1. Ecosystems
Chapter 42

2. What you need to know How energy flows through the ecosystem
The difference between gross primary productivity and net primary productivity
The carbon and nitrogen biogeochemical cycles

3. Ecosystem
The sum of all the organisms living within boundaries (biotic community) and all the abiotic factors with which they interact
Two key parts:
Energy flow (Conservation of Energy)
Chemical cycling (Conservation of Matter)

5. 1. Energy Flow
Traced through feeding relationships (trophic levels) of food chains and webs
Energy cannot be recycled (Entropy)
It must be resupplied
Sunlight provides 1022 J/day of solar radiation

6. Energy Pyramid
Bottom Level: primary producers (aka autotrophs) support all other organisms
1.5 x 1014 kg/year
Upper levels: consumers (aka heterotrophs)
Herbivores (primary consumers) eat primary producers
Carnivores that eat primary consumers are secondary consumers, carnivores that eat secondary consumers are tertiary consumers

7. Detritivores Decomposers that get their energy from detritus
Detritus is nonliving organic material such as the remains of dead organisms, feces, dead leaves, and wood
Essential organisms that recycle organic material from all trophic levels and deposit the nutrients back into the soil for use by producers

8. Primary Production
The amount of light* energy converted to chemical energy by autotrophs
Spending limit for energy budget
Total primary production in an ecosystem is gross primary production (GPP)
GPP is not all available to consumers (some is used by the autotrophs)

9. Primary Production
Net primary production (NPP) = GPP minus the energy used for respiration by the autotrophs
NPP = GPP - Ra
Aquatic ecosystems depend on nutrients (nitrogen and phosphorus) and light availability (photic zone)
Terrestrial ecosystems depend on temperature and moisture

10. Energy Transfer
10% of energy is transferred from primary producers to primary consumers
Only 1% makes it to the secondary consumers
Keeps food chains short

11. Secondary Production
Food that is converted to new biomass relative to the total food consumed
Production efficiency is the % of energy stored in assimilated food that is used for growth and reproduction (not for respiration).
Production Eff =secondary production (new biomass)
Assimilation of primary production
Calculate secondary production and production efficiency for the caterpillar

12. Secondary Efficiency Birds and mammals are low: 1% - 3%
High body temperature
Fish are about 10%
Insects and microorganisms are the most efficient: 40%+

13. 2. Chemical Cycling
Biogeochemical cycles are nutrient cycles that contain both biotic and abiotic components:
Water cycle recycles fresh water
Phosphorus cycle moves nitrogen throughout terrestrial and aquatic ecosystems
Carbon cycle is a balance between photosynthesis and cellular respiration
Nitrogen cycle moves nitrogen from the atmosphere through the living world
Common limiting factor for plant growth (makes this cycle especially important)

18. Nitrogen Cycle Most nitrogen is N2 (unusable by plants)
Nitrogen fixation: Bacteria convert N2 into usable forms of nitrogen
Nitrification is the process by which ammonium is oxidized to nitrite and then nitrate
Plants can absorb ammonium and nitrates
Denitrification by bacteria releases nitrogen to the atmosphere (N2)

19. Human Activities
Acid precipitation – rain, snow, or fog with a pH lower than 5.6
Created by the burning of wood and fossil fuels which mix into sulfuric and nitric acid
Biological magnification – toxins become more concentrated in higher trophic levels
Greenhouse effect – blanket of CO2 traps heat (global warming)
Ozone layer reduces UV light