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APES: Chapter 9
Population Dynamics, Carrying Capacity,
Conservation Biology
*INTRODUCTION: 9-1 Population
Dynamics and Carrying Capacity
Populations are dynamic, constantly
undergoing changes in size, density, and
age distribution due to environmental
stress and changing environmental
conditions.
In general there are four factors that
influence the size of a population: birth (+),
deaths (-), immigration (+), and
emigration (-).
Different populations vary in their ability
to grow (biotic potential). The intrinsic
rate of increase refers to a population’s
growth rate if it had access to unlimited
resources.
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Organisms with high intrinsic rates of
increase typically have the following
characteristics:
- early reproductive age
- short generation times
- can reproduce several times
- have many offspring each time
The intrinsic rate of increase of many
species depends upon having a certain
minimum population size (minimum viable
population).
Passenger Pigeon Reading
Environmental resistance consists of
the factors that prevent a population from
reaching its intrinsic rate of increase.
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The carrying capacity refers to the
number of individuals that can be supported
in a given area in a sustainable manner.
Populations with unlimited access to
resources grow slowly at first and at a faster
rate with time (exponential growth). When
graphed this yields a J-shaped curve.
As populations experience environmental
resistance the rate of growth begins to slow
as the carrying capacity is reached (logistic
growth). When graphed this yields an Sshaped curve (see Fig. 9-4).
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At times a population may overshoot the
carrying capacity and eventually suffer a
population crash or dieback (See Fig. 9-6).
Human populations are not exempt from
dieback although technology and cultural
changes have increased the carry capacity of
the earth for our species.
http://www.youtube.com/watch?v=9_9SutNmfFk
human population growth
HW #1: page 201: #’s 2, 5, 6 (all parts), 7, 8
http://www.youtube.com/watch?v=BSVbdaubxxg section summary
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**DENSITY FACTORS
Some controls on populations have an
impact independent of the population’s
density (density independent controls):
- floods - fire - severe weather
- habitat destruction - pesticides
Other controls have a greater impact if
the density of the population is large
(density dependent controls):
- competition for resources
- infectious disease (bubonic plague)
- parasitism
Overall there are four common patterns
of population fluctuations:
- stable: the population stays pretty
close to the carrying capacity.
- Irruptive: populations explode to high
levels then return to a stable level or
crash.
- Chaotic: irregular fluctuations that
are not predictable
- Cyclic: population’s size varies on a
fairly regular basis.
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2- Predation and Population Size
The role of predators in ecosystems has
been studied extensively.
At one time most biologists accepted the
top-down control hypothesis. Predators
(higher trophic level) controlled the
population size of their prey (lower trophic
level). This idea was used to explain the
cycling of hare and lynx populations studied
since the 1800’s (see Fig 9-8).
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It is now believed the size of some
populations might be better explained using
the bottom-up control hypothesis. The size
of a herbivore population (higher trophic
level) is determined by how much food they
consume or the quality of the food source
(lower trophic level).
Although some bottom-down controls are
still believed to exist, the size of predatorprey populations are probably a combination
of both factors.
HW #2: page 201 #’s: 9, 10, 11, 12.
***9-3 Reproductive Patterns
All organisms are constantly struggling
for genetic immortality. Remember,
Darwinian Fitness is a measure of the
reproductive success of an organism or
population.
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There is not however one reproductive
strategy that is always better than another.
Asexual reproduction involves no
exchange of genetic information and the
offspring are genetic clones of the original
cell.
Binary Fission
Budding
Sexual reproduction involves an
exchange of genetic information between
organisms and is estimated to occur in 97%
of all life.
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There are many costs associated with
sexual reproduction
1- time consuming
2- disease
3- genetic errors (recombination)
4- predation risks
... but these are outweighed by the
advantage of generating genetic diversity.
Scientists have identified two fundamental
reproductive patterns:
r- selected (opportunists): put most of
their energy and resources into
reproduction.
- many small offspring but few reach
sexual maturity
- little if any parental care
- high intrinsic rates of growth
- early successional species
- generalist niche
K- selected: tend to do well in
competitive situations when their
population is near the carrying capacity.
- few large offspring
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- late reproductive age
- extensive parental care
- typically follow a logistic growth
pattern
- because the intrinsic rate of growth is
low they are prone to extinction
No matter what pattern organisms used
their ultimate population size is
determined by available suitable habitat.
****Survivorship Curves
Survivorship curves indicate the number
of individuals alive in a population during
a given time. There are three generalized
patterns:
Late loss curves: common in K-selected
species (most die late)
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Early loss curves: typical for r-selected
species (most die early)
Constant loss curves: mortality rates
are constant at all age levels
HW #3: page 201 #’s: 13, 14, 15, 16.
9-4 Conservation Biology
Conservation biology began in the
1970’s in attempt to use science to preserve
species and ecosystems. There are several
fundamental questions they ask:
1- what species are in danger of
extinction?
2- what is the status of functioning
ecosystems and the services they
provide?
3- what actions can be taken to sustain
ecosystems, their services, and their
populations?
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Conservation biology is heavily dependent
upon field research and focuses upon three
essential principles:
1- biodiversity is essential to all life
and should be preserved
2- humans should not hasten the
extinction of species or disrupt
ecological processes
3- the best way to preserve biodiversity
and ecological functions is to protect
intact ecosystems
The new discipline of bioinformatics has
contributed enormously to the field of
Conservation Biology by providing access to
key biological information through
databases.
