Notes – Ch. 54 (Ecology)

Big Idea 1, Essential knowledge 4.A.5

Overview: Ecosystems, Energy, and Matter

• An ecosystem consists of all the organisms living in a community, as well as the abiotic factors with which they interact (living + nonliving)

• Ecosystems range from a microcosm, such as an aquarium or your garden, to a large area such as a lake or forest

Overview cont.

• Regardless of an ecosystem’s size, its dynamics involve two main processes: energy flow and chemical cycling

• Energy flows through ecosystems while matter cycles within them – (food webs vs. water

cycles for example)

Energy Flow - Trophic Levels

• Organisms in a community are related to each other through feeding relationships

• Each step up in the transfer of energy is known as a trophic level

• All energy ultimately comes from the SUN

Trophic Levels

• Producers– Convert solar (or chemical)

energy into organic compounds

• Primary consumers– Eat producers

• Secondary consumers– Eat primary consumers

• Tertiary consumers– Eat secondary consumers

Trophic Relationships• Energy and nutrients pass from

primary producers (autotrophs) to primary consumers (herbivores) and then to secondary consumers (carnivores)

• Energy flows through an ecosystem, entering as light and exiting as heat (still follows the laws of thermodynamics – energy can’t be created or destroyed, but it can be transformed)

• Nutrients cycle within an ecosystem

Food chains

• A food chain is a linear sequence of links starting from a species that are called producers in the web and ends at a species that is called decomposers.

• A food chain also shows how the organisms are related with each other by the food they eat.

• A straight-line sequence of who eats whom– Simple food chains are rare in

nature

Food Webs

• A food web is a series of connected food chains with complex trophic interactions

Tall-Grass Prairie Food Web

earthworms, insects

sparrow

vole pocketgopher

groundsquirrel

coyotebadgerweasel

spider

frog

snake

sandpiper crow

marsh hawk

grasses, composites

Pyramid of Numbers/Biomass/Energy

• A pyramid of net production represents the loss of energy with each transfer in a food chain

• Numbers, energy, & biomass decreases as one moves up the food chain.– (Biomass- dry mass of organic

matter)

• Most biomass pyramids show a sharp decrease at successively higher trophic levels

Trophic Levels• Ten-Percent Law

– Usable energy is lost through each transfer of energy• Why? (Remember the law of conservation of energy says energy cannot

be created or destroyed; it only changes form.)– Only about 10% of the energy at one trophic level is transferred to the

next trophic level. 90% is lost as heat with each transfer.

• Dynamics of energy flow in ecosystems have important implications for the human population

• Eating meat is a relatively inefficient way of tapping photosynthetic production

• Worldwide agriculture could feed many more people if humans ate only plant material

LE 54-14

Trophic level

Secondary consumers

Primary consumers

Primary producers

Physical and chemical factors limit primary production in ecosystems

• Primary production in an ecosystem is the amount of light energy converted to chemical energy (glucose) by autotrophs during a given time period

• The extent of photosynthetic production sets the spending limit for an ecosystem’s energy budget– The amount of solar radiation reaching the Earth’s

surface limits photosynthetic output of ecosystems– Only a small fraction of solar energy actually strikes

photosynthetic organisms

Gross and Net Primary Production

• Total primary production is known as the ecosystem’s gross primary production (GPP)– GPP: the amount of light energy that is converted to chemical

energy by photosynthesis per unit time• Net primary production (NPP) is GPP minus energy used

by primary producers for respiration• Only NPP is available to consumers• Ecosystems vary greatly in net primary production and

contribution to the total NPP on Earth

LE 54-4

Open oceanContinental shelf

Upwelling zonesExtreme desert, rock, sand, ice

Swamp and marshLake and stream

Desert and semidesert scrubTropical rain forest

Temperate deciduous forestTemperate evergreen forest

Tropical seasonal forest

SavannaCultivated land

EstuaryAlgal beds and reefs

Boreal forest (taiga)Temperate grassland

Woodland and shrublandTundra

0.40.4

1.01.31.51.61.71.82.42.72.93.33.54.7

0.30.10.1

5.265.0

Freshwater (on continents)TerrestrialMarine

Key Percentage of Earth’ssurface area

Average net primaryproduction (g/m2/yr)

