Albia Dugger • Miami Dade College

Cecie StarrChristine EversLisa Starr

www.cengage.com/biology/starr

Chapter 42Ecosystems

(Sections 42.1 - 42.6)

42.1 Too Much of a Good Thing

• Human activities can disrupt nutrient cycles that have been operating since long before humans existed

• Phosphorus is often a limiting factor for aquatic producers, and sudden addition of phosphorus (eutrophication) causes algal blooms that cloud water and threaten aquatic species

• eutrophication • Nutrient enrichment of an aquatic ecosystem

Experiment: Phosphorus Enrichment

Fig. 42.1, p. 709

nitrogen, carbon, phosphorus added

nitrogen, carbon added

Experiment: Phosphorus Enrichment

42.2 The Nature of Ecosystems

• In ecosystems, organisms and their environment interact through a one-way flow of energy and a cycling of nutrients

• Ecosytems require ongoing inputs of energy (open systems)

• Nutrients taken up by producers are returned to the environment by decomposers, then taken up again

Energy Flows, Nutrients Cycle

• Light energy that enters the system returns to the environment as heat

• Nutrients are continually recycled

Fig. 42.2, p. 710

heat energy

Consumers animals; fungi; heterotrophic

protists, bacteria, and archaeans

materials cycling

Producers plants; photosyntheticprotists and bacteria

energy in chemical bonds

light energy

Energy Flows, Nutrients Cycle

Producers plants; photosyntheticprotists and bacteria

light energy

Fig. 42.2, p. 710

heat energy

Consumers animals; fungi; heterotrophic

protists, bacteria, and archaeans

materials cycling

energy in chemical bonds

Stepped Art

Energy Flows, Nutrients Cycle

ANIMATION: One-way energy flow and materials cycling

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Primary Producers and Production

• An ecosystem runs on energy captured by primary producers

• primary producer (autotroph)• An organism that obtains energy and nutrients from

inorganic sources to build organic compounds

• primary production • Rate at which producers capture and store energy• Varies by ecosystem, season, and nutrient availability

The Roles of Consumers

• Consumers are described by their diets:• Herbivores (plants)• Carnivores (animal flesh)• Parasites (tissues of a living host)• Omnivores (plants and animals)• Detritivores (detritus)• Decomposers (waste and remains)

Key Terms

• consumer • Organism that obtains energy and carbon by feeding on

tissues, wastes, or remains of other organisms

• detritivore • Consumer that feed on small bits of organic material

• decomposer • Organism that feeds on biological remains and breaks

organic material down into its inorganic subunits

Energy Flow and Nutrient Cycling

• Heat energy is not recycled:• Energy captured by producers is converted to bond energy

in organic molecules, and released by metabolic reactions that give off heat

• Nutrients are recycled: • Producers take up inorganic molecules (nutrients) from the

environment to form organic molecules• Decomposers break down organic molecules and return

nutrients to the environment

ANIMATION: The role of organisms in an ecosystem

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ANIMATION: Food chain

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42.3 Food Chains

• Food chains describe how energy and materials are transferred from one organism to another

• food chain • Description of who eats whom in one path of energy in an

ecosystem – transfer of energy to higher trophic levels

• trophic level• Position of an organism in a food chain

A Food Chain

• First trophic level (primary producer):• Autotroph (grass) converts light to chemical energy

• Second trophic level (primary consumer):• Grasshopper eats grass

• Third trophic level (second-level consumer):• Bird eats grasshopper

• Fourth trophic level (third-level consumer):• Coyote eats bird

A Food Chain

Fig. 42.3, p. 711

First Trophic Level Primary producer

Second Trophic Level Primary consumer

Third Trophic Level Second-level consumer

Fourth Trophic Level Third-level consumer

big bluestem grass

grasshopper

coyote

sparrow

A Food Chain

Fig. 42.3.1, p. 711

A Food Chain

Fig. 42.3.2, p. 711

A Food Chain

Fig. 42.3.3, p. 711

A Food Chain

Fig. 42.3.4, p. 711

A Food Chain

Food Chain Limits

• Energy captured by producers usually passes through no more than four or five trophic levels

• The length of food chains is restricted by the inefficiency of energy transfers

• Only 5-30% of energy in an organism at one trophic level ends up in tissues of an organism at the next trophic level

42.4 Food Webs

• Food chains of an ecosystem cross-connect as a food web

• Food web structure reflects environmental constraints and the inefficiency of energy transfers among trophic levels

• food web • Set of cross-connecting food chains

Types of Food Chains

• Food webs include two types of interconnecting food chains:

• grazing food chain • Energy transferred from producers to herbivores (grazers)

• detrital food chain • Energy transferred directly from producers to detritivores

(worms or insects)• Major food chain in land ecosystems

Arctic Food Web

Fig. 42.4, p. 712

Detritivores and decomposers (nematodes,

annelids, saprobic insects,

protists, fungi, bacteria)

purple saxifrage

This is just part of the buffet of primary producers.

