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Ecosystems: What Are They and How Do They Work?

Chapter 3 WHAT KEEPS US AND OTHER ORGANISMS ALIVE?

Section 3-1

Earth’s life-support system has four major components

•  The atmosphere is the thin membrane of air around the planet. –  The troposphere is the air layer about 4–11 miles above sea

level. It contains greenhouse gases that absorb and release energy which warms the inner layer of the atmosphere.

–  The stratosphere lies above the troposphere between 11–31 miles; it filters out the sun’s harmful radiation.

•  The hydrosphere consists of earth’s water, found in liquid water, ice, and water vapor.

•  The geosphere is the hot core, a thick mantle, and thin crust.

•  The biosphere includes parts of the atmosphere, hydrosphere, and geosphere.

General Structure of the Earth

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Fig. 3-2, p. 42

Soil Biosphere (living organisms)

Atmosphere

Rock Crust

Mantle

Geosphere (crust, mantle, core) Mantle

Core Atmosphere (air)

Hydrosphere (water)

Three factors sustain the earth’s life

•  One-way flow of high-quality energy. •  Cycling of nutrients. •  Gravity.

Fig. 3-3, p. 42

Solar radiation

Reflected by atmosphere

Radiated by atmosphere as heat UV radiation

Lower Stratosphere (ozone layer) Most UV

absorbed by ozone Visible

light Heat added to troposphere

Troposphere Heat radiated by the earth

Greenhouse effect Absorbed

by the earth WHAT ARE THE MAJOR COMPONENTS OF AN ECOSYSTEM?

Section 3-2

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Ecologists study interactions in nature

•  Ecology focuses on how organisms interact with each other and with their non-living environment. They study interactions within and among these following levels of organization: –  Population is a group of individuals of the same

species living in a particular place. –  Community is populations of different species living in

a particular place, and potentially interacting with each other.

–  Ecosystem is a community of different species interacting with one another and with their nonliving environment of matter and energy

Levels of Organization of Matter in Nature

Smallest unit of a chemical element that exhibits its chemical properties

Atom

Molecule Chemical combination of two or more atoms of the same or different elements

Cell The fundamental structural and functional unit of life

Organism An individual living being

Population A group of individuals of the same species living in a particular place

Community Populations of different species living in a particular place, and potentially interacting with each other

Stepped Art

Ecosystem A community of different species interacting with one another and with their nonliving environment of matter and energy

Biosphere Parts of the earth's air,water, and soil where life is found

Oxygen Hydrogen

Water

Fig. 3-4, p. 43

Key Living and Nonliving Components of an Ecosystem

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Fig. 3-5, p. 44

Precipitaton Oxygen (O2)

Carbon dioxide (CO2)

Producer

Secondary consumer (fox)

Primary consumer (rabbit)

Producers

Water Decomposers

Soluble mineral nutrients

Ecosystems have several important components

•  Every organism belongs to a particular trophic level depending on its source of nutrients.

•  Producers, or autotrophs, use photosynthesis to make nutrients from components in the environment.

•  Consumers, or heterotrophs, get their nutrients by feeding on other organisms or their remains.

•  Consumers can be herbivores (feed on plants), carnivores (feed on animals) or omnivores (feed on both plants and animals).

Producers Consumers

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Ecosystems have several important components

•  Consumers can be primary, secondary or tertiary consumers, depending upon their trophic level.

•  Decomposers (bacteria/fungi) break down organic detritus into simpler inorganic compounds.

•  Detritivores (detritus feeders) feed on waste or dead bodies.

•  Producers, consumers and decomposers utilize chemical energy stored in organic molecules. In most cells, this energy is released by aerobic respiration.

Various Detritivores and Decomposers

Fig. 3-8, p. 45

Detritus feeders Decomposers

Carpenter ant

galleries Bark beetle engraving

Termite and

Dry rot fungus

Long-horned beetle holes

Wood reduced to powder

Fungi

Time progression Powder broken down by decomposers into plant nutrients in soil

carpenter ant work

Main Structural Components of an Ecosystem

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Fig. 3-9, p. 46

Solar energy Chemical nutrients

(carbon dioxide, oxygen, nitrogen,

minerals)

Heat

Heat Heat

Decomposers (bacteria, fungi)

Producers (plants)

Consumers (plant eaters, meat eaters) Heat Heat

WHAT HAPPENS TO ENERGY IN AN ECOSYSTEM?

Section 3-3

Energy flows through ecosystems in food chains and food webs

•  A food chain is a sequence of organisms, each of which serves as a source of nutrients and energy for the next organisms. Organisms are assigned to trophic levels in a food chain.

Food Chain

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Fig. 3-10, p. 47

First Trophic Level

Producers (plants)

Heat

Solar energy

Third Trophic Level

Secondary consumers (carnivores)

Heat

Heat

Fourth Trophic Level

Tertiary consumers

(top carnivores)

Heat

Heat

Second Trophic Level

Primary consumers (herbivores)

Heat

Heat

Decomposers and detritus feeders

Stepped Art

Energy flows through ecosystems in food chains and food webs

•  A food web is a series of interconnected food chains.

