Chapter 4

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Lecture Outlines
Chapter 4
Environment:
The Science behind the
Stories
4th Edition
Withgott/Brennan
© 2011 Pearson Education, Inc.
This lecture will help you understand:
• Species interactions
• Feeding relationships,
energy flow, trophic
levels, and food webs
• Keystone species
• The process of succession
• Potential impacts of
invasive species
• Restoration ecology
• Terrestrial biomes
© 2011 Pearson Education, Inc.
Case Study: black and white and spread all
over
• In 1988, Zebra mussels were
accidentally introduced to
Lake St. Clair
- In discharged ballast
water
• By 2010, they had invaded
30 states
- No natural predators,
competitors, or parasites
• They cause millions of
dollars of damage to
property each year
© 2011 Pearson Education, Inc.
Species interactions
• Species interactions are the backbone of communities
• Natural species interactions:
- Competition = both species are harmed
- Exploitative = one species benefits and the other is
harmed
- Predation, parasitism, and herbivory
- Mutualism = both species benefit
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Competition
• Competition = multiple organisms seek the same limited
resources
- Food, space, water, shelter, mates, sunlight
• Intraspecific competition = between members of the
same species
- High population density = increased competition
• Interspecific competition = between members of 2 or
more species
- Strongly affects community composition
- Leads to competitive exclusion or species coexistence
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Results of interspecific competition
• Competitive exclusion = one species completely
excludes another species from using the resource
- Zebra mussels displaced native mussels in the Great
Lakes
• Species coexistence = neither species fully excludes the
other from resources, so both live side by side
- This produces a stable point of equilibrium, with stable
population sizes
- Species minimize competition by using only a part of
the available resource (niche)
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Niche: an individual’s ecological role
• Fundamental niche = the full niche of a species
• Realized niche = the portion of the fundamental
niche that is actually filled
- Due to competition or other species’ interactions
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Resource partitioning
• Resource partitioning =
species use different
resources
- Or they use shared
resources in different
ways
- Ex: one species is
active at night, another
in the day
- Ex: one species eats
small seeds, another
eats large seeds
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Character displacement
• Character displacement = competing species diverge in
their physical characteristics
- Due to the evolution of traits best suited to the
resources they use
- Results from resource partitioning
• Birds that eat larger seeds evolve larger bills
- Birds that eat smaller seeds evolve smaller bills
Competition is reduced when two species become more
different
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Exploitation: predation
• Exploitation = one member
exploits another for its own
gain (+/- interactions)
- Predation, parasitism,
herbivory
• Predation = process by which individuals of one species
(predators) capture, kill, and consume individuals of
another species (prey)
- Structures food webs
- The number of predators and prey influences
community composition
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Zebra mussel predation on phytoplankton
• Zebra mussels eat phytoplankton and zooplankton
- Both populations decrease in lakes with zebra mussels
• Zebra mussels don’t eat cyanobacteria
- Population increases in lakes with zebra mussels
• Zebra mussels are becoming prey for some North
American predators:
- Diving ducks, muskrats, crayfish, flounder, sturgeon,
eels, carp, and freshwater drum
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Effects of predation on populations
• Increased prey populations increase predators
- Predators survive and reproduce
• Increased predator populations decrease prey
- Predators starve
• Decreased predator populations increase prey populations
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Predation has evolutionary ramifications
• Natural selection leads to evolution of adaptations that
make predators better hunters
• Individuals who are better at catching prey:
- Live longer, healthier lives
- Take better care of offspring
• Prey face strong selection pressures: they are at risk of
immediate death
- Prey develop elaborate defenses against being eaten
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Defenses against being eaten
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Exploitation: parasitism
• Parasitism = a relationship in which one organism
(parasite) depends on another (host)
- For nourishment or some other benefit
- The parasite harms, but doesn’t kill, the host
• Some are free-living
- Infrequent contact with
their hosts
- Ticks, sea lampreys
• Some live within the host
- Disease, tapeworms
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Parasites evolve in response to each other
• Parasitoids = insects that parasitize other insects
- Killing the host
• Coevolution = hosts and parasites become locked in a
duel of escalating adaptations
- Has been called an evolutionary arms race
- Each evolves new responses to the other
- It may not be beneficial to the parasite to kill its host
© 2011 Pearson Education, Inc.
Exploitation: herbivory
• Herbivory = animals feed on the tissues of plants
- Widely seen in insects
• May not kill the plant
- But affects its growth and survival
• Defenses against herbivory include:
- Chemicals: toxic or distasteful
- Thorns, spines, or irritating hairs
- Other animals: protect the plant
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Mutualism
• Two or more species benefit from their interactions
• Symbiosis = mutualism in which the organisms live in
close physical contact
- Each partner provides a service the other needs (food,
protection, housing, etc.)
