APES Notes – Chapter 8
Community Ecology: Structure,
Species Interactions, Succession, and
Sustainability

General Types of species


Native: species that normally live and thrive in a
particular ecosystem
Non-native species: species that migrate into an
ecosystem or are deliberately or accidentally
introduced into an ecosystem by humans. Also
known as: exotic, alien species, invasive or
introduced
Problems caused by Non-native
species:

the non-natives have no natural enemies so
they can thrive in the new ecosystem and
crowd out the native species: Examples
Indicator Species:




species that serve as early warnings that a
community or ecosystem is being damaged
or changed:
Birds are good indicators because: Birds are
good indicators because: very sensitive to
environmental changes
Trout and macro-invertebrates are good
indicators of: water quality
Amphibians indicate: chemical pollution
Keystone species:

species that play a pivotal role in the structure, function,
and integrity of an ecosystem because
 Their strong interactions with other species affect the
health and survival of these species
 They process material out of proportion to their
numbers and biomass
 Keystone species:
 Pollinate
 Scatter seeds
 Modify habitats
 Predation to control prey populations
 Help plants get nutrients
 Recycle animal waste
 Examples: bees, sharks, alligators, bats, dung beetles, sea otter elephant
Species in an ecosystem who are
very important are called…
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Keystone species
Indicator species
Non-native species
Exotic species
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Species that serve as early
warnings for ecosystem imbalance
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Keystone species
Indicator species
Non-native species
Exotic species
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Which term means the opposite
of the others?
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Non-native
Exotic
Native
Alien
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Species Interactions


Five Types of
Interactions:
Competition: Two or
more animals competing
for the same resources.
Two Types:


Intraspecific:
competition between
members of the same
species
Interspecific:
competition between
members of two
different species
Territoriality:

when animals mark an
area around their
home or nesting area.
This has
disadvantages because
animals exclude other
males from breeding
and: they expend a lot
of energy defending
their territory
The more a species niche overlaps,
then the more competition


Interference Competition: when one species
limits another species access to some
resource regardless of its abundance.
Examples:
When a larger more established cat interferes
with another cat accessing food by swatting
at it every time it tries to feed


Exploitation Competition: competing species
have roughly equal access to a specific
resource, but differ in how fast they exploit
it. Examples:
An older more established cat will gobble up
all the food before the other animal has a
chance to eat
Competitive Exclusion Principle:

No two species can occupy the same niche
indefinitely in a habitat where there is not
enough of a particular resource to meet the
needs of both species.
High
Relative population density
Paramecium
aurelia
Paramecium
caudatum
Low
0
2
4
6
8
10
12
14
16
18
Days
Each species grown alone
Fig. 8.8a, p. 182
High
Relative population density
Paramecium
aurelia
Paramecium
caudatum
Low
0
2
4
6
8
10
12
14
16
18
Days
Both species grown together
Fig. 8.8b, p. 182
If one kitty gobbles up all the
food so the other does not get any
22%
1.
6%
2.
72%
3.
0%
4.
Interference competition
Interspecific competition
Exploitation competition
Territoriality
Competition between two
members of the same species
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Interspecific
Intraspecific
Exploitation
Interference
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Avoiding Competition:

Resource Partitioning: dividing up of
scarce resources so that species with similar
needs use them at different times, in different
ways, or in different places. “Share the
wealth” Examples: being nocturnal or
diurnal
Fig. 8.11, p. 184
Character Displacement:

Species develop characteristics over time
through evolution to allow them to exploit
different resources Examples: Darwin’s
finches each developed a different shaped
beak to exploit different food types
Black skimmer
seizes small fish
at water surface
Flamingo
feeds on
minute
organisms
in mud
Brown pelican dives for fish,
which it locates from the air
Scaup and other
diving ducks feed on
mollusks, crustaceans,
and aquatic vegetation
Avocet sweeps bill through
mud and surface water in
search of small crustaceans,
insects, and seeds
Louisiana heron wades into
water to seize small fish
Dowitcher probes deeply
into mud in search of
snails, marine worms,
and small crustaceans
Oystercatcher feeds on
clams, mussels, and
other shellfish into which
it pries its narrow beak
Herring gull is a
tireless scavenger
Ruddy turnstone searches
under shells and pebbles
for small invertebrates
Knot (a sandpiper)
picks up worms and
small crustaceans left
by receding tide
Piping plover feeds
on insects and tiny
crustaceans on
sandy beaches
Fig. 8.9, p. 182
Predator-Prey Interactions:

members of one species feed directly on all
or part of a living organism or other species.
They do not live on or in the other species.
One species is clearly harmed and the other
clearly benefits. However predation can be a
good thing for the population of prey species
as predators often weed out the sick and
dying animal thereby reducing competition
amongst the prey species.
Predators

Predators have characteristics that help them
catch prey, such as:
 Running fast, ex. jaguar
 Good eyesight, Ex. hawk
 Hunting in packs, ex. coyote
 Camouflage for ambush, ex. frog
Prey