•  Food webs occur in most ecosystems. Organisms are also assigned to trophic levels in food webs. –  Producers are the first level. –  Primary consumers are the second. –  Secondary consumers belong to the third. –  Tertiary consumers are the fourth level. –  Detritivores and decomposers process detritus from

all trophic levels.

Food Web

Fig. 3-11, p. 48

Humans

Blue whale Sperm whale

Elephant seal Crabeater seal Killer

whale

Leopard seal

Adelie penguin

Emperor penguin

Squid Petrel

Fish

Carnivorous zooplankton

Krill Herbivorous zooplankton

Phytoplankton

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Usable energy decreases with each link in a food chain or web •  There is less high-quality energy available

to organisms at each succeeding feeding level because when chemical energy is transferred from one trophic level to the next, about 90% the energy is lost as heat

Pyramid of Energy Flow

Fig. 3-12, p. 49

Usable energy available at each trophic level

(in kilocalories) Heat

Tertiary consumers (human)

10 Heat

Secondary consumers (perch) Heat Decomposers Heat

100

Primary consumers (zooplankton) Heat

1,000

10,000 Producers (phytoplankton)

Some ecosystems produce plant matter faster than others do

•  The rate of an ecosystem’s producers converting energy into biomass is the gross primary productivity (GPP).

•  Some of the biomass must be used for the producers’ own respiration. Net primary productivity (NPP) is the rate that producers use photosynthesis to store biomass minus the rate at which they use energy for aerobic respiration. NPP measures how fast producers can provide biomass needed by consumers in an ecosystem.

•  Ecosystems and aquatic life zones differ in their NPP. The three most productive systems are swamps and marshes, tropical rain forests, and estuaries. The three least productive are tundra, desert scrub, and extreme desert.

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NPP in Major Life Zones and Ecosystems

Fig. 3-13, p. 49

Terrestrial Ecosystems Swamps and marshes

Tropical rain forest Temperate forest

Northern coniferous forest (taiga) Savanna

Agricultural land Woodland and shrubland

Temperate grassland Tundra (arctic and alpine)

Desert scrub Extreme desert

Aquatic Ecosystems Estuaries

Lakes and streams Continental shelf

Open ocean

WHAT HAPPENS TO MATTER IN AN ECOSYSTEM?

Section 3-4

Nutrients cycle within and among ecosystems

•  Elements and compounds move through air, water, soil, rock and living organisms in biogeochemical, or nutrient, cycles.

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The water cycle

•  Solar energy evaporates water; the water returns as precipitation (rain or snow), goes through organisms, goes into bodies of water, and evaporates again.

•  Water is filtered and partly purified as it moves through the hydrological cycle.

•  Water can be stored as ice in glaciers or in underground aquifers.

The water cycle

•  Unique properties of water include that it: –  Is held together by hydrogen bonds. –  Exists as a liquid over a wide temperate range. –  Stores a large amount of heat. –  Requires a large amount of energy to be evaporated. –  Dissolves a variety of compounds. –  Filter’s some UV rays from the sun. –  Can move through capillary action. –  Expands when freezes.

–  Exists in all three phases at the Earth’s surface.

The water cycle

•  Humans alter the water cycle in 3 ways: – Withdrawing freshwater at faster rates than

nature can replenish it. – Clearing vegetation which increases runoff

and decreases replenishment of groundwater supplies.

– Draining wetlands which interferes with flood control.

The Water Cycle

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Fig. 3-14, p. 51

Condensation Condensation

Ice and snow

Transpiration from plants

Precipitation to land Evaporation of

surface water Evaporation from ocean

Runoff

Lakes and reservoirs Precipitati

on to ocean Runoff

Increased runoff on land covered with crops, buildings and pavement

Infiltration and percolation into aquifer

Increased runoff from cutting forests and filling wetlands

Runoff

Groundwater in aquifers

Overpumping of aquifers Runoff

Water pollution

Ocean

Natural process Natural reservoir Human impacts Natural pathway Pathway affected by human activities

The carbon cycle

•  Carbon is the basic building block of carbohydrates, fats, proteins, DNA, and other compounds.

•  Carbon circulates through the biosphere, hydrosphere, and atmosphere.

•  Producers, consumers and decomposers circulate carbon in the biosphere.

•  Fossil fuels contain carbon. •  Humans are altering atmospheric carbon dioxide

mostly by our use of fossil fuels and our destruction of the carbon-absorbing vegetation.

The Carbon Cycle

Fig. 3-15, p. 53

Carbon dioxide in atmosphere Respiration

Photosynthesis

Animals (consumers) Burning

fossil fuels Diffusion Forest fires

Plants (producers) Deforestation

Transportation Respiration Carbon

in plants (producer

s) Carbon dioxide dissolved in ocean

Carbon in animals

(consumers) Decomposition

Marine food webs Producers, consumers, decomposers

Carbon in fossil

fuels

Carbon in limestone or dolomite sediments

Compaction

Process Reservoir Pathway affected by humans Natural pathway

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The nitrogen cycle: bacteria in action

•  Nitrogen gas (N2), which makes up 78% of the atmosphere, cannot be used directly by most living organisms.

