Population Ecology
G. Tyler Miller’s
Living in the Environment
14th Edition
Chapter 9
Applying Population Ecology:
The Human Population
G. Tyler Miller’s
Living in the Environment
14th Edition
Chapter 10
Chapter 9 Key Concepts – Population Ecology
 Factors affecting population size
 Species reproductive patterns
 Species survivorship patterns
 Conservation biology and human impacts on
ecosystems
Population Dynamics and Carrying Capacity
 Population dynamics
 Biotic potential (intrinsic rate of increase [rmax])
 Environmental resistance
 Carrying capacity
 Exponential and Logistic Growth
 Population Density
The Study of Population Dynamics
Populations change in size, density, dispersion and age structure.
Population density —the number of individuals of a population that
inhabit a certain unit of land or water area.
Population dispersion —refers to how individuals of a population are
spaced within a region.
Age structure of a population is usually described as the
pre-reproductive stage, the reproductive stage and the postreproductive stage. A population with a large reproductive stage is
likely to increase, while a population with a large post-reproductive
stage is likely to decrease.
Population Size
Four variables influence/govern
population size: (1) births, (2)
deaths, (3) immigration, and (4)
emigration.
Increase in population occurs by birth
and immigration.
Decrease in population occurs by death
and emigration.
Rapidly growing populations have four
characteristics:
1. Individuals in the population reproduce early in
life.
2. Individuals have short periods between
generations.
3. Individuals have long reproductive lives.
4. Individuals produce multiple offspring each time
they reproduce.
Biotic Potential vs.
Environmental Resistance
The biotic potential max (rmax) is the population's
capacity for growth. The intrinsic rate of increase
(r) is the rate of population growth with unlimited
resources.
environmental resistance
consists of factors that limit population growth.
limiting Factors
No population can grow
indefinitely due to
limited resources such
as light, water, and
nutrients and also due
to competitors and/or
predators.
Limiting Factors Examples:
Extrinsic
Biotic – Density Dependent
Abiotic – Density Independent
Intrinsic
Social Hierarchy
Gender changing
Density-independent population
controls affect a population's size
regardless of its density. These are
abiotic factors in the community.
Density-dependent factors or
population controls have a greater
affect on the population as its
density increases. Infectious
disease is an example of densitydependent population control.
Biotic Potential v. Environmental Resistance
(Logistic Population Growth)
Environmental
resistance
Population size (N)
Carrying capacity (K)
Carrying capacity (K)
is determined by biotic
potential and environmental
resistance.
(K) is is the number of a
species individuals that can
be sustained indefinitely in a
specific space.
Biotic
potential
Figure 9-4
Page 166
Exponential
growth
Time (t)
As a population reaches its
carrying capacity, its
growth rate will decrease
because resources
become more scarce.
Natural Population
Curves
Population sizes may stay
about the same, suddenly
increase and then decrease,
vary in regular cycles, or
change erratically.
Four general types of
population fluctuations in
nature are (1) stable, (2)
irruptive, (3) cyclic, and (4)
irregular.
A stable population fluctuates
slightly above and below
carrying capacity and is
characteristic of many
species Living under fairly
constant environmental
conditions.
Fig. 9-7 p. 168
Some species have a fairly stable population size
That may occasionally irrupt to a high peak and then
crash to below carrying capacity. This is
characteristic of short-lived, rapidly reproducing
species.
Cyclic fluctuations occur over a regular time period,
generally a multiple year cycle.
Irregular behavior is poorly understood. Some
scientists attribute irregular behavior to chaos in the
system; others disagree.
Exponential and Logistic Growth
The Role of Predation in Controlling Population Size
Interactions between
predators and their prey
change in cycles and appear
to be caused by species
interactions, but other factors
may be involved.
The hypothesis of top-down
control of prey by predators
may not be the only
explanation for the boomand-bust cycles seen in these
populations. This may also be
related to the food supply of
prey.
The bottom-up control
hypothesis states that plants
are consumed too rapidly by
prey for replacement to keep
up. This may lead to a crash
of herbivores, and that may
lead to a crash of higher
predators.
Fig. 9-8 p. 168
These are not mutually exclusive
hypotheses; more probably have
interaction between predation and
food supplies.
Population dispersion
Fig. 9-2 p. 164
Most species live in clumps or groups; reasons may
include:
Availability of resources varies from place to place.
Living in groups offers better protection from
predators.
Some predator species live in packs to better have a
chance to get a meal.
Temporary groups may form for mating and caring
for young.
Uniform pattern distribution may occur where a
resource, such as water, is scarce.
clumping dispersion the
most common dispersion
pattern for populations. In
this type of dispersion,
individuals "flock together.“
uniform dispersion a type of
population dispersion in
which the members of the
population are uniformly
spaced throughout their
geographic region.
random dispersion a type of
population dispersion in
which the position of each
individual is not determined
or influenced by the other
members of the population.
Reproductive Patterns and Survival
Some species reproduce without having sex, and others reproduce by having
sex.
Asexual reproduction does not utilize sex; each cell can divide and produce two
identical cells that are replicas of the original cell.
Sexual reproduction occurs when gametes from each parent combine to
produce offspring with a combination of genetic traits from each parent.
Three disadvantages to sexual reproduction:
Males do not give birth; females have to produce twice the offspring to
maintain the same number of young as an asexual organism.
Chance of genetic errors/defects increase during splitting and
recombination.
Courtship/mating consume energy and time, transmit disease, and
inflict injury on males in some cases
Two important advantages are genetic diversity for survival of species in
the face of changes in environment and males may help with food
gathering and/or rearing of young.
Reproductive Patterns and Survival
Fig. 9-10 p. 170
Reproductive patterns can be classified into two fundamental reproductive
patterns: r-selected and K-selected species.
Availability of a suitable habitat for individuals of a population ultimately
determines the population size.
Reproductive Strategies
r-Selected species are opportunists and
reproduce when conditions are
favorable or when disturbance opens a
niche for invasion. Most species of this
type go through irregular and unstable
boom-and-bust cycles in population
size.
K-selected species generally follow a
logistic growth curve. Many of the
larger species with long generation
times and a low reproductive rate are
prone to extinction.
Survivorship Curves
Populations of different
species vary in how long
individual members typically
live.
A survivorship curve is one
way to represent age
structure of a population.
Three generalized types of
survivorship curves are: late
loss, early loss, and constant
loss.
Fig. 9-11 p. 171
A life table shows the
numbers of individuals at
each age on a survivorship
curve.
Insurance companies use life
tables to determine the cost
of insurance policies.
Effects of Genetic Variations on Population Size
Variations in genetic diversity can affect the survival of small, isolated
populations. Several factors can play a role in loss of genetic diversity
and survival of a small population.
The founder effect is when a few individuals move to a new location
that is isolated from the original population. There is limited genetic
diversity in such a population.
A demographic bottleneck occurs when only a few individuals
survive a catastrophe.
Genetic drift is a third factor and involves random changes in gene
frequencies in a population. This may help or hurt the survival of the
population.
Inbreeding occurs when members of a small population mate one
another; this may increase the numbers of defective genes in a population.
Metapopulations occur where some mobile populations occasionally exchange
genes when some members get together. Conservation biologists use this
information to establish migration routes that will enhance population size,
genetic diversity, and survival of related local populations.
Human Impacts on Ecosystems