Prey have characteristics that help them escape predators, such as:
 Run fast
 Good sense of smell and eyesight to alert them to the presence
of predators
 Protective shell
 Spines
 Camouflage
 Chemical warfare like poisonous skin
 Foul smells
 Bad tasting
 Warning coloration
 Mimicking a predator
 Examples:
African stoneplants
Canyon tree frog
Bombardier beetle
Foul tasting monarch
butterfly
Poison dart frog
Viceroy butterfly mimics
monarch butterfly
Hind wings of io moth
resemble eyes of a much
larger animal
When touched, the snake
caterpillar changes shape to
look like the head of a snake
Fig. 8.12, p. 186
Symbiosis:


a long lasting relationship in which species
live together in an intimate association.
Parasitism: when one species feeds on part of
another organism (host) by living on or in the
host. In this relationship the host is harmed
and the parasite benefits. Example:
Which of the following predators avoid competition
by being active at different times?
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Snakes and hawks
Lions and tigers
Owls and hawks
Zebras and antelopes
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The obvious relationship
illustrated by a food chain is..
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Predation
Parasitism
Mutualism
Commensalism
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Prey are least likely to defend
themselves against predators by..
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Camouflage
Acute senses of smell and hearing
Protective shells
Pursuit and ambush
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Mutualism:
symbiotic relationship in which both species
involved benefit from the relationship. Ways in
which this happens are pollination, providing
food, and providing shelter. Examples:

Fig. 8.13, p. 187
Commensalism:

a symbiotic
relationship in which
one species benefits
and the other species
is neither helped nor
harmed. For example:
epiphytes
The Win-Win relationship in nature.
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Commensalism
Parasitism
Competition
Mutualism
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A relationship in which one
organism feeds in or on another
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Parasitism
Mutualism
Commensalism
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Ecological Succession

Succession: One characteristic of all
ecosystems is that they change over time.
This is called ecological succession. There
are two types of succession: Primary and
secondary.
Primary Succession:

Succession that starts with an essentially lifeless area
where there is no soil or bottom sediment in an aquatic
area. Examples include new lava or an abandoned parking
lot. Succession happens in stages:




Pioneer species move in and make soil: Ex. Lichens and mosses
When enough soil is made and spread out then plants that are
small and close to the ground move in. These plants can live
under harsh conditions and usually have short lives. They are
called early successional species. Examples: heath and shrubs
After hundreds of years there is enough soil for Midsuccessional species. Examples: pine trees
As the Mid-successional plants grow they create enough shelter
for Late successional species such as: spruce and fir trees
Exposed
Lichens
rocks and mosses
Small herbs
and shrubs
Heath mat
Jack pine,
black spruce,
and aspen
Balsam fir,
paper birch, and
white spruce
climax community
Time
Fig. 8.15, p. 188
Secondary Succession:

begins in an area where the natural
community of organisms has been disturbed
or destroyed, but the soil remains. For
example abandoned farms, burned or cut
forests, and heavily polluted streams.
Secondary succession occurs in the same
way as primary starting with pioneer species
and ending with late successional species.
Mature oak-hickory forest
Young pine forest
Annual
weeds
Perennial
weeds and
grasses
Shrubs
Time
Fig. 8.16, p. 189
Succession

Descriptions of succession usually focus on
plants, but animals also change with succession
as different types of plants become available for
food and shelter.




Early successional species:
Mid-successional species:
Late successional species:
Wilderness species:
Early Successional
Species
Midsuccessional
Species
Late Successional
Species
Wilderness
Species
Rabbit
Quail
Ringneck pheasant
Dove
Bobolink
Pocket gopher
Elk
Moose
Deer
Ruffled grouse
Snowshoe hare
Bluebird
Turkey
Martin
Hammond’s
Flycatcher
Gray squirrel
Grizzly bear
Wolf
Caribou
Bighorn sheep
California condor
Great horned owl
Ecological succession
Fig. 8.17, p. 190
Disturbances can Affect Succession



Some disturbances can be beneficial in the long run
like fire, because they increase biodiversity, clear out
excess brush, renew nutrients and encourage other
species to grow
Some catastrophic disturbances can convert the
ecosystem back to a lower level of succession
We used to think that succession was predictable and
that it would continue until a stable climax community
was reached. We now know that is false. We cannot
predict the course of a given succession or view it as
preordained progress toward an ideally adapted
climax community. Succession is an ongoing struggle.
The stability of an ecosystem
depends on three things:



Inertia: the ability of species to resist
change
Constancy: the ability of a population to
keep its numbers within the limits imposed
by availability of natural resources.
Resilience: the ability of a living system to
bounce back after a disturbance
Species diversity
0
100
Percentage disturbance
Fig. 8.18, p. 192

