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5-1 How Populations Grow
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5-1 How Populations Grow
Characteristics of Populations
What characteristics are used to describe a
population?
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5-1 How Populations Grow
Characteristics of Populations
Characteristics of Populations
Three important characteristics of a
population are its:
• geographic distribution
• population density
• growth rate
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5-1 How Populations Grow
Population Growth
What factors affect population size?
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5-1 How Populations Grow
Population Growth
Population Growth
Three factors can affect population size:
• the number of births
• the number of deaths
• the number of individuals that enter or leave
the population
A population can grow when its birthrate is greater
than its death rate.
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5-1 How Populations Grow
Population Growth
Immigration, the movement of individuals into
an area, is another factor that can cause a
population to grow.
Emigration, the movement of individuals out
of an area, can cause a population to decrease
in size.
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5-1 How Populations Grow
Exponential Growth
What are exponential growth and logistic
growth?
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5-1 How Populations Grow
Exponential Growth
Exponential Growth
Under ideal conditions with unlimited resources,
a population will grow exponentially.
Exponential growth occurs when the individuals in
a population reproduce at a constant rate.
The population becomes larger and larger until it
approaches an infinitely large size.
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5-1 How Populations Grow
Exponential Growth
Exponential Growth
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5-1 How Populations Grow
Logistic Growth
Logistic Growth
As resources become less available, the growth
of a population slows or stops.
Logistic growth occurs when a population's growth
slows or stops following a period of exponential
growth.
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5-1 How Populations Grow
Logistic Growth
Logistic growth is characterized by an Sshaped curve.
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5-1 How Populations Grow
Limiting Factors
What factors limit population growth?
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5-1 How Populations Grow
Density-Dependent Factors
Wolf and Moose Populations on Isle Royale
Moose
Wolves
Density-Dependent Activity
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5-1
Population density is the number of individuals
a. that are born each year.
b. per unit area.
c. that immigrate.
d. that emigrate.
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5-1
When the birthrate of a population exceeds its
death rate, the population
a. decreases.
b. increases.
c. stays the same.
d. increases then decreases.
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5-1
An S-shaped curve on a graph of population
growth is characteristic of
a. exponential growth.
b. logistic growth.
c. carrying capacity.
d. delayed growth.
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5-1
Exponential growth in a population slows down
or stops as
a. resources become limited.
b. rate of immigration increases.
c. rate of emigration decreases.
d. birth rate increases.
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5-1
Exponential growth rate means that each new
generation of a population
a. adds the same number of new individuals as
the previous generation did.
b. increases at the same rate as the previous
generation.
c. is the same size as the generation before.
d. increases by a varying amount.
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5-2 Limits to Growth
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Limiting Factors
What factors limit
population 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.
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Density-Dependent Factors
•Density-Dependent Factors
A limiting factor that depends on
population size is called a densitydependent limiting factor.
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Density-Dependent Factors
Density-dependent limiting
factors include:
•
competition
•
predation
•
parasitism
•
disease
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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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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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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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Density-Dependent Factors
Wolf and Moose Populations on Isle Royale
Moose
Wolves
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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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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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Density-Independent Factors
Examples of densityindependent limiting factors
include:
•
•
•
•
unusual weather
natural disasters
seasonal cycles
certain human activities—such as
damming rivers and clear-cutting
forests
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1. 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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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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