Community Ecology
Chapter 47
Mader: Biology 8th Ed.
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
Mader: Biology 8th Ed.
Community Concept
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A community is an assemblage of
populations interacting with one another
within the same environment.
– Composition is a listing of various species
in the community.
– Diversity includes both species richness
and species diversity.
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Diversity and Composition Models
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Gleason - Individualistic Model
– Each population in community is there
because its own particular abiotic
requirements are met by a particular
habitat.
Clements - Interactive Model
– Community is the highest level of
organization.
 Dependent on biotic interactions.
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Island Biogeography
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MacArthur and Wilson developed a general
model of island biogeography to explain and
predict the effects of distance from the
mainland and size of an island on
community diversity.
– Island size and distance from population
source affects species diversity.
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Model of Island Biogeography
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Community Structure
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Competition for limited resources between
two species has a negative effect on the
abundance of both species.
– Predation and parasitism are expected to
increase the abundance of the predator
and parasite at the expense of the
abundance of the prey and its host.
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Habitat and Ecological Niche
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Habitat is the area an organism lives and
reproduces in.
Ecological niche is the role an organism
plays in its community, including its habitat
and its interactions with other organisms.
– Fundamental niche - All conditions under
which the organism can survive.
– Realized niche - Set of conditions under
which it exists in nature.
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Feeding Niches for Wading Birds
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Competition Between Populations
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Interspecific competition occurs when
members of different species try to utilize a
resource in limited supply.
– Competitive Exclusion Principle - No two
species can occupy the same niche at the
same time.
 Resource Partitioning decreases
competition.
 Can lead to character displacement.
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Competition Between Barnacle Species
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Character Displacement in Galápagos Finches
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Predator-Prey Interactions
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Predation occurs when one living organism,
the predator, feeds on another, the prey.
– Presence of predators can decrease prey
densities, and vice-versa.
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Lynx-Snowshoe Hare Interactions
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Prey Defenses
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Prey defenses are mechanisms that thwart
the possibility of being eaten by a predator.
– Spines
– Tough Epidermis
– Poisonous Chemicals
– Camouflage
– Bright Coloration
– Flocking Behavior
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Camouflage in the Anglerfish
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Mimicry
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Mimicry occurs when one species
resembles another that possesses an overt
antipredator defense.
– Batesian - Mimic lacks defense of the
organism it resembles.
– Müllerian - Mimic shares same protective
defense.
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Symbiotic Relationships
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Symbiosis refers to interactions in which
there is a close relationship between
members of two populations.
– Parasitism
 Parasite derives nourishment from a
host, and may use host as habitat and
mode of transmission.
 Endoparasites
 Ectoparasites
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Commensalism
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Commensalism is a symbiotic relationship in
which one species is benefited and the other
is neither benefited nor harmed.
– Remoras and Sharks
 Many examples may turn out to be
mutualism or parasitism.
 Amount of harm or benefit two
species do to one another is partially
determined by the investigator.
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Mutualism
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Mutualism is a symbiotic relationship in
which both members of the association
benefit.
– Often help organisms obtain food or avoid
predation.
 Bacteria in human intestinal tact.
– Need not be equally beneficial to both
species.
 Cleaning Symbiosis
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Mutualism Between Bullhorn Acacia and Ants
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Cleaning Symbiosis
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Community Development
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Ecological Succession
– A change involving a series of species
replacements in a community following a
disturbance.
 Primary Succession occurs in areas
where there is no soil formation.
 Secondary Succession begins in areas
where soil is present.
 Pioneer Species
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Secondary Succession in a Forest
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Succession Models
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Facilitation Model
– Succession in a particular area will always
lead to the same type of community.
 Climax Community
 Each stage facilitates invasion and
replacement by organisms of the
next stage.
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Succession Models
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Inhibition Model
– Colonists hold onto their space and inhibit
growth of other plants until the colonists
are damaged or die.
Tolerance Model
– Different types of plants can colonize an
area at the same time.
 Chance determine which seeds arrive
first.
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Community Diversity
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Community stability can be recognized in
three ways.
– Persistence through time.
– Resistance to change.
– Recovery once a disturbance has
occurred.
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Intermediate Disturbance Hypothesis
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Moderate amounts of disturbances at
moderate frequency are required for a high
degree of community diversity.
– If widespread disturbances occur
frequently, diversity will be limited.
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Intermediate Disturbance Hypothesis
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Predation, Competition, and Biodiversity
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In certain communities, predation by a
particular species reduces competition and
increases diversity.
– 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.
Mader: Biology 8th Ed.
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
Mader: Biology 8th Ed.
Mader: Biology 8th Ed.