Testing the sequence of successional processes in miniature ecosystems.

Dispersal, environmental filtering, and biotic interactions define the species inventory of local communities. Along successional gradients, these assembly processes are predicted to sequentially vary in their relative importance with dispersal as the dominating process early in succession, followed by environmental filtering and biotic interactions at later stages. While observational data from field studies supported this prediction, controlled experiments confirming a sequence of successional processes are still lacking. We designed miniature ecosystems to explicitly test these assumptions under controlled laboratory conditions. Our "Ecosystems on a Plate" (EsoaP) are 3D-printed customized microplates with 24 connected wells allowing us to track dispersal, niche filtering, and biotic interactions among bacteria and plants in time and space. Within EsoaPs, we created heterogeneous habitat landscapes by well-specific nutrient levels or by providing plant seedlings as mutualistic partners in a checkerboard pattern. Bacteria of a single strain were released in one well and subsequently distributed themselves within the plates. We measured the spatial distribution of bacterial abundances at two time points as a function of abiotic or biotic heterogeneity. Bacterial abundance distribution confirmed a shift from initial dispersal-dominated processes to later niche filtering and biotic interactions as more important processes. Our approach follows the principles of IMPORTANCE: Hypotheses regarding the underlying processes of ecological successions have primarily emerged from and have been tested in observational studies, lacking substantial support through controlled experiments. The design of such experiments should focus on testing contemporary ecological theories at the intersection of community assembly and successional research. To achieve this, we developed and employed 3D-printed "Ecosystems on a Plate" (EsoaP) within controlled laboratory settings. EsoaPs surmount several limitations of nanoscale instruments that had hindered their application in ecologically meaningful research. By sharing 3D printing designs, experimental protocols, and data openly, we facilitate reproducibility of our experiments by researchers across diverse ecological disciplines. Moreover, our approach facilitates cost-effective replication of experiments, democratizing access to tools for ecological research, and thus holds the potential to serve as a model for future studies and educational purposes.