Transcript Community - Cloudfront.net

Community Ecology
Chapter 56
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Biological Communities
• Community: all the organisms that live
together in a specific place
– Evolve together
– Forage together
– Compete
– Cooperate
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Biological Communities
• Interactions in a community
– Predation
– Mutualism
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Biological Communities
Most ecologists favor the
individualistic concept
• In communities, species
respond independently
to changing
environmental
conditions
• Community composition
changes gradually
across landscapes
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Ecological Niche
• Niche: the total of all the ways an
organism uses the resources of its
environment
– Space utilization
– Food consumption
– Temperature range
– Appropriate conditions for mating
– Requirements for moisture and more
Billock
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Ecological Niche
• Other causes of niche
restriction
– Predator absence or
presence
• Plant species
– Absence of pollinators
– Presence of herbivores
Billock
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Billock
Realized niche: actual set of environmental
conditions, presence or absence of other species,
in which the species can establish a stable
population
High tide
Chthamalus
Balanus
Chthamalus
realized niche
Balanus
realized niche
Ocean
EXPERIMENT
Low tide
Ecological Niche
• Fundamental niche: the entire niche that a
species is capable of using, based on
physiological tolerance limits
and resource needs
EXPERIMENT
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Ecological Niche
• Interspecific competition: 2 species
attempt to use the same resource and there
is not enough resource for both
• Competitive exclusion: Strong competition
can lead to competitive exclusion, local
elimination of a competing species
• The competitive exclusion principle states
that 2 species competing for the same
limiting resources cannot coexist in the
same place
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Principle of competitive exclusion
• G.F. Gause’s experiment on competitive
exclusion using three Paramecium species
shows this principle in action
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• Competitive exclusion
redefined: no two
species can occupy the
same niche indefinitely
when resources are
limiting-found in two of
his Paramecium species
• Niche overlap and
coexistence
• Species may divide
up the resources,
this is called
resource
partitioning
Ecological Niche
• Niche overlap and coexistence
• Competitive exclusion redefined: no
two species can occupy the same niche
indefinitely when resources are limiting
• Species may divide up the resources,
this is called resource partitioning
• Gause found this occurring with two of
his Paramecium species
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• Resource partitioning
- seen in similar
species that occupy
same geographic area
• result from the
process of natural
selection
Resource partitioning
among sympatric lizard
species
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Predator-Prey
• Predation: consuming of one organism by
another
• Predation strongly influences prey populations
• Prey populations can have explosions and
crashes
– White-tail deer in Eastern US
– New Zealand: Stephen Island wren extinct
because of a single cat introduction of rats,
dogs, cats on islands
–
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Predator-Prey
• Predation and coevolution
– strong selective pressure on the prey
population
– Features that decrease the probability
of capture are favored
– Predator populations counteradapt to
continue eating the prey
– Coevolution
race may
ensue
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Predator-Prey
• Plants adapt to predation
– Chemical: secondary compounds
• Oils, chemicals, poison milky sap
and others
– Herbivores
coevolve to
continue eating
the plants
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Chemical defenses in animals
• - Monarch butterfly
– caterpillars feed on milkweed
and dogbane plants
– incorporate chemicals from
the plants for protection from
predation
– Butterflies are eaten by birds,
but the Monarch contains the
chemical from the milkweed
that make the birds sicklearns not to eat butterflies
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Chemical defenses Defensive coloration
Predator-Prey
– Insects and other animals
that are poisonous use
warning coloration
– Organisms that lack
specific chemical
defenses are seldom
brightly colored
– Poison-dart frogs produce
toxic alkaloids in the
mucus that covers their
brightly colored skin
Predator-Prey
• Defensive coloration
– Camouflage or Aposematic
(cryptic) coloration help nonpoisonous
animals
– Camouflaged animals blend with their
surroundings; do not usually live together in
groups
Animals closely resemble
surroundings
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Predator-Prey
• Mimicry allows one species to capitalize
on defensive strategies of another
Hawkmoth larva puffs up to
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look like poisonous snake
Predator-Prey
• Batesian mimicry
– Palatable insects that resembled brightly
colored, distasteful species
– Mimics would be avoided by predators
because they looked like distasteful species
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Predator-Prey
• Müllerian mimicry
– Several unrelated but poisonous species
come to resemble one another
– Predator learns quickly to avoid them
– Some predators evolve an innate avoidance
• Both mimic types
must look and act
like the dangerous
model
green parrot snake
hawkmoth
larvae
Hawkmoth larva puffs up to
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look like poisonous snake
Predator-Prey
What kind of mimicry?
Coral snake
King snake is
is poisonous
not
Red on yellow, poison fellow;
red on black, safe from attack
Species Interactions
• Symbiosis: two or more kinds of organisms
interact in more-or-less permanent relationships
• All symbiotic relationships carry the potential for
coevolution
• Three major types
– Commensalism, Mutualism,
Parasitism
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Species Interactions
• Commensalism benefits one species
and is neutral to the other
– Spanish moss: an epiphyte hangs
from trees
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Commensalism?
• Oxpickers and grazing animals
– Oxpickers eat parasites off of grazers
– Sometimes pick scabs and drink
blood
– Grazers could be unharmed by
the insects the oxpickers eat
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Species Interactions
• Mutualism benefits both species
• Coevolution: flowering plants and
insects
Ants and acacias
– Acacias provide
hollow thorns and food
– Ants provide protection
from herbivores
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Species Interactions
• Parasitism benefits one species at the
expense of another
• External parasites: feed on
exterior/interior surface of an
organism
flatworm that lives
in ants changes the
behavior of the ant
to climb to the top
of a blade of grass
to be eaten
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Species Interactions
• Ecological processes have interactive effects
– Superior competitors may be reduced in
number by predation
• This allows other species to survive when
they could have been out competed
Starfish eat
barnacles, allowing
other species to
thrive instead of
being crowded out
by the explosive
population of
barnacles 29
• Indirect effects: presence of one
species may affect a second by way of
interactions with a third species
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• Keystone species: species whose effects on
the composition of communities are greater
than one might expect based on their
abundance
Sea otter is a
keystone
predator in
North Pacific
What is the
impact of the
Orca whale?
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Keystone Species
Beavers construct dams and transform
flowing streams into ponds, creating new
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habitats for many plants and animals
Succession and Disturbance
• Succession happens because species alter the habitat
and the resources available in ways that favor other
species entering the habitat
• Primary succession: occurs on bare, lifeless
substrate; organisms gradually move into an area and
change its nature
• Secondary succession: occurs in areas where an
existing community has been disturbed but organisms
still remain
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Succession and Disturbance
Primary succession on glacial moraines
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Succession and
Disturbance
• Three dynamic concepts in the process
– Tolerance: early species are characterized by r-selected
species tolerant of harsh conditions
– Facilitation: early species introduce local changes in the
habitat. K-selected species replace r-selected species
– Inhibition: changes in the habitat caused by one species
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inhibits the growth of the original species
Succession and Disturbance
Succession after a volcanic eruption
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