Unit 1: What is Biology?
Unit 2: Ecology
Unit 3: The Life of a Cell
Unit 4: Genetics
Unit 5: Change Through Time
Unit 6: Viruses, Bacteria, Protists, and Fungi
Unit 7: Plants
Unit 8: Invertebrates
Unit 9: Vertebrates
Unit 10: The Human Body
Unit 1: What is Biology?
Chapter 1: Biology: The Study of Life
Unit 2: Ecology
Chapter 2: Principles of Ecology
Chapter 3: Communities and Biomes
Chapter 4: Population Biology
Chapter 5: Biological Diversity and Conservation
Unit 3: The Life of a Cell
Chapter 6: The Chemistry of Life
Chapter 7: A View of the Cell
Chapter 8: Cellular Transport and the Cell Cycle
Chapter 9: Energy in a Cell
Unit 4: Genetics
Chapter 10: Mendel and Meiosis
Chapter 11: DNA and Genes
Chapter 12: Patterns of Heredity and Human Genetics
Chapter 13: Genetic Technology
Unit 5: Change Through Time
Chapter 14: The History of Life
Chapter 15: The Theory of Evolution
Chapter 16: Primate Evolution
Chapter 17: Organizing Life’s Diversity
Unit 6: Viruses, Bacteria, Protists, and Fungi
Chapter 18: Viruses and Bacteria
Chapter 19: Protists
Chapter 20: Fungi
Unit 7: Plants
Chapter 21:
Chapter 22:
Chapter 23:
Chapter 24:
What Is a Plant?
The Diversity of Plants
Plant Structure and Function
Reproduction in Plants
Unit 8: Invertebrates
Chapter 25: What Is an Animal?
Chapter 26: Sponges, Cnidarians, Flatworms, and
Roundworms
Chapter 27: Mollusks and Segmented Worms
Chapter 28: Arthropods
Chapter 29: Echinoderms and Invertebrate
Chordates
Unit 9: Vertebrates
Chapter 30: Fishes and Amphibians
Chapter 31: Reptiles and Birds
Chapter 32: Mammals
Chapter 33: Animal Behavior
Unit 10: The Human Body
Chapter 34: Protection, Support, and Locomotion
Chapter 35: The Digestive and Endocrine Systems
Chapter 36: The Nervous System
Chapter 37: Respiration, Circulation, and Excretion
Chapter 38: Reproduction and Development
Chapter 39: Immunity from Disease
Ecology
Principles of ecology
Communities and Biomes
Population Biology
Biological Diversity and Conservation
Chapter 4 Population Biology
4.1: Population Dynamics
4.1: Section Check
4.2: Human Population
4.2: Section Check
Chapter 4 Summary
Chapter 4 Assessment
What You’ll Learn
You will explain how populations grow.
You will identify factors that inhibit the
growth of populations.
You will summarize issues in human
population growth.
Section Objectives:
• Compare and contrast exponential and linear
population growth.
• Relate the reproductive patterns of different
populations of organisms to models of
population growth.
• Predict effects of environmental factors on
population growth.
Principles of Population Growth
• Population dynamics – This refers to the fact
that populations are constantly changing.
• A population is a group of organisms, all of
the same species, that live in a specific area.
• A healthy population will grow and die at a
steady rate unless it runs out of food or
space, or is attacked in some way by disease
or predators.
• Scientists study changes in populations in a
variety of ways.
Principles of Population Growth
• Population Growth - This is
the change in the size of a
population over time.
A. One method involves introducing
organisms into an environment that
contains abundant resources and then
watching how the organisms react.
B. Another method involves the
growth of bacteria or yeast in a
culture.
Principles of Population Growth
• Studies of populations of larger organisms,
such as an elk population in a national park,
require methods such as the use of radio
monitors.
Linear Growth
Money received
The growth of populations is unlike the growth of
pay you get from a job, which is linear growth.
Hours worked
How fast do populations grow?
Populations of organisms, do not experience
linear growth. Rather, the graph of a growing
population starts out slowly, then begins to
resemble a J-shaped curve.
How fast do populations grow?
• Growth is slow at first because the number
of reproducing individuals is small.
• Rapid growth comes later because the total
number of individuals that are able to
reproduce has increased.
Is growth unlimited?
• A J-shaped growth curve illustrates
exponential population growth.
