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Chapter 3Ecosystem Ecology
Ecology
OrganismsPopulationsCommunitiesEcosystemsBiosphere
Fig. 3-5, p. 58
Ecological Organization
Abiotic CLIMATE!!
WaterAir
NutrientsRocksHeat
Solar energy
BioticLiving and once
living
Fig. 3-6, p. 59
Ecosystem Ecology Examines Interactions Between the Living and
Non-Living World
Ecosystem Boundaries
• ecosystems interact with other ecosystems
Energy Flows through Ecosystems
One-way flow of high-quality energy:Sun → autotroph → heterotroph→ environment as heat → radiation to
space
Photosynthesis and Respiration
Trophic Levels, Food Chains, and Food Webs
• Decomposers
• Consumers that release nutrients
• Bacteria
• Fungi
• Detritivores
• Feed on dead bodies of other organisms
• Earthworms
• VulturesFig. 3-9a, p. 61
Many of the World’s Most Important Species Are Invisible
to Us
Microorganisms
• Bacteria
• Protozoa
• Fungi
Fig. 3-10, p. 61
Fig. 3-14, p. 61
Abiotic chemicals(carbon dioxide,
oxygen, nitrogen, minerals)
Heat
Heat
Heat
Heat
Heat Solarenergy
Consumers(herbivores, carnivores)
Producers(plants)
Decomposers(bacteria, fungi)
Ecosystem Productivity
• Energy captured via photosynthesis over a given amount of time.
• Energy captured minus the energy respired by producers.
Productivity varies among ecosystems
• NPP = GPP – respiration by producers
• Measured in g C/m2/year
• Productivity = NPP/GPP*100
The amount of increase in organic matter per unit of time.
Usable Energy Decreases with Each Link in a Food Chain or Web
• Biomass
• represents the chemical energy stored at each energy level
• dry weight, water is neither a source of energy, nor has any nutritional value
• Standing Crop
• amount of biomass at a given time
• may be high even if productivity is low due to accumulation
Fig. 3-14, p. 65
Energy Flow in an Ecosystem: Losing Energy in Food Chains and
Webs
• Ecological efficiency can range from 5-20% across ecosystems
• Measured in Joules
• On average, 90% of energy is lost with each transfer through the trophic pyramid
Figure 3-19Figure 3-19
10% Rule AKA the Ecological Rule of
Thumb• In accordance with the 2nd law of thermodynamics, there is a
decrease in the amount of energy available to each succeeding organism in a food chain or web.
Most trophic pyramids assume 10% ecological efficiency
Fig. 3-7, p. 55
Nitrogencycle
Biosphere
Heat in the environment
Heat Heat Heat
Phosphoruscycle
Carboncycle
Oxygencycle
Watercycle
Nutrient Cycles in the Biosphere
The Hydrologic Cycle
Alteration of the hydrologic cycle by
humans
Fig. 3-18, p. 69Fig. 3-17, p. 68
1.Withdrawal of large amounts of freshwater at rates faster than nature can replace it
2.Clearing vegetation
3.Increased flooding when wetlands are drained
The Carbon Cycle
Carbon's Special Knack for Bonding
• Animals also release gases, like CH4, as flatulence or burps.
• C is also released as CH4
through decomposition by fungi and bacteria
Carbon Reservoirs in Oceans
• shells, skeletons, coral reefs
• Biological pump: organisms in the upper ocean sink to the bottom
• CO2 can dissolve into ocean water OR can dissolve into precipitation that ends up in the ocean
• form carbonates, limestone, dolomite
Carbon Reservoirs on Land
• Old growth forests/trees that live for thousands of years
• Trapped in ice caps/glaciers
• CaCO3 (limestone or sedimentary rocks)
• Incorporated into the soil
• Freshwater wetlands/bogs
• Peat formation (burial of plant material under anaerobic conditions)
• Dissolved in aquifers
Why Do We Need Carbon?
• Carbon is the basic building block required to form
• proteins
• carbohydrates
• fats
Effects of Human Activities on Carbon Cycle
• We alter the carbon cycle by adding excess CO2 to the atmosphere through:
1. Burning fossil fuels.
Coal: C (s) + O2 CO2
Natural gas: CH4 + 2O2 CO2 + 2H2O
Gasoline: 2C8H18 + 25O2 16CO2 + 18H2O
2. Clearing vegetation faster than it is replaced.
3. Burning biomass, trash, or waste releasing CO, CO2, C particulates (slash & burn agriculture)
4. Release of CO2 by deep plowing or strip mining
5. Landfills release methane (CH4 )
Effects of Human Activities
on Carbon Cycle5. Raising cows and other ruminants that burp
and fart
6. Manufacture of carbon containing compounds like CFCs
7. Destruction of wetlands
8. Production of cement releases CO2
Breaking Carbon Bonds
Consequences of Human Activities
on Carbon Cycle1. Climate change
a. Loss of some speciesb. Climate zones shiftc. Flooded habitats
2. Sea level risea. Coastal habitats flooded
3. Ice caps/glaciers meltinga. Flooding and habitat loss
4. Ocean acidificationa. Shells of marine organisms dissolveb. Lower pH below tolerance level
The Nitrogen Cycle
• Heavily dependent on bacteria for each step:
1nitrogen-fixation, 2assimilation, 3ammonification, 4nitrification, and 5denitrification.
