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Cecie Starr
Christine Evers
Lisa Starr
www.cengage.com/biology/starr
Chapter 42
Ecosystems
(Sections 42.1 - 42.6)
Albia Dugger • Miami Dade College
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
Experiment: Phosphorus Enrichment
nitrogen,
carbon
added
nitrogen, carbon,
phosphorus added
Fig. 42.1, p. 709
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
Energy Flows, Nutrients Cycle
light
energy
Producers
plants; photosynthetic
protists and bacteria
energy in
chemical
bonds
materials
cycling
Consumers
animals; fungi; heterotrophic
protists, bacteria, and archaeans
heat energy
Fig. 42.2, p. 710
Energy Flows, Nutrients Cycle
light
energy
Producers
plants; photosynthetic
protists and bacteria
energy in
chemical
bonds
materials
cycling
Consumers
animals; fungi; heterotrophic
protists, bacteria, and archaeans
heat energy
Stepped Art
Fig. 42.2, p. 710
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
A Food
Chain
Fourth Trophic Level
Third-level consumer
coyote
Third Trophic Level
Second-level consumer
sparrow
Second Trophic Level
Primary consumer
grasshopper
First Trophic Level
Primary producer
big bluestem grass
Fig. 42.3, p. 711
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
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
Arctic Food Web
Higher
Trophic
Levels
human (Inuk)
arctic wolf
arctic fox
A sampling
of carnivores
that feed on
herbivores and
one another
gyrfalcon
snowy owl
ermine
mosquito
flea
Second
Trophic
Level
Parasitic consumers
feed at more than one
trophic level.
Major parts
of the buffet
of primary
consumers
(herbivores)
vole
arctic hare
lemming
Detritivores and
decomposers
(nematodes,
annelids,
saprobic insects,
protists, fungi,
bacteria)
First Trophic Level
This is just part of
the buffet of
primary
producers.
grasses, sedges
purple saxifrage
arctic willow
Fig. 42.4, p. 712
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
human (Inuk)
arctic wolf
Higher
Trophic
Levels
A sampling
of
carnivores
that feed
on
herbivores
gyrfalcon
snowy owl
and one
another
Second
Trophic
Level
Major parts
of the buffet
of primary
consumers
(herbivores)
vole
arctic hare
lemming
First Trophic
Level
This is just
part of the
buffet of
primary
grasses, sedges
purple saxifrage
arctic fox
ermine
mosquito
flea
Parasitic
consumers
feed at more than
one
trophic level.
arctic willow
Detritivores
and
decomposers
(nematodes,
annelids,
Stepped Art
saprobic
insects,
Fig. 42.4, p. 712
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
Florida Aquatic Ecosystem
Fig. 42.6, p. 713
Florida Aquatic Ecosystem
top carnivores
(gar and bass)
1.5
carnivores (smaller
fishes, invertebrates)
11
herbivores
(plant-eating fishes,
invertebrates, turtles)
37
producers (algae
and aquatic plants)
5
809
detritivores
(crayfish) and
decomposers
(bacteria)
A Biomass pyramid (grams per square meter)
Fig. 42.6a, p. 713
Florida Aquatic Ecosystem
top carnivores
(gar and bass)
1.5
carnivores (smaller
fishes, invertebrates)
11
herbivores
(plant-eating fishes,
invertebrates, turtles)
37
producers (algae
and aquatic plants)
5
809
detritivores
(crayfish) and
decomposers
(bacteria)
A Biomass pyramid (grams per square meter)
Stepped Art
Fig. 42.6a, p. 713
Florida Aquatic Ecosystem
Fig. 42.6b, p. 713
Florida Aquatic Ecosystem
top carnivores
carnivores
herbivores
21
detritivores + decomposers = 5,060
383
3,368
producers
20,810
B Energy flow pyramid (kilocalories per square meter per year)
Fig. 42.6b, p. 713
Florida Aquatic Ecosystem
top carnivores
carnivores
herbivores
21
detritivores + decomposers = 5,060
383
3,368
producers
20,810
B Energy flow pyramid (kilocalories per square meter per year)
Stepped Art
Fig. 42.6b, p. 713
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
Biogeochemical Cycles
Atmosphere
Living
organisms
Rocks
and
sediments
Seawater
and
fresh water
Nonliving
environmental
reservoirs
Fig. 42.7, p. 714
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