Parasitic consumers feed at more than one

trophic level.

lemming

Major parts of the buffet of primary consumers (herbivores)

flea

erminesnowy owlgyrfalcon

A sampling of carnivores that feed on herbivores and one another

arctic foxarctic wolfhuman (Inuk)

grasses, sedges arctic willow

mosquitoSecond TrophicLevel

Higher Trophic Levels

vole arctic hare

First Trophic Level

Arctic Food Web

Fig. 42.4.1, p. 712

Arctic Food Web

Fig. 42.4.2, p. 712

Arctic Food Web

Fig. 42.4.3, p. 712

Arctic Food Web

Fig. 42.4.4, p. 712

Arctic Food Web

Fig. 42.4.5, p. 712

Arctic Food Web

Fig. 42.4.6, p. 712

Arctic Food Web

Fig. 42.4.7, p. 712

Arctic Food Web

Fig. 42.4.8, p. 712

Arctic Food Web

Fig. 42.4.9, p. 712

Arctic Food Web

Fig. 42.4.10, p. 712

Arctic Food Web

Fig. 42.4.11, p. 712

Arctic Food Web

Fig. 42.4.12, p. 712

Arctic Food Web

Fig. 42.4.13, p. 712

Arctic Food Web

Fig. 42.4.14, p. 712

Arctic Food Web

Fig. 42.4, p. 712

lemming

Major parts of the buffet of primary consumers (herbivores)

Second TrophicLevel

vole arctic hare

Stepped Art

erminesnowy owlgyrfalcon

A sampling of carnivores that feed on herbivores and one another

arctic foxarctic wolfhuman (Inuk)Higher Trophic Levels

purple saxifrage

This is just part of the buffet of primary producers.

grasses, sedges arctic willow

First Trophic Level

Detritivores and

decomposers (nematodes,

annelids, saprobic insects, protists,

fungi, bacteria)

Parasitic consumers

feed at more than one

trophic level.

fleamosquito

Arctic Food Web

ANIMATION: Food webs

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Trophic Interactions in Ecosystems

• Understanding links in food webs helps ecologists predict how ecosystems respond to change

• Computer models show that all species in an ecosystem are closely linked by trophic interaction

• Even in large communities with many species, 95% of species are within three links of one another

A Land Food Web

ANIMATION: Rainforest food web

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BBC Video: Seed Banks Helping to Save Our Fragile Ecosystem

BBC Video: The Vanishing Honeybee’s Impact on Our Food Supply

BBC Video: What is the Environmental Cost for Your Food?

42.5 Ecological Pyramids

• Ecological pyramid diagrams illustrate the inefficiency of transfers between trophic levels

• A biomass pyramid shows amounts of organic material in bodies of organisms at each trophic level at a specific time

• An energy pyramid shows energy flow through each trophic level in a given interval

Florida Aquatic Ecosystem

Fig. 42.6, p. 713

Florida Aquatic Ecosystem

Fig. 42.6a, p. 713

A Biomass pyramid (grams per square meter)

809

detritivores (crayfish) and decomposers (bacteria)

top carnivores (gar and bass) 1.5

11

37

5

carnivores (smaller fishes, invertebrates)

herbivores (plant-eating fishes, invertebrates, turtles)

producers (algae and aquatic plants)

Florida Aquatic Ecosystem

Fig. 42.6a, p. 713

detritivores (crayfish) and decomposers (bacteria)

5

A Biomass pyramid (grams per square meter)

809producers (algae and aquatic plants)

11carnivores (smaller fishes, invertebrates)

top carnivores (gar and bass) 1.5

37herbivores (plant-eating fishes, invertebrates, turtles)

Stepped Art

Florida Aquatic Ecosystem

Fig. 42.6b, p. 713

Florida Aquatic Ecosystem

Fig. 42.6b, p. 713

detritivores + decomposers = 5,06021carnivores

3,368

383

top carnivores

20,810producers

herbivores

B Energy flow pyramid (kilocalories per square meter per year)

Florida Aquatic Ecosystem

Fig. 42.6b, p. 713

detritivores + decomposers = 5,060

20,810producers

B Energy flow pyramid (kilocalories per square meter per year)

21top carnivores

carnivores383

3,368herbivores

Stepped Art

Florida Aquatic Ecosystem

Food and Energy

• Feeding a population of meat-eaters requires far greater crop production than sustaining a population of vegetarians

• A person who eats a plant food gets most of the calories in that food

• When plant food is used to grow livestock, only a small percentage of the plant’s calories ends up in meat

Key Concepts

• Organization of Ecosystems• A one-way flow of energy and the cycling of raw materials

among species maintain an ecosystem• Nutrients and energy are transferred in a stepwise fashion

through food chains that interconnect as complex food webs

ANIMATION: Energy flow at Silver Springs

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42.6 Biogeochemical Cycles

• Elements essential to life move between a community and its environment in a biogeochemical cycle

• biogeochemical cycle • A nutrient moves between environmental reservoirs and in

and out of food webs• Chemical and geologic processes move elements to, from,

and among environmental reservoirs (rocks, sediments, water, atmosphere)

Biogeochemical Cycles

Fig. 42.7, p. 714

Nonliving environmental

reservoirs

Seawater and

fresh water

Atmosphere

Rocks and

sediments

Living organisms

Biogeochemical Cycles

Key Concepts

• Biogeochemical Cycles• In a biogeochemical cycle, a nutrient moves relatively

slowly among its environmental reservoirs• The reservoirs may include air, water, and rocks• Nutrients moves more quickly into, through, and out of

food webs