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Chapter 4: Populations
Georgia Performance Standards:
•Investigate the relationships among organisms,
populations, communities, ecosystems, and biomes.
EQ: How would changes in populations affect the
flow of energy and matter in the ecosystem?
EQ: How are populations regulated over time?
EQ: How does the growing human population threaten
the biosphere?
Warm-up:
 A laboratory jar containing a population of
beetle larvae (mealworms) has reached a
stable population size. We decide to add
twice as much food per day to the jar, but
this turns out to have no effect on
population size.
 What is the most likely explanation?
Populations
 Defined by different
geographical
boundaries
 Important
characteristics:
 Density
 Geographical
Distribution
 Growth Rate
 Age Structure
What is POPULATION DENSITY?
 The number of individuals
of a species per unit area
or volume.
 Three factors can affect
population size
 # of births
 # of deaths
 # of individuals that enter
or leave the population
 Immigration (im-uhgray-shun), the
movement of individuals
into an area, can cause
a population to grow.
 Emigration (em-uhgray-shun), the
movement of individuals
out of a population, can
cause a population to
decrease in size.
How do populations grow?
 Exponential Growth
 Under ideal conditions
with unlimited resources,
a population will grow
exponentially
 The whole population
multiplies by a constant
factor during constant
time intervals
 Organisms do not
usually grow
exponentially for very
long.
Exponential
Growth
 Both of these
hypothetical graphs
show the characteristic
J-shape of exponential
population growth.
Logistic Growth
 As resources
become less
available, the
growth of a
population slows or
stops= Logistic
growth
 Can follow a period of
exponential growth
•S-shaped curve of
this growth pattern
•birthrate=deathrate
immigration
=emigration
Logistic Growth of Yeast
Population
Carrying Capacity
Number of yeast cells
Time (hours)
Carrying Capacity
 The number of individuals in a population
that the environment can just maintain
with no net increase or decrease
Concept Map
Population
Growth
can be
Logistic
growth
Exponential
growth
characterized by
No limits on
growth
Unlimited
resources
represented by
Constant
growth rate
J-shaped
curve
characterized by
Limits on
growth
which cause a
Falling
growth rate
represented by
S-shaped
curve
5–1 Summary:
How Populations Grow



Three important characteristics of a
population are:
 geographic distribution
 density
 growth rate.
Three factors affect population size:
# of births
# deaths,
# of individuals that enter or
leave the population.
Under ideal conditions and unlimited
resources, a population will continue
to grow in a pattern called
exponential growth. As resources
are used up and population growth
slows or stops, the population
exhibits logistic growth.
 Vocabulary
 population density
 immigration
 emigration
 exponential growth
 logistic growth
 carrying capacity
Checkpoint!!!
 Which of the following is NOT a
condition for a population to reach
exponential growth?
 presence of unlimited resources
 absence of predation and disease
 movement of individuals out of a population
EQ:
How are populations
regulated over time?
Population Limiting Factors
 Environmental factors that restrict population
growth.
 Some limiting factors depend on the size of the
population.
 Other limiting factors affect all populations in
similar ways, regardless of the population size.
Warm-up: Population Limiting
Factors
1. Imagine a small island that has a population of five
rabbits. How might each of the following factors affect
the rabbit population?
a. climate
b. food supply
c. predation
2. Now imagine another small island that has a population
of 500 rabbits. How would the same factors affect this
population?
3. Which of the factors depend on population size? Which
factors do not depend on population size?
Density-dependent
Factors
 Factors that depend on
the population density
 Factors affect a greater
percentage of individuals
in a population as the
number of individuals
increases.
 Death rate increases
and the birth rate
decreases
 Limited food supply




Competition
Predation
Parasitism
Disease
 Buildup of poisonous
wastes
Density-independent
Factors
 Limiting factors whose
occurrence is not affected
by population density
 Abiotic factors; climate and
weather or natural disasters
and human activity
 Affect the same percentage of
individuals regardless of the
population size.
 Abiotic factors
 climate and weather
 natural disasters
 human activity
 Damming rivers
 Clear-cutting forests
5–2 Summary: Limits to Growth
 Density-dependent
limiting factors include
competition, predation,
parasitism, and disease.
 Unusual weather, natural
disasters, seasonal
cycles, and certain
human activities—such
as damming rivers and
clear-cutting forests—
are all examples of
density-independent
limiting factors.
 Vocabulary
 limiting factor
 density-dependent
limiting factor
 predator-prey
relationship
 density-independent
limiting factor
The Human Population
 EQ: How does the growing human
population threaten the biosphere?
The size of the human population
tends to increase with time
Demography
 The scientific study
of human
populations
 Birth rates
 Death rates
 Age structure of
population
 All help to predict
why some
countries have high
growth rates while
other countries
grow more slowly.
Demographic Transition
 A dramatic change in
birth and death rates
 The demographic
transition is complete
when the birthrate falls
to meet the death rate,
and population growth
stops.
 Birthrates and death rates fall during the demographic
transition. Initially, both rates are high (A). Then, the death
rate drops while the birthrate remains high (B). Finally, the
birth rate also decreases (C).
Age-structure diagrams
 A population profile that can predict
future growth.
 Shows the number of people in different
age groups in the population
Section 6-1
Human
Activities
that have changed the biosphere include
Hunting and
gathering
may have once caused
Industrial
growth
Agriculture
often relies on the methods of the
Extinctions of
large animals
Green
revolution
Food supply
Go to
Section:
Pesticide use
have resulted in
High standard
of living
which increased
Monoculture
use
Urban
development
Increased
pollution
Threats to Biodiversity
 Human activity can
reduce biodiversity by
altering habitats (Habitat
fragmentation), hunting
species to extinction,
introducing toxic
compounds into food
webs, and introducing
foreign species (Invasive
species) to new
environments.
 Extinction occurs when a
species disappears from all or
part of its range.
 A species whose population
size is declining in a way that
places it in danger of
extinction is called an
endangered species.
 As the population of an
endangered species declines,
the species loses genetic
diversity
5–3 Summary: Human Population
Growth
 Like the populations of
many other living
organisms, the size of the
human population tends to
increase with time.
 The characteristics of
populations, and the social
and economic factors that
affect them, explain why
some countries have high
population growth rates
while populations of other
countries grow slowly or
not at all.
 Vocabulary
 demography
 demographic
transition
 age-structure diagram