Chapter 4 Pyramids and Productivity

1. Chapter 4Pyramids and Productivity

2. Three types of pyramids: • Pyramid of energy flow • Pyramid of biomass • Pyramid of numbers

3. Pyramid of Energy Flow • Illustrates the greater cumulative loss of usable energy as energy flows through the various trophic levels • Always will be an upright pyramidal shape due to the automatic degradation of energy quality required by the second law of thermodynamics

4. Average Ecological Efficiency: 10%

5. Pyramid of Energy Flow explains three concepts… • It shows why the earth can support more people if they eat at lower trophic levels (eat less meat) • It shows why there are usually only four or five trophic levels in a food chain • It shows why there are so few large top predators

6. Pyramid of Numbers

7. Upright pyramid: Grassland (summer)- many grass plants Inverted pyramid: Temperate forest (summer) – one large tree makes up primary producer level

8. Biomass Pyramids can also be upright or inverted, depending on the ecosystem – In Figure b for example, phytoplankton grow and reproduce quickly and the zooplankton eat phytoplankton so fast that there is never a lot of phytoplankton at any one time (small biomass)

9. Gross Primary Productivity (GPP) Definition: the rate at which an ecosystem’s producers convert solar energy into chemical energy as biomass

10. Net Primary Productivity (NPP) NPP = (rate at which producers store chemical energy as biomass) – (rate at which producers use chemical energy stored as biomass) In other words, total energy stored in photosynthesis minus energy used in respiration

11. NPP - June

12. NPP - December

14. Most productive ecosystems: Based on average NPP: • estuaries • Swamps, marshes • Tropical rainforests Based on total NPP: • Open ocean (because it covers so much of the earth)

15. Agricultural land: Super productive? Despite our addition of nutrients, agricultural land has a NPP of about 3200 kcal/m2/yr Compare to estuaries at over 8800 kcal/m2/yr

16. “The planet’s NPP ultimately limits the number of consumers (including humans) that can survive on earth.” How can we feed more people with the land we have?

17. Solution 1: harvest plants from naturally productive areas, such as estuaries, swamps and marshes Problem: Humans cannot survive on these foods and using them for food would disrupt the natural spawning grounds that provide us with other high-protein foods (e.g., shrimp)

18. Solution 2: Clear areas with demonstrated high NPP, such as tropical rainforest, and use the land for crops Problem: Soil there is very poor, nutrients are tied up in plants, can’t support crops for long

19. Solution 3: harvest food (phytoplankton) from open ocean Problem: Phytoplankton are so widely dispersed that it would take too much energy to collect them; it would also disrupt marine food webs

20. Solution 4: Eat at a lower trophic level Problems: ???

21. Solution 5: Waste less (humans waste 27% of the earth’s total NPP and 40% of the earth’s terrestrial ecosystems’ NPP) Problems: ???