Network heterogeneity and metapopulation persistence in Pseudomonas syringae
The population dynamics of a metapopulation are affected by factors beyond the within-patch dynamics of its constituent subpopulations, including its network topology, which can be characterized by the distance and degree of connectivity between subpopulations. Habitat patches may be connected by many dispersal pathways or few. In addition to mean degree of connectivity, metapopulations can vary in the heterogeneity of connection between subpopulations, ranging from entirely homogeneous metapopulations, in which all subpopulations are equally connected to their neighbors, to strongly heterogeneous metapopulations, in which most subpopulations are connected to only one or two neighbors while a few “hub” subpopulations are more highly connected. A highly connected subpopulation can be recolonized by many neighboring populations, increasing its probability of persistence through time. A metapopulation containing such subpopulations, therefore, is also expected to have a higher probability of persistence than a metapopulation with fewer highly connected subpopulations. I tested these expectations by culturing the bacterium Pseudomonas syringae in metapopulation habitats composed of wells and corridors in four configurations ranging from a totally homogenous lattice to a highly heterogeneous scale-free network. A short-duration high-temperature shock was applied to each habitat and metapopulation and subpopulation sizes were monitored.
Bacterial populations in heterogeneous networks returned to their pre-shock abundances and varied in subpopulation size. Network heterogeneity was correlated with metapopulation persistence, ability to recover from disturbance, and heterogeneity of subpopulation persistence. Metapopulation network topology was associated with recovery from disturbance and the probability of constituent subpopulations remaining occupied.