• Exponential growth means that as a
population gets larger, it also grows at a
faster rate.
• Exponential growth results in unchecked
growth or a population explosion.
How fast do populations grow?
Population Growth of Houseflies
Population size
1 million
500,000
100
One year
What can limit growth
Limits of the Environment
• Limiting factors, such as availability of food,
disease, predators, or lack of space, will
cause population growth to slow.
• Under these pressures, the population may
stabilize in an S-shaped growth curve.
What can limit growth?
Carrying capacity
• The number of organisms of one species that
an environment can support indefinitely is its
carrying capacity.
Click image to view movie.
• When a population
overshoots the
carrying capacity,
then limiting factors
may come into
effect.
Carrying capacity
• Deaths
begin to
exceed
births and
the
population
falls below
carrying
capacity.
Carrying capacity
Reproduction Patterns
• In nature, animal and plant populations
change in size.
• Biologists study the factor that determines
population growth—an organism’s
reproductive pattern, also called its lifehistory pattern.
• A variety of population growth patterns are
possible in nature.
Rapid life-history patterns
• This pattern is found in organisms that produce
many offspring in a short period of time – flies,
mosquitos, mice, bacteria
• Rapid life-history patterns are common among
organisms from changeable or unpredictable
environments.
• Rapid life-history organisms
have a small body size, mature
rapidly, reproduce early, and
have a short life span, and a
short gestation period.
Slow life-history patterns
• This pattern is found in organisms that produce
fewer offspring over a long period of time –
elephants, hippos, whales, some plants
• Large species that live in
more stable environments
usually have slow lifehistory patterns.
Slow life-history patterns
• Slow life-history
organisms tend to be larger
in size, mature slowly,
reproduce later in life,
have a longer life span and
longer gestation period.
They maintain population
sizes at or near carrying
capacity.
Density factors and population growth
• How organisms are dispersed can be
important.
• Three patterns of dispersal are random,
clumped, and uniform.
Random
Clumped
Uniform
Density factors and population growth
• Ecologists have identified two kinds of
limiting factors that are related to dispersal:
density-dependent and density-independent
factors.
• Population density describes the number of
individuals in a given area.
Density factors and population growth
• Density-dependent factors are factors that
have an increasing effect as populations
become more dense. These include disease,
competition, predators, parasites, and food.
• Disease, for example, can spread more
quickly in a population with members that
live close together.
Density factors and population growth
• Density-independent factors can affect all
populations, regardless of their density.
• Most densityindependent factors are
abiotic factors, such as
temperature, storms,
floods, drought, and
major habitat disruption.
Organism Interactions Limit
Population Size
• Population sizes are limited not only by
abiotic factors, but also are controlled by
various interactions among organisms that
share a community.
Predation affects population size
• When a predator consumes prey on a large
enough scale, it can have a drastic effect on
the size of the prey population. Normally,
predations causes populations to fluctuate
slightly.
• Populations of predators
and their prey are known to
experience cycles or
changes in their numbers
over periods of time.
Predation affects population size
• The data in this graph reflect the number of
hare and lynx pelts sold to the Hudson’s Bay
Company in northern Canada from 1845
through 1935.
Number of organisms(in thousands)
Lynx and Hare Pelts Sold to the Hudson’s Bay Company
Lynx
Hare
Times (in years)
Predation affects population size
• In field studies, predation increases the
chance that resources will be available for
the remaining individuals in a prey
population.
• Predation keeps natural populations healthy.
WHY?
• Predators prey on the sick, injured, old,
weak – this results in a healthier population.
Competition within a population
• Competition is a density-dependent factor.
• When only a few individuals compete for
resources, no problem arises.
• When a population increases to the point at
which demand for resources exceeds the
supply, the population size decreases
because some organisms go w/o food,
shelter, etc. and thus die.
The effects of crowding and stress
• When populations of certain organisms
become crowded, individuals may exhibit
symptoms of stress.
• As populations increase in size in
environments that cannot support increased
numbers, individual animals can exhibit a
variety of stress symptoms.
The effects of crowding and stress
• These include aggression, decrease in
parental care, decreased fertility, and
decreased resistance to disease. All of these
will lead to a population decrease.
• They become limiting factors for growth and
keep populations below carrying capacity.
Question 1
Exponential growth means that as a
population gets larger, it also _____.
