Outline
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Outline• The Concept of the Community
– Diversity and Composition Models
• The Structure of Communities– Island Biogeography– Habitat and Ecological Niche– Competition Between Populations– Predator-Prey Interactions– Symbiotic Relationships
• Community Development• Community Biodiversity
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Community Concept
• 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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Community Structure
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Diversity and Composition Models
• Gleason - Individualistic Model– Each population is there because its abiotic
requirements are met• Clements - Interactive Model– Community is the highest level of organization– Dependent on biotic interactions
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Species Richness of Communities
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Island Biogeography
• MacArthur and Wilson– Developed a general model of island biogeography– Explains and predicts how the community
diversity of an island is affected by• Distance from the mainland, and• Size of the island
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Model of Island Biogeography
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Habitat and Ecological Niche
• Habitat– The area an organism lives and reproduces in
• Ecological niche– The role a species plays in its community
• Includes 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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Community Structure Competition
• When two species compete, the abundance of both species is negatively impacted
Predation (or parasitism)• Expected to increase the abundance of the predator (or parasite)• And reduce the abundance of the prey (or host)
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Competition Between Populations• Interspecific competition– Members of different species require the same
resource
– The supply of the resource is limited
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Competition Between
Two Laboratory Populations of Paramecium
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Competitive Exclusion Principle
No two species can occupy the same niche at the same time
Resource Partitioning decreases competition
Can lead to character displacement
Competition Between Populations
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Character Displacement in Finches
on the Galápagos Islands
When on the same island, the beak sizes are appropriate for eating small, medium, and large-sized seeds.
When on separate islands, beaks have the same intermediate size, allowing them to eat seeds that vary in size.
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Niche Specialization Among
Five Species of Coexisting Warblers
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Competition BetweenTwo Species of Barnacles
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Predator-Prey Interactions• Predation– One living organism, the predator, feeds on another, the
prey• Predator is larger• Predator has lower reproductive rate• Prey usually entirely consumed
– Presence of predators can decrease prey densities, and vice-versa
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Predator-prey Interaction Between
Paramecium caudatum and Didinium nasutum
Didinium ate all the Paramecium and then dies out
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Predator-prey InteractionBetween a Lynx and a Snowshoe Hare
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Prey Defenses• Prey defenses– Mechanisms that thwart the possibility of being
eaten by a predator• Spines• Tough Epidermis• Poisonous Chemicals• Camouflage
(cryptic coloration)• Bright Coloration
(warning coloration)• Flocking Behavior
http://www.youtube.com/watch?v=B2JdRPKYyTc
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Camouflage in the
Anglerfish
http://www.youtube.com/watch?v=fUDY9Y_3TNc
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Mimicry– One species resembles another species– Mimicked species possesses an overt
antipredator defense (warning coloration)• Batesian Mimicry - Mimic lacks defense
of the organism it resembles
• Müllerian Mimicry - Mimic shares same protective defense
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Anti-predator Defenses
Poison arrow frog used to make arrows lethal weapons.
Eastern tiger swallowtail butterfly caterpillar has false eyespots to confuse predator.
South American lantern fly has a large false head that resembles and alligator.
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Mimicry Among Insects with
Yellow and Black Stripes
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Symbiotic Relationships• Symbiosis– Interactions in which there is a close relationship
between members of two species– Parasitism• Parasite derives nourishment from a host, and may use
host as habitat and mode of transmission– Endoparasites -Inside host body– Ectoparasites – Outside host body
Beetle infected with wasp larvae Fleas on your dog/cat/you
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Commensalism
• Symbiosis, cont.– Commensalism• A symbiotic relationship in which one species benefits
and the other is indifferent– Remoras and Sharks
• Many supposed examples may turn out to be mutualism or parasitism• Inferred amount of harm or benefit two species do to
one another is subject to investigator bias
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Clownfish AmongSea Anemone’s Tentacles
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Mutualism
• Symbiosis, cont.
– Mutualism
• A symbiotic relationship in which both members of the association benefit
• Need not be equally beneficial to both species
– Cleaning Symbiosis
• Often help each other obtain food or avoid predation
– Bacteria in human intestinal tract
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Mutualism Betweenthe Bullhorn Acacia Tree
and Antsa. Tree provides nourishment for ants. Ants live inside hollow thorns.
b. Nectaries at base of leaves from which ants feed.
c. Ants harvest larval food at tips of leaves
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Cleaning Symbiosis
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Community Development
• Ecological Succession– A predictable pattern of change in species
replacements 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
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Secondary Successionin a Forest
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Succession Models
• Facilitation Model– Each stage facilitates invasion and replacement by
organisms of the next stage– Succession in a particular area will always lead to
the same type of community– Climax Community
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Succession Models
• Inhibition Model– Colonists remain 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
• 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
• If widespread disturbances occur frequently, diversity will be limited
• If diversity is high, only moderate disturbances have been occurring with moderate frequency
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The Intermediate Disturbance Hypothesis
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Predation, Competition, and Biodiversity
• Predation by a particular species may reduce competition and increases diversity– Such predators are referred to as keystone
predators• Exotic species– May lead to unbridled competition– Resultant reduction in biodiversity
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Effect of a Keystone Species
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Review• The Concept of the Community
– Diversity and Composition Models
• The Structure of Communities– Island Biogeography– Habitat and Ecological Niche– Competition Between Populations– Predator-Prey Interactions– Symbiotic Relationships
• Community Development• Community Biodiversity