Demographic Diversity and Community Dynamics
Nature is a full of diverse life history strategies (demographic diversity); however, our understanding of its effects on community structure and dynamics is still limited. I compared a food web model with stage-structured populations with an equivalent model with unstructured populations. Both models included the maximum of 15 populations, incorporated energetic processes, and allowed existing populations to go extinct and new populations to invade over time.
When the structured model reached stability, three distinct life history strategies emerged, corresponding to life history strategies observed in aquatic systems, demonstrating consistency between the model result and observed natural communities. Results from the structured and unstructured models shared some similarities. All initial, randomly-formed, food web communities were unstable, but extinction and invasion rates declined over time as communities assembled through a series of extinctions and invasions. Total biomass of primary producers declined over time. There were also clear differences between the two models. Reducing niche width led to an increased number of populations under the unstructured model, but led to a reduced number of populations under the structured model. The numbers of persisting populations in both models were very similar after attaining stability, but the average trophic level of consumers in the unstructured model was almost always lower than in the structured model. These results suggest that incorporating stage structures into food web models are needed to bridge current theories in food web dynamics and empirical observations.