Community Ecology

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Community Ecology

• Chapter 54

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Outline

• Biological Communities
• Realized Niche
• Principle of Competitive Exclusion
• Resource Partitioning
• Predation and Prey Populations
• Mimicry
• Coevolution and Symbiosis
• Interactions Among Ecological Processes
• Succession

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Biological Communities

• A community refers to the species that occur
  together at any particular locality.
• Interaction among community members govern many
  ecological and evolutionary processes.
• environment changes abruptly in ecotones
• Individualistic concept - Gleason
• Holistic concept - Clements

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Community Composition Changes
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Fundamental and Realized Niches

• An organisms niche is the total of all ways it
  utilizes the resources of its environment.
• fundamental - entire niche potentially available
  to an organism
• realized - actual niche utilized by an organism
• Habitat is the place where an organism lives.

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Realized Niche

• Interspecific competition - Occurs when different
  species attempt to utilize the same resource.
• interference - individuals fighting over the same
  resource
• exploitative - individuals utilizing shared
  resources

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Principle of Competitive Exclusion

• The principle of competitive exclusion states
  that no two species utilizing the same niche can
  coexist indefinitely.
• one will eventually eliminate the other
• Gauses Paramecium experiments

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Competitive Exclusion Among Paramecium
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Resource Partitioning

• Resource partitioning occurs when species living
  in the same area partition available resources to
  avoid direct competition.
• Sympatric species are similar species that live
  in the same geographical area.
• tend to exhibit greater differences in morphology
  than allopatric species (species that live apart
  from each other)
• character displacement

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Character Displacement
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Detecting Interspecific Competition

• Negative effects of one species on another do not
  automatically indicate competition.
• Presence of one species may attract a predator
  that consumes both, causing one species to have a
  lower population size than the other.
• must always look at underlying ecological
  mechanisms

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Predation and Prey Populations

• Predation occurs when one organism consumes
  another.
• provides strong selective pressure on prey
  populations
• Any physiologic characteristic or behavior that
  would decrease the probability of capture should
  be strongly favored.
• increased fitness

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Plant Defenses Against Herbivores

• Morphological
• thorns, spines, etc.
• Chemical
• secondary chemical compounds
• Evolutionary response of herbivores
• Certain groups of herbivores are associated with
  each group of plants protected by a particular
  secondary compound.
• coevolution

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Animal Defenses Against Predators

• Some animals that feed on plants rich in
  secondary compounds receive an extra benefit.
• caterpillars that feed on members of the milkweed
  family

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Animal Defenses Against Predators

• Chemical defenses
• poisons and stings
• Defensive coloration
• aposematic coloration (warning coloration)
• individuals advertise poisonous nature
• cryptic coloration
• camouflage (blending coloration)

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Mimicry

• Batesian mimicry
• Palatable insects resemble brightly colored,
  distasteful species.
• Mullerian mimicry
• Unrelated protected species resemble one another.
• predators learn more quickly

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Mimicry
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Coevolution and Symbiosis

• Coevolution involves long-term mutual
  evolutionary character adjustments of two or more
  species.
• predator-prey interactions
• symbiotic relationships
• two or more kinds of organisms live together in
  permanent relationships
• commensalism, mutualism, and parasitism

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Commensalism

• One species in symbiotic relationship benefits
  while the other is neither helped or hurt.
• tropical fish and sea anemones
• No clear distinction between mutualism as it is
  difficult to determine if the second member of
  the relationship benefits.
• can easily transform into parasitism

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Mutualism

• Both species in relationship benefit.
• mutual cooperation
• ants and acacias

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Parasitism

• Parasite is much smaller than the prey and
  benefits while inflicting some form of harm to
  the prey.
• ectoparasites
• external parasites - lice
• parasitoids - lay eggs on living hosts
• endoparasites
• internal parasites
• extreme specialization

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Interactions Among Ecological Processes

• Predation reduces competition
• reduce numbers of competitive species
• Parasitism can counter competition
• Parasite may affect sympatric species and thus
  influence interspecific interactions.
• Indirect effects
• Presence of one species may affect a second
  species through interactions with a third species.

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Interactions Among Ecological Processes

• Keystone species
• Species that have a particularly strong effect on
  community composition.
• top predators

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Succession

• Succession is the process of ecosystems changing
  from a simple to a more complex structure.
• primary succession - occurs in bare or open areas
• eutrophication of oligotrophic lakes
• secondary succession - occurs following
  disturbance

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Succession

• Climax community is the eventual stable point of
  succession. Concept is now tempered by several
  realizations
• Climate is dynamic.
• Succession is often slow.
• A regions vegetation is determined to an extent
  by human activities.

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Succession

• Succession occurs because species alter the
  habitat and available resources in ways that
  favor other species.
• key concepts
• tolerance
• facilitation
• inhibition

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The Role of Disturbance

• Disturbances interrupt and potentially alter the
  succession of plant communities.
• intermediate disturbance theory
• Communities experiencing moderate levels of
  disturbance will have greater species richness
  than communities experiencing either smaller or
  larger levels of disturbance.
• simultaneous successional stages
• dominant competitors kept at bay

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Summary

• Biological Communities
• Realized Niche
• Principle of Competitive Exclusion
• Resource Partitioning
• Predation and Prey Populations
• Mimicry
• Coevolution and Symbiosis
• Interactions Among Ecological Processes
• Succession

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