1. ECOLOGICAL PYRAMIDS

2.  AS A RESULT OF THE SECOND LAW OF THERMODYNAMICS, MOST OF THE ENERGY GOING FROM ONE TROPHIC LEVEL TO THE NEXT IN A FOOD CHAIN OR FOOD WEB IS LOST TO THE ENVIRONMENT.

3. ECOLOGICAL PYRAMIDS  ARE A WAY TO GRAPHICALLY REPRESENT THE RELATIVE ENERGY VALUES OF EACH TROPHIC LEVEL.  THERE ARE THREE MAIN TYPES:

4. PYRAMID OF NUMBERS  SHOWS THE NUMBER OF ORGANISMS AT EACH TROPHIC LEVEL  IN MOST PYRAMIDS, THE ORGANISMSAT THE BASE OF THE FOOD CHAIN ARE THE MOST ABUNDANT, AND EACH SUCCESSIVE TROPHIC LEVEL IS OCCUPIED BY FEWER OFGANISMS.

5. Abandoned FieldOcean Tertiary consumers Secondary consumers Primary consumers Producers © 2004 Brooks/Cole – Thomson Learning

6.  Pyramids of numbers have limited usefulness because they DO NOT indicate the biomass of the organisms at each level. A baby rabbit does not have the biomass as an adult rabbit.

7. PYRAMID OF BIOMASS  Illustrates the total biomass at each trophic level  BIOMASS is a quantitative estimate of the total amount of living material  It indicates the total amount of fixed energy at a particular time  Can be dry weigh or live weight  Generally represent a reduction of biomass at each trophic level

8. Assuming that there is on average a 90% reduction of biomass in each succeeding trophic level:  10,000 kg of grass  1,000 kg grasshoppers  100 kg of toads  Toad eaters, such as snakes, at most,could be only about 10 kg  Even though carnivores do not eat vegetation, it takes a great deal of vegetation to support them.  Give an example of an inverted pyramid of biomass

9. Pyramid of Energy  Illustrates the energy content (kilocalories/square meter/per year) of the biomass of each trophic level.  Always have large energy bases and get smaller with each trophic level  Shows that energy disipates into the environment  Approximately 90% of the energy is lost at each trophic level.  Is it possible to have an inverted pyramid of energy? Why or why not?