1. Communities and Ecosystems

2. Trophic structure is a key factor in community dynamics
Every community has a trophic structure
A pattern of feeding relationships consisting of several different levels
The sequence of food transfer from producer to consumer is called a food chain.
Producers are autotrophs (“self feed”)
Consumers are heterotrophs (“different feed”)

3. Food chains interconnect, forming food webs
A food web
A network of interconnecting food chains
Arrows indicate direction of nutrient transfer
Several 1° Consumers depend on same producer
Some eat at multiple levels
Figure 37.10

4. Includes a community and the abiotic factors with which it interacts.
Ecosystem ecology emphasizes the processes
energy flow and chemical cycling
Transfer substances through trophic levels. But one flows out the other cycles within.
An ecosystem
Includes a community and the abiotic factors with which it interacts.
Chemical
cycling
Energy
flow
Light
energy
Chemical elements
Heat
Figure 37.11

5. Each day Earth receives energy from the sun
Each day Earth receives energy from the sun equivalent to 100 million atomic bombs…
Most is absorbed, scattered, and reflected by our atmosphere or by the Earths surface.
Only 1% of all the light energy the Earth receives is converted into chemical energy by primary producers through photosynthesis (the process of changing light into sugar and other foods/chemical energy).
However, on a global scale this is enough to produce170 billion tons of organic material per year.

6. The amount of living organic material in an ecosystem is its Biomass.
The amount of solar energy converted to chemical energy (organic material) by producers in a given area at a given time is called primary production.
Primary production

7. Primary production sets the energy budget for ecosystems
Is the rate at which producers convert sunlight to chemical energy in organic matter (biomass)
Open ocean
Estuary
Algal beds and coral reefs
Tundra
Temperate grassland
Cultivated land
Boreal forest (taiga)
Savanna
Temperate deciduous forest
Tropical rain forest
500
1,000
1,500
2,000
2,500
Average net primary productivity (g/m2/yr)
Figure 37.12
Desert and semidesert scrub
Contributes most to Earth’s total net production due to its size

8. Energy supply limits the length of food chains
A pyramid of production
Shows the flow of energy from producers to primary consumers and to higher trophic levels
1/1000 of the sun’s energy makes it this far
Tertiary
consumers
Secondary consumers
Primary
Producers
10 kcal
100 kcal
1,000 kcal
10,000 kcal
1,000,000 kcal of sunlight
Can’t eat all
Can’t digest all
2/3 digested used by cells
Rest to mass (growth)
Only this can be eaten by next level.
(1% of sun’s energy)
Figure 37.13

9. Limited by availability of energy
Only about 10% of the energy stored at each trophic level is available to the next level
Only a tiny amount of the energy converted by primary producers flows through he food chain to the top consumer
This is why top level consumers require so much territory…
It takes a lot of vegetation to support trophic levels so many steps removed from photosynthetic production.
Also why food chains are limited in size
Limited by availability of energy

10. CONNECTION
A production pyramid explains why meat is a luxury for humans
A field of corn
Can support many more human vegetarians than meat-eaters (less energy is wasted)
Trophic level
Secondary consumers
Primary consumers
Producers
Human
vegetarians
Corn
meat-eaters
Cattle
Figure 37.14

11. Chemicals are recycled between organic matter (organisms) and abiotic reservoirs
Biogeochemical cycle
Consumers
Producers
Nutrients
available
to producers
Abiotic reservoir
Detritivores 3 2 1 4
Decomposers
Figure 37.15
Soil

12. Water moves through the biosphere in a global cycle
Transport over land
Solar energy
Net movement of water vapor by wind
Runoff and
groundwater
Percolation
through soil
Precipitation over land
Evaporation and
transpiration from
land
Precipitation
over ocean
Evaporation from ocean
Solar heat
drives the global water cycle through
precipitation, evaporation, and transpiration
Figure 37.16

13. Human activity affects the global water cycle
Important source of atmospheric water is transpiration, so destruction of the rain forests will change amount of water in the atmosphere and can alter local and global weather patterns.
2) Pumping large amounts of ground water to the surface for irrigation can increase evaporation and deplete ground water supplies.

14. The carbon cycle relies on photosynthesis, respiration, and decomposition
Carbon compounds (organic) are consumed.
Respiration returns CO2 to the atmosphere.
Photosynthesis = Respiration
Burning fossil fuels is increasing CO2 levels and is causing global warming.

15. The nitrogen cycle relies heavily on bacteria
Nitrogen is a constituent of DNA and proteins…is essential for life.
Various bacteria in soil convert gaseous N2 to compounds that plants use:
ammonium (NH4+) and nitrate (NO3–)
Detritivores decompose organic matter and recycle nitrogen to plants.
Figure 37.18

16. Humans are altering the nitrogen cycle
Humans are altering the nitrogen cycle
Sewage treatment facilities often empty large amounts of nitrogen into rivers and streams
2) Fertilizer is routinely applied
These nitrogen sources continue to fertilize when they enter lakes and streams causing algae blooms
Nitrates enter ground water used as drinking water and can be toxic

17. The phosphorus cycle depends on rock weathering
Phosphorus is needed for nucleic acids (DNA), phospholipids (cell membranes), bones and ATP (energy)
It and other soil minerals are recycled locally.
Weathering is a slow process so phosphorus is limited.
Figure 37.19

18. In aquatic systems that have not been altered by humans the limited amount of phosphorus keeps algae to a minimum.
In areas affected by humans (sewage, fertilizers, pesticides) phosphate pollution leads to heavy algal growth.
Major algae blooms can kill aquatic organisms and be toxic to humans.