Topology matters: Network topology affects outcomes from community ecology neutral models

Topology affects outcomes of processes in planar networks. Hexagon tessellations have different performance than, and are often superior to, square tessellations in applications such as fluid dynamics, percolation theory, self-avoiding walks, survey sample design, and quantization. Hexagon tessellations and square tessellations using both von Neumann and Moore neighborhoods were examined as a network topology for neutral ecology community models, following the simulation approach of Graham Bell. These models, which assume identical life history and movement properties for each individual of each species, produce collective properties of communities, such as abundance distributions, range distributions, spatial variation in abundance, species–area curves, and spatial variation in species composition, that match many empirical patterns. The simulations in this study varied the dispersal rate but kept birth, death, and immigration rates constant. For these experiments, ending community populations, species richness, Shannon diversity, and Simpson diversity were clearly different for the different topologies, but the relationship between the topologies varied as the dispersal rate changed. Empirical distributions of the performance measures also showed clear differences among topologies. The interaction of topology with dispersal, spatial boundary effects, and other parameters of these models appears to be quite complex and warrants further research.