- Microbes within digestive tracts
- Mycorrhizae: plant roots and fungi
- Coral and algae (zooxanthellae)
• Pollination = bees, bats, birds and others transfer pollen
from one flower to another, fertilizing its eggs
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Pollination
In exchange for the plant nectar, the animals pollinate
plants, which allows them to reproduce
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Relationships with no effect on one member
• Amensalism = a relationship in which one organism is
harmed while the other is unaffected
- Difficult to confirm, because usually one organism
benefits from harming another
- Allelopathy = certain plants release harmful chemicals
- Or, is this a way to outcompete another for space?
• Commensalism = a relationship in which one organism
benefits, while the other remains unaffected
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Ecological communities
• Community = an assemblage of populations of
organisms living in the same place at the same time
- Members interact with each other
- Interactions determine the structure, function, and
species composition of the community
• Community ecologists are people interested in how:
- Species coexist and relate to one another
- Communities change, and why patterns exist
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Energy passes through trophic levels
• One of the most important species interactions
- Who eats whom?
• Matter and energy move through the community
• Trophic levels = rank in the feeding hierarchy
- Producers (autotrophs)
- Consumers
- Detritivores and
decomposers
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Producers: the first trophic level
• Producers, or autotrophs (“self-feeders”) = organisms
capture solar energy for photosynthesis to produce sugars
- Green plants
- Cyanobacteria
- Algae
• Chemosynthetic bacteria use the geothermal energy in hot
springs or deep-sea vents to produce their food
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Consumers: consume producers
• Primary consumers = second trophic level
- Organisms that consume producers
- Herbivores consume plants
- Deer, grasshoppers
• Secondary consumers = third trophic level
- Organisms that prey on primary consumers
- Carnivores consume meat
- Wolves, rodents
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Consumers occur at higher trophic levels
• Tertiary Consumers = fourth trophic level
- Predators at the highest trophic level
- Consume secondary consumers
- Are also carnivores
- Hawks, owls
• Omnivores = consumers that eat both plants and animals
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Detritivores and decomposers
• Organisms that consume nonliving organic matter
- Enrich soils and/or recycle nutrients found in dead
organisms
• Detritivores = scavenge waste products or dead bodies
- Millipedes, soil insects
• Decomposers = break down leaf litter and other nonliving material
- Fungi, bacteria
- Enhance topsoil and recycle nutrients
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Energy, biomass, and numbers decrease
• Most energy organisms use is lost as waste heat
through cellular respiration
- Less and less energy is available in each
successive trophic level
- Each level contains only 10% of the energy of the
trophic level below it
• There are also far fewer organisms and less biomass
(mass of living matter) at the higher trophic levels
A human vegetarian’s ecological footprint is smaller
than a meat-eater’s footprint
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Pyramids of energy, biomass, and numbers
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Food webs show relationships and energy
flow
• Food chain = a series of feeding relationships
• Food web = a visual map of feeding relationships and
energy flow
- Includes many different
organisms at all various
levels
- Greatly simplified; leaves
out most species
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Some organisms play big roles
• Community dynamics are
complex
- Species interactions differ in
strength and over time
• Keystone species = has a
strong or wide-reaching impact
- Far out of proportion to its
abundance
• Removal of a keystone species
has substantial ripple effects
- Alters the food chain
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Species can change communities
• Trophic Cascade = predators at high trophic levels
indirectly affect populations at low trophic levels
- By keeping species at intermediate trophic levels in
check
- Extermination of wolves led to increased deer
populations, which overgrazed vegetation and changed
forest structure
• Ecosystem engineers = physically modify the
environment
- Beaver dams, prairie dogs, ants, zebra mussels
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Communities respond to disturbances
• Communities experience many types of disturbance
- Removal of keystone species, spread of invasive
species, natural disturbances
- Human impacts cause major community changes
• Resistance = community of organisms resists change and
remains stable despite the disturbance
• Resilience = a community changes in response to a
disturbance, but later returns to its original state
• A disturbed community may never return to its original
state
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Primary succession
• Succession = the predictable series
of changes in a community
- Following a disturbance
• Primary succession = disturbance
removes all vegetation and/or soil
life
- Glaciers, drying lakes, volcanic
lava
• Pioneer species = the first species
to arrive in a primary succession
area (i.e. lichens)
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Secondary succession
• Secondary succession = a disturbance dramatically
alters, but does not destroy, all local organisms
- The remaining organisms form “building blocks”
which help shape the process of succession
- Fires, hurricanes, farming, logging
• Climax community = remains in place with few
changes
- Until another
disturbance restarts
succession
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Communities may undergo shifts
• The dynamics of community change are more variable
and less predictable than thought
- Conditions at one stage may promote another stage
- Competition may inhibit progression to another stage
- Chance factors also affect changes
• Phase (regime) shift = the overall character of the
community fundamentally changes
- Some crucial threshold is passed, a keystone species is
lost, or an exotic species invades
- i.e. overfishing and depletion of fish and turtles has
allowed algae to dominate corals
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Community cohesion
• Frederick Clements = viewed communities as cohesive
entities, with integrated parts
- Its members remain associated over space and time
- The community shared similar limiting factors and
evolutionary histories
• Henry Gleason = maintained that each species responds
