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?