1. Ecosystem Ecology
Ecosystem ecology emphasizes energy flow and chemical cycling.
An ecosystem consists of all of the organisms in a community as well as the abiotic components they interact with.

2. ECOSYSTEM

3. Energy from the sun fuels global ecosystems
The Earth is not a closed system. Energy comes in from outside (i.e., from the sun), moves through ecosystems and ultimately is dissipated into space as heat.

4. Primary Efficiency How much solar radiation is converted into biomass?
Tropical Rain Forests : 1-3%
Temperate deciduous forest : 0.5-1%
Hot deserts : %

5. Food Chains Show energy flow from one trophic level to another
Trophic Levels: groups of organisms that obtain their energy in a similar manner

6. Food Chains
Total number of levels in a food chain depends upon locality and number of species
Highest trophic levels occupied by adult animals with no predators of their own
Secondary Production: total amount of biomass produced in all higher trophic levels

7. Energy Non-cyclic, unidirectional flow
Losses at each transfer from one trophic level to another
- Losses as heat from respiration
- Inefficiencies in processing
Total energy declines from one transfer to another
- Limits number of trophic levels

8. Energy Flow

9. Transfer Efficiencies
Efficiency of energy transfer called transfer efficiency
Units are energy or biomass
Pt = annual production at level t
Pt-1 = annual production at t-1
Et = Pt
Pt-1

10. Transfer Efficiency Example
Net primary production = 150 g C/m2/yr
Herbivorous copepod production = 25 g C/m2/yr
= Pcopepods
Et = Pt
Pt-1
= 25 = 0.17
Pphytoplankton
150
Typical transfer efficiency ranges
*Level 1-2 ~20%
*Levels 2-3, …: ~10%

11. Net Productivity of species n Assimilation of species n
Production Efficiency =
Net Productivity of species n
Assimilation of species n
Group
Production Efficiency
Respiration
Mammals and birds
1 – 3%
97 – 99%
Insects
10 – 41%
59 – 90%
Why the difference?  Homeothermy (it takes a lot of energy to keep warm)

12. Why Is Energy Transfer Not 100% Efficient?
When energy is changed from one form to another, some is degraded in the form of heat. This law of thermodynamics is true for all physical-chemical systems, including living ones.
One ecologist summarized this fact by the statement: “There is no such thing as a free lunch.” All physical transactions come at a cost of energy.

13. Secondary Efficiency
Worldwide : mean = 10% per level

14. Energy and Biomass Pyramids
Kaneohe Bay
10 J
Tertiary consumers
100 J
Secondary consumers
1000 J
Primary consumers
10,000 J
Primary producers
1,000,000 J of sunlight

15. Biomass
Why does the ocean have such a low biomass of primary producers?

16. Inverted Pyramids
In lakes & open sea algae are the main primary producers.
Algae multiple fast but also consumed at a higher rate therefore the pyramid appears inverted.

17. Food Webs Food chains don’t exist in real ecosystems
Almost all organisms are eaten by more than one predator
Food webs reflect these multiple and shifting interactions

18. Antarctic Food Web

19. Nutrients
Unlike energy, nutrients are constantly recycled from one form to another and pass through multiple trophic levels to decomposers to abiotic forms and back to living organisms again.

20. (decomposers and detritus feeders)
Heat
First Trophic
Level
Second Trophic
Third Trophic
Fourth Trophic
Solar
energy
Producers
(plants)
Primary
consumers
(herbivores)
Tertiary
(top carnivores)
Secondary
(carnivores)
Detritvores
(decomposers and detritus feeders)

21. Detritivores
Main decomposers are fungi and bacteria. These break down organic matter and release chemical elements into the soil, water and air where producers can recycle them into organic compounds.
Without the action of decomposers life would cease because essential nutrients would remain locked up in detritus and unavailable to organisms.

22. Detritivores
Detritivores (species that feed on the dead remains of organisms) are also known as decomposers. These include bacteria, fungi and invertebrate animals of numerous species.
2O & HIGHER LEVEL
CONSUMERS
DECOMPOSERS 1O
CONSUMERS
PRODUCERS

23. Fungal decomposition
of a tree stump

25. Primary Production
About 1% of the visible light that strikes earth is converted by photosynthesis into chemical energy.
This is enough energy to create about 170 billion tons of organic matter annually.

