Energy transfer - Ecosystems

Question 1

Secondary Production

Answer 1

Net secondary production (NSP): The amount of
energy in a consumers’ food that is converted to
biomass (GSP - respiration)
Gross secondary production (GSP): total energy taken in minus excretion (food eaten - excretion

Question 2

Production efficiency

Answer 2

We can calculate efficiency as the percentage of energy assimilated from food that is used for growth (i.e. new biomass)
Net secondary
Production
———————-
Gross secondary
production

Question 3

How do inefficiencies occur

Answer 3

Inefficiencies occur because not all of what an organism eats can be digested AND organisms use energy (i.e. energy is respired)

Question 4

Trophic efficiency

Answer 4

We can also estimate the efficiency of transfer between trophic levels (i.e. % production transferred at each trophic step)
Trophic efficiency always less than production efficiency (some portion of each trophic level is not consumed)
* Trophic efficiencies typically ~10% (range from 5-20%)

Question 5

Decomposers

Answer 5

breakdown dead organic matter externally and subsequently absorb nutrients (e.g. bacteria, fungi, protists)

Question 6

Detritivores

Answer 6

eat/consumer dead organic
matter/detritus (e.g. earthworms, millipedes,
slugs, termites)

Question 7

Coprovores

Answer 7

Organisms that consume and re-digest the waste produced by others

Question 8

Pyramid of biomass

Answer 8

Pyramid of biomass a consequence of inefficient energy flow (thermodynamics)
Some biomass pyramids are inverted – aquatic food webs

Question 9

Why is so much ‘food’ left uneaten?

Answer 9

Global terrestrial NPP ~6x1010 metric tons per year, of which herbivores consume less than 20%

Question 10

The green world Hypothesis

Answer 10

Top-down control of herbivores by predators allows plant biomass to accumulate (Hairston et al. 1960)
Kelp + urchins + otters = green world

Question 11

The bad tasting world hypothesis

Answer 11

“The world is prickly and tastes bad” (Murdoch 1966)
Plants evolve defences that force herbivores to compete for a limited amount of palatable
food –> bottom-up regulation

Question 12

Warming affects trophic transfer efficiency

Answer 12

Faster rates of energy transfer in
warmed systems
56% decline in trophic transfer efficiency in warmed systems