Download Community Ecology Chapter 56

CHAPTER 57
LECTURE
SLIDES
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Interspecific Interactions and
the Ecology of Communities
Chapter 57
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Biological Communities
• Community
– Species that occur at any particular locality
– Characterized by
• Species richness
–Number of species present
• Primary productivity
–Amount of energy produced
– Interactions among members govern many
ecological and evolutionary processes
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Biological Communities
• Two views of structure and functioning
of communities
– Individualistic concept: a community
is nothing more than an aggregation
of species that happen to occur
together at one place
– Holistic concept: a community is an
integrated unit; superorganism –
more than the sum of its parts
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Biological Communities
• Most ecologists today favor the
individualistic concept
• In communities, species respond
independently to changing
environmental conditions
• Community composition changes
gradually across landscapes
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• Abundance of tree species along a moisture gradient in
the Santa Catalina Mountains of Southeastern Arizona
• Each line represents the abundance of a different tree
species
• Community composition changes continually along the
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gradient
Biological Communities
• Sometimes the
abundance of species
in a community does
change
geographically in a
synchronous pattern
• Ecotones: places
where the
environment changes
abruptly
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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
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Ecological Niche
• Interspecific competition
– Occurs when two species attempt to use
the same resource and there is not enough
resource to satisfy both
• Interference competition
– Physical interactions over access to
resources
• Exploitative competition
– Consuming the same resources
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Ecological Niche
• Fundamental niche
– Entire niche that a species is capable of using,
based on physiological tolerance limits and
resource needs
• Realized niche
– Actual set of environmental conditions, presence
or absence of other species, in which the species
can establish a stable population
• Other causes of niche restriction
– Predator absence or presence
– Absence of pollinators
– Presence of herbivores
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Ecological Niche
J.H. Connell’s classical study of barnacles
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Ecological Niche
• Principle of competitive exclusion
• If two species are competing for a limited
resource, the species that uses the
resource more efficiently will eventually
eliminate the other locally
• G.F. Gause’s classic experiment on
competitive exclusion using three
Paramecium species shows this
principle in action
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Ecological Niche
• Paramecium caudatum and P. bursaria
– Expected same results – one winner
– Both species survived by dividing
resources
• Realized niche did not overlap too much
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• Resource
partitioning
among
sympatric
lizard
species
• Subdivided
niche to
avoid direct
competition
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• Resource partitioning is often seen in similar species
that occupy the same geographic area
– Thought to result from the process of natural selection
• Character displacement
– Differences in morphology evident between sympatric
species
– May play a role in adaptive radiation
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SCIENTIFIC THINKING
Question: Does interspecific interaction occur between rodent
species?
Hypothesis: The larger kangaroo rat will have a negative effect
on other species.
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SCIENTIFIC THINKING
Question: Does interspecific interaction occur between rodent
species?
Hypothesis: The larger kangaroo rat will have a negative effect
on other species.
Experiment: Build large cages in desert areas. Remove kangaroo
rats from some cages, leaving them present in others.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
SCIENTIFIC THINKING
Number of Captures
Of Other Rodents
Question: Does interspecific interaction occur between rodent
species?
Hypothesis: The larger kangaroo rat will have a negative effect
on other species.
Experiment: Build large cages in desert areas. Remove kangaroo
rats from some cages, leaving them present in others.
Result: In the absence of kangaroo rats, the number of other
rodents increases quickly and remains higher than in the control
cages throughout the course of the experiment.
kangaroo rats removed
kangaroo rats present
15
10
5
0
1988
1989
1990
Ecological Niche
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
SCIENTIFIC THINKING
• Seed-eating rodents and
Kangaroo rats
– 50 m x 50 m
enclosures
– Enclosures had
openings large
enough for seedeating rodents but not
the Kangaroo rats
– Monitor the number of
small rodents
• Results indicate that kangaroo rats compete with the
other rodents and limit their population sizes
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Number of Captures
Of Other Rodents
Question: Does interspecific interaction occur between rodent
species?
Hypothesis: The larger kangaroo rat will have a negative effect
on other species.
Experiment: Build large cages in desert areas. Remove kangaroo
rats from some cages, leaving them present in others.
Result: In the absence of kangaroo rats, the number of other
rodents increases quickly and remains higher than in the control
cagesthroughout the course of the experiment.
kangaroo rats removed
kangaroo rats present
15
10
5
0
1988
1989
1990
Interpretation: Why do you think population sizes rise and fall in
synchrony in the two cages?
Predator–Prey
• Predation
– Consuming of one organism by another
• Predation strongly influences prey
populations
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Predator–Prey
• Prey populations can have explosions and
crashes
– White-tailed deer in Eastern U.S.
