Ecosystems

Chapter 30

Ecosystem

An array of organisms and their physical environment, interconnected through a one-way flow of energy and cycling of raw materials

Modes of Nutrition

• Photoautotrophs– Capture sunlight or chemical energy– Primary producers

• Heterotrophs– Extract energy from other organisms or

organic wastes– Consumers, decomposers, detritivores

Simple Ecosystem

Model

Energy input from sun

NutrientCycling

ProducersAutotrophs (plants and other

self-feeding organisms)

ConsumersHeterotrophs (animals, most fungi,

many protists, many bacteria)

Energy output (mainly metabolic heat)

The role of organisms in an ecosystemThe role of organisms in an ecosystem

Simple Ecosystem ModelSimple Ecosystem Model

marsh hawk

crow

garter snake

cutworm

flowering plants

fifth trophic leveltop carnivore

(fourth-level consumer)

fourth trophic levelcarnivore

(third-level consumer)

third trophic levelcarnivore

(second-level consumer)

second trophic levelherbivore

(primary consumer)

first trophic levelautotroph

(primary producer)Fig. 30-3, p.528

Tall-Grass Prairie Food Web

earthworms, insects

sparrow

vole pocketgopher

groundsquirrel

coyotebadgerweasel

spider

frog

snake

sandpiper crow

marsh hawk

grasses, composites

marsh hawk

crow

upland sandpiper

garter snake

frog

spiderweasel badger coyote

ground squirrelpocket gopherprairie vole

sparrow

earthworms, insects

First Trophic Level

Second Trophic Level

Higher Trophic Levels

Connections in a tallgrass prairie food web

grasses, composites

Fig. 30-4, p.529

Which statement about ecosystems is false?

1 2 3 4

25% 25%25%25%

1. energy flows in a cycle between producers and consumers

2. nutrients are recycled by passing from producers to consumers and back again via decomposers

3. in most ecosystems, energy flow begins with the capture of solar energy by photosynthesizers

4. heterotrophs include bacteria and fungi

Rain-forest food webRain-forest food web

Rain ForestRain Forest

Energy Losses

• Energy transfers are never 100% efficient

• Some energy is lost at each step

• Limits number of trophic levels in an ecosystem

Two Types of Food Webs

Producers (photosynthesizers)

Energy Input: Energy Input:

herbivores

carnivores

decomposers

decomposers

detritivores

energy in organic wastes, remains

Energy Output

Energy Output

energy lossesas metabolic heat and as net export from ecosystem

Producers (photosynthesizers)

decomposers

detritivores

Transfers: Transfers:

Grazing Food Web

Detrital Food Web

energy in organic wastes, remains

energy lossesas metabolic heat and as net export from ecosystem

Ecological Pyramids

• Primary producers are bases for successive tiers of consumers

• Biomass pyramid– Dry weight of all organisms

• Energy pyramid– Usable energy decreases as it is

transferred through ecosystem

Biomass Pyramid

• Aquatic ecosystem, Silver Springs, Florida

• Long-term study of a grazing food web

5

decomposers, detritivores(bacteria, crayfish)

1.5

1.1

37

third-level carnivores(gar, large-mouth bass)

second-level consumers(fishes, invertebrates)

first-level consumers(herbivorous fishes,turtles, invertebrates)

primary producers (algae,eelgrass, rooted plants)

809

Energy Pyramid

• Primary producers trapped about 1.2% of the solar energy that entered the ecosystem

• 6–16% passed on to next level

21

383

3,368

20,810 kilocalories/square meter/year

top carnivores

carnivores

herbivores

producers

decomposers + detritivores = 5,080

Energy flow at Silver SpringsEnergy flow at Silver Springs

Silver Springs StudySilver Springs Study

Biogeochemical Cycle

• Flow of an essential substance from the environment to living organisms and back to the environment

