community interactions chapter 29. forest of new guinea community includes nine species of pigeons...
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![Page 1: Community Interactions Chapter 29. Forest of New Guinea Community includes nine species of pigeons that partition the food supply Pigeons disperse seeds](https://reader030.vdocuments.us/reader030/viewer/2022032704/56649d3a5503460f94a1552a/html5/thumbnails/1.jpg)
Community Interactions
Chapter 29
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Forest of New Guinea
• Community includes nine species of
pigeons that partition the food supply
• Pigeons disperse seeds of the trees
that provide their food (fruit)
• These are just a few of the many
interactions that shape this community
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Community
• All the populations that live together in a
habitat
• Habitat is the type of place where
individuals of a species typically live
• Type of habitat shapes a community’s
structure
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Factors Shaping Community Structure
• Climate and topography
• Available foods and resources
• Adaptations of species in community
• Species interactions
• Arrival and disappearance of species
• Physical disturbances
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Niche
Sum of activities and relationships in
which a species engages to secure and
use resources necessary for survival
and reproduction
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Realized & Fundamental Niches
• Fundamental niche – Theoretical niche occupied in the absence
of any competing species
• Realized niche – Niche a species actually occupies
• Realized niche is some fraction of the fundamental niche
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Species Interactions
• Most interactions are neutral; have no
effect on either species
• Commensalism helps one species and
has no effect on the other
• Mutualism helps both species
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Species Interactions
• Interspecific competition has a negative
effect on both species
• Predation and parasitism both benefit
one species at a cost to another
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Symbiosis
• Living together for at least some part of
the life cycle
• Commensalism, mutualism, and
parasitism are forms of symbiosis
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Mutualism
• Both species benefit
• Many examples in nature
• Some mutualisms are obligatory;
partners depend upon each other
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Yucca and Yucca Moth
• Example of an obligatory mutualism
• Each species of yucca is pollinated only
by one species of moth
• Moth larvae can grow only in that one
species of yucca
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Mycorrhizae
• Obligatory mutualism between fungus
and plant root
• Fungus supplies mineral ions to root
• Root supplies sugars to fungus
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Competition
• Interspecific - between species
• Intraspecific - between members of the
same species
• Intraspecific competition is most intense
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Forms of Competition
• Competitors may have equal access to
a resource; compete to exploit resource
more effectively
• One competitor may be able to control
access to a resource, to exclude others
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Competitive Exclusion Principle
When two species compete for identical
resources, one will be more successful
and will eventually eliminate the other
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Competitive Exclusion Expt
Paramecium caudatum
Paramecium aurelia
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Keystone Species
• A species that can dictate community
structure
• Removal of a keystone species can
cause drastic changes in a community;
can increase or decrease diversity
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Lubchenco Experiment
Tidepools Rocks exposed at high tide
Periwinkles promote or limit diversity in different habitats
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Resource Partitioning
• Apparent competitors
may actually have
slightly different niches
• Species may use
resources in a different
way or time
• Minimizes competition
and allows coexistence
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Predation
• Predators are animals that feed on other
living organisms
• Predators are free-living; they do not
take up residence on their prey
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Coevolution
• Natural selection promotes traits that
help prey escape predation
• It also promotes traits that make
predators more successful at capturing
prey
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Predator-Prey Cycles
• Predator and prey populations may show an apparent correspondence
PREY POPULATION
PREDATOR POPULATION
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Variation in Cycles
• An association in predator and prey
abundance does not always indicate a
cause and effect relationship
• Variations in food supply and additional
predators may also influence changes
in prey abundance
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Prey Defenses
• Camouflage
• Warning coloration
• Mimicry
• Moment-of-truth defenses
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Predator Responses
• Any adaptation that protects prey may
select for predators that can overcome
that adaptation
• Prey adaptations include stealth,
camouflage, and ways to avoid chemical
repellents
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Parasitism
• Parasites drain nutrients from their
hosts and live on or in their bodies
• Natural selection favors parasites
that do not kill their host too quickly
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Types of Parasites
• Microparasites
• Macroparasites
• Social parasites
• Parasitoids
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Succession
Change in the composition of species
over time
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Types of Succession
• Primary succession - new
environments
• Secondary succession -
communities were destroyed
or displaced
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Pioneer Species
• Species that colonize barren habitats
• Lichens, small plants with brief life
cycles
• Improve conditions for other species
who then replace them
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Climax Community
• Stable array of species that persists
relatively unchanged over time
• Succession does not always move
predictably toward a specific climax
community; other stable communities
may persist
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Cyclic Changes
• Cyclic, nondirectional changes also
shape community structure
• Tree falls cause local patchiness in
tropical forests
• Fires periodically destroy underbrush in
sequoia forests
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Restoration Ecology
• Natural restoration of a damaged
community can take a very long time
• Active restoration is an attempt to
reestablish biodiversity in an area
• Ecologists are actively working to
restore reefs, grasslands, and wetlands
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Community Instability
• Disturbances can cause a
community to change in ways that
persist even if the change is
reversed
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Species Introductions
• Introduction of a nonindigenous species
can decimate a community
• No natural enemies or controls
• Can outcompete native species
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Exotic Species
• Species that has left its home range
and become established elsewhere
• Becomes part of its new community
• Can have beneficial, neutral, or
harmful effects on a community
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Endangered Species
• A species that is extremely vulnerable
to extinction
• Close to 70 percent of endangered
species have been negatively affected
by exotic competitors
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Nile Perch in East Africa
• Nile perch were introduced into Lake
Victoria as a food source
• This predator ate native cichlids; drove
many species to extinction
• Now Nile perch species is close to
crashing
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Rabbits in Australia
• Rabbits were introduced for food and
hunting
• Without predators, their numbers
soared
• Attempts at control using fences or
viruses have thus far been unsuccessful
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Kudzu in Georgia
• Imported for erosion control
• No natural herbivores, pathogens, or competitors
• Grows over landscapes and cannot be dug up or burned out
• May turn out to have some commercial use
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Diversity by Latitude
• Diversity of most groups is greatest in tropics; declines toward poles
Ant diversity
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Why Are Tropical Species Rich?
• Resources are plentiful and reliable
• Species diversity is self-reinforcing
• Rates of speciation are highest in the
tropics
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Distance Effect
• The farther an island is from a
mainland, the fewer species
• Closer islands receive more immigrants
• Species that reach islands far from
mainland are adapted for long-distance
dispersal and can move on
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Distance Effect