Population Dynamics
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Outline
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Dynamics of Population Growth
 Exponential vs. Arithmetic Growth
 Malthusian vs. Logistic Growth
Population Increase
Population Decrease
Survivorship
Regulating Population Growth
 Density Dependence vs. Independence
Conservation Biology
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What caused the demise of Easter Island’s human
population?
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Major Characteristics of a Population
Populations are dynamic
Change in response to environmental pressures
Changes include
1.
Size (# of individuals)
2.
Density (# of individuals in certain space
3.
Dispersion (spatial pattern such as clumping,
uniform dispersion, or random dispersion)
4.
Age distribution (proportion of individuals of each
age in a population)
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Spatial Distribution of Populations for Plants
Regular
Random
Aggregated
Regular – seen with trees. Occurs because of light patterns on the
forest floor are determined by tree canopy
Random – based on wind, animal or other forms of seed dispersal
Aggregated – plants occur in “clumps”; plants may aggregate to
survive
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Population Dynamics
Changes are referred to as population
dynamics
Respond to
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Environmental stress
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Changes in environmental conditions
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FACTORS THAT INCREASE OR
DECREASE POPULATIONS
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Natality - Production of new individuals.
Referred to also as births or B
 Fecundity - Physical ability to reproduce.
 Fertility - Measure of actual number of
offspring produced.
Immigration - Organisms introduced into new
ecosystems. Referred to by letter I
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Mortality, Survivorship, and Emigration
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Mortality - Death Rate or D
 Survivorship - Percentage of cohort surviving to a
certain age.
 Life expectancy - Probable number of years of
survival for an individual of a given age.
- Increases as humans age.
 Life Span - Longest period of life reached by a
given type of organism.
Emigration - Movement of individuals out of a
population. Emigration usually applies to humans;
few species actually leave the group if they are a
herd animal. Represented by letter E.
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FACTORS THAT REGULATE
POPULATION GROWTH
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Intrinsic factors - Operate within or between
individual organisms in the same species.
Extrinsic factors - Imposed from outside the
population.
Biotic factors - Caused by living organisms.
Abiotic factors - Caused by non-living
environmental components.
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Biotic Potential and Carrying Capacity
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Biotic Potential Maximum
reproductive rate of
an organism.
Intrinsic rate of
increase (r) –
rate at which a
population would
grow if it had
unlimited resources
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Organisms with high r
1.
2.
3.
4.
Reproduce early in life
Have short generation times (time between
successive generations)
Can reproduce many times (long
reproductive life)
Have many offspring every time they
reproduce
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Environmental Resistance and Carrying Capacity
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Environmental Resistance Any environmental factor
that reduces population
growth.
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Biotic potential +
environmental resistance =
the carrying capacity of a
given population
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Carrying Capacity Maximum number of
individuals of any species
that can be indefinitely
supported in a given area.
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Population Viability Analysis
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Minimum Viable Population is the minimum
population size required for long-term
viability of a species.
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Minimum Viable Population
If population declines below MVP needed to
support a breeding population:
1.
Certain individuals may not be able to
locate mates
2.
Genetically-related individuals may
interbreed and produce weak/malformed
offspring
3.
Genetic diversity may be too low to enable
adaptation to new environmental conditions
Intrinsic rate of increase will fall and extinction
likely
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Endangered Species Act of 1973
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Purposes of this Act are to provide a means
whereby
1. the ecosystems upon which endangered species
and threatened species depend may be conserved,
2. to provide a program for the conservation of such
endangered species and threatened species, and
3. to take such steps as may be appropriate to
achieve the purposes of the treaties and
conventions set forth in subsection (a) of this
section.
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Examples of Threatened or Endangered Species
under protection
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http://ecos.fws.gov/tess_public/Boxscore.do
Why would an organism be counted more
than once?
