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Competition
Exploring the niche
concept
ESRM 450
Wildlife Ecology and
Conservation
The Niche
•  A niche represents the range of conditions
and resources within which a species can
persist
–  Conditions: e.g., temperature
–  Resources: e.g., nesting sites
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The Niche
•  “sum of all the environmental factors
acting on the organism…
G. Evelyn Hutchinson (1944)
The Niche
•  “sum of all the environmental factors
acting on the organism…defined [as] a
region of n-dimensional hyperspace”
–  Each factor acting on the organism is one
dimension
G. Evelyn Hutchinson (1944)
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N-dimensional Hyperspace
Moisture
Outside the hyperspace –
not part of a species’ niche
Temperature
Two-dimensional niche as defined by
moisture and temperature
Moisture
N-dimensional Hyperspace
Temperature
Three-dimensional niche as defined by moisture,
temperature, and sunlight
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N-dimensional Hyperspace
- add factors, niche becomes n-dimensional
Habitat and the Niche
•  For an area to be habitat for a species…
–  it must provide the required n-dimensional
hyperspace
–  i.e., proper range of resources, conditions in
every dimension
–  or more simply, sufficient niche space
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Competition
Any use or defense of a resource that reduces the
availability of that resource to other individuals
Competition
Any use or defense of a resource that reduces the
availability of that resource to other individuals
Active demand by two or more species
for a common vital resource*
*or more broadly for niche space
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Moisture
Competition and the Niche
Temperature
Fundamental niche: the full extent of the n-dimensional
hyperspace in the absence of competition
- The full range of environmental conditions and resources an organism
can possibly occupy and use
Moisture
Competition and the Niche
Temperature
Fundamental niche: the full extent of the n-dimensional
hyperspace in the absence of competition
- The full range of environmental conditions and resources an organism
can possibly occupy and use
Realized niche: the part of the n-dimensional hyperspace to which
a species is restricted due to competition
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Niche Overlap and
Competitive Exclusion
•  Niche overlap determines how
strongly two species might
compete with each other
–  two species that are too similar in
their ecological requirements
cannot coexist for long or
–  In other words, no two species can
have the same niche; the lesser
competitor will be excluded from
an area or go extinct (Gause’s
exclusion principle)
Niche Differentiation
•  Strong competition (niche overlap) in ecological
communities often leads to niche differentiation
•  One mechanism – resource partitioning, or
subdivision of available resources through
specialization
•  e.g., stingless bees
Sp 2 forages in low density
patches alone
Sp 1. forages in groups
in high density patches
Johnson and Hubbell (1975) Ecology 56: 1398-1406
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Niche Differentiation
•  e.g., shorebird foraging diversity
•  or, the “ghost of competition past”
Niche Differentiation
•  African Ungulates
–  Feed on different
parts, or species, of
plants
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Niche Differentiation
•  Character displacement – two species living apart
have similar traits (e.g. morphology or feeding habits)
but differ when living together
Character Displacement in
Darwin’s Finches
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Niches and Community
Organization
•  Prevailing view - every community offers a total
niche space within which the niches of all species
must fit
–  adding or removing species may result in compression or
expansion of the realized niches of other species
•  Change in competitive interactions (e.g., competitive release)
•
Removal of wolves in western
United States released
coyotes
–  Increased population size
–  and niche breadth (closer
to fundamental)
Arjo et al. (2002) J Mammal 83: 754-766
Niches and Community
Organization
•  Communities with different numbers of species
may differ with respect to
–  Total community niche space
–  Degree of niche overlap among species
–  Niche breadth of individual species
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Adding More Species to the
Community
Species can be added given…
–  (b) an increase in total niche
space (with no change in
breadth or overlap)
•  can include adding more axes!
Adding More Species to the
Community
Species can be added given…
–  (b) an increase in total niche
space (with no change in
breadth or overlap)
•  can include adding more axes!
–  (c) an increase in niche overlap
(with no change in breadth or
total space)
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Adding More Species to the
Community
Species can be added given…
–  (b) an increase in total niche
space (with no change in
breadth or overlap)
•  can include adding more axes!
–  (c) an increase in niche overlap
(with no change in breadth or
total space)
–  (d) a decrease in niche breadth
(with no change in total space
or overlap)
Niches and Community
Organization - Upshot
•  Community differences explained by
–  Differences in available niche space, and
–  Differences in niche characteristics of constituents
•  Within communities, niche differences maintain
diversity (i.e., are stabilizing)
–  Niche limitations restrict competitive exclusion
(domination), offer opportunities for stable coexistence
–  i.e., each species can only become so abundant
•  can only dominate its own niche space
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Five Minute Paper
Questions & Insights
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