Transcript Chapter 7

Chapter 7
Community
Interactions
Let’s get
ready to
ruuuuumble!
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
Four Characteristics of Community
Structure
• Species Diversity/Richness: number of
different species
Four Characteristics of Community
Structure
• Species Abundance: number of individuals
of each species
Four Characteristics of Community
Structure
• 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”
Differing Physical Appearances
• Edge Effects: differences in physical
appearance at boundaries between
ecosystems
Edge Effects
Edge Effects
Ecological Niche
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)
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Ecological Niche vs. Habitat
Habitat: actual location where an organism lives
• habitat is like an "address"
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Generalists vs. Specialists
• 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 Species
Native Species: species that normally live
& thrive in a particular ecosystem
Nonnative Species: (also called exotic,
invasive, or alien species) originate in other
ecosystems; deliberate or accidental introduction
by humans causes problems
•e.g., "killer bees”, imported from Africa to
Brazil to increase honey production; displace
native bees
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Indicator Species
Indicator Species: species that serve as
early warnings that a community or
ecosystem is being damaged
• e.g., northern spotted owls are indicators of
healthy old–growth forest
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Keystone Species
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 & disperse tropical trees such as
durian
“The loss of a keystone species is like a drill
accidentally striking a power line. It causes
lights to go out all over.”
– E.O. Wilson
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Species Interactions
• the effects of one species on another
may be negative, positive, or neutral
• five kinds of interactions:
POPULATION A
COMPETITION
PREDATION
PARASITISM
COMMENSALISM
MUTUALISM
POPULATION B
Interspecific Competition
When two or more species use the same limited
resource (food, space, etc.) and adversely affect
each other
•–/–
• niche overlap
• Ex: fire ants & native ants in North America
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No Competition
High
Relative population density
Paramecium
aurelia
Paramecium
caudatum
Low
0
2
4
6
8
10
12
Days
Each species grown alone
14
16
18
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
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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Warblers
Predation
Members of one species (predator) feed on
another species (prey);
•+/–
• Ex: lion feeding on zebra
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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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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
Prey
• Chemical warfare
• Ex: skunk
Prey
• Warning colors
• Ex: poison dart frog
Prey
• Mimicry
• Ex: king snake
Prey
• Behavior
• Ex: blowfish
Ecological Succession
Succession: gradual & fairly predictable change in
species composition over time
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Primary Succession
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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
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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
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"
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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
• examples of natural disturbances: fires, hurricanes,
tornadoes, droughts, & floods
• examples of human-caused disturbances:
deforestation, overgrazing, plowing
• disturbance initiates secondary succession
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The Circle of Life in
Secondary Succession
Intermediate Disturbance Hypothesis
Ecosystem Stability
• Inertia: the ability of an
ecosystem to resist
being disturbed
• 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”