Tennessee
Yellow-eyed
Grass
Florida panther
Mead’s
Milkweed
Four petal
Paw Paw
Short-tailed
albatross
Pig footed
Bandicoot
Quino Checkerspot
Butterfly
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First “declared” casualty of Global Warming
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The Polar Bear (Ursus maritimus)
Maturation at 3 to 5 years old
Females give birth to one or two cubs
Cubs remain with female for 2 1/4 years
Females breed every third year
Males travel long distances to find females
Eat seal and walrus
Need ice pack to hunt
Current estimated population 20,000 to 25,000 globally
Are under protection of Marine Mammal Protection Act of
1972
U.S. shares protection responsibilities with Norway, Russia,
Denmark (Greenland) and Canada under international
conservation agreement in 1976
Shared, unified management with Federation of Russia,
which involves Native Peoples
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Population Count
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Counting ALL of the members of a population
is next to impossible
Therefore, you need to develop a method
that will give you an estimation of the size of
the population
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Estimation of Population Size
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Mark and recapture
Used by wildlife biologists to determine
number of animals in a population for a given
community
Tagging, tattooing, leg bands, subdermal
radio transmitters, paint or other marking
substance to mark captured organisms
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Mark and Recapture
By performing a number of mark and
recaptures, the field biologist can use the
data to estimate the number of organisms in
a given population
Depending on the species, can take one year
or more
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Estimating Population Laboratory
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Use washable pen to mark beans (blow on
ink to dry it before placing bean back into
bag)
When lab is completed, remove all beans
from bag and wipe off marks with dampened
paper towel.
Place beans back in the bag.
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Estimating Population Size
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Estimate of total population =
(total # captured) x (number marked)
total number recaptured with mark
Show the math!
Then see Ms. P. for the actual number in the
bag
Continue with the analysis
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Consider this…
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You take a job where the boss offers you
$15.00/hour. You decline, asking the boss to
pay you $1.00 the first day, $2.00 the
second, and so on, doubling your pay each
day you work. Calculate what you would
receive for pay on Day 30.
Should your boss take this deal? Why or
why not?
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Solve it!
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The deer population in Maryland is doubling
at a rate of 5.2% per year
Using the equation below, calculate the five
year estimated growth for the Maryland deer
population if the annual percentage growth
rate is 5.2%. The population currently stands
at an estimated 250,000
- 70/annual percentage growth rate
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Rule of 70
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A quantity grows exponentially when its
increase is proportional to what is already
there
You boss would be a fool to take your
request!
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Density Dependent Factors
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Higher proportion of population is affected as
population density increases.
Tend to reduce population size by decreasing
natality or increasing mortality.
 Interspecific Interactions
- Predator-Prey oscillations
 Intraspecific Interactions
- Territoriality
 Stress and Crowding
- Stress-related diseases
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DYNAMICS OF POPULATION GROWTH
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Exponential Growth
- Growth at a
constant rate of
increase per unit
time. (Geometric)
Arithmetic/Logistic
Growth - Growth at
a constant amount
per unit time.
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Growth to a Stable Population
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Logistic Growth - Growth rates regulated by
internal and external factors until coming into
equilibrium with environmental resources.
 Growth rate slows as population
approaches carrying capacity.
 S curve
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Exponential Growth and Doubling Times
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Number of individuals added to a population
at the beginning of exponential growth is
relatively small. But numbers increase
quickly as the population, and thus the given
percentage of that population, grows.
 J curve
 What is an example of a J curve
population?
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Rule of 70
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Doubling Time of a population:

70_____________
 annual percentage growth rate.

Keep this mind!
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Money
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A common example is
compound interest,
where $100 invested at
7% per year annual
compound interest will
double in 10 years!
Exponential growth
applies to populations,
too -- if a population
grows at 7% per year,
it, too, will double in 10
years.
70/7 = 10 years to double
your money!
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Rule of 70
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However, to really
make some money, it
takes time to actually
get to a point where
you are making real
money!
Populations are like
this too – they start
small and then take off!
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Problem is…
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Unfortunately, exponential growth works
against us, too. When populations continue
to grow, the impact of growth becomes
increasingly significant over time. In other
words, because of the nature of exponential
growth, "when things get bad, they get bad in
a hurry".
Example: Maryland Deer population
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Overpopulation!
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Consider a deer
population with 100
deer, growing at 7%
per year. In 10 years,
the population will
double to 200 deer, in
another 10 years it will
double again to 400
people, and ten years
after that it will double
again to 800 deer.
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Density Dependent Factors
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Higher proportion of population is affected as
population density increases.
Tend to reduce population size by decreasing
natality or increasing mortality.
 Interspecific Interactions
- Predator-Prey oscillations
 Intraspecific Interactions
- Territoriality
 Stress and Crowding
- Stress-related diseases
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Example of Intraspecific Competition
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In the summer of 1980, much of southern New England was struck by an
infestation of the gypsy moth (Porthetria dispar). As the summer wore on,
the larvae (caterpillars) pupated;
the hatched adults mated, and
the females laid masses of eggs (each mass containing several hundred eggs)
on virtually every tree in the region.
