Lecture 11

Topics

• Food chain transformations

• Efficiency calculations

The Main Points

• Lindeman felt that the key to understanding the observed structure of communities lay in the way energy was transformed and passed through the "food chains."

• Especially, it became clear that the length of "food chains" would be dictated by the relative "inefficiency" of biological transformations.

• I presented a linear model of energy transformations with plants, herbivores and carnivores and defined the terms we use in the model.
  1. P_g is the symbol we use for Gross Primary Productivity. This is the photosynthetic rate or the rate that energy is being fixed by the plants and stored in simple sugars

  2. R is used for Respiration. We will use this as the sum of all the organisms metabolic costs. It represents a loss of energy along the chain.

  3. P_n is Net Primary Productivity. This is the rate that new biomass is being made by the plants. It can also be thought of as the rate that new food is being made for the herbivores.

  4. Non-Utilized material is that energy not passing along the food chain that eventually ends up in the ooze of the lake or the litter of the terrestrial commmunity. It also represents a loss from the food chain.

  5. Ingestion is intake by animals. It is the rate that energy is being removed from the previous trophic level.

  6. Assimilation is the rate that energy is being brought into the fluids of the animal after digestion. This is a comparable state in animals to P_g in plants.

  7. Egestion is the word Ricklefs uses for the rate that waste is eliminated from the animal after digestion.

  8. Biological efficiency is the ratio of the rate of energy being "fixed" by one trophic level to that of some previous level. Ricklefs presents different sorts of effeciencies in Table 10-3. These are the examples I presented in lecture.