Succession in a water column An adapting ecosystem maneuvering between autotrophy and heterotrophy Jorn Bruggeman Theoretical biology Vrije Universiteit Amsterdam

Ecosystem building blocks: species 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, no initial state available phytoplankton zooplankton nitrogen detritus NO 3 - NH 4 + DON labile stable, severely underdeterminedForever incomplete

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 size autotrophy heterotrophy predation defense

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

2b. Species projection in trait space Discrete distributionContinuous approximation

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

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

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

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

Setting: plankton in a water column biological activity immigrationvertical diffusion

Results nutrient, biomass, organic matter

Results autotrophic and heterotrophic biomass

Results autotrophy & heterotrophy ratio and correlation

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