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5-2 Limits to Growth
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5-2 Limits to Growth
Limiting Factors
What factors limit population growth?
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5-2 Limits to Growth
Limiting Factors
Limiting Factors
The primary productivity of an ecosystem can be
reduced when there is an insufficient supply of a
particular nutrient.
Ecologists call such substances limiting nutrients.
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5-2 Limits to Growth
Limiting Factors
A limiting nutrient is an example of a more general
ecological concept: a limiting factor.
In the context of populations, a limiting factor is a
factor that causes population growth to decrease.
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5-2 Limits to Growth
Density-Dependent Factors
Density-Dependent Factors
A limiting factor that depends on population size is
called a density-dependent limiting factor.
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5-2 Limits to Growth
Density-Dependent Factors
Density-dependent limiting factors
include:
• competition
• predation
• parasitism
• disease
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5-2 Limits to Growth
Density-Dependent Factors
Density-dependent factors operate only when the
population density reaches a certain level. These
factors operate most strongly when a population is
large and dense.
They do not affect small, scattered populations as
greatly.
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5-2 Limits to Growth
Density-Dependent Factors
Competition
When populations become crowded, organisms
compete for food, water space, sunlight and other
essentials.
Competition among members of the same species
is a density-dependent limiting factor.
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5-2 Limits to Growth
Density-Dependent Factors
Competition can also occur between members of
different species.
This type of competition can lead to evolutionary
change.
Over time, the species may evolve to occupy different
niches.
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5-2 Limits to Growth
Density-Dependent Factors
Predation
Populations in nature are often controlled by
predation.
The regulation of a population by predation takes
place within a predator-prey relationship, one of
the best-known mechanisms of population control.
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5-2 Limits to Growth
Density-Dependent Factors
Wolf and Moose Populations on Isle Royale
Moose
Wolves
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5-2 Limits to Growth
Density-Dependent Factors
Parasitism and Disease
Parasites can limit the growth of a population.
A parasite lives in or on another organism (the
host) and consequently harms it.
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5-2 Limits to Growth
Density-Independent Factors
Density-Independent Factors
Density-independent limiting factors affect all
populations in similar ways, regardless of the
population size.
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5-2 Limits to Growth
Density-Independent Factors
Examples of density-independent limiting
factors include:
• unusual weather
• natural disasters
• seasonal cycles
• certain human activities—such as
damming rivers and clear-cutting
forests
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5-2
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5-2
A limiting factor that affects all populations in
similar ways regardless of their size might be
a. drought.
b. disease.
c. predation.
d. crowding.
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5-2
Which of the following would be a limiting factor
affecting the panda population of China?
a. programs that educate people about
endangered species
b. capture of some pandas for placement in
zoos
c. laws protecting habitat destruction
d. a disease that kills bamboo plants
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5-2
Density-dependent factors operate most strongly
when a population is
a. large and dense.
b. large but sparse.
c. small and sparse.
d. small, but growing.
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5-2
Within a limited area, if the population of a
predator increases, the population of its prey is
likely to
a. increase.
b. decrease.
c. remain about the same.
d. become extinct.
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5-2
Which of the following is a density-independent
factor affecting populations?
a. predation
b. disease
c. a destructive hurricane
d. parasites
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