A. grows at a slower rate
B. grows at a faster rate
C. grows at a steady rate
D. stabilizes in an S-shaped growth curve
The answer is B. A J-shaped growth curve illustrates
exponential growth.
Population Growth of Houseflies
Population size
1 million
500,000
100
One year
Question 2
Which of the following would you expect to
observe after a population exceeds its
carrying capacity?
A. population increases exponentially
B. births exceed deaths
C. deaths exceed births
D. population growth rate is unaffected by
limiting factors
The answer is C. Limiting factors may come into
effect after a population exceeds its carrying capacity.
Deaths begin to exceed births and the population falls
below carrying capacity.
Population
Carrying
capacity
0
S curve
J curve
Time
FOOD
PREDATORS
Exponential
growth
SPACE
DISEASE
Characteristics of Population Growth
Question 3
Organism
mosquito
elephant
humans
oak tree
Offspring per Individual
Life Span
250
5
2
50
A. grows at a slower rate
B. grows at a faster rate
C. grows at a steady rate
D. stabilizes in an S-shaped growth curve
1 month
70 years
77 years
100 years
The answer is A. Rapid life-history organisms
have a small body size, mature rapidly,
reproduce early, and have a short life span.
Organism
mosquito
elephant
humans
oak tree
Offspring per Individual
250
5
2
50
Life Span
1 month
70 years
77 years
100 years
Question 4
The number of organisms of one species that
an environment can support indefinitely is its
_____.
A. life-history pattern
B. growth rate
C. demographic
D. carrying capacity
The answer is D. If
population size rises
above the carrying
capacity, more
organisms die than are
born and the population
drops back below the
carrying capacity.
Carrying capacity
Question 5
Compare the terms “density-dependent
factors” and “density-independent factors”.
Both are limiting factors for organisms.
Density-dependent factors have an increasing
effect as the population increases and include
disease, competition, parasites, and food.
Density-independent factors can affect all
populations regardless of density. Most are
abiotic factors such as temperature, rainfall, and
major habitat destruction.
Section Objectives:
• Identify how the birthrate and death rate affect
the rate at which a population changes.
• Compare the age structure of rapidly growing,
slow-growing, and no-growth countries.
• Explain the relationship between a population
and the environment.
World Population
• In the United States, a census is taken every ten
years.
• One of the most useful pieces of data is the rate
at which each country’s population is growing or
declining.
• These figures are the basis for demography,
the study of human population size, density
and distribution, movement, and its birth
and death rates.
Human population growth
• Human population growth is different because
humans have the ability to change their
environment.
• People live longer and are able to produce
offspring that live long enough to produce
offspring, hence, a population grows.
Calculating growth rate
• There are a number of factors that determine
population growth rate.
• These are births, deaths, immigration and
emigration.
• Birthrate is the number of live births per 1000
population in a given year.
Calculating growth rate
• Death rate is the number of deaths per 1000
population in a given year.
• Movement of individuals into a population is
immigration.
Calculating growth rate
• Movement out of a population is emigration.
• Birthrate – Death rate = Population Growth
Rate (PGR)
• If the birth rate of a population equals its
death rate, then the population growth rate
is zero.
Calculating growth rate
• If the PGR is above zero, more new
individuals are entering the population than
are leaving, so the population is growing.
• A PGR can also be less than zero.
Doubling time
• Another quantitative factor that demographers
look at is the doubling time of a population.
• Doubling time is the time needed for a
population to double in size.
• The time it takes for a population to double
varies depending on the current population and
growth rate.
Doubling time
• Doubling
time can be
calculated for
the world, a
country, or
even a small
region, such
as a city.
Age structure
Population Distribution Per Age Range for Several Countries
Stable growth
Rapid growth
Male
Slow growth
Reproductive years
Age
Female
Population (percent of total for each country)
Ecology and growth
• The needs of populations differ greatly
throughout the world.
• Sometimes, a population grows more
rapidly than the available resources can
handle.
Ecology and growth
• Resources that are needed for life, such as food
and water, become scarce or contaminated.
Ecology and growth
• The amount of waste produced by a population
becomes difficult to dispose of properly.
• These conditions can lead to stress on current
resources and contribute to the spread of
diseases that affect the stability of human
populations both now and to come.
Question 1
What is the study of human population size,
density and distribution, movement, and birth
and death rates called?
