Ecological Stoichiometry: Population Dynamics

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.