Competition along a spatial gradient of resource supply: A microbial experimental model

In a set of laboratory experiments, we examined competition for phosphorus between algae and bacteria under various carbon : phosphorus (C : P) supply ratios in spatially homogeneous and heterogeneous microcosms. Experimental results were compared to those predicted by theoretical models of resource competition. In the spatially heterogeneous microcosm, algae that were inf erior competitors for P persisted in vessels with high local C : P supply r atios that would cause exclusion in the spatially homogeneous microcosms. R esource competition theory, adapted to this system, provided a starting poi nt for explaining these results. Spatial structure can enhance local divers ity because locally inferior competitors are transported from source habita ts into sink habitats where they would otherwise be excluded. Such local so urces were determined by their resource supply ratios. These results verify the hypothesis that spatial processes enhance local diversity when a syste m of local habitats is divided into sources and sinks in such a way that ea ch persisting species has at least one source within the system. However, e xisting theoretical models did not accurately predict distributions of comp etitor abundance within this experimental system.