In early May of 1981, the young caterpillars that hatched from these eggs began
feeding and molting.
The results were dramatic:
 In 72 hours, a 50-ft beech tree or a 25-ft white pine tree would be completely
defoliated.
 Large patches of forest began to take on a winter appearance with their
skeletons of bare branches.
In fact the infestation was so heavy that many trees were completely defoliated
before the caterpillars could complete their larval development. [View!]
The result: a massive die-off of the animals; very few succeeded in completing
metamorphosis.
Here, then, was a dramatic example of how competition among members of one
species for a finite resource — in this case, food — caused a sharp drop in
population.
http://home.comcast.net/~john.kimball1/BiologyPages/P/Populations2.html
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Stress and Crowding
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Stress causes cortisol to increase in the body
 This increases blood pressure, heart rate
 Causes body to age faster, increasing rate of
illness
Crowding increases probability of being infected by
transmissible diseases
 also increases stress on immune system,
lowering immunity
- Example: Black Plague epidemic more
prevalent in major cities then in smaller
villages
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Density-dependent factors are impacted by Biotic
Factors
Reproductive rate
Niche type (generalized or specialized)
Food supply
Habitat
Competition for resources
Ability to hide or defend against predators
Ability to resist disease and parasites
Ability to migrate and live in other habitats
Ability to adapt
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Density Independent Factors
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Constant proportion of the population is
affected regardless of population density.
Tend to be abiotic components.
 light
 temperature
 chemical environmental (optimal level of
critical nutrients)
Do not directly regulate population size.
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Density-independent checks on population growth
Include:
• Tornados
• Hurricanes
• Droughts
• Floods
• Freezes
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Increase or Decreasing Population Size
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Depends on both biotic and abiotic factors
Consider this: the snowfall in Colorado is
higher than normal, causing problems for
humans, animals and plant life. However,
how will this snowfall prove auspicious come
spring?
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Population Oscillations
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Overshoot - Measure of extent to which
population exceeds carrying capacity of its
environment. Ex. Easter Island
Dieback - Negative growth curve.
 Severity of dieback generally related to the
extent of overshoot.
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Population Curves found in Nature
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Four general types:
 Stable
 Irruptive
 Irregular
 Cyclic
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Stable Growth
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Population fluctuates slightly above and
below it’s carrying capacity
Characteristic of many species in
undisturbed tropical rain forests where there
is very little variation in avg. temp and rainfall
Most organisms that enter a new habitat
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Irruptive Growth
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Malthusian Growth (Irruptive) - Population
explosions followed by population crashes.
 Malthus concluded human populations
tend to grow until they exhaust their
resources and then crash.
 Example: Easter Island, Lemmings
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Irregular Growth
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No recurring pattern of population size
change
Considered “chaotic”
May be caused by chaos in the environment
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Cyclic Growth
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Can be due to top-down control or bottom-up
control
Here, depends on number of lynx for topdown or availability of food for hares for
bottom-up
Ex: Fir-Moose-Wolf populations on Isle
Royale
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Growth Rate Study of Sea Pines Deer
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Expanding populations of deer affected by
shrinking habitats due to human development
 Only controls are parasites, lack of feed and auto
collisions
 *Deer affected by parasites such as ticks
Culling populations important to stop dramatic
increases in populations
 People dislike the selective “culling” by
sharpshooters and bow hunters, said as natural
reserve cannot do this
Use of immunocontraception PGF2a
Court case to save the deer still pending
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Growth Rate Studies
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Determine population size of Sea Pines Deer
Growth expected
Compare your data to published projections
Evaluate data/analyze/conclusion
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Calculation Formulae Part 1
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r = intrinsic rate of increase
r = ((lnP2 – lnP1)/t) x 100
Where P1 = population at time one
P2 = population at time two
ln refers to natural log
t = number of years
Doubling time
t = 0.693/r
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Example
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r = ((lnP2 – lnP1)/t) x 100
= ((ln120-ln70)/50 x 100
= ((4.487 – 4.248)/50) x 100
= 0.53/50 x 100
= 1.0779 or 1.08%
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Calculation Formulae Part 2
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P = P0 ert where
P = final population
P0 = initial population
e = don’t worry about this
r = rate of increase for 1998 – 1999,
which is 33.6% or 0.0336
t = time (for this, number of years)
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Example for years 0 to 1
P = 500 e(.3364)(1)
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= 500 .3364
Now punch in .3364, then punch INV, then ln
(that is, you are taking the inverse of the
natural log of .3364)
= 500 ( 1.399)
= 699.949 or 700 (round up or down to
nearest whole number)
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Malthusian Strategies – r Strategy (Barrons
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Short life
• Adapted to unstable
environment.
