Succession in a water column An adapting ecosystem maneuvering between autotrophy and heterotrophy

1. Succession in a water columnAn adapting ecosystem maneuvering between autotrophy and heterotrophy Jorn Bruggeman Theoretical biology Vrije Universiteit Amsterdam

2. NO3- NH4+ DON labile stable Ecosystem building blocks: species nitrogen phytoplankton zooplankton detritus • Differential changes in abundance produce patterns of interest • total biomass: chlorophyll concentrations, prey fields, fish stocks • mass fluxes: carbon exports • individual abundances: harmful algae • total number of species: biodiversity indices Forever incomplete , severely underdetermined , no initial state available

3. 1. Omnipotent population • Standardization: one model for all species • Dynamic Energy Budget theory (Kooijman 2000) • Species differ in allocation to strategies • Allocation parameters: traits generic species defense predation heterotrophy autotrophy size

4. 2a. Continuity in traits: distributions Phototrophs and heterotrophs: a section through diversity bact 1 heterotrophy bact 2 bact 3 ? ? ? mix 1 mix 2 mix 3 ? phyt 1 mix 4 ? phyt 2 ? phyt 2 phyt 3 phototrophy

5. 2b. Species projection in trait space Discrete distribution Continuous approximation

6. 3. Succession & persistence of species • The environment changes • External forcing (light, mixing) • Ecosystem dynamics (e.g. depletion of nutrients) • Changing environment drives succession • Best strategy will be time- and space-dependent • Trait value combinations define species & strategy • Trait distribution will change in space and time • “Everything is everywhere; the environment selects” • Assumption: background concentrations of all possible species • Actual invasion will depend on niche presence

7. Dynamics of the trait distribution Trait distribution approximated by a normal distribution: trait specific growth rate total biomass trait mean trait variance total biomass mean Lande (1976) – quantitative genetics Abrams at al. (1993) – adaptation Wirtz & Eckhardt (1996) – ecosystem dynamics Dieckmann & Law (1996) – evolution Norberg et al. (2001) – ecosystem dynamics variance • Extensions • log-normal distribution • multiple (potentially correlated) traits • diffusion and advection of moments

8. Trait 1: investment in autotrophy Trait 2: investment in heterotrophy Phytoplankton and bacteriaautotrophy & heterotrophy maintenance + light harvesting nutrient + structural biomass + organic matter harvesting organic matter death +

9. Model characteristics • Ecosystem state variables • nutrient, organic matter, structural biomass • mean autotrophy • mean heterotrophy • variance of autotrophy • variance of heterotrophy • covariance autotrophy-heterotrophy • Parameters • maximum autotrophic and heterotrophic production • half-saturation constants for light, nutrient, organic matter • maintenance rate, death rate

10. Setting: plankton in a water column immigration vertical diffusion biological activity

11. Resultsnutrient, biomass, organic matter

12. Resultsautotrophic and heterotrophic biomass

13. Resultsautotrophy & heterotrophy ratio and correlation

14. Discussion • Phytoplankton-bacteria ecosystem • time: seasonal shift from pure autotrophy to mixotrophy • depth: deep chlorophyll maximum • depth: mixotrophy near surface, pure heterotrophs in deep water • Information in trait distribution moments • traits means give an impression of the ecosystem strategy • correlation coefficient gives insight in underlying community structure • cf. Adaptive Dynamics • no separation of ecological and adaptation (evolutionary) time scales • source of diversity = immigration, not mutation