Testing the intermediate disturbance hypothesis in species-poor systems: A simulation experiment for mangrove forests

Questions: What factors influence tree species diversity of mangrove forests, an example of species-poor systems? What are the respective importance and interactions of these factors? Is the intermediate disturbance hypothesis applicable to such systems? Methods: We used the spatially explicit individual-based model KiWi to investigate the effects on species diversity of perturbation frequency and intensity, different abiotic conditions, and interspecific competition simulated at the individual level. The simulation system considered the three dominant Caribbean mangrove species: Rhizophora mangle, Avicennia germinans and Laguncularia racemosa, applying species-specific growth and mortality characteristics. Firstly, effects on species dominance of the abiotic conditions nutrient availability and porewater salinity were tested with two competition scenarios. Secondly, the effect of perturbation frequency and intensity were investigated with selected abiotic conditions. Results: Abiotic conditions influenced species dominance and, in extreme cases, excluded one or two species. Abiotic and competition settings controlled the successional dynamics and the response of species dominance to perturbation regimes. A response consistent with the intermediate disturbance hypothesis was observed only with a configuration of plant interaction in which one species behaved as a pioneer so that succession occurred by competitive exclusion. Conclusions: We suggest that successional dynamics interact with the intensity and timing of perturbations and determine whether or not mangrove tree diversity conforms to predictions of the intermediate disturbance hypothesis. For mangroves, these successional dynamics are site-specific depending on abiotic conditions and species configurations.