This is ultimately set by limiting factors:

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Carrying Capacity
CARRYING CAPACITY (K) - The population density
where births and deaths are equal and population
size is constant.
This is ultimately set by limiting
factors shortages of resources (food, space,
water), extreme conditions (cold temperature),
physiological disruptions (predation, disease).
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Density-dependent Population Regulation
--case were birth rate and/or death rate varies
with population density.
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Density-dependent Population Regulation
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Density-dependent Population Regulation
Intraspecific competition - competition among
members of a population. Interference
competition - direct interactions among
individuals where one individual prevents
another from gaining access to a resource.
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Interference competition Territoriality
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Interference competition Territoriality
Numbers of breeding females on island
Density-dependent reproduction in a population of
song sparrows on Mandarte Island, BC, Canada
(from Arcese Smith 1988). Squares denote data
for each year from 1975-1986. Notice how
reproduction increased in 1985 for pairs where
food was provided.
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Interference competition Display and Fighting
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Density-dependent Population Regulation
Intraspecific competition - competition among
members of a population. Interference
competition - direct interactions among
individuals where one individual prevents
another from gaining access to a
resource. Exploitation competition -
individuals consume a resource making it less
available to other individuals
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SELF THINNING - process where by some plants out
compete others leading to more and more biomass
being concentrated in fewer and fewer
individuals.
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DENSITY-INDEPENDENT POPULATON REGULATION - Rates
(per individual) of birth and/or death do not
vary with population density.
E.g., fire, flood, volcano, etc.
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DISCUSSION QUESTIONS What are possible examples
of density-independent factors regulating
ungulates in YNP? How might density-independent
and density-dependent factors interact to
influence populations of ungulates in YNP?
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CASE STUDY - GYE ELK Coughenour, M. B., F. J.
Singer. 1996. Elk Population Processes in the
Yellowstone National Park Under the Policy of
Natural Regulation. Ecological Applications 6,
no. 2 573-93.
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Wintering Ranges of Elk in the GYE
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Regression between precipitation and winter
mortality rates of elk calves. (Cougenhour and
Singer 1997).
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CONCLUSIONS POPULATION REGULATION IN REALITY 1.
K is usually a moving target, so a population
stays within a range of variation. 2. Density
independent factors may keep population size
below K, and cause variation in population
size. 3. Time lags and density dependent
controls may cause population cycles.