Habitat degradation and fragmentation

Ecosystem simplification

Genetic resistance

Predator elimination

Introduction of non-native species

Overharvesting renewable resources

Interference with ecological systems
Humans have altered
nature in ways that
threaten the survival
of many species,
including our own
species.
Humans have directly
affected changes on
about 83% of the
earth's land surface.
Human Impacts on Ecosystems
Humans have altered nature to meet needs and wants in nine major
ways.
1. Destruction, fragmentation, and degrading of wildlife habitats have reduced
biodiversity.
2. The simplification and homogenization of natural ecosystems by clearing
land and planting a single species (monoculture) reduces numbers of
species and interactions. Opportunistic species and pest organisms are
costing time, energy, and money to control. Invasion of pathogenic
organisms is another threat.
3. Destruction of the earth's net primary productivity is a third type of
alteration.
4. Certain types of intervention have unintentionally strengthened pest species
and disease-causing bacteria.
5. Some predator species have been deliberately eliminated from ranching
areas.
6. Alterations have occurred due to the introduction of nonnative (invasive) or
new species into an ecosystem.
Human Impacts on Ecosystems
7. A number of renewable resources have been over-harvested, such as
overgrazing of grasslands, over-hunting of wildlife, and pumping out
aquifers for freshwater faster than they can recharge.
8. Some human activities also interfere with normal chemical cycling and
energy flows in ecosystems
9. Human-dominated ecosystems are increasingly dependent on nonrenewable
energy from fossil fuels that produce pollution and add greenhouse gases
to the atmosphere.
Alteration of natural ecosystems needs to be slowed down, and we need to
maintain a balance between simplified, human-altered ecosystems and
more complex, natural ecosystems
Learning from Nature