A. ecology
B. demography
C. phylogeny
D. biodiversity
The answer is B. When various demographic
data are monitored, societies are able to
improve environmental conditions and quality
of life.
Question 2
Year
1
2
3
Birthrate
270
250
390
A. Growing at a greater rate each year
B. Declining at a greater rate each year
C. Growing at a decreasing rate each year
D. Declining at a decreasing rate each year
Death rate
170
190
370
The answer is C. In each of these years, the
population growth rate is above zero, but is
decreasing.
Year
1
2
3
Birthrate
270
250
390
Death rate
170
190
370
Question 3
Which interval in the diagram below represents
the population reaching equilibrium near
carrying capacity?
A. 1
B. 2
C. 3
D. 4
The answer is D. The number of organisms
tends to rise above and fall below the carrying
capacity due to limiting factors.
Population Dynamics
• Populations of some organisms do not exhibit
linear growth. If there is nothing to stop or
slow growth, a population’s growth appears
as a J-shaped curve on a graph.
• Populations grow slowly at first, then more
rapidly as more and more individuals begin to
reproduce.
Population Dynamics
• Under normal
conditions, with
limiting factors,
populations show an
S-shaped curve as
they approach the
carrying capacity of
the environment
where they live.
Population Dynamics
• If a population overshoots the environment’s
carrying capacity, deaths exceed births and the
total population falls below the environment’s
carrying capacity. The number of individuals
will fluctuate above and below the carrying
capacity.
Population Dynamics
• Density-dependent factors and densityindependent factors affect population growth.
Density-dependent factors include disease,
competition for space, water, and food supply.
Density-independent factors are volcanic
eruptions and changes in climate that result in
catastrophic incidents such as floods, drought,
hurricanes, or tornadoes.
Human Population
• Demography is the study of population
characteristics such as growth rate, age
structure, and movement of individuals.
• Birthrate, death rate, immigration, emigration,
doubling time, and age structures differ
considerably among different countries. There
are uneven population growth patterns
throughout the world.
Question 1
The answer is B. The graph of exponential
growth is a J-shaped curve.
Question 2
What shape of age structure graph represents
a rapidly growing population?
A. steep triangle
B. thin rectangle
C. circle
D. square
The answer is A.
Population Distribution Per Age Range for Several Countries
Stable growth
Rapid growth
Male
Slow growth
Reproductive years
Age
Female
Population (percent of total for each country)
What type of
growth is shown
in this graph?
Population Growth of Houseflies
1 million
Population size
Question 3
500,000
100
One year
A. slowly increasing
C. exponential
B. slowly decreasing
D. equilibrium
The answer is C. Exponential growth is rapid
and is represented on a graph by a J-shaped
curve.
Population Growth of Houseflies
Population size
1 million
500,000
100
One year
Question 4
Assume that each time interval on the graph is equal to
one year. How long did it take this population to reach
carrying capacity?
B. 4 years
D. 9 years
Population
C. 5 years
Carrying
capacity
0
J curve
S curve
Time
FOOD
DISEASE
Exponential
growth
PREDATORS
A. 2 years
SPACE
Characteristics of Population Growth
The answer is D. After 9 years, this population
has nearly reached carrying capacity.
Population
Carrying
capacity
0
S curve
J curve
Time
FOOD
PREDATORS
DISEASE
Exponential
growth
SPACE
Characteristics of Population Growth
Question 5
Which of the following is characteristic of a
species having a slow life-history pattern?
A. short life span
B. long life span
C. small body size
D. mature rapidly
The answer is B. Rapid life-history organisms
have a small body size, short life span, and
mature rapidly.
Question 6
During which time period was population
growth the most rapid?
A. 1800 to 1930
B. 1930 to 1960
Question 6
During which time period was population
growth the most rapid?
C. 1960 to 1975
D. 1975 to 1987
The answer is D. World population grew by
1 billion in just 12 years.
Question 7
If the birthrate is 125 and the death rate is
135, what is the population growth rate?
A. 260
B. -260
C. 10
D. -10
The answer is D. Use the formula:
Birthrate – Death rate = Population Growth Rate
Photo Credits
• Corbis
• Carolina Biological Supply Co.
• Digital Stock
• Matt Meadows
• PhotoDisc
• Alton Biggs
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