6050403020100 2,5002,0001,5001,0005000

Percentage of Earth’s netprimary production

2520151050

125

2,500

3601,500

5003.0

90

900600

800

2,200

600

250

1,6001,200

1,3002,000

700140

0.3

7.99.19.6

5.43.5

0.67.1

4.93.8

2.3

24.45.6

1.20.9

0.10.040.9

22

• Overall, terrestrial ecosystems contribute about two-thirds of global NPP

• Marine ecosystems contribute about one-third

LE 54-5

North Pole

60°N

30°N

South Pole

Equator

60°S

30°S

60°W 60°E 120°E120°W180° 0° 180°

Energy transfer between trophic levels

• Secondary production of an ecosystem is the amount of chemical energy in food converted to new biomass during a given period of time

• An organism’s production efficiency is the fraction of energy stored in food that is not used for respiration• When a caterpillar feeds on a

leaf, only about one-sixth of the leaf’s energy is used for secondary production

Decomposition• Decomposition connects all

trophic levels• Detritivores, mainly bacteria

and fungi, recycle essential chemical elements by decomposing organic material and returning elements to inorganic reservoirs– Eat detritus (organic

waste/remains of dead organisms)

– Can fit in to a food chain or web at any location

Limiting Nutrients

• What limits primary production?– Aquatic Ecosystems

• Light (depth penetration)• Nutriens/Minerals

– Nitrogen– Phosphorus

– Terrestrial Ecosystems• Temperature• Moisture• Minerals (N & P are the main limiting factors for plants.)

Primary Production in Terrestrial and Wetland Ecosystems

• In terrestrial and wetland ecosystems, climatic factors such as temperature and moisture affect primary production on a large scale

• On a more local scale, a soil nutrient is often the limiting factor in primary production

• Actual evapotranspiration is the water annually transpired by plants and evaporated from a landscape

• The addition of large amounts of nutrients to lakes has a wide range of ecological impacts

• In some areas, sewage runoff has caused eutrophication (the addition of artificial or natural substances, such as nitrates and phosphates, through fertilizers or sewage, to an aquatic system) of lakes, which can lead to loss of most fish species

– Can cause a lowering of the oxygen content

– Can cause an increase the numbers of one species that may harm others

LE 54-8

Mountain coniferous forest

Temperate forest

Tropical forest

Temperate grassland

Arctic tundra

Desertshrubland

1,5001,00050000

1,000

2,000

3,000

Actual evapotranspiration (mm/yr)

Net

prim

ary

prod

uctio

n (g

/m2 /

yr)

Chemical cycles

• Life depends on recycling chemical

elements

• Biogeochemical cycles-The flow of a

nutrient from the environment to living

organisms and back to the environment

LE 54-16

Fossilization

Reservoir a Reservoir b

Reservoir c Reservoir d

Organicmaterialsavailable

as nutrients

Organicmaterialsunavailableas nutrients

Inorganicmaterialsavailable

as nutrients

Inorganicmaterialsunavailableas nutrients

Livingorganisms,detritus

Coal, oil,peat

Atmosphere,soil, water

Mineralsin rocks

Assimilation,photosynthesis Burning

of fossil fuels

Weathering,erosion

Formation ofsedimentary rock

Respiration,decomposition,excretion

Water cycle• 1. Water vapor rises and begins to cool in

the atmosphere (it’s a lot colder the higher up in elevation you go – which is why there is snow in the mountains but not in the valley)

• 2. Clouds form when the cooling water vapor condenses into droplets around dust particles in the atmosphere

• 3. Water falls from clouds in the form of rain or snow, which transfers water to Earth’s surface.

• 4. Groundwater and runoff from land surfaces flow into streams, rivers, lakes, and oceans, where they evaporate into the atmosphere to continue through the water cycle

– Approx. 90% of water vapor evaporates from oceans, lakes, and rivers, and the rest comes from the surfaces of plants (through a process called transpiration)

– Freshwater makes up only about 3% of all water on earth; of that, only about 31% of that is available, because 69% is frozen in ice caps and glaciers

– Some environmentalists have stated water will soon be more valuable than oil, due to its scarcity and the fact that so much of it is being polluted (a bottle of water is already more expensive than a similar amount of oil)

Hydrologic (Water) CycleAtmosphere

Ocean Land

evaporation from ocean

425,000

precipitation into ocean

385,000

evaporation from land plants (evapotranspiration) 71,000

precipitation onto land 111,000

wind-driven water vapor40,000

surface and groundwater flow 40,000

The Carbon Cycle• All living things contain carbon• Carbon and oxygen often make

up molecules essential for life• During photosynthesis, plants

convert carbon dioxide (made of carbon and oxygen) into sugar (glucose) and release oxygen back into the air

• These sugars are used as a source of energy for all organisms in the food web.