Dependence on Nature

Interdependence

Unpredictability

Limited resources

Recycle wastes
See Connections p. 173
Learning from Nature
By mimicking four major ways
that nature has adapted and
sustained itself, we can develop
more sustainable economies.
We are totally dependent on the
sun and Earth for life. We are an
expendable species.
Everything is interconnected and
interdependent. What connections
are strongest, most important,
and most vulnerable are those
that we must discover.
Any intrusion into nature has
unexpected and unintended side
effects. We must not deplete and
degrade the earth's natural
capital.
Solutions
Principles of Sustainability
How Nature Works
Lessons for Us
Runs on renewable solar
energy.
Rely mostly on renewable solar
energy.
Recycles nutrients and wastes.
There is little waste in nature.
Prevent and reduce pollution and
recycle and reuse resources.
Uses biodiversity to maintain
itself and adapt to new
environmental conditions.
Preserve biodiversity by protecting
ecosystem services and preventing
premature extinction
of species.
Controls a species population
size and resource use by
interactions with its
environment and other species.
Reduce births and wasteful resource
use to prevent environmental
overload and depletion and
degradation of resources.
Figure 9-15
Page 174
Applying Population Ecology: The Human
Population Chapter 10
Key Concepts
 Factors affecting human population size
 Human population problems
 Managing population growth
Factors Affecting Human Population Size
Demography is the study of the size, composition, and distribution of human
populations and the causes and consequences of changes in these
characteristics.
Population change equation
Population
Change
=
(Births + Immigration) – (Deaths + Emigration)

Crude birth rate (BR) The crude birth rate is the number of live
births per 1,000 people in a population in a specific year.|

