Ecological Communities: Change

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Ecological Communities Change Balance
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Ecological Niche

• Ecological Niche - Description of the role a
  species plays in a biological community, or the
  total set of environmental factors that
  determines species distribution.
• Generalists - Broad niche
• Specialists - Narrow niche

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Ecological Niche

• Fundamental Niche - Full range of resources or
  habitat a species could exploit if there were no
  competition with other species.
• Realized Niche - Resources or habitat a species
  actually uses.

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Competition

• Intraspecific - Competition among members of the
  same species.
• influences which individuals are successful
• Interspecific - Competition between members of
  different species.
• influences which species are successful

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Resource Partitioning
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Resource Partitioning (Realized Niche)

• Law of Competitive Exclusion - No two species
  will occupy the same niche and compete for
  exactly the same resources for an extended period
  of time.
• One will either become locally extinct, or
  partition the resource and utilize a sub-set of
  the same resource.
• Interactions among species are added to
  regulation by each species response to the
  physical environment

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Other limits to success eating your neighbor

• A predator or parasite or herbivore is an
  organism that feeds directly upon another living
  organism
• Reduces competition, population overgrowth, and
  stimulates natural selection.

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Keystone Species

• Keystone Species - A species or group of species
  whose impact on its community or ecosystem is
  much larger and more influential than would be
  expected from mere abundance (or biomass).
• Wolves, browsers, and vegetation
• Starfish, intertidal animals, algae
• Beavers, aquatic communities

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Ecosystems are dynamic, changing

• Habitats are defined by the dominant organisms,
  the populations of which can rise or fall
• Changes can be driven by altering the physical
  environment (promoting species with niches
  appropriate for the change)
• Changes can be driven biologically by altered
  interactions among species

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Habitats are dynamic in space time

• Edge Effects Areas between different habitats
  can be important to species success
• Ecotones can be refuges or areas of high
  productivity

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The composition of communities varies from place
to place

• Each species has its own fundamental niche,
  rarely perfectly correlated with any other
  species
• e.g., beech-maple forests in Ohio and
  Pennsylvania will have different sets of species
  overall
• Given this uniqueness would we have to conserve
  every beech-maple forest?

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Communities change through time

• Ecological Succession
• Primary Succession - A community begins to
  develop on a site previously unoccupied by living
  organisms.
• Pioneer Species
• Secondary Succession - An existing community is
  disrupted and a new one subsequently develops at
  the site.

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Primary Succession
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Ecological Succession

• Ecological Development - Process of environmental
  modification (facilitation) by organisms.
• Climax Community - Community that develops and
  seemingly resists further change (reached in 400
  yrs for some forests).
• BUT, over long periods of time, climates change
  (e.g., glaciers in Ohio 15,000 years bp)

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How do we deal with complexity?

• Numbers of components involved
• Indirect effects (domino effects)
• Complex feedback systems
• Gradients in
• distributions of species
• degrees of influence
• change through time