Populations with more biodiversity are more
stable. More biodiversity means greater
primary productivity and more resilience.
Examples: Don’t put all your eggs in one
basket
Grizzly
bear
NORTH
AMERICA
More than 60% of the
Pacific Northwest
coastal forest has
been cut down
40% of North America’s
range and cropland
has lost productivity California
condor
Hawaiian
monk seal
Eastern
cougar
Spotted
owl
Black
footed Florida
ferret panther
Mangroves
cleared
in Equador for
shrimp ponds
Fish catch in the north-west Atlantic has fallen
42% since its peak in 1973
Chesapeake Bay is overfished and polluted
Golden
toad
Coral reef destruction
Every year 14,000
Square kilometers of
Rain forest is destroyed
in the Amazon Basin
Columbia has
lost one-third of
its forest
PACIFIC
OCEAN
Vanishing biodiversity
Humpback
whale
Manatee
Much of Everglades National Park has dried out
and lost 90% of it’s wading birds
Kemp’s
ridley
turtle
Half of the forest
in Honduras and
Nicaragua has
disappeared
Environmental degradation
St. Lawrence
beluga whale
Black lion
tamarin
SOUTH
AMERICA
Little of Brazil’s
Atlantic forest
remains
ATLANTIC
OCEAN
Southern
Chile’s rain
forest is
threatened
Endangered species
6.0 or more children
per woman
Fig. 8.19a, p. 194
Poland is one of
the world’s most
polluted countries
Imperial eagle
640,000 square kilometers
south of the Sahara have
surned to desert since 1940
EUROPE
Mediterranean
Many parts of
former Soviet Union
ASIA
are polluted with
industrial and radioactive waste
Central Asia from the
Middle East of China
has lost 72% of range
and cropland
Area of
Aral Sea has
Shrunk 46%
Giant
panda
Japanese timber imports
are responsible for much
of the world’s tropical
deforestation
Saudi
Arabia
Deforestation in the Himalaya
Asian
causes flooding in Bangladesh
Liberia
elephant
Oman
Kouprey
Eritrea
Mali AFRICA
Yemen
90% of the coral reefs
India and
are threatened in the
Burkina Niger
Ethiopia
Sri Lanka
Philippines. All virgin
Faso
Benin Chad Golden
have almost
forest will be gone
Sierra
tamarin
no
rain
Nigeria
by 2010
Leone
forest left
Togo
Congo Uganda
Sao Tome Rwanda
Somalia
In peninsular Malaysia
Queen Alexandra’s
68% of the
Burundi
almost all forests have
Birdwing butterfly
Congo’s
Angola
been cut
rain forest
Indonesia’s
is slated
Zambia
Coral reefs are
Nail-tailed
for cleaning
INDIAN OCEAN threatened
wallaby
and
Aye-aye
Fish catches in
mangrove AUSTALIA
Black
Southeast Atlantic
forests
Madagascar has
has dropped by more rhinoceros
Much of
have been
lost 66% of its
than 50% since 1973
Australia’s
cut
in
half
tropical forest
Range and
Cropland
has turned
to desert
A thinning of the ozone layer occurs
over Antarctica during summer
Blue whale
Fig. 8.19b, p. 195
ANTARCTICA
Poland is one of
the world’s most
polluted countries
Imperial eagle
640,000 square kilometers
south of the Sahara have
surned to desert since 1940
EUROPE
Mediterranean
Many parts of
former Soviet Union
ASIA
are polluted with
industrial and radioactive waste
Central Asia from the
Middle East of China
has lost 72% of range
and cropland
Area of
Aral Sea has
Shrunk 46%
Giant
panda
Japanese timber imports
are responsible for much
of the world’s tropical
deforestation
Saudi
Arabia
Deforestation in the Himalaya
Asian
causes flooding in Bangladesh
Liberia
elephant
Oman
Kouprey
Eritrea
Mali AFRICA
Yemen
90% of the coral reefs
India and
are threatened in the
Burkina Niger
Ethiopia
Sri Lanka
Philippines. All virgin
Faso
Benin Chad Golden
have almost
forest will be gone
Sierra
tamarin
no
rain
Nigeria
by 2010
Leone
forest left
Togo
Congo Uganda
Sao Tome Rwanda
Somalia
In peninsular Malaysia
Queen Alexandra’s
68% of the
Burundi
almost all forests have
Birdwing butterfly
Congo’s
Angola
been cut
rain forest
Indonesia’s
is slated
Zambia
Coral reefs are
Nail-tailed
for cleaning
INDIAN OCEAN threatened
wallaby
and
Aye-aye
Fish catches in
mangrove AUSTALIA
Black
Southeast Atlantic
forests
Madagascar has
has dropped by more rhinoceros
Much of
have been
lost 66% of its
than 50% since 1973
Australia’s
cut
in
half
tropical forest
Range and
Cropland
has turned
to desert
A thinning of the ozone layer occurs
over Antarctica during summer
Blue whale
Fig. 8.19b, p. 195
ANTARCTICA

There is overwhelming evidence that human
disturbances are disrupting important
ecosystem services that support and sustain all
life and economies. Our ignorance about the
effects of our actions means that we should
destroy ecosystems only with great caution.
Once destroyed we are finding out that they
cannot be restored by humans very easily. This
is called: the precautionary principle
How long does it take natural
sources to create fertile soil?
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Weeks to months
Months to years
Decades
Several centuries
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Which of the following would
exhibit primary succession?
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An abandoned farm
A recent lava flow
A forest that has been clear cut
A recently flooded reservoir
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