Ecological Stoichiometry: Population Dynamics

by Noam Ross, 13 November 2012


Lauren Yamane talked about Andersen et al. (2004) in our Ecological Stoichiometry course today. Here are her slides, and below, my rough notes on the paper:

Notes on the Paper

  • Stoichiometry is a way of representing food quality - there is evidence that consumers have preference for high quality (e.g., low C:N) food.
  • There is often a mismatch between composition of prey (autotrophs) and needs of consumers. Autotrophs have variable C:N ratios, consumers are more constrained.
    • This mismatch affects carbon transfer efficiency
  • Food quality can drive population fluctuations

Biological Basis

  • N and P driven by needs of protein and RNA
  • The growth rate hypothesis states that high P-content in organisms that are
  • Among plants there is much more flexibility, but also lower relative N and P requirements
  • Heterotrophs have CNP ratios an order of magnitude below autotrophs
  • Differences between autotrophs and heterotrophs are limiting but also drive nutrient cycling and release
  • Threshold element ratio (TER) is the critical ratio where limitation shifts from C/energy to another element. However above this, transfer efficiency decreases as consumers need to excrete extra nutrients.
  • Nutrient requirements vary throughout development. Some stages may be more limiting.

Density Dependence

  • Density dependence of food quality could be positive or negative
    • Grazing of plants may lead to density dependence via quality reduction due to either selective grazing of choice nutrients or induced plant defenses.
    • Alternatively, grazers can mobilize nutrients otherwise difficult for other organisms to acquire, speed up cycling due to lower plant biomass under same nutrient inputs
    • Chemostat experiments with Daphnia have confirmed the latter effect
  • In elaborations on L-V models1, including nutrient limitation bounds the possible regions of predator-prey phase space. The constraint stabilizes the system.
  • Nutrient limitation implies that growth is limited by populations of all species in the system
  • The effect of nutrient on dynamics is limited to nutrient-constrained systems.

Idea - stoichiometry is a great mechanism for looking at seasonal and transient effects

References

Andersen, T., J. J. Elser, and D. O. Hessen. 2004. Stoichiometry and population dynamics. Ecology Letters 7:884–900.


  1. Alan points out that Lotka himself actually talked quite a bit about stoichiometry.