Transcript Chapter 7

Chapter 7
Community
Interactions
7-1 COMMUNITY STRUCTURE
AND SPECIES DIVERSITY
Community
• Community: populations of all
species living and interacting in an
area at a particular time
Four Characteristics of Community Structure
• Physical Appearance: size and
distribution of its population and
species
• Species Diversity/Richness: number
of different species
• Species Abundance: number of
individuals of each species
• Niche Structure: number of niches,
how they compare, and how they
interact
Differing Physical Appearances
• Patch Effects: most large
communities usually consist
of a mosaic of vegetation
“patches”
• Edge Effects: differences in
physical appearance at
boundaries between
ecosystems
Species Diversity
• Species Rich Environments
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Tropical Rain Forests
Coral Reefs
Deep Sea
Large Tropical Lakes
Tend to have high species diversity
but low species abundance
• Factors that Affect Diversity
– Latitude (terrestrial) – distance
from equator
– Depth (aquatic)
– Pollution (aquatic)
Species Abundance
• Determined by:
– Rate at which new species immigrate
– Rate at which species become extinct
Ecological Niche vs. Habitat
Niche: role an organism
plays in an ecosystem
•niche is like an
"occupation“ – a
species’ interactions
with habitat and
other organisms (their
role in food web)
Habitat: actual location
where an organism lives
•habitat is like an
"address"
7-2 GENERAL TYPES OF
SPECIES
GENERAL TYPES OF SPECIES
•Generalist Species
•Specialist Species
•Native Species
•Nonnative Species
•Indicator Species
•Keystone Species
Generalist vs. Specialist
•Generalist Species have broad niches,
can live many places, use a variety of
resources
e.g., dandelions, cockroaches, coyotes,
humans
•Specialist Species have narrow niches,
live only in specific places
e.g., spotted owls, giant pandas
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Native vs. Nonnative Species
• Native Species: species that
normally live & thrive in a
particular ecosystem
• Nonnative Species:
•also called exotic, invasive,
or alien species
•originate in other
ecosystem
•deliberate or accidental
introduction by humans
causes problems
•may thrive and crowd out
native species
The Case of the Killer Bees
• 1957 Brazil imported wild African
bees to help increase honey
production
• Displaced domestic honeybees
• Actually reduced honey
production
• Moved north in Central America
• Established populations in Texas,
Arizona, New Mexico, Puerto
Rico, and California
Snakehead Fish
CANE TOADS!
The Simpsons!
• Bart vs. Australia
Indicator Species
• Indicator Species: species that
serve as early warnings that a
community or ecosystem is being
damaged
•Birds are good indicator species
•Found everywhere
•Respond to environmental
change quickly
•northern spotted owls are
indicators of healthy old–
growth forest
•Fish are good indicator species in
aquatic ecosystems (i.e. trout)
“The loss of a keystone species is like a
drill accidentally striking a power line.
It causes lights to go out all over.”
Keystone Species
– E.O. Wilson
Keystone Species: species that
play a critical role in an
ecosystem
•Ex: sea otters are keystone
species because they prevent
sea urchins from depleting kelp
beds
•Ex: flying foxes are keystone
species because they pollinate
tropical trees and disperse seeds,
such as durian fruit trees
7-3 SPECIES INTERACTIONS:
COMPETITION AND
PREDATION
Species Interactions
• The effects of one species on another may be
negative, positive, or neutral
• Five kinds of interactions:
•Interspecific competition
•Predation
•Parasitism
•Mutualism
•Commensalism
Intra- vs. Inter- specific competition
• Intraspecific Competition –
members of the SAME species
compete for resources
•Interspecific Competition –
members from 2 or more
DIFFERENT species compete for
resources
•When two or more species use
the same limited resource
(food, space, etc.) they may
adversely affect each other
•niche overlap
•Ex: fire ants & native ants in
North America
No Competition
High
Relative population density
Paramecium
aurelia
Low
Paramecium
caudatum
0
2
4
6
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10
12
Days
Each species grown alone
14
16
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Interspecific Competition
High
Relative population density
Paramecium
aurelia
Paramecium
caudatum
Low
0
2
4
6
8
10
12
Days
Both species grown together
14
16
18
Resource Partitioning
Species with similar
resource
requirements can
coexist because
they use limited
resources:
•at different times
•in different ways
•in different places
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Resource Partitioning
Where are the 2
species competing?