– Introduction of rats, dogs, cats on islands
– New Zealand: Stephen Island wren extinct
because of a single cat
• Predation and coevolution
– Predation provides strong selective pressure on
the prey population
– Features that decrease the probability of capture
are strongly favored
– Coevolution race may ensue
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Predator–Prey
• Plants adapt to predation
(herbivory) by evolving
mechanisms to defend themselves
– Chemical defenses: secondary
compounds
• Oils, chemicals to attract predators to
eat the herbivores, 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 families
– Monarchs incorporate cardiac glycosides from the
plants for protection from predation
– Butterflies are eaten by birds, but the Monarch
contains the chemical from the milkweed that
makes the birds sick
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Predator–Prey
Poison-dart frogs
of the family
Dendrobatidae
produce toxic
alkaloids in the
mucus that covers
their brightly
colored skin
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• Defensive coloration
– Insects and other animals that are poisonous use
warning coloration
– Organisms that lack specific chemical defenses
are seldom brightly colored
• Camouflage or cryptic coloration help
nonpoisonous animals blend with their
surroundings
• Camouflaged animals do not usually live
together in groups
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Predator–Prey
• Mimicry allows one species to capitalize on
defensive strategies of another
– Resemble distasteful species that exhibit warning
coloration
– Mimic gains an advantage by looking like the
distasteful model
– Batesian mimicry
• Mimics look like distasteful species
– Müllerian mimicry
• Several unrelated but poisonous species come
to resemble one another
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Species Interactions
• Symbiosis
– 2 or more kinds of organisms
interact in more-or-less
permanent relationships
– Potential for coevolution
– Three major types of
symbiosis
• 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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Species Interactions
• When commensalism may
not be commensalism
• Oxpeckers and grazing
animals
– Oxpeckers eat parasites
off of grazers
– Sometimes pick scabs
and drink blood
– Grazers could be
unharmed by the insects
the oxpeckers 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
• Not all ant and acacia relationships are
mutualism
– In Kenya, several species of ants live on
acacias
• One species clips the acacia branches to
prevent other ants from living in the tree
• Clipping branches sterilizes the tree
• A parasitic relationship
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Species Interactions
• Parasitism benefits one species at the
expense of another
– External parasites
• Ectoparasites: feed on exterior surface of
an organism
• Parasitoids: insects that lay eggs on
living hosts
–Wasp, whose larvae feed on the body
of the host, killing it
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External parasite: the yellow vines are the flowering
plant dodder; it is a parasite that obtains its food from
the host plant it grows on
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Species Interactions
• Internal parasites
– Endoparasites live inside the host
– Extreme specialization by the parasite as
to which host it invades
– Structure of the parasite may be simplified
because of where it lives in its host
– Many parasites have complex life cycles
involving more than one host
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Species Interactions
• Dicrocoelium dendriticum
is a flatworm that lives in
ants as an intermediate
host with cattle as its
definitive host
• To go from the ant to a
cow, it changes the
behavior of the ant
• Causes the ant to climb
to the top of a blade of
grass to be eaten with
the grass
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Species Interactions
• Ecological processes have interactive
effects
– Predation reduces competition
• Predators choice depends partly on
relative abundance of the prey options
• Superior competitors may be reduced in
number by predation
• This allows other species to survive
when they could have been outcompeted
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Species Interactions
Starfish eat barnacles, allowing other species
to thrive instead of being crowded out by the
explosive population of barnacles
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Species Interactions
• Parasitism may counter competition
– Parasites may affect sympatric species
differently, changing the outcome of
interspecific interactions
– Flour beetles and a competition experiment
• Without a parasite T. castaneum is
dominant
• With the parasite: T. confusum is
dominant
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Species Interactions
• Indirect effects: presence of one species
may affect a second by way of
interactions with a third species
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Species Interactions
• Keystone species
– Species whose effects on the composition
of communities are greater than one might
expect based on their abundance
– Sea star predation on barnacles greatly
alters the species richness of the marine
community
– Keystone species can manipulate the
environment in ways that create new
habitats for other species
• Beavers
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Beavers construct dams and transform
flowing streams into ponds, creating new
habitats for many plants and animals
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Succession and Disturbance
• Succession
– Communities have a tendency to change
from simple to complex
• Primary succession occurs on bare,
lifeless substrate
–Open water
–Rocks
– Organisms gradually move into an area
and change its nature
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Succession and Disturbance
• Secondary succession
– Occurs in areas where an existing
community has been disturbed but
organisms still remain
• Field left uncultivated
• Forest after a fire
• Succession happens because species
alter the habitat and the resources
available in ways that favor other
species entering the habitat
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Succession and Disturbance
• Three dynamic concepts in the process
– Tolerance: early successional species are
characterized by r-selected species
tolerant of harsh conditions
– Facilitation: early successional species
introduce local changes in the habitat. Kselected species replace r-selected
species
– Inhibition: changes in the habitat caused by
one species inhibits the growth of the
original species
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Succession and Disturbance
• Animal species in a community can also
change over time
– Krakatau island
• Volcanic eruption
• Fauna changed in synchrony with the
vegetation
• Changes in animals affect plant
occurrences; pollination, animal
dispersion
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Succession and Disturbance
Succession after a volcanic eruption
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Succession and Disturbance
• Communities are constantly changing
as a result of
– Climatic changes
– Species invasions
– Disturbance events
• Nonequilibrium models that emphasize
change rather than stability are used to
study communities and ecosystems
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Succession and Disturbance
• Intermediate disturbance hypothesis
– Communities experiencing moderate
amounts of disturbance will have higher
levels of species richness than
communities experiencing either little or
great amounts of disturbance
• Patches of habitat will exist at different
successional stages
• May prevent communities from reaching
the final stages of succession
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Succession and Disturbance
• Disturbance is common,
rather than exceptional
in many communities
• Understanding the role
that disturbances play in
structuring communities
is an important area of
ecology
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