Crude death rate (DR) The crude death rate is the number of
deaths per 1,000 people in a population in a specific year
Describing Population Changes
 Doubling Times “Rule of 70”: Doubling time is one measure of
population growth.
 Fertility-is the number of births that occur to an individual woman in a
population.
 Replacement-level Fertility —the number of children a couple must
have in order to replace themselves in a population.
 Total Fertility Rate (TFR) —the number of children a woman will bear
during her lifetime; this information is based on an analysis of data
from preceding years in the population in question.
Who is Over Populated?
Factors Affecting Human Population Size (2005 Data)
There are currently more births than deaths throughout the world.
1. The annual rate of natural population change (%) equals birth rate
minus death rate divided by 1,000 persons multiplied by 100.
2.
The rate of the world's population growth has decreased.
3.
The annual population growth dropped by almost half between 1963
and 2004, from 2.2% to 1.2%. But during this same period, the
population base doubled from 3.2 to 6.4 billion.
4.
There is a big difference in the exponential population growth rates
of developed and developing countries, with developed countries
growing at 0.25% and developing countries growing at 1.46%—
almost six times faster.
5.
The six fastest growing countries in terms of population are: India,
China, Pakistan, Nigeria, Bangladesh, and Indonesia.
The populations of China and India comprise 38% of the world's
population. The next most populated country is the United Stated
with 4.6% of the world's population.
Factors Affecting Birth Rates and Total Fertility
Rates
Many factors influence birth and fertility rates.
1.
More children work in developing countries; they are important to the
labor force.
2.
The economic cost of raising and educating children determines their
numbers. The more children cost, the less children people tend to
have.
3.
If there are available private/public pension systems, adults have
fewer children because they don't need children to take care of them
in old age.
4.
People in urban areas usually have better access to family planning,
so they have fewer children.
5.
If women have educational
and economic choices,
they tend to have fewer
children.
6.
When the infant mortality
rate is low, people have
fewer children because
children are not being lost
to death.
7.
The older the age at which
women marry, the fewer
children they bear.
8.
If abortions are available
and legal, women have
fewer children.
9.
The availability of reliable
birth control allows women
to space children and
determine the number of
children they bear.
Births per thousand population
U.S. Birth Rates: 1910-2004
32
30
28
26
24
22
20
18
16
14
0
1910
Demographic
transition
End of World War II
Depression
Baby boom
1920
Fig. 10-8, p. 180
1930
1940
1950
1960
Baby bust
1970
Echo baby boom
1980
1990
2000
Year
From 1946-1964, the United States had a sharp rise in birth rate, called
the baby-boom period. At its peak, the TFR reached 3.7 children per
woman. There has been a gradual decline since then. The population
growth of the United States is still greater than any other developed
country and is not close to leveling off.
2010
Factors Affecting Human Population Size
About 2.7 million people were
added to the U.S.
population in 2004.
Fifty-five percent of this
population growth came
from more births than
deaths, and forty-five
percent came from
immigration.
Other major developed
countries have slower
population growth, and
most are expected to
have declining
populations after 2010
The high U.S. per capita
resource rate use
produces enormous
environmental impact.
Immigration Policy
Arguments to limit immigration
into the U.S.
•
Limitations would aid in
stabilizing the population
sooner.
•
Limitations would help
reduce the enormous
environmental impact of the
U.S.
Arguments for generous
immigration policies in the
U.S.
• Historically, the U.S. has been
the land of opportunity for the
world's poor.
• Immigrants do work that
Americans won't do or handle
jobs for which there are not
enough trained natives.
• Immigrants contribute to the
economy and pay taxes.
Factors Affecting Human Population Size
Factors, which have caused a decline in death rates, are the following:
1.
2.
Better food supplies and nutrition and safer water supplies
contribute to people living longer.
Advances in medicine and public health and improved sanitation
and personal hygiene also contribute to people living longer.
Life expectancy is the average number of years a newborn can expect
to live.
Infant mortality rate (IMR) is the number of babies out of every 1,000
born who die before their first birthday.
a. This rate reflects a country's level of nutrition and health care.
b. It is the single best measure of a society's quality of life.
U.S. infant mortality rate is higher than 35 other countries due to:
a. inadequate health care for poor women and for their babies,
b. drug addiction among pregnant women, and
c. a high birth rate among teenagers.
Population Age
Structure
Male
Female
Rapid Growth
Guatemala
Nigeria
Saudi Arabia
Ages 0-14
Slow Growth
United States
Australia
Canada
Ages 15-44
Zero Growth
Spain
Austria
Greece
Negative Growth
Germany
Bulgaria
Sweden
Ages 45-85+
Fig. 10-14 p. 184
Global Aging
The Demographic Transition
Fig. 10-20 p. 189
Stage 2
Transindustrial
Stage 3
Industrial
Stage 4
Postindustrial
High
80
70
Relative population size
Birth rate and death rate
(number per 1,000 per year)
Stage 1
Preindustrial
60
50
Birth rate
40
30
Death rate
20
10
0
Total population
Low
Increasing Growth Very high Decreasing
Low
Zero
growth rate
growth rate
growth rate growth rate growth rate growth rate
Time
Low
Negative
growth rate
Solutions: Influencing
Population Size
Migration
Environmental refugees
Reducing births
Family planning
Empowerment of women
Economic rewards and penalties
Case Study: Slowing Population Growth in India
Generally disappointing
results:
Poor planning
Bureaucratic inefficiency
Low status of women
Extreme poverty
Lack of support
World in the
Balance - India
Case Study: Slowing Population Growth in China
Economic incentives
Free medical care
Preferential treatment
Locally administered
Very intrusive and
coercive
World in the
Balance - China
Population Growth in Sub-Saharan Africa
How do different
populations compare?
Sub-Saharan Africa
Cutting Global Population Growth
 Family planning
 Improve health care
 Elevate the status of women
 Increase education
 Involve men in parenting
 Reduce poverty
 Sustainability