• Main reservoir is in the environment

• Geologic processes, decomposers aid cycles

Three Categories

• Hydrologic cycle– Water

• Atmospheric cycles – Nitrogen and carbon

• Sedimentary cycles – Phosphorus and other

nutrients

Hydrologic Cycle

atmosphere

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

Watershed

• A region where precipitation is funneled into a single stream or river

Hubbard Brook Experiment

• A watershed was experimentally stripped of vegetation

• All surface water draining from watershed was measured

• Deforestation caused six-fold increase in calcium content of runoff water

Global Water Crisis

• Limited amount of fresh water

• Desalinization is expensive and requires large amounts of energy

• Aquifers are being depleted

• Groundwater is contaminated

• Sewage, agricultural runoff, and industrial chemicals pollute rivers

Aquifer Depletion

Hawaiian Islands Alaska

When the Earth's waters move from ocean to atmosphere to land and back again, it is called the

_____ cycle.

1 2 3 4

25% 25%25%25%

1. water

2. hydrologic

3. hydrodynamic

4. precipitation

A watershed is _____.

1 2 3 4

25% 25%25%25%1. a stream or river

2. a river that discharges water directly into the ocean

3. a region where precipitation becomes funneled into a single stream or river

4. a region where precipitation becomes funneled into a reservoir for use in human communities

Carbon Cycle

• Carbon moves through atmosphere, food webs, ocean, sediments, and rocks

• Sediments and rocks are the main reservoir

• Combustion of fossil fuels changes natural balance

diffusion between atmosphere and ocean

bicarbonate and carbonate in ocean water

marine food webs

marine sediments

combustion of fossil fuels

incorporation into sediments

death, sedimentation uplifting

sedimentation

photosynthesis aerobic respiration

Carbon Cycle: Marine

Carbon Cycle: Land

photosynthesis aerobic respirationterrestrial

rocks

soil water

land food webs

atmosphere

peat, fossil fuels

combustion of wood

deforestation

volcanic action

death, burial, compaction over geologic time

leaching, runoff

weathering

combustion of fossil fuels

My Carbon Cycle

1. I eat carbohydrate molecules.– These are molecules of fuel which I will

“burn”.– Some of the energy released when I burn

them will be trapped for me to use. The rest will be lost as heat.

2. The waste products of burned fuel are carbon dioxide and water. I breathe these out.

3. Plants (or other producers) take in carbon dioxide from the atmosphere and use it to make carbohydrate.

According to the last slide, why do I eat carbohydrates?

25% 25%25%25%1. Because they taste good.

2. Because they contain lots of vitamins.

3. Because they contain lots of energy.

4. Because they are low in calories.

Energy saved from burning up my fuel is saved in the form of :

25% 25%25%25%1. Muscle

2. ATP

3. Fat

4. Heat

The only reason I need to breathe in oxygen is :

25% 25%25%25%1. I need oxygen to “burn” fuel molecules.

2. All living things need oxygen.

3. Oxygen + carbon = carbon dioxide.

4. Oxygen is corrosive.

Breathing out :

25% 25%25%25%1. Helps me regulate my body temperature.

2. Gets rid of excess fuel molecules.

3. Burns extra calories.

4. Gets rid of the waste products of burned fuel.

The carbon in the plants I eat comes from :

25% 25%25%25%1. The atmosphere.

2. The food they eat.

3. The soil.

4. Water.

The carbon in the steak I eat comes from :

25% 25%25%25%1. Supplements in animal feed.

2. Vitamins.

3. The cow’s drinking water.

4. The plants eaten by the cow.

Greenhouse Effect

• Greenhouse gases impede escape of heat from Earth’s surface

Global Warming

Long-term increase in temperature of

Earth’s lower atmosphere

Carbon Dioxide Increase

• Carbon dioxide levels fluctuate seasonally

• Average level is steadily increasing

• Burning of fossil fuels and deforestation are contributing to the increase

Other Greenhouse Gases

• CFCs: synthetic gases used in plastics and in refrigeration

• Methane: released by natural gas production, livestock

• Nitrous oxide: released by bacteria, fertilizers, and animal wastes

Greenhouse Gases Increasing

Table 30-1, p.537

Nitrogen Cycle

• Nitrogen is used in amino acids and nucleic acids

• Main reservoir is nitrogen gas in the atmosphere

• Nitrogen gas can’t enter food web

Fig. 30-16, p.538

Nitrogen Fixation

• Plants cannot use nitrogen gas

• Nitrogen-fixing bacteria convert nitrogen gas into ammonia (NH3)

• Ammonia and ammonium can be taken up by plants

Air Pollution

• Effects of nitrogen oxides released by burning fossil fuels