•  Nitrogen-fixing bacteria convert N2 into compounds that are useful nutrients for plants and animals.

The nitrogen cycle: bacteria in action

•  The nitrogen cycle includes the following steps: –  Specialized bacteria convert gaseous nitrogen to

ammonia in nitrogen fixation. –  Specialized bacteria convert ammonia in the soil to

nitrite ions and nitrate ions; the latter is used by plants as a nutrient. This process is nitrification.

–  Decomposer bacteria convert detritus into ammonia and water-soluble salts in ammonification.

–  In denitrification, anaerobic bacteria in soggy soil and bottom sediments of water areas convert NH3 and NH4

+ back into nitrite and nitrate ions, then into nitrogen gas and nitrous oxide gas, which are released into the atmosphere.

The nitrogen cycle: bacteria in action

•  Human activities have more than doubled the annual release of nitrogen from the land into the rest of the environment, mostly from the greatly increased use of inorganic fertilizers to grow crops. This excessive input of nitrogen into the air and water contributes to pollution and other problems.

The Nitrogen Cycle

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Fig. 3-16, p. 54

Process Nitrogen in atmosphere

Denitrification by bacteria Reservoir Nitrification by bacteria Pathway affected by

humans Natural pathway Nitrogen

in animals (consumers) Nitrogen oxides

from burning fuel and using inorganic fertilizers

Volcanic activity

Electrical storms

Nitrogen in plants

(producers)

Decomposition Nitrates from

fertilizer runoff and

decomposition

Uptake by plants

Nitrate in soil

Nitrogen loss to deep ocean sediments

Nitrogen in ocean sediments

Bacteria

Ammonia in soil

The phosphorus cycle •  Phosphorus circulates through water, Earth’s crust, and

living organisms in the phosphorus cycle. Phosphorus does not cycle through the atmosphere.

•  The major reservoirs of phosphorus on Earth are rock formations and ocean bottom sediments.

•  Phosphorus is transferred by food webs and is an important component of many biological molecules.

•  Phosphorus is often the limiting factor for plant growth. •  Human activity removes phosphate from the earth to

make fertilizer and reduces phosphate levels in tropical soils by clearing forests. Phosphate-rich runoff from the land can produce huge populations of algae, which can upset chemical cycling and other processes.

The Phosphorus Cycle

Fig. 3-17, p. 54

Process Reservoir Pathway affected by humans Natural pathway

Phosphates in sewage

Phosphates in fertilizer

Plate tectonics Phosphates

in mining waste

Runoff Runoff Sea birds

Runoff Phosphate in rock (fossil bones, guano)

Erosion Ocean food webs

Animals (consumers) Phosphate

dissolved in water

Phosphate in shallow ocean sediments

Phosphate in deep ocean sediments

Plants (producers)

Bacteria

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The sulfur cycle

•  Much of the earth’s sulfur is stored underground in rocks and minerals.

•  Hydrogen sulfide (H2S) is released from volcanoes and anaerobic decomposition of organic matter in bogs and swamps.

•  Humans have been increasing atmospheric sulfur dioxide by burning sulfur-containing fuels, refining sulfur-containing fuels, and converting sulfur containing metallic mineral ores into free metals.

The Sulfur Cycle

Fig. 3-18, p.56

Sulfur dioxide in

atmosphere

Sulfuric acid and Sulfate deposited

as acid rain Smelting Burning

coal Refining fossil fuels Dimethy

l Sulfide

a bacteria byprodu

ct

Sulfur in animals

(consumers)

Sulfur in plants

(producers) Mining and extraction Uptake

by plants

Sulfur in ocean sediments

Decay

Decay

Process Sulfur in soil, rock

and fossil fuels Reservoir Pathway affected by humans Natural pathway

HOW DO SCIENTISTS STUDY ECOSYSTEMS?

Section 3-5

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Some scientists study nature directly

•  Field research (“muddy-boots biology”) involves making direct measurements and observations of ecosystems in natural settings.

•  Remote sensing devices can gather data on the earth’s surface that can be converted into usable forms by geographic information systems (GIS), such as computerized maps of an area that are used to examine forest cover, water resources, air pollution emissions, coastal changes, and changes in global sea temperatures.

Some scientists study ecosystems in the laboratory

•  Ecologists use tanks, greenhouses, and controlled indoor and outdoor chambers to study ecosystems in laboratory research. This allows control of light, temperature, CO2, humidity, and other variables.

We need to learn more about the health of the world’s ecosystems

•  Mathematical models and computer simulations can help scientists understand large and very complex systems.

•  Simulations are no better than the data and assumptions used to develop models.

•  We need more baseline data about components and physical and chemical conditions in order to determine how well the ecosystem is functioning and anticipate how best to prevent harmful environmental changes.

Three Big Ideas

•  Life is sustained by the flow of energy from the sun through the biosphere, the cycling of nutrients within the biosphere, and gravity.

•  Some organisms produce the nutrients they need, some survive by consuming other organisms, and others recycle nutrients back to producers.

•  Human activities are altering the flow of energy through food chains and webs, and the cycling of nutrients within ecosystems and the biosphere.