• Carbon dioxide is recycled when autotrophs and heterotrophs release it back into the air during cellular respiration (the process that is the opposite of photosynthesis – remember?)

Carbon Cycle cont.• Carbon enters a long term cycle when

organic (living) matter is buried underground and converted into coil, oil, or gas deposits.

• The carbon might remain as fossil fuel for millions of years (we call them fossil fuels because they are literally made from long-dead material like dinosaurs and ancient plants)

• Carbon is released from fossil fuels when they are burned, which adds carbon dioxide to the atmosphere

– While carbon is naturally released into the atmosphere through this cycle, because we are digging up and burning these fuels, we are releasing carbon at a much faster rate than is natural, and the earth cannot reabsorb it from the atmosphere fast enough

– We are giving off the equivalent of 4 atomic bombs a second

LE 54-17b

Cellularrespiration

Burning offossil fuelsand wood

Carbon compoundsin water

Photosynthesis

Primaryconsumers

Higher-levelconsumers

Detritus

Decomposition

CO2 in atmosphere

Carbon in Atmosphere

• One pressing problem caused by human activities is the rising level of atmospheric carbon dioxide– Atmospheric carbon is

mainly carbon dioxide

• Carbon dioxide is added to atmosphere– Aerobic respiration, volcanic

action, burning fossil fuels

• Removed by photosynthesis

The Nitrogen Cycle• Nitrogen is an element found

in proteins• The largest concentration of

nitrogen is found in the atmosphere

• Plants and animals can’t use it directly from the atmosphere; it’s captured from the air by bacteria that live in water, soil, or grow on the roots of some plants.

Nitrogen cycle cont.• The process of capture and conversion of

nitrogen into a form that is usable by plants is called nitrogen fixation

• Nitrogen enters the food web when plants absorb nitrogen from the soil and convert them it into proteins

• Consumers (heterotrophs that eat other organisms) get nitrogen by eating plants or animals that contain nitrogen;

– they reuse the nitrogen and make their own proteins

• Because the supply of nitrogen in a food web depends on the amount of nitrogen that is fixed, nitrogen is often a factor that limits the growth of producers (so it’s used in a lot of fertilizers, or you could use nitrogen-fixing plants like beans)

• Nitrogen is returned to the soil in several ways:

– when an animal urinates, – when organisms die and decomposers

convert it into usable material, – and bacteria convert it back into a gas

which returns it to the atmosphere

LE 54-17c

Assimilation

N2 in atmosphere

DecomposersNitrifyingbacteria

Nitrifyingbacteria

Nitrogen-fixingsoil bacteria

Denitrifyingbacteria

NitrificationAmmonification

Nitrogen-fixingbacteria in rootnodules of legumes

NO3–

NO2–NH4

+NH3

Decomposition and Nutrient Cycling Rates

• Decomposers (detritivores) play a key role in the general pattern of chemical cycling

• Rates at which nutrients cycle in different ecosystems vary greatly, mostly as a result of differing rates of decomposition

Nutrient Enrichment

• In addition to transporting nutrients from one location to another, humans have added new materials, some of them toxins, to ecosystems

Agriculture and Nitrogen Cycling• Agriculture removes nutrients

from ecosystems that would ordinarily be cycled back into the soil

• Nitrogen is the main nutrient lost through agriculture; thus, agriculture greatly impacts the nitrogen cycle

• Industrially produced fertilizer is typically used to replace lost nitrogen, but effects on an ecosystem can be harmful

Contamination of Aquatic Ecosystems

• Critical load for a nutrient is the amount that plants can absorb without damaging the ecosystem

• When excess nutrients are added to an ecosystem, the critical load is exceeded

• Remaining nutrients can contaminate groundwater and freshwater and marine ecosystems

• Sewage runoff causes cultural eutrophication, excessive algal growth that can greatly harm freshwater ecosystems (red tides)

