Transcript Understanding Our Environment

Ecological Communities: Change & Balance
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Ecological Niche
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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
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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
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Intraspecific - Competition among members
of the same species.
 influences which individuals are successful
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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)
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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
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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
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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
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“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
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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
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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
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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?
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Numbers of components involved
Indirect effects (“domino effects”)
Complex feedback systems
Gradients in
 distributions of species
 degrees of influence
 change through time
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