Rapid growth
• Pioneers, colonizers
Early maturity
Many small offspring • Niche generalists
• Prey
Less parental care
• Regulated mainly by
Little investment in
extrinsic factors.
individual offspring.
OpportunisticAble to • Low trophic level
colonize new areas • Type III survivorship
rapidly
curve
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Examples of r strategists
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Bacteria
Most fish species (ID a fish that is a r strategist)
Mollusk species
Amphibian species
Most reptile species
Rodents
Rabbits
Most insects (grasshoppers, flies, butterflies, etc.)
Weeds
Trees
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Logistic Strategies or K strategy (Barrons 164)
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Long life
Slower growth
Late maturity
Fewer large offspring
High parental care and
protection.
High investment in
individual offspring.
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Adapted to stable
environment.
Later stages of
succession.
Niche specialists
Predators
Regulated mainly by
intrinsic factors.
High trophic level
Type I or III
survivorship curve
Considered a more “progressive” evolutionary strategy
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Examples of K strategists
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Primates, including humans, gorillas,
chimpanzees
Elephants and Rhinos
Turtles
Orchids
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Query
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Which type of organisms, r or K, will benefit
from global warming?
Consider the following in your answer
 Change in climate
 Change in habitat
 Effects on organisms
 Nature of r and K strategists
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Survivorship Curves (Barrons 161)
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Four general patterns:
 Full physiological life span.
 Probability of death unrelated to age.
 Mortality peaks both early and late in life.
 Mortality peaks early in life.
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Survivorship Curves
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Type I or a – seen in
elephants and humans; K
strategists; lower death
rate; fewer offspring, high
degree of parental care
Type II or b – amphibians;
death is likely no matter
what the age
Type III or d – seen in fish
and oysters; r strategists;
high death rate due to form
of reproduction (usually
external) and lack of
parental care in early
formation
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The vertical axis gives the fraction of
survivors at each age.
Curve A is characteristic of organisms
that have low mortality until late in life
when aging takes its toll.
Cure B is typical of populations in which
such factors as starvation and disease
obscure the effects of aging, and infant
mortality is high.
Curve C is a theoretical curve for
organisms for which the chance of death
is equal at all ages. This might be the
case for organisms that do not age
(some fishes) or those (e.g., many
songbirds) that suffer severe random
mortality throughout life. K-strategists
usually have survivorship curves
somewhere between A and C.
Curve D is typical of organisms, oysters
for example, that produce huge numbers
of offspring accompanied by high rates
of infant mortality. Many r-strategists
have such a curve.
Comparision of
Survivorship Curves
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Life Tables and Organisms
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Life tables – give information on the
survivorship of organisms at each part of life
 Used by insurance companies to
determine the relationship of a client’s age
and likelihood they will pay enough in
insurance premiums to cover the cost of
the policy.
Can also be used to create age-sex
diagrams, calculate age-dependency ratios,
and other information that gives a “picture” of
a species “life history”
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Human Population Ecology: Demography
In this laboratory you will calculate, analyze
research differences in mortality rates in the
human population before and after 1950.
Use of cemetery data for laboratory, because
humans keep data records of their natalities
and mortalities.
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Reasons for Human Mortalities Before and After 1950
Before 1950
After 1950
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Develop a Hypothesis Regarding Mortality based on
Time Period of Death and Gender
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Select one of these cemeteries to obtain data!
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http://www.interment.net/us/
Select a county in Maryland (each person take a different one)
Select a cemetery (you may need more than one cemetery to collect all
your data)
Write down data for 80 people in the specific data table based on
 Females who died before 1950
 Females who died after 1950
 Males who died before 1950
 Males who died after 1950
 Each student will collect data for 80 individuals!
 Calculate age at death (Year of death – Year of Birth)
 Do not collect information for people who actually died in 1950!!!
(Why?)
 We will use this information to calculate the data for Table 2 AND to
create a graph of the data for the ENTIRE CLASS.
