Sack Lunch Seminar (SLS)

Nature Made Simple: Simple Adaptive Models for Complex Plankton Communities









Plankton communities contribute significantly to global biogeochemical cycling. The direction and magnitude of their contribution depends on their species composition, which varies in time and space. This becomes all the more relevant under environmental change, as species diversity ensures that the community will adapt to changing conditions. Most global climate models do not account for this. This is understandable: explicitly incorporating many distinct species only makes models intractable and underdetermined. There is, thus, much to gain from parameterizations of community diversity, sufficiently detailed to resolve shifts in species composition, yet simple enough to permit efficient simulation and constraint by observations. To obtain such a parameterization, I describe the plankton community by a distribution of biomass over one or more continuous traits, e.g., the size, growth and sensitivity to predation of species. This distribution can be characterized by a few key statistics: the total biomass, the mean (community strategy), and variance (biodiversity). These statistics can be directly embedded in global circulation models, replacing the hundreds of species that govern community behavior in nature. Application of this aggregate model in simulations of a lake and of the global ocean shows that it can realistically capture dominant changes in species composition. This suggests that it can improve marine biogeochemical models, without resulting in loss of tractability or performance.