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Characteristics of Populations
Three important characteristics of a population are
its:
a. geographic distribution
b.population density
c. growth rate
http://www.youtube.com/watch?v=RBOsqmBQBQk
Population Growth
Three factors can affect population size:
a. the number of births
b.the number of deaths
c. the number of individuals that enter or leave the
population
A population can grow when its birthrate is greater
than its death rate.
Immigration, the movement of individuals into an
area
Emigration, the movement of individuals out of an
area
Under perfect conditions with unlimited resources, a
population will grow exponentially.
Exponential Growth
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As resources become less available (no more space,
food, water, etc.), the growth of a population slows
or stops.
Called carrying capacity
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Are humans experiencing exponential or
logistic growth?
Do you think humans are close to the Earth’s
carrying capacity? Why?
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In the context of populations, a limiting factor
is a factor that causes population growth to
decrease.
Can be:
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Density-dependent
Density-independent
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Density-Dependent Factors
a. A limiting factor that depends on population size is
called a density-dependent limiting factor.
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Density-dependent limiting factors include:
a. competition
b.predation
c. parasitism
d.Disease
e. Most impact with larger populations
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Competition
a. When populations become crowded, organisms
compete for food, water space, sunlight and other
essentials.
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Competition can also occur:
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between members of same species (intraspecific)
between members of different species (interspecific)
Intraspecific
Interspecific
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Predation
a. Populations in nature are often controlled by predation.
Or Predator – Prey Relationship
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Wolf and Moose Populations on Isle Royale
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Parasitism and Disease
a. Parasites can limit the growth of a population.
b. http://www.ted.com/talks/ed_yong_suicidal_wasps_
zombie_roaches_and_other_tales_of_parasites
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Density-Independent Factors
a. Density-independent limiting factors affect all
populations in similar ways, regardless of the population
size.
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unusual weather
natural disasters
seasonal cycles
certain human
activities—such
as damming rivers
and clear-cutting
forests