Community Ecology
Chapter 47
Outline
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Diversity and Composition Models
Island Biogeography
Habitat and Ecological Niche
Competition Between Populations
Predator-Prey Interactions
Symbiotic Relationships
Community Development
Community Diversity
Community Concept
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What is a community?
Factors to consider
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Composition is a listing of various species in
the community.
Diversity includes both species richness and
species diversity.
Diversity and Composition
Models
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Gleason - Individualistic Model
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Each population in community is there
because its own particular abiotic
requirements are met by a particular habitat.
Clements - Interactive Model
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Community is the highest level of
organization.
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Dependent on biotic interactions.
Island Biogeography
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MacArthur and Wilson--effects of distance
from the mainland and size of an island on
community diversity.
Conclusions?
Model of Island Biogeography
Habitat and Ecological Niche
Habitat -- Home.
 Ecological niche ---occupation in the
community
 Fundamental niche - potential
 Realized niche - actual
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Feeding Niches for Wading Birds
Species interactions
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Community interactions can be potent
selective pressures
Competition
 Intraspecific
 Interspecific
Predator/Prey
Symbiosis
RESULTS OF INTERACTION
 (+)
organism benefits (how?)
 (-) organism suffers (how?)
 (0) neutral, no benefit or loss (RU
sure?)
Competition Between
Populations
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Intraspecific competition (?)
Interspecific competition (?)
 Competitive Exclusion Principle
 Resource Partitioning decreases
competition.
 Can lead to character displacement.
Resource Partitioning –more specialized
niches
Competition Between Barnacle Species
Character Displacement in Galápagos
Finches
Predator-Prey Interactions
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Predation
 Selective
pressure?
Interaction = +,  Population effects
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Lynx-Snowshoe Hare
Interactions
Prey Defenses
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Prey defenses -adaptations that thwart the
possibility of being eaten by a predator.
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Concealment/cryptic coloration/other
coloration
Warning coloration
Armor/weaponry
Chemicals
Behavior
Gecko?
Gecko
Gecko?
Stoneplant
Walking
stick
Camouflage in the Anglerfish
Mimicry
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Mimicry occurs when one species
resembles another that possesses an
overt antipredator defense.
 Batesian – Harmless mimics
harmful
 Müllerian – Harmful mimics harmful
Batesian I:
Coral snake
or Milk
Snake?
Would you
bet your
life on it?
Batesian or Mullerian?
Vertebrate Eye Mimicry
 Similar
to Batesian
 Can startle or confuse predator
Eye Mimicry 2
Aposematic (Warning) Coloration
Chemical Defenses
Chemical Defenses 2
Deceptive Coloration Example
Sea Hare
PHAGOMIMICRY
Symbiotic Relationships
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Symbiosis close relationship between
members of two populations. We’ll be
interested in 3:
 Parasitism (+, -)
 Commensalism (+, 0)
 Mutualism (+,+)
Parasitism (+, -)
 Endoparasites
Ex?
 Ectoparasites EX?
 Social Parasites
 Brood parasites
 Kleptoparasites
Endoparasite Life cycles
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Complex, spend different stages in
different hosts
Definitive host (primary host)
 Intermediate host
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Tapeworm Life Cycle
Schistosomiasis
Elephantiasis
Brood Parasitism-European Cuckoo
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The behavior of
the cuckoo
hatchling ejecting
the host eggs
from the nest
The feeding
behavior of a
foster mother to
the cuckoo chick
Figure 37.3B
Kleptoparasite—Red Billed Gull
Commensalism --+, 0
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Shark
(0)
Remora
(+)
Pseudocopulation
Some orchids offer no nectar at all, but
they resemble the female of various
insect species. Or at least, resemble
closely enough to fool a desperate
male of the species – the mimicry is
chemical as well as visual. The
unfortunate male has to be deceived
twice and engage in two acts of
pseudocopulation before pollination
takes place. Common european
species doing this are the bee orchids
in the genus Ophrys. In fact some
populations of bee orchid seem to be
self-fertile in the absence of
pollination.
Bee orchid
Ophrys apifera
Mutualism
Mutualism (+,+) both members of
the association benefit.
 ADVANTAGES?
 EX?
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Mutualism Between Bullhorn
Acacia and Ants
Cleaning Symbiosis
Community Development
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Ecological Succession
 A change involving a series of species
replacements in a community following a
disturbance.
 Primary Succession
 Secondary Succession
Pioneer Species
 Climax Species
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Secondary Succession in a
Forest
Succession Models
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Facilitation Model
 Succession in a particular area will
always lead to the same type of
community
 Climax Community—Endpoint of
succession
 Oldest, most supported
Changes in soil structure over time
Soil changes over time.
Nitrogen levels start out low and
increase because of symbiotic
nitrogen-fixing bacteria in alder.
Then other trees can survive.
Succession Models
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Inhibition Model
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Colonists hold onto their space and inhibit
growth of other plants until the colonists are
damaged or die.
Tolerance Model
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Different types of plants can colonize an area
at the same time.
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Chance determine which seeds arrive first.
Ecological succession:
Primary succession
pioneering plant
retreating glaciers leave
moraines. autotrophic mosses and lichens are species are next
first macroscopic
bacteria are first
autotrophs. soil forms
colonizers.
gradually
Succession continues until a
climax community is formed.
spruce replace alder and
cottonwood
final stage is a spruce and hemlock
forest
Secondary succession occurs after disturbance
that leaves the soil intact. Other examples?
Fig. 53.18 – 1988 fires in Yellowstone
Community Diversity
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Community stability can be recognized in
three ways.
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Persistence through time.
Resistance to change.
Recovery once a disturbance has occurred.
Intermediate Disturbance
Hypothesis
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Moderate amounts of disturbances at
moderate frequency are required for a
high degree of community diversity.
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If widespread disturbances occur frequently,
diversity will be limited.
Intermediate Disturbance
Hypothesis
Predation, Competition, and
Biodiversity
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In certain communities, predation by a
particular species reduces competition and
increases diversity.
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Predators that regulate competition and
maintain community diversity are referred to
as keystone predators.
Introduction of exotic species into a new
area may lead to unbridled competition
and resultant reduction in biodiversity.
Predation, Competition, and
Biodiversity
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In certain communities, predation by a
particular species reduces competition and
increases diversity.
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Predators that regulate competition and
maintain community diversity are referred to
as keystone predators.
Introduction of exotic species into a new
area may lead to unbridled competition
and resultant reduction in biodiversity.
Review
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Diversity and Composition Models
Island Biogeography
Habitat and Ecological Niche
Competition Between Populations
Predator-Prey Interactions
Symbiotic Relationships
Community Development
Community Diversity