Acid Precipitation

• Combustion of fossil fuels is the main cause of acid precipitation

• North American and European ecosystems downwind from industrial regions have been damaged by rain and snow containing nitric and sulfuric acid– By the year 2000, acid precipitation

affected the entire contiguous United States

LE 54-22

Field pH5.3

5.2–5.35.1–5.25.0–5.14.9–5.04.8–4.94.7–4.84.6–4.74.5–4.64.4–4.54.3–4.4<4.3

5.3

5.3

5.35.3

5.3 5.3

5.3

5.2

5.3

5.6

5.9

5.4

5.2

5.2

5.2

5.2

5.4

5.56.0

5.0

5.4

6.3

5.3

5.3

6.15.5

5.4

5.4

5.4

5.4

5.6

5.5

5.5

5.6

5.65.2

5.1

5.15.74.9

5.7

5.0

5.0

5.0

5.04.9

4.9

4.9

4.9

4.14.3

4.3

4.3 4.4

4.44.44.4

4.4

4.5

4.54.5

4.54.5

4.54.5

4.54.5

4.54.5

4.5

4.5

4.54.5

4.54.5

4.54.54.5

4.5

4.64.6

4.64.6

4.6

4.6

4.64.6

4.64.64.6

4.64.6

4.6

4.7

4.7

4.74.74.7

4.7

4.7

4.74.7

4.7

4.74.7

4.7

4.7

4.7

4.84.8

4.8

4.8

4.8

4.8

4.8

4.8

4.8

5.0

5.0

5.3

5.2

5.1

5.1

5.1

5.1

5.2

5.25.2

5.3

5.4

5.4

5.5

5.5

4.74.7

4.7

4.7

4.7

4.7

4.7

4.9

4.84.8

4.64.7

4.7

4.7

4.84.8

4.8

4.8

4.9

4.9

4.9

5.0

5.0

5.0

5.1

5.1

5.0

5.0 5.05.1

5.2

5.3

5.45.4

5.7

Toxins in the Environment

• Humans release many toxic chemicals, including synthetics previously unknown to nature

• In some cases, harmful substances persist for long periods in an ecosystem

• One reason toxins are harmful is that they become more concentrated in successive trophic levels

• In biological magnification, toxins concentrate at higher trophic levels, where biomass is lower

LE 54-23

Zooplankton0.123 ppm

Phytoplankton0.025 ppm

Lake trout4.83 ppm

Smelt1.04 ppm

Herringgull eggs124 ppm

Conc

entr

ation

of P

CBs

Greenhouse Effect

• Greenhouse gases impede the escape

of heat from Earth’s surface

Figure 48.18, Page 880

The Greenhouse Effect and Global Warming

• The greenhouse effect caused by atmospheric CO2 keeps Earth’s surface at a habitable temperature

• Increased levels of atmospheric CO2 are magnifying the greenhouse effect, which is causing global warming and climatic change

Global Warming

Long-term increase in the temperature of

Earth’s lower atmosphere

Figure 48.19, Page 881

Depletion of Atmospheric Ozone

• Life on Earth is protected from damaging effects of UV radiation by a protective layer or ozone molecules in the atmosphere

• Satellite studies suggest that the ozone layer has been gradually thinning since 1975

LE 54-26

Ozo

ne la

yer t

hick

ness

(Dob

son

units

)

350

300

250

200

150

100

50

01960 1965 1970 1975 1980 1985 1990 1995 2000 2005

Year (Average for the month of October)

1955

• Destruction of atmospheric ozone probably results from chlorine-releasing pollutants produced by human activity

LE 54-27

Chlorine atoms

O3Chlorine

Cl2O2

CIO

O2

O2

CIO

Chlorine from CFCs interacts with ozone (O3), forming chlorine monoxide (CIO) and oxygen (O2).

Sunlight causes Cl2O2 to break down into O2 and free chlorine atoms. The chlorine atoms can begin the cycle again.

Two CIO molecules react, forming chlorine peroxide (Cl2O2).

Sunlight

• Scientists first described an “ozone hole” over Antarctica in 1985; it has increased in size as ozone depletion has increased

LE 54-28

October 1979 October 2000

• http://www.youtube.com/watch?v=Ot_KmOTYfRA