*****Human Impacts on Nature
Humans have used technology to modify
nature extensively in numerous ways:
1- fragmentation and degradation of
habitats
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http://www.youtube.com/watch?v=KEINq3-9Tu0
2- simplified natural ecosystems
3- use and/or waste an increasing
percentage of the planet’s net primary
productivity
4- strengthen some pest species
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5- eliminate predators
6- introduce non-native species
http://www.youtube.com/watch?v=2iKYcqKyXic
Answer the following questions as you watch the video.
1. How did Burmese Pythons arrive in the Everglades?
2. What is the economic cost?
3. What is the ecological cost?
4. How has ballast water contributed to the invasive species problem?
5. Describe one impact (ecological/economic) zebra mussels have had on the great
lakes.
7. over-harvest natural resources
8. interfere with the normal cycling of
chemicals and the flow of energy in
ecosystems
Solutions
Many biologists now believe the best way
for us to live more sustainably is to learn
how nature sustains itself and then to
mimic these strategies. These lessons
include:
1- we are totally dependent upon the
earth and sun
2- everything is connected
3- we can never merely do one thing
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4- we should reduce the damage we are
doing to nature and heal some of the
ecological wounds we have caused
5- we should use care, restraint,
humility, and cooperation with nature as
we alter it to meet our needs.
APES: Chapter 12
Human Population: Growth, Demography,
and Carrying Capacity
12-1 Factors Affecting Human Population
Demography is the study of the changes and
influences on the human population.
http://www.worldometers.info/worldpopulation/
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http://www.npr.org/2011/10/31/141816460/visu
alizing-how-a-population-grows-to-7-billion
The rate at which the human population
changes is frequently measured by
subtracting the crude death rate (the
number of deaths per 1,000) from the crude
birth rate (number of births per 1,000).
This is usually expressed as a percentage
using the following equation:
% change = birth rate- death rate X 100
1,000
which equals: birth rate- death rate
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Even though the birth rate has fallen
around the world the death rate has fallen
much faster. Exponential growth has
slowed in the last 40 years but the base
population has still almost doubled.
Calculation: student notes
Problem: Calculate the number of people that would be added to
a population of 3 billion people at a fertility rate of 5%:
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Problem: Calculate the number of people that would be added to
a population of 6 billion people at a fertility rate of 2.6 %:
Two types of fertility rates affect a country’s
population size and growth rate.
1- replacement fertility level: the number of
children a couple must have to replace
themselves (approximately 2.1 children).
Even when (if?) this number was to be achieved
the global population would continue to grow
for another 50 years (assuming death rates
stay the same) POPULATION MOMENTUM.
2- total fertility rate (TFR): the average
number of children a women will have in her
lifetime.
TFR has dropped significantly since 1950 from
about 5.0 to 2.6. Notice however it is still far
above the replacement level of 2.1.
http://www.youtube.com/watch?v=uOuzC0UMBHQ fertility rates
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More than 95% of the human population
growth by the year 2050 is expected to take
place in developing countries where living in
acute poverty (less than $1.00 a day) is a
way of life.
-----------------------------------------------------There are many factors that affect fertility
rates:
- importance of children in the labor force
- urbanization
- cost of raising and educating children
- educational and employment
opportunities for women
- infant mortality rates
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- average age at marriage
- availability of abortions
- availability of reliable birth control
methods
- religious beliefs, traditions, cultural
norms.
Death Rates are influenced by access to:
food supply
- medical care
medical and health technology
improved sanitation
safe water (#1)
Two common ways of measuring the overall
health of people in a country are:
1- life expectancy- the average number of
years a newborn can expect to live
http://www.youtube.com/watch?v=p6qhwUd9uw0 life expectancy
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2- infant mortality rates (commonly defined
as death before the age of one)
Although infant mortality rates are falling,
almost 22,000 infants die each day due to
preventable causes.
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There are 37 countries that have lower
infant mortality rates than the United
States due mainly to:
inadequate health care for the poor
drug addiction during pregnancy
high birth rates among teenage girls (the
highest of any industrialized country).
MINI HW #4Review Questions (page 275 #’s 2, 15, 17
12-2 Population Age Structure Diagrams
Age structure diagrams show the proportion
of a population (or gender) at a particular
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age. They are typically divided into three
broad categories:
1- prereproductive (ages 0-14)
2- reproductive (14- 44)
3- postreproductive (45 and up).
Age structure diagrams that have a
triangular shape have the potential to grow
rapidly. About 30% of the world’s
population is in the prereproductive group.
The more rectangular the diagram becomes
the slower the birth rate.
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Rapid changes in population growth rates
can have severe cultural impacts (Social
Security in this country). If population
decline is gradual the harmful effects can
usually be managed.
HIV/AIDS is having a major impact of the
age structure of many African countries. Life
expectancy may drop 35-40 years with the
greatest impact on the most productive
adults.
Increases in the number of orphans and
reduction in food production are expected to
follow.
The international community, especially
developed countries, are being called upon to
spearhead the effort to slow the spread of
AIDS through improved education, health
care, family planning, and contributing
economic aid.
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12-3 Solutions
There are several proposed solutions to the
problem of human population growth:
1. limiting migration (the United States
allows large numbers to immigrate compared
to many of the other countries of the world.)
2. reducing birth rates through economic
incentives, family planning, and empowering
women.
Many question the need to limit birth rates
arguing:
a- we do not know the carrying capacity of the
earth
b- humans are the world’s most valuable
resource when it comes to solving global
problems
c- it violates their private or religious beliefs.
3- Economic development typically reduces
birth rates in a fairly recognizable pattern
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known as demographic transition. You
should be familiar with this model in detail.
4- A small number of countries use economic
rewards or penalties to help reduce birth
rates. China has instituted the most
extensive and intrusive controls and
arguably the most effective.
Mini HW #5: Review Questions page 275 #’s: 8,
9, 12, 14.
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