Why is there
no
competition
here?
Resource Partitioning
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Resource Partitioning Example
Five species of insect–eating warblers coexist in
spruce forests of Maine:
•feed in different portions of trees
•consume somewhat different insects
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Predation
•Members of one species (predator) feed
on another species (prey);
•+ / –
•Ex: lion feeding on zebra
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Predator-Prey Relationship
• What do predators do to increase
their chances of getting a meal?
• What do prey do to avoid being
eaten?
Predator-Prey Relationship
• Predators get better at
catching prey
• Prey get better at
avoiding capture
• Similar to an “arms race”
– Ex: During the Cold War, the
US and the USSR tried to
intimidate the other with
bigger and better weapons
Predators
• Pursuit
– Faster (cheetahs)
– Better eyesight (eagles)
– Hunting in packs (wolves)
• Ambush
– Camouflage (praying mantis)
– Mimicry (alligator snapping turtles)
Prey
• Camouflage
• Ex: walking stick
• Warning colors
• Ex: poison dart frog
• Mimicry
• Ex: king snake
• Behavior
• Ex: blowfish
• Chemical warfare
• Ex: skunk
7-4 SPECIES INTERACTIONS:
PARASITISM, MUTUALISM,
AND COMMENSALISM
Parasitism
One organism (parasite) lives on part of another
organism (host)
•+ / –
•Ex: flea living on a dog
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Mutualism
Two species interact in a way that benefits both
•+ / +
•Ex: lichens (algae & fungi)
•Ex: clownfish & anemones
•Ex: ants & acacias
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Commensalism
One organism benefits from another, but neither
helps nor harms the other organism
•+ / 0
•Ex: epiphyte growing on a tree
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Species Interactions
• The effects of one species on another
may be negative, positive, or neutral
• five kinds of interactions:
COMPETITION
PREDATION
PARASITISM
COMMENSALISM
MUTUALISM
POPULATION A
POPULATION B
+
+
+
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0
+
7-5 ECOLOGICAL SUCCESSION:
COMMUNITIES IN TRANSITION
Ecological Succession
Succession: gradual & fairly predictable change in
species composition over time
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Primary Succession
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Primary Succession
• Type of succession that
occurs where there was
no ecosystem before
• Occurs on rocks, cliffs,
and sand dunes
• Pioneer species: the first
organism to colonize
any newly available
area and begin the
process of ecological
succession
Primary Succession
Primary Succession: gradual establishment of
biotic communities in an area where no life
existed before
•Ex: succession on newly formed islands & after
the retreat of a glacier
•Early Communities: lichens & mosses colonize bare
rock
•Mid Communities: small herbs & shrubs colonize
•Late Communities: tree species colonize
Lichens
Mosses
Parking Lot
Secondary Succession
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Secondary Succession
Secondary Succession: gradual reestablishment
of biotic communities in an area where a biotic
community was previously present
•Ex: "old field succession"
Secondary Succession:
Mount St. Helens
• Erupted in 1980
• 44,460 acres were
burned and
flattened
• After the eruption,
plants began to
colonize the debris
Disturbance
Disturbance: a distinct event that disrupts an
ecosystem or community
•disturbance initiates secondary succession
•Natural disturbances: fires, hurricanes, tornadoes,
droughts, & floods
•Human-caused disturbances: deforestation,
overgrazing, plowing
Intermediate Disturbance Hypothesis:
moderate disturbances in communities
promote greater species diversity than small
or major disturbances
Climax Community
• Climax community: the
final and stable
community in an
ecosystem
• Will continue to
change in small ways,
but will remain primarily
the same over time
(unless disturbed)
The Circle of Life in
Secondary Succession
7-6 ECOLOGICAL STABILITY
AND SUSTAINABILITY
Stability - complex networks of positive and
negative feedbacks loops
Ecosystem Stability
• Inertia/Persistence: the ability of an ecosystem to resist
being disturbed
• Constancy: the ability of a living sysmte such as a
population to keep its numbers within the limits imposed
by available resources
• Resilience: the ability of an ecosystem to “bounce back”
after it has been disturbed
Precautionary Principle
• We should try to prevent potential harm
to an ecosystem even though we don’t
understand all of the cause-and-effects
• “better safe than sorry”