5-2 limits to growth - mr. taubitz's science...

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5-2 Limits to Growth


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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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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.

Density-Dependent Factors

A limiting factor that depends on population

size is called a density-dependent limiting

factor.


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Density-dependent limiting factors include:

• competition

• predation

• parasitism

• disease


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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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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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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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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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Wolf and Moose Populations on Isle Royale

Moose Wolves

Resources/ActiveArt/pred_prey.html

Resources/ActiveArt/pred_prey.html


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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.

Density-Independent Factors

Density-independent limiting factors affect all

populations in similar ways, regardless of the

population size.


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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

- or -

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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

5-2 limits to growth - mr. taubitz's science...

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