Ecosystems

Chapter 30

Bye-Bye Bayou

• Louisiana’s coastal wetlands are disappearing

• Global warming contributes to wetland’s demise

• Sea levels rising worldwide

• Burning fossil fuels raises global temperature

Impacts, Issues Video

Bye-Bye, Blue Bayou

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

Consumers

• Herbivores

• Carnivores

• Parasites

• Omnivores

• Decomposers

• Detritivores

SPRING

rodents, rabbits

fruits

insects

birds

SUMMER

rodents, rabbits

fruits

insects

birds

seasonal variation in the diet of an omnivore (red fox)

Trophic Levels

• Feeding relationships– All organisms at a trophic level are the

same number of steps away from the energy input into the system

• Autotrophs are producers– closest to energy input– first trophic level

Trophic Levels

5th

4th

3rd

2nd

1st

Fourth-level consumers (heterotrophs):

Top carnivores, parasites, detritivores, decomposers

Third-level consumers (heterotrophs):

Carnivores, parasites, detritivores, decomposers

Second-level consumers (heterotrophs):

Carnivores, parasites, detritivores, decomposers

First-level consumers (heterotrophs):

Herbivores, parasites, detritivores, decomposers

Primary producers (autotrophs):

Photoautotrophs, chemoautotrophs

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

Food chainFood chain

Food ChainFood Chain

Food Chain

• A straight-line sequence of who eats whom

• Simple food chains are rare in nature

marsh hawk

upland sandpiper

garter snake

cutworm

plants

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

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

Biological Magnification

Nondegradable or slowly degradable substances become more and more concentrated in tissues of organisms at higher trophic levels of a food web

DDT in Food Webs

• Synthetic pesticide banned in United States since 1970s

• Carnivorous birds accumulate DDT in their tissues, produce brittle egg shells

Fig. 30-5, p.530

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

Hydrologic cycleHydrologic cycle

Hydrologic CycleHydrologic Cycle

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

Threats to aquifersThreats to aquifers

Aquifer ProblemsAquifer Problems

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

Carbon cycleCarbon cycle

Carbon CycleCarbon Cycle

Greenhouse Effect

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

Greenhouse effectGreenhouse effect

Greenhouse EffectGreenhouse Effect

Global Warming

Long-term increase in temperature of

Earth’s lower atmosphere

Carbon dioxide and temperatureCarbon dioxide and temperature

Greenhouse GasesGreenhouse Gases

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 gasesGreenhouse gases

Greenhouse GasesGreenhouse Gases

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

Nitrogen CycleNitrogen Cycle

Nitrogen cycle

Human Effects

• Humans increase rate of nitrogen loss by clearing forests and grasslands

• Humans increase nitrogen in water and air by using fertilizers and by burning fossil fuels

• Too much or too little nitrogen can compromise plant health

Air Pollution

• Effects of nitrogen oxides released by burning fossil fuels

DeforestationDeforestation

Effect of air pollution in forests

Phosphorus Cycle

• Phosphorus is part of phospholipids, nucleotides, NADH, ATP

• Main limiting factor in ecosystems

• Reservoir is Earth’s crust; no gaseous phase

Phosphorus CyclePhosphorus Cycle

Phosphorus cycle

Human Effects

• In tropical countries, clearing lands for agriculture may deplete phosphorus-poor soils

• In developed countries, fertilizer causes phosphorus overloads in soil

Eutrophication

• Phosphorus is limiting factor in many freshwater ecosystems

• Runoff from phosphate fertilizers accelerates algal growth in waterways

• Resulting dense algal blooms cause system overload and death

Clouds MoveClouds Move

StreamStream