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Chapter 4 Pyramids and Productivity. Three types of pyramids:. Pyramid of energy flow Pyramid of biomass Pyramid of numbers. Pyramid of Energy Flow. Illustrates the greater cumulative loss of usable energy as energy flows through the various trophic levels

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three types of pyramids
Three types of pyramids:
  • Pyramid of energy flow
  • Pyramid of biomass
  • Pyramid of numbers
pyramid of energy flow
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
pyramid of energy flow explains three concepts
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
Upright pyramid: Grassland (summer)- many grass plants

Inverted pyramid: Temperate forest (summer) – one large tree makes up primary producer level


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)

gross primary productivity gpp
Gross Primary Productivity (GPP)

Definition: the rate at which an ecosystem’s producers convert solar energy into chemical energy as biomass

net primary productivity npp
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

most productive ecosystems
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)
agricultural land super productive
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

“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?

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)

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

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

Solution 5: Waste less

(humans waste 27% of the earth’s total NPP and 40% of the earth’s terrestrial ecosystems’ NPP)

Problems: ???