#1: Nitrogen Fixation
• Atmospheric nitrogen is converted to ammonia or ammonium ion by nitrogen-fixing bacteria that live in legume root nodules or in soil OR atmospheric nitrogen is converted to nitrogen oxides by lightening.
• N2 NH3 or NH4+
Nitrogen-fixing bacteria
•N2 NOx
Lightening
#2: Assimilation
• Plant roots absorb ammonium ions and nitrate ions for use in making molecules such as DNA, amino acids and proteins.
• Consumers assimilate nitrogen through eating producers.
#3: Ammonification
• When plants and animals die, bacteria and fungi take up some of the N-molecules.
• The remaining is released as ammonium ions or ammonia gas.
• R- NH2 + H2O NH4+ NH3 + OH- + CO2
Decomposing bacteria
•Assimilation can occur here also
#4: Nitrification• Soil bacteria oxidize ammonia and ammonium
ions to nitrite & nitrate ions.
• NH3 or NH4+ NO2
-
• NO2- + H2O NO3
- + 2H
Soil bacteria
#5: Denitrification• Denitrifying bacteria reduce ammonia, nitrite,
nitrate back to nitrogen gas (under anaerobic conditions).
• NH3 or NO2- or NO3
- N2
Denitrifiying bacteria
Why Do We Need Nitrogen?
• Your body needs nitrogen
• to make other amino acids to synthesize proteins
• for metabolic processes that depend upon enzymes
• to make DNA, which makes up your genes
• to make RNA, which is involved in protein synthesis
Human intervention in the nitrogen cycle
1. Additional NO and N2O in atmosphere from burning fossil fuels; also causes acid rain
2. N2O to atmosphere from bacteria acting on fertilizers and manure
3. Destruction of forest, grasslands, and wetlands
4. Add excess nitrates to bodies of water
5. Remove nitrogen from topsoil
Effects of Human Activities
on the Nitrogen Cycle• Human activities
such as production of fertilizers now fix more nitrogen than all natural sources combined.
Figure 3-30Figure 3-30
The Phosphorus Cycle
• Bacteria are not as important
• Not usually found in the atmosphere (only as dust)
• Limiting factor for plant growth (except in Alabama!)
• Usually insoluble in water and is not found in most aquatic environments
• SLOW PROCESS
Why Do We Need
Phosphorus?• Your body needs phosphorus
• to make nucleotides (DNA & RNA)
• to make ATP in cells
• to make phospholipids (cell membranes)
• to give strength to your bones and teeth enamel
Effects of Human Activities
on the Phosphorous Cycle1. Clearing forests
2. Removing large amounts of phosphate from the earth to make fertilizers
3. Erosion leaches phosphates into streams
Excess Phosphorus
• Limiting factor in aquatic ecosystems
• Causes algal blooms
• Algae die
• Decomposers use lots of O2
• Hypoxic conditions result
• Comes from agriculture, residential runoff & household detergents
Calcium, magnesium, and potassium are important
macronutrients• Regulate cellular
processes
• Transmit signals between cells
• Derived from rocks & decomposing vegetation
• Attracted to soil particles by positive charges
The Sulfur Cycle
• Generalized representation of sulfur oxides is SOx
• The primary air pollutant, sulfur dioxide, is oxidized, once in the atmosphere, to sulfur trioxide.• 2SO2 + O2 2SO3
• Sulfur trixoide dissolves in atmospheric water droplets to form sulfuric acid. • SO3 + H2O H2SO4
Why Do We Need Sulfur?
• Sulfur is a part of
• some of the amino acids in your body and is involved in protein synthesis
• several enzyme reactions
• the production of collagen (forms connective tissues, cell structure and artery walls)
• keratin (gives strength to hair, skin and nails)
We add sulfur dioxide to the atmosphere by:
1. Burning coal and oil
2. Refining sulfur containing petroleum.
3. Convert sulfur-containing metallic ores into free metals such as copper, lead, and zinc releasing sulfur dioxide into the environment.
Ecosystems respond to disturbance
July 2001
August 2005
• An ecosystem has high resistance when a disturbance has no overall effect on the flow of matter and energy.
• An ecosystem that returns to its original state quickly after a disturbance has high resilience.
Restoration Ecology
The Intermediate Disturbance Hypothesis
• Ecosystems experiencing intermediate levels of disturbance are more diverse than those with high or low disturbance levels
Favor best competitors
Eliminate most species
Both extremes exist
Instrumental Values of Ecosystems
Provisions
Regulating servicesSupport systems
Instrumental Values of Ecosystems
Resilience
Regulating services
Intrinsic Values of Ecosystems
Should we value only what we can put a price on as humans?