Lecture 14: Energy Flow

Question 1

What is the simple model for energy flow through an ecosystem?

Answer 1

Solar energy fuels producers
Producers fuel consumers
Consumers fuel decomposers
All 3 lead to dead organic matter

Question 2

How is energy transferred in food chains?

Answer 2

From one trophic level to the next
(ex: grass give energy to antelopes which give energy to cheetahs)

Question 3

Why are food chains typically short?

Answer 3

• Longer chains tend to be unstable
• Increasingly less energy reaches higher trophic levels (due to excretion/respiration or the fact that not all available food is/can be consumed)

Question 4

Does biomass increase or decrease up the food chain?

Answer 4

Decreases! (less consumer mass than producer mass)

Question 5

When can a biomass pyramid be inverted (more consumer mass than producer mass)?

Answer 5

When the biomass of procedures is replaced rapidly
(ex: constant 20 kg of algae can feed 30kg of fish if the algae regenerated super fast)

Question 6

When can energy pyramids be inverted?

Answer 6

Never!

Question 7

What is gross primary production?

Answer 7

Amount of CO2 fixed by the plant in photosynthesis

Question 8

What is net primary production?

Answer 8

Gross primary production minus respiration
(accumulation of carbon)

Question 9

Ex: gross primary production of 1000g/m2/year with respiration of 200g/m2/yr and energy transfer efficiency is 20%. How much energy passes to herbivores?

Answer 9

(1000-200)*0.2 = 160 g/m2/yr

Question 10

What is net ecosystem production?

Answer 10

gross primary production minus respiration from:
- plants
- carnivores
- herbivores
- decomposers

Question 11

What happens in net ecosystem production > 0

Answer 11

more carbon produced than lost = carbon sink

Question 12

What happens if NEP < 0?

Answer 12

Less carbon produced than lost = carbon source

Question 13

How is water limiting to terrestrial primary production?

Answer 13

Water needed for photosynthesis
Less water means less photosynthesis which means less organic carbon produced.

Question 14

How does deforestation affect carbon cycling?

Answer 14

1. forest removal means CO2 sink removal
2. Burned wood = uncontrolled release of CO2
3. increases decomposition of organic soil matter (increased CO2 released)
4. Land use change: agriculture/industry replaces carbon sink with a source