independently to its own limiting factors
- Species join or leave communities without greatly
altering the community’s composition
- The most widely accepted view of ecologists today
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Invasive species threaten stability
• Invasive species = non-native (exotic) organisms that
spread widely and become dominant in a community
- Introduced deliberately or accidentally from
elsewhere
- Growth-limiting factors (predators, disease,
competitors, etc.) are removed or absent
- They have major ecological effects
- Chestnut blight from Asia wiped out American
chestnut trees
• Some species help people (i.e., European honeybees)
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Two invasive mussels
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Controlling invasive species
• Techniques to control invasive species
- Removing them manually
- Applying toxic chemicals
- Drying them out
- Depriving them of oxygen
- Stressing them with heat, sound, electricity,
carbon dioxide, or ultraviolet light
• Control and eradication are hard and expensive
Prevention, rather than control, is the best policy
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Altered communities can be restored
• Humans have dramatically changed ecological systems
- Severely degraded systems cease to function
• Ecological restoration = efforts to restore communities
• Restoration is informed by restoration ecology = the
science of restoring an area to an earlier condition
- To restore the system’s functionality (i.e. filtering of
water by a wetland)
- It is difficult, time-consuming, and expensive
• It is best to protect natural systems from degradation in
the first place
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Restoration efforts
• Prairie restoration = replanting native species,
controlling invasive species
• The world’s largest project = Florida Everglades
- Flood control and irrigation removed water
- Populations of wading birds dropped 90-95%
- It will take 30 years
and billions of dollars
to restore natural
water flow
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Widely separated regions share similarities
• Biome = major regional complex of similar
communities recognized by
- Plant type
- Vegetation
structure
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Multiple factors determine a biome
• The type of biome depends on
abiotic factors
- Temperature, precipitation,
soil type, atmospheric
circulation
• Climatographs = a climate
diagram showing
- An area’s mean monthly
temperature and
precipitation
- Similar biomes occupy
similar latitudes
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Aquatic systems have biome-like patterns
• Various aquatic systems comprise distinct communities
- Coastlines, continental shelves
- Open ocean, deep sea
- Coral reefs, kelp forests
• Some coastal systems (estuaries, marshes, etc.) have both
aquatic and terrestrial components
• Aquatic systems are shaped by
- Water temperature, salinity, and dissolved nutrients
- Wave action, currents, depth, light levels
- Substrate type, and animal and plant life
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Temperate deciduous forest
• Deciduous trees lose their
leaves each fall
- They remain dormant
during winter
• Mid-latitude forests in Europe,
East China, Eastern North
America
• Even, year-round precipitation
• Fertile soils
• Forests = oak, beech, maple
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Temperate grasslands
• More extreme temperature
difference
- Between winter and summer
• Less precipitation
• Also called steppe or prairie
- Once widespread, but has
been converted to agriculture
- Bison, prairie dogs, groundnesting birds, pronghorn
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Temperate rainforest
• Coastal Pacific Northwest
• Great deal of precipitation
• Coniferous trees: cedar,
spruce, hemlock, fir
• Moisture-loving animals
- Banana slug
• Erosion and landslides
affect the fertile soil
• Lumber and paper
• Most old-growth is gone
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Tropical rainforest
• Southeast Asia, west Africa
Central and South America
• Year-round rain and warm
temperatures
• Dark and damp
• Lush vegetation
• Diverse species
- But in low densities
• Very poor, acidic soils
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Tropical dry forest
• Also called tropical
deciduous forest
- Plants drop leaves
during the dry season
• India, Africa, South
America, north Australia
• Wet and dry seasons
• Warm, but less rainfall
• Converted to agriculture
- Severe soil erosion
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Savanna
• Grassland interspersed
with trees
• Africa, South America,
Australia, India
• Precipitation is only
during the rainy season
• Animals gather near water
holes
• Zebras, gazelles, giraffes,
lions, hyenas
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Desert
• Minimal precipitation
• Some are bare, with sand
dunes (Sahara)
• Some are heavily vegetated
(Sonoran)
• They are not always hot
- Temperatures vary widely
• Saline soils
• Animals = nocturnal, nomadic
• Plants = thick skins, spines
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Tundra
• Russia, Canada, Scandinavia
• Minimal precipitation
• Extremely cold winters
• Permafrost = permanently
frozen soil
- Melting due to climate
change
• Few animals: polar bears, musk
oxen, caribou, migratory birds
• Lichens, low vegetation, few
trees
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Boreal forest (taiga)
• Canada, Alaska, Russia,
Scandinavia
• A few evergreen tree species
• Cool and dry climate
- Long, cold winters
- Short, cool summers
• Nutrient poor, acidic soil
• Moose, wolves, bears, lynx,
migratory birds
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Chaparral
• Occurs in small patches
around the globe
• Mediterranean Sea, Chile,
California, south Australia
• High seasonal biome
- Mild, wet winters
- Warm, dry summers
• Frequent fires
• Densely thicketed,
evergreen shrubs
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Altitudes create “latitudinal patterns”
• Vegetative communities rapidly change along mountain
slopes
• The climate varies with altitude
• A mountain climber in the Andes
- Begins in the tropics and ends
on a glacier
• Rainshadow effect = air going
over a mountain releases
moisture
- Creating an arid region
on the other side
Hiking up a mountain in the southwest U.S. is like
walking from Mexico to Canada
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Conclusion
• Biomes and communities help us understand how the
world functions
• Species interactions affect communities
- Predation, parasitism, competition, mutualism
- Causing weak and strong, direct and indirect effects
• Feeding relationships are represented by trophic levels
and food webs
• Humans have altered many communities
• Ecological restoration attempts to undo the negative
changes that we have caused
© 2011 Pearson Education, Inc.
