Announcements
• Extra credit screenplays due Thursday
• Assignment 1 ended today
– Will discuss results on Thursday
• First exam on Feb 2nd in class
• Study guide for midterm 1 posted on under
“Lecture Notes”
– Watch for updates
• Note taker
• Today: Ecosystems
Problems with environmental
economics
• Externalities: Company budgets don’t count
the cost of environmental degradation.
• Public goods: Lack of ownership of
ecosystem goods and services (e.g., air, fish)
• Imperfect information: Lack of knowledge
of harm done to ecosystems
• Topic for today: How do ecosystems work?
Biomes pole-to-pole
• Survey of the earth’s major biomes
• Things to consider when taking notes:
– What is the energy source for most
ecosystems?
– What environmental factors are most
important in determining the distribution of
different biomes?
– Beware: Animals are eaten in nature
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Pole-to-pole concepts
Ecosystem - definitions
• Which of earth’s biomes were covered?
• What were the primary producers in each?
• What environmental factors determined
the distribution of these biomes?
• How does the sun’s energy get
transmitted throughout the ecosystem?
• Eco = house
• System = two or more components that interact
• Ecosystem: Definable unit of organisms interacting with
the environment
• Smallest definable units that can sustain life
David Latimer, from Great Britain,
planted four seedlings and sealed
this terrarium in 1960! It’s been a
self-contained ecosystem since 1972
when he last added water.
Ecosystems
• Hierarchy of ecological elements in the biosphere
• Biotic elements:
organism (species) → population → community
ecosystem
• Abiotic elements:
resources, environmental conditions
•
Global distribution of biomes
ecosystem → landscape → biomes → biosphere
Enger and Smith 2011
2
Global patterns of precipitation
Ecosystems
• Abiotic components of ecosystems
Resources: water, light, oxygen, carbon dioxide,
nutrients, space, …
Conditions: temperature, salinity, pH, wave
energy, wind, …
From Wright and Nebel (2002)
Ecosystems
• Biotic components:
Ecosystem trophic structure
Primary producers: Plants, protists, photosynthetic bacteria
Consumers: Animals, fungi, bacteria
• Primary consumers: Herbivores – e.g, caribou
• Secondary consumers: Carnivores – e.g., wolves
• Decomposers: Detritivores – e.g., bacteria, fungi, worms, insects
Ecosystem Function: Examples
• Most productive ecosystems:
– Marshes, tropical rain forests, algal beds
High nutrient supply or storage
• Least productive ecosystems:
– Deserts (limited by water availability)
– Open ocean (limited by low levels of nutrients)
– Tundra (limited by water, light, temperature, or
nutrient availability, depending upon location)
3
Upwelling, nutrients, and productivity
in marine ecosystems
Upwelling, nutrients, and productivity
in marine ecosystems
NE Pacific upwelling
Equatorial upwelling
Equatorial upwelling
Antarctic upwelling
Important regions of coastal upwelling
Ecosystem services
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UV protection
Air purification
Flood mitigation
Drought mitigation
Pest control
Water purification
Waste decomposition
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Soil formation
Seed dispersal
Aesthetic, cultural
Recreation
Climate stabilization
Erosion protection
Nutrient cycling
Primary functions: Energy capture and distribution
Nutrient cycling
Satellite image indicating spatial pattern of chlorophyll
Ecosystem Functions
• Photosynthesis (plants)
(light)
6CO2 + 6H2O → C6H12O6 + 6O2 (requires energy)
carbon water glucose oxygen
dioxide
• Respiration (plants, animals, bacteria,…)
C6H12O6 + 6O2 → 6CO2 + 6H2O (oxidation releases
energy)
Demo
4
Ecosystem Function: Production and
respiration
Ecosystem Function: Food Chains
• Food-chain trophic levels
6CO2 + 6H2O + nutrients, light ↔
C6H12O6 + 6O2
nonliving
↔
living
inorganic compounds ↔ organic compounds
CO2 and nutrients ↔ biomass
kinetic energy ↔ potential energy
(energy of motion) (stored energy)
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–
–
–
Producers
Primary consumers
Secondary consumers
Tertiary consumers
Materials are recycled, energy is consumed
Ecosystem Function: Energy
transfer among trophic levels
• Only about 10%
of E transferred
to the next level
• 90% lost to
respiration
• This results in
the biomass
“pyramid”
Ecosystem Function: Food Webs
• Simple food
chains are rare
in nature
• Many species of
producers and
consumers
create complex
food webs
5
Summary of Ecosystem Functions
Essential
Global
Carbon
Cycle
• Energy flow
Rivers
• Nutrient flow
• (Energy + Nutrients)
Sustainability lesson:
Energy from the sun
Nutrients recycled
Changes in atmospheric CO2
Arrows and purple numbers: Fluxes in 1015 g C/y
Black numbers: Storage pools in 1015 g C
Nitrogen Cycle
• Nitrogen fixation: Bacteria convert nitrogen gas into
amino acids (N2 → biomass (NH3-acid))
• Nitrogen uptake: Plants take up N (NH3 and NO3-)
during photosynthesis, moves up food chain
• Ammonification: Organism wastes release ammonia
(NH3, NH4+ )
• Nitrification: Bacteria convert ammonium to nitrate
(NH4+ → NO2- → NO3-)
• Denitrification: Bacteria convert nitrate to nitrogen gas
(NO3- → N2 or NH4+ + NO2− → N2 + 2H2O)
• Fertilizer production and use: N2 → NH3 + NO3-
CO2 data from http://scrippsco2.ucsd.edu
6
Simplified Nitrogen Cycle
N mostly
unavailable
N2 in atmosphere
N fixation
Ammonification
organic
matter
(NH3)
N a component of:
proteins
DNA
chlorophyll
etc.
Nitrification
NH4+
Nitrogen and “dead zones”
NO2+
NO3+
Denitrification
(anaerobic
conditions)
Available N
Photosynthesis
N as a nutrient
From Diaz and Rosenberg, “Spreading dead zones and consequences
for marine ecosystems”. Science, 15 August 2008
Ecosystem function summary
• Ecosystems sustain life
• Many functions
– Primary: Energy capture and transfer
Nutrient recycling
• Food webs transfer energy, nutrients
• Global biogeochemical cycles
• Humans activity changes ecosystem function
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