27. Gross and net primary productivity
In an ecosystem gross primary productivity (GPP) is the amount of light energy converted into chemical energy per unit time.
Net primary productivity (NPP) is gross primary productivity minus the energy used by the primary producers for respiration.

28. Net primary productivity
Net primary productivity indicates how much energy is available for use by other trophic levels.
It is measured as biomass of vegetation added to the ecosystem per unit area per unit time (g/m2/yr).

29. Net primary productivity
NPP is influenced by light and nutrient availability and differs among ecosystems.
Tropical rain forests have high NPP as do estuaries and coral reefs. Lakes, tundra and the open ocean have relatively low NPP.

31. Global net primary productivity
Tropical rainforests contribute about 22% of the Earth’s total NPP and open ocean about 24%. The open ocean has a much lower rate of NPP, but covers a far larger area.
Various temperate forests and grasslands and the continental shelf (shallow continental waters) contribute most of the rest.

32. Global net primary productivity
Overall, terrestrial ecosystems contribute about 66% of NPP and marine ecosystems the remainder.

33. NET PRODUCTION IN SOME MAJOR BIOMES
Net Production / Unit Area
( grams / meter 2 / year)
BIOME
RANGE
AVERAGE
Desert & Semi-desert
0-250 40
Artic & Alpine Tundra
10-400
140
Coniferous Forest
400-2,000
800
Deciduous Forest
600-2,500
1,250
Grassland
200-1,500
600
Tropical Forest
1,000-3,500
2,000

35. Limits on primary productivity
In marine and freshwater ecosystems both light and nutrients are important in controlling NPP.
The inability of light to penetrate the water limits photosynthesis to the upper layers. More than 50% of solar radiation is absorbed in the first meter. Even in clear water, only about 5-10% of radiation reaches a depth of 20m.

36. Regional annual net primary production for Earth

37. Limits on primary productivity
Nutrient limitation is a major factor affecting NPP in aquatic biomes.
In marine environments the nutrients limiting primary productivity are usually nitrogen and phosphorus, which are scarce in the photic zone.

39. Decomposition and nutrient cycling rates
The rates at which nutrients cycle is strongly affected by the rates at which decomposers work. In the tropics, warmer temperatures and abundant moisture cause organic material to decompose 2-3 times faster than it does in temperate regions.

40. Decomposition and nutrient cycling rates
High rate of decomposition means little organic material accumulates as leaf litter.
In tropical forest about 75% of nutrients are in woody trunks of trees and only about 10% in soil. In temperate forest about 50% of nutrients are in the soil because decomposition is slower.

41. An Ecological Mystery

42. Keystone Species
Kelp Forests

43. An Ecological Mystery
Long-term study of sea otter populations along the Aleutians and Western Alaska
1970s: sea otter populations healthy and expanding
1990s: some populations of sea otters were declining
Possibly due to migration rather than mortality
1993: 800km area in Aleutians surveyed
- Sea otter population reduced by 50%

44. Vanishing Sea Otters 1997: surveys repeated
Sea otter populations had declines by 90%
: ~53,000 sea otters in survey area
: ~6,000 sea otters
Why?
- Reproductive failure?
- Starvation, pollution disease?

45. An Ecological Mystery
Long-term study of sea otter populations along the Aleutians and Western Alaska
1970s: sea otter populations healthy and expanding
1990s: some populations of sea otters were declining
Possibly due to migration rather than mortality
1993: 800km area in Aleutians surveyed
- Sea otter population reduced by 50%

46. Vanishing Sea Otters 1997: surveys repeated
Sea otter populations had declines by 90%
: ~53,000 sea otters in survey area
: ~6,000 sea otters
Why?
- Reproductive failure?
- Starvation, pollution disease?

47. Cause of the Decline
1991: one researcher observed an orca eating a sea otter
Sea lions and seals are normal prey for orcas
Clam Lagoon inaccessible to orcas- no decline
Decline in usual prey led to a switch to sea otters
As few as 4 orcas feeding on otters could account on the impact
- Single orca could consume 1,825 otters/year

48. Carrying Capacity – the number or weight of animals of a single or mixed population that can be supported permanently on a given area
Ecological Carrying Capacity – maximum density of animals that can be sustained without inducing negative effects on ecosystem
Economic Carrying Capacity – density of animals that enables maximal sustained harvesting and is always lower than the ecological carrying capacity