Ch. 6: Community Ecology

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Ch. 6 Community Ecology

• Community Structure
• Roles of Species
• Interactions
• Population Growth

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Community Structure

• Diversity of species increases the sustainability
  of a community
• Species diversity the number of different
  species and their relative abundance
• Sustainability ability to survive and adapt to
  changing conditions

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Species Roles in a Community

• Native / Non-native
• Indicator
• Keystone

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Native vs. Non-native

• NON-NATIVE
• Introduced from outside
• Disruptive?
• E.g., killer bees, sea lamprey, coho salmon,
  Asian lady beetles, velvetleaf, nightshade

• NATIVE
• Normally live, thrive in an ecosystem
• Have evolved, adapted, co-evolved
• E.g., native grasses, White Oak, White-tailed deer

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Indicator Species

• Early warning of damage (biol. smoke alarms)
• Sensitive
• E.g., birds, trout, frogs

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Keystone Species / Foundation Species

• A species that has a much bigger effect than its
  numbers would suggest
• Pollinators
• Predators
• Engineers
• Recyclers

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Keystone Species / Foundation Species

• Pollinators
• Predators
• Engineers
• Recyclers

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Species Interactions

• Competition ? Predation ?
  Cooperation

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Various Interactions

• Prey / predator
• Parasitism
• Mutualism
• Commensalism
• Competition

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Competition

• Not only for sun
• Mostly below ground
• For
• Water
• Nutrients
• Space

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• Resource Partitioning a means of reducing
  competition a means of increasing the number of
  species that can share a resource
• Dividing up scarce resources so that species with
  similar needs can use them in different ways, at
  different times.

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Predator Prey Interaction
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Parasitism

• A specialized kind of predation
• Parasite (predator) smaller than host (prey)
• Prey may not be killed
• Many parasites to one host

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Mutualism

• Mutually beneficial
• Often involves nutrition
• Plant / pollinator
• Nitrogen fixation

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Commensalism

• One species benefits, other neutral
• E.g., barnacles on hermit crab
• Epiphytes

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Change in Population Size

• Population Change (births immigration)
  - (deaths emigration)

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Population Dynamics

• Biotic potential intrinsic capacity for growth
• r intrinsic rate of growth

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Logistic growth

• Exponential growth,
• Then levels off