Community Ecology

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Chapter 53 Community Ecology
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Community Ecology

• The study of the interactions between the species
  in an area.

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Community Hypothesis

• 1. Individualistic
• 2. Interactive

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Individualistic Hypothesis

• H.A. Gleason
• Community as a chance assemblage of species
  because of similar abiotic requirements.

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Interactive Hypothesis

• F.E. Clements
• Community as a linked assemblage of species that
  function as an integrated whole.

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Predictions

• Individualistic - fuzzy borders
• Interactive - sharp borders
• Robert Whittaker tested the two ideas against
  each other.

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Results

• If abiotic factors form a continuum, then borders
  are fuzzy.
• Individualistic Hypothesis is correct.

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Comment

• Abiotic factors may form sharp borders.
• Ex soil types
• Result the Community may look very much like
  the Interactive Hypothesis.

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Interspecific Interactions

• Interaction between species.
• May be positive, negative, or neutral.
• Ex
• 1. Coevolution
• 2. Predation
• 3. Mimicry
• 4. Competition
• 5. Symbiosis

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Coevolution

• When two species have reciprocal evolution to
  each other.
• Ex
• Flowers and their pollinators.

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Predation (/-)

• Predator and prey relationships.
• Ex Lynx and Hares

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Predation

• Often results in interesting defenses or
  adaptations.
• Ex
• Plant defenses
• Cryptic coloration
• Aposematic coloration

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Cryptic Coloration

• A passive defense where the prey is camouflaged
  against its environment.

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Aposematic Coloration

• The use of conspicuous colors in toxic or
  unpalatable organisms to warn off predators.

• poison arrow frogs

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Mimicry

• Defense mechanism where the mimic has a
  resemblance to another species, the model.
• Types
• Batesian
• Mullerian

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Batesian Mimicry

• Palatable species mimics an unpalatable model.

Hawk moth larva
Snake
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Mullerian Mimicry

• Two unpalatable species resemble each other.

Yellow Jacket
Cuckoo Bee
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Competition

• When two species rely on the same limiting
  resource.
• Intraspecific competition usually more severe
  than Interspecific competition.
• Why?

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Competitive Exclusion Principle

• Predicts that two species with the same
  requirement can not co-exist in the same
  community.
• One species will survive and the second will go
  extinct.

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Ecological Niche

• The n-hyperspace of requirements for a species.
• How a species fits into an ecosystem.
• Species can not have niche overlap, the
  Competitive Exclusion
  Principle

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Niche Types

• 1. Fundamental - what a species is theoretically
  capable of using.
• 2. Realized - what a species can actually use.

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Resource Partitioning

• A way that species avoid niche overlap by
  splitting up the available resources.
• Ex Anolis lizards

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• A. distichus

• A. insolitus

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Symbiosis

• When two different species live together in
  direct contact.
• Types
• 1. Parasitism
• 2. Commensalism
• 3. Mutualism

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Parasitism (/-)

• Parasite harms the host.
• Parasites may be external or internal.
• Well adapted parasites don't kill the host.

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Parasitic behavior A female
Nasonia vitripennis laying a clutch of eggs into
the pupa of a blowfly (Phormia regina)
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Commensalism (/o)

• One partner benefits while the other is
  unchanged.
• Ex. Cattle and Egrets

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Mutualism (/)

• Both partners benefit from the interaction.
• Ex Pollinators and flowers

Acacia Tree and Ants
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Succession

• Changes in species composition over time.

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Succession Stages

• Sere unstable stage usually replaced by another
  community.
• Climax stable stage, self-reproducing.

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Succession Types

• 1. Primary
• 2. Secondary

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Primary Succession

• Building a community from a lifeless area.
• Ex volcanic islands glaciated areas
  road cuts

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Comment

• The first example of primary succession was
  worked out on the Indiana Dunes.
• Stages
• Open Beach
• Beach Grasses
• Conifers (Junipers and Pines)
• Oaks
• Beech-Maple forest (Climax)

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Secondary Succession

• Where a community has been disturbed and the soil
  is mostly intact.
• Ex
• Cutting down a forest
• Blow-outs on the Dunes

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Causes of Succession

• 1. Autogenic Factors
• 2. Allogenic Factors

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Autogenic Factors

• Changes introduced by the organisms themselves.
• Ex toxins acids

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Allogenic Factors

• Outside disturbances
• Ex Fire Floods

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Prairie Succession in Oklahoma - Stages

• 1. Annual Weeds
• 2. Triple-Awn Grass
• 3. Bunch Grass
• 4. Climax Tall-grass Prairie

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Annual Weed Stage

• Lasts 2-3 years.
• Very robust growth (1-2 m).
• Species Sunflower Pigweed
  Lamb's Quarter

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Annual Weed Stage
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Annual Weed Stage
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Annual Weed Stage
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Annual Weed Stage
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Triple-Awn Stage

• Lasts 10 - 50 years.
• Very poor growth (5-12 cm).
• Species Triple-Awn Grass

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Triple Awn Stage
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Question

• How can Triple-Awn replace the more robust annual
  weeds?

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Allelopathy

• The release of chemical inhibitors into the
  environment.
• Sunflower autotoxic
• Triple Awn tolerant

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Triple-Awn

• Inhibits Nitrogen fixing bacteria species
• Result soil N stays low which stalls succession.

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Bunch Grass Stage

• Lasts 20 - 100 years.
• Good growth (30-50 cm).
• Species Little Bluestem

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Bunch Grass Stage
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Succession Causes

• Bunchgrass eventually shades out Triple-Awn,
  releasing the inhibition of the nitrogen fixers.
• Result soil fertility increases, allowing the
  next group of species to invade.

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Climax Prairie Stage

• Lasts centuries if maintained by fire.
• High growth (up to 2 meters).
• Species Big Bluestem, Indiana Grass, Switch
  Grass, Little Bluestem

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Tall Grass Prairie
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Tall Grass Prairie
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Question

• Stages 3 and 4 are the best for cattle grazing.
• Normal succession takes 20 - 50 years.
• Can the time needed for restoring the prairie be
  decreased?

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Solution

• Add more N to soil (NH4)
• Seed climax species
• Result prairie in 3-10 years.
• Maintain the prairie by burning.

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Upland, IN Prairie
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Upland, IN Prairie
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Upland, IN Prairie
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Point

• If you understand the causes and controlling
  factors of succession, you can manipulate them.

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Productivity Lab Report

• Graph and data are on BlackBoard.
• Graph - Analysis of results 7 questions
• DO Readings Analysis of results - 2 questions

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Biogeography

• Study of the past and present distributions of
  individual species and communities.

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Range Limitations

• 1. Lack of dispersion.
• 2. Failure to survive in new areas.
• 3. Retraction from former range area.

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Proof

• Fossil Evidence
• Pollen Studies
• Transplant Experiments

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Islands

• Special cases in Biogeography.
• Must be colonized from other areas.

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Island Species Factors

• Island size.
• Distance from mainland.

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Island Size

• Small islands hold few species.
• Why?
• Fewer niches available for species to occupy.

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Distance from Mainland

• Closer islands have more species.
• Why?
• Easier for colonization.

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Comment

• Islands tend to have high numbers of Endemic
  species
• Why?
• Adaptive Radiation and Evolution of new species.

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Summary

• Know the two hypothesis of community structure.
• Know the various types of interspecific
  interactions.
• Know the Competitive Exclusion Principle and
  Niche Concept.

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Summary

• Know some examples and causes of succession.
• Know how island communities are shaped.