimentally using spatially dispersing laboratory populations of yeast. Consistent with previous theory, we predicted and experimentally observed that spatial dispersal increased total equilibrium population abundance in heterogeneous environments. Refuting previous theory, however, this work discovered that homogeneously distributed resources support higher total carrying capacity than heterogeneously distributed resources, even with species dispersal. Recently, we extend our previous work to multiple interacting species to understand their coexistence. Mathematical analysis of models of competition between two identical species moving at different rates of symmetric diffusion in heterogeneous environments show that the slower mover excludes the faster one. The models have not been tested empirically and lack inclusions of a component of directed movement toward favorable areas. To address these gaps, we extended previous theory by explicitly including exploitable resource dynamics and directed movement. We tested the mathematical results experimentally using laboratory populations of the nematode worm, Caenorhabditis elegans. Our results not only support the previous theory that the species diffusing at a slower rate prevails in heterogeneous environments but also reveal that moderate levels of a directed movement component on top of the diffusive movement allow species to coexist. Our results broaden the theory of species coexistence in heterogeneous space and provide empirical confirmation of the mathematical predictions.