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Ecological stoichiometry and the paradox of enrichment: A new approach to a classical problem. Presentation of postdoctoral project Jannicke Moe (Div. of Zoology, Dep. of Biology, University of Oslo, Norway) Also involved: Nils Chr. Stenseth (Div. of Zoology)

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Ecological stoichiometry and the paradox of enrichment: A new approach to a classical problem


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ecological stoichiometry and the paradox of enrichment a new approach to a classical problem

Ecological stoichiometry and the paradox of enrichment: A new approach to a classical problem

Presentation of postdoctoral project

Jannicke Moe

(Div. of Zoology, Dep. of Biology,

University of Oslo, Norway)

Also involved:

Nils Chr. Stenseth (Div. of Zoology)

Dag O. Hessen (Div. of Limnology)

Ole Christian Lingjærde (Dep. of Informatics)

daphnia individuals can be measured by image analysis

Image 1

Image 2

Processed image

Daphnia individuals can be measured by image analysis

Information from image analysis:

  • no. of individuals
  • size of individuals
  • condition of individuals (width:length)
  • dead individuals

(Færøvig, Hessen & Andersen 2002)

experimental setup chemostats
Experimental setup: chemostats
  • 2 L bottles containing algae + Daphnia
  • Continuous input of nutrient medium
  • Gradient of input phosphorous concentration
data collection
Data collection
  • Daphnia populations:
    • number of individuals
    • size of individuals ( age / stage)
    • concentrations of P, C and N
  • Algal populations:
    • number algal cells
    • volume of algal cells
    • concentrations of P, C and N
  • Nutrient medium
    • concentrations of P, C and N
lotka volterra models may not be suitable for all consumer resource systems
INTRODUCTIONLotka-Volterra models may not be suitablefor all consumer-resource systems

Predator-prey systems:

  • Resource similar to consumer
  • Energy limiting factor
  • Lotka-Volterra-based models suitable

Herbivore-plant systems:

  • Resource different from consumer
  • Nutrients additional limiting factor
  • Lotka-Volterra-based models less suitable?
a stoichiometric model the daphnia algae phosphorpus system

Consumer quantity Z

(Daphnia carbon biomass)

Resource quantity C

(algal carbon biomass)

Resource quality Q

(algal P content)

Recycling of P

P (phosphorous in environment)

Phosphorous influx PL

BACKGROUND

A stoichiometric model: The Daphnia-algae-phosphorpus system
a stoichiometric model the daphnia algae phosphorpus system1
BACKGROUNDA stoichiometric model: The Daphnia-algae-phosphorpus system

Z = biomass of Daphnia (mg C L-1)

C = biomass of algae (mg C L-1)

P = mass of phosphorous (mg P L-1)

model predictions effect of p enrichment on dynamics

Stable eqilibrium

Unstable equilibrium

Algal isocline

Daphnia isocline

Daphnia (mgC/L)

Algae (mg C/L)

Algae (mg C/L)

BACKGROUND

Model predictions: effect of P enrichment on dynamics

high P influx

Low P influx

aim of experiments different type of population dynamics along p gradient

Algae

Daphnia

Medium P

High P

Plankton biomass

Time

Plankton biomass

Plankton biomass

Time

Time

EXPERIMENTS

Aim of experiments: Different type of population dynamics along P gradient

Low P

problem with stoichiometric model ignores demography
Problem with stoichiometric model: ignores demography

The stoichiometric model does not distinguish between populations with ...

  • equal biomass
  • different number of individuals
  • equal biomass
  • different size structure

Real population

Stoic. model

what type of model is optimal for analysing the daphnia algae system
What type of model is optimal for analysing the Daphnia-algae system?

Population Physiological Stoichiometric

models models models

Limiting factors: energy only energy only energy + nutrients

Currency: no. of ind. ind. biomass total biomass

Density dependence: + - +

Demograpic structures: + - -

An Individual-based population model could consider

  • limitation by energy + nutrients
  • no. of individuals + biomass
  • individuals condition (width:length)
  • density dependence
  • demographic structures (size / stage)
  • demographic stochasticity
ibpm of the daphnia system some challenges
IBPM of the Daphnia system - some challenges
  • Individuals cannot be "recognised" - can data still be used for IBPM?

What kind of assumptions must be made?

  • How can discrete models (IMPB) be combined with continuous models (stoichiometric)?
  • Will an IBPM that includes stoichiometry get too complicated?