1. Ecological Pyramids

2. Ecological Pyramids
Ecological pyramids represent numerical relationships between successive trophic levels in a community.
Which pyramid is chosen for examination depends on the type and quantity of data collected.

3. Pyramids
Graphic models of quantitative differences between trophic levels
By second law of thermodynamics energy decreases along food webs
Pyramids are thus narrower as one ascends

5. Losses in the pyramid
Energy is lost between each trophic level, so less remains for the next level
Respiration, Homeostasis, Movement, Heat
Mass is also lost at each level
Waste, shedding, …

7. Pyramids of Numbers
One way to simplify food webs is to assign the organisms to trophic levels and then count the number of organisms in each trophic level.

8. Pyramids of Numbers
Needs sampling similar to Biomass and therefore has the same limitations
Also measures the storages

9. Pyramids of Numbers
Represents the numbers of individual plants and animals present in the food web.
It does not take into account the relative size of any organisms.
Consequently, it is possible to have an inverted pyramid of numbers.

10. © 2004 Brooks/Cole – Thomson Learning
Pyramids of Numbers
Grassland
(summer)
Temperate Forest
(summer)
Tertiary consumers
Secondary consumers
Primary consumers
Producers

11. Pyramids of Biomass A pyramid of biomass takes body size into account
You have to find the dry mass of the organisms in your sample and their energy content (this must be measured in a fixed area).
However, it does seem to be logical i.e. big organisms support lots of little ones.

12. Pyramids of Biomass
Represents the standing stock of each trophic level (in grams of biomass per unit area g / m2)
Represent storages along with pyramids of numbers

13. How do we get the biomass of a trophic level to make these pyramids?
Why can’t we measure the biomass of an entire trophic level?
Take quantitative samples – known area or volume
Measure the whole habitat size
Dry samples to remove water weight
Take Dry mass for sample then extrapolate to entire trophic level

14. How do we get the biomass of a trophic level to make these pyramids?
Evaluation  It is an estimate based on assumption that
all individuals at that trophic level are the same
The sample accurately represents the whole habitat

15. Pyramids of Biomass
Biomass decreases at each trophic level because the transfer of energy from the primary producer to the primary consumer and between the consumers is inefficient. Energy is lost at each stage, that is, at each of the transfers.

16. Pyramids of Biomass See example on your sheet
green plant  zebra  lion

17. © 2004 Brooks/Cole – Thomson Learning
Pyramids of Biomass
Abandoned Field
Ocean
Tertiary consumers
Secondary consumers
Primary consumers
Producers

18. Pyramids of productivity
Pyramids of productivity require much more data to construct since many samples, separated by intervals of time, are needed to estimate productivity,
They provide a coherent view of how an ecosystem works.

19. Pyramids of productivity
Production by primary producers must be greater than production by secondary consumers and so on.
Do not need to consider numbers or differences in size because all organisms can be converted to their energy equivalent.

20. Pyramids of productivity
Flow of energy through trophic levels
Energy decreases along the food chain
Lost as heat
Productivity pyramids ALWAYS decrease as they go higher – 1st and 2nd laws of thermodynamics

21. Pyramids of productivity
Shows rate at which stock is generated at each level
Productivity measured in units of flow
(J / m2 yr or g / m2 yr )

22. © 2004 Brooks/Cole – Thomson Learning Decomposers/detritivores
Energy
Input:
20, ,679,190
1,700,000 (100%)
Energy Output
Total Annual Energy Flow
Metabolic heat,
export
Waste,
remains
1,700,000
kilocalories
Producers
Herbivores
Carnivores
Top
carnivores
Decomposers,
detritivores
Transfers
20,810
(1.2%)
Incoming solar energy
not harnessed
1,679,190
(98.8%)
4,245
3,368
13,197
720
383
2,265 90 21
272 5 16
© 2004 Brooks/Cole – Thomson Learning
Top carnivores
Decomposers/detritivores 21
Carnivores
5,060
383
Herbivores
3,368
Producers
20,810

23. Figure 54.11 An idealized pyramid of net production

24. Efficiency of trophic levels in relation to the total energy
Figure Food energy available to the human population at different trophic levels
Efficiency of trophic levels in relation to the total energy
available decreases with higher numbers
But efficiency of transfer always remains around that 10% rule

25. How does pyramid structure effect ecosystem function?
Limited length of food chains
Rarely more than 4 or 5 trophic levels
Not enough energy left after 4-5 transfers to support organisms feeding high up
Possible exception marine/aquatic systems b/c first few levels small and little structure

26. How does pyramid structure effect ecosystem function?
Vulnerability of top carnivores
Effected by changes at all lower levels
Small numbers to begin with
Effected by pollutants & toxins passed through system