QUESTION: Review
Mutualism is a form of species interaction where:
a) Both species are harmed
b) One species benefits, but the other is harmed
c) Both species benefit
d) One species excludes another from a particular area
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QUESTION: Review
Which of the following is NOT an exploitative interaction?
a) Predation
b) Herbivory
c) Parasitism
d) All of these are exploitative interactions
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QUESTION: Review
An example of resource partitioning would be:
a) One species eating larger berries, another species
eating smaller berries
b) One species moving out of an area to find new
resources
c) A host species becoming more vulnerable to
parasitism
d) A pine tree evolving thicker pinecones to reduce
consumption by squirrels
© 2011 Pearson Education, Inc.
QUESTION: Review
Which statement is NOT true about trophic levels?
a) Plants are autotrophs and occupy the first trophic
level.
b) Detritivores consume waste products or dead
bodies.
c) Biomass and energy decrease going up the food
chain.
d) There are more predator species than prey species
in an area.
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QUESTION: Review
Primary succession would take place on all of the
following EXCEPT:
a) The slopes of a newly formed volcanic island
b) Wetlands in Texas, following Hurricane Rita
c) A receding glacier
d) Vegetation regrowing in a drying lake
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QUESTION: Review
Because communities can undergo phase (regime) shifts,
we must remember that:
a) Secondary succession results in a predictable series
of stages.
b) We can count on being able to reverse damage
caused by human disturbance.
c) We cannot count on being able to reverse damage
caused by human disturbance.
d) Changes humans set in motion will not be
permanent.
© 2011 Pearson Education, Inc.
QUESTION: Review
All of the following are ways to control invasive species,
EXCEPT:
a) Remove individuals from the area
b) Stress them by noise
c) Trap them
d) Encourage them to hybridize with another species
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QUESTION: Review
Which biome has year-round rain and warm temperatures,
is dark and damp, and has lush vegetation?
a) Tropical rainforest
b) Temperate grasslands
c) Chaparral
d) Taiga
© 2011 Pearson Education, Inc.
QUESTION: Review
Which biome is dominated by a few evergreen species,
has long, cold winters, and moose, wolves, bear, and
lynx?
a) Tropical rainforest
b) Temperate grasslands
c) Temperate rainforest
d) Taiga
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QUESTION: Weighing the Issues
Would you be willing to decrease the amount of meat you
consume (e.g., eat lower on the food chain) to decrease
your ecological footprint?
a) Yes, if the extra food was sent to countries with
starving people.
b) Yes, because it would decrease environmental
degradation.
c) I don’t eat meat now.
d) No, I don’t see the need to eat lower on the food
chain.
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QUESTION: Weighing the Issues
Although mustangs are not native to the United States, they
exist in several western states on federally owned land. As
an introduced species, what should be done with them?
a) As an exotic species, they should immediately be
removed and adopted or killed.
b) Although they are an exotic species, they are part
of our heritage, and should be allowed to stay.
c) They have been here so long, we should just
leave them alone.
d) Many countries eat horse flesh, so we should
round them up and export them to horse-eating
countries.
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QUESTION: Interpreting Graphs and Data
What does this figure
illustrate?
a) A predator–prey cycle
b) Competitive exclusion
c) Resource partitioning
d) Succession
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QUESTION: Interpreting Graphs and Data
In this climatograph for Vaigach, Russia, in the tundra
biome, winters are:
a) Long and warm
b) Short and cool
c) Long and cold
d) Short and warm
© 2011 Pearson Education, Inc.
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