Robustness of size–structure across ecological networks in pelagic systems

Abstract

The study of biomass size distributions has become an important tool for addressing aquatic ecosystem complexity and the consequences of anthropogenic disturbances. However, it remains unclear how changes in pelagic food web topology affect the biomass size–structure. Employing a dynamic multispecies bioenergetic consumer-resource model, we simulated biomass trajectories over time in 10,000 virtual networks of varying topology to address which food web properties are important in determining size–structure in pelagic systems. The slopes of the normalized biomass size spectra (NBSS) and Pareto’s shape parameter (γ) of our modeled communities are consistent with theoretically expected values for steady-state systems and empirical values reported for several aquatic ecosystems. We found that the main drivers of the NBSS slope and Pareto’s γ were the slope of the relationship between body mass and trophic level, the maximum trophic level of the food web, and the stability of total community biomass. Our analyses showed a clear conservative trend in pelagic community size–structure as demonstrated by the robustness of the NBSS slope and Pareto’s γ against most of the topological changes in virtual networks. Nevertheless, these analyses also caution that major disturbances in large-bodied or top-trophic level individuals may disrupt this stable pattern.