Predators’ switching towards the most abundant prey is a mechanism that stabilizes population dynamics and helps overcome competitive exclusion of species in food webs. However, current formulations of active prey-switching in marine ecosystem models display non-maximal feeding; the total ingestion of prey by predators decays exponentially with the number of prey species even though the total prey biomass stays constant.

In this new study from Darwin Project researchers Sergio Vallina (now at the Marine Sciences Institute, Barcelona, Spain), Ben Ward (École Normale Supérieure, France), Stephanie Dutkiewicz and Mick Follows, the authors describe a new “kill-the-winner“ formulation that combines active switching and ensures maximal feeding. The ecological impact of the mechanism is illustrated in global simulations using the MITgcm ocean model and a marine ecosystem comprised of 64 phytoplankton species belonging to 4 major functional groups. The simulations illustrate that the species richness and biogeography of phytoplankton are very sensitive to the choice of the functional response for grazing. A key finding is that simulated phytoplankton diversity significantly increases when active switching is combined with maximal feeding: perhaps an explanation for the very high diversity of phytoplankton observed in nature?

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Vallina, S. M. , B. A. Ward, S. Dutkiewicz, and M. J. Follows(2013), Maximal feeding with active prey-switching: a kill-the-winner functional response and its effect on global diversity and biogeography, Progress in Oceanography, doi: 10.1016/j.pocean.2013.08.001