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Calculating Survivorship
Column A Mortality –number of deaths for that
age cohort or interval from everyone; make sure
to tally the total number of deaths at the bottom of
the column
2.
Column B Alive – subtract the number who died in
A from the number of individuals alive at the
beginning of the age interval. You need to get
this info from everyone and tally the number up.
3. Column C Survivorship – leave empty. We will
calculate this once we have collated everyone’s
data.
1.
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Raw Data
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You will be given a master sheet for each
gender and death time (before or after 1950)
Write down all the data from the individuals
from the computer screen
Add up information for each age cohort
Total up Column A for each master sheet
Calculate Column C – Divide total for age
cohort in Column B by the TOTAL at the
bottom of column A.
This is the Survivorship for that age cohort.
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Graphing the data
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Make a graph with Y axis as survivorship and
each age cohort as the X axis.
There will be 4 separate lines on the graph
 Females who died before 1950
 Females who died after 1950
 Males who died before 1950
 Males who died after 1950
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When you are finished
Both the graph and the essay for this lab will be
part of your exam grade:
• Answer the five questions from the laboratory in an
ESSAY format.
• Use good thinking and writing skills.
• Directly address the data from the lab
• Work MUST be original
• Email your essay to www.turnitin.com by midnight,
1/21
• Hand in the graph, with your name on it, before the
exam begins on Monday, 1/22.
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Questions to Address
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Conservation Genetics
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Genetic Drift
 Random reduction in gene frequency.
 Changes gene pool of population
Founder Effect
 Few individuals start a new population.
 Smaller gene pool.
 Limits genetic differences
 Can see increased effects of mutations
Demographic Bottleneck
 Few individuals survive catastrophe.
- Inbreeding
 Mating between related individuals.
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Genetic Drift
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" Random change in gene frequency within a
population" (Meffe et al.)
Not necessarily adaptive
Stronger in small populations
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Founder Effect
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"The establishment of a new
population by a few original
founders which carry only a
small fraction of the total
genetic variation of the
parental population." (Ernst
Mayr)
Over time, the unique traits
become found throughout the
population
Amish
Fugate family
Can also occur in genetic drift,
although without the new
population
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Demographic Bottleneck
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Population suffers reduction in size and then
recovers
Random losses of genetic diversity
Usually associated with catastrophic events or
diseases
Genetic variation doesn't rebound from a decrease
as quickly as population size.
Examples:
Irish Potato famine emigrations and deaths
changed the population of Ireland
Mass wasting disease in deer populations
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Metapopulations
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A collection of populations that have regular
or intermittent gene flow between
geographically separate units.
 Bay Checkerspot Butterfly
- Source - Sink Model
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Source-Sink Model
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Some habitats become sources from which
surplus population migrates to less suitable
habitats that act as sinks for the surplus
populations.
To a certain degree, some countries (e.g.,
Italy) with a human reproductive rate below
the replacement rate are serving as sinks for
countries (especially those nearby) with
expanding populations and increasingly
scarce resources.
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Conservation Biology
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Science of protecting and managing Earth's biological
diversity
First seen in 18th and 19th C. Germany and India
The term conservation came into use in the late 19th cent.
and referred to the management, mainly for economic
reasons, of such valuable natural resources as timber, fish,
game, topsoil, pastureland, and minerals, and also to the
preservation of forests (see forestry), wildlife (see wildlife
refuge), parkland, wilderness, and watershed areas.
In recent years the science of ecology has clarified the
workings of the biosphere; i.e., the complex
interrelationships among humans, other animals, plants, and
the physical environment.
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Conservation Biology
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Species can be considered to have an intrinsic
value.
That is, the survival of a species may be viewed to
be in the interest of the species itself, without
regard for the utilitarian benefits to humans.
In this view, non-human populations are perceived
to have interests, including an interest in their own
continued survival.
This view is espoused by deep ecology, which
shifts emphasis away from the anthropocentric
reasons for conservation and species survival.
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CONSERVATION BIOLOGY
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Island biogeography - Small islands far from
a mainland have fewer terrestrial species
than larger, closer islands.
 MacArthur and Wilson proposed that
species diversity is a balance between
colonization and extinction rates.
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Introduction of Non-native Species
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On islands, can devastate the delicate
balance within a community, upsetting the
food web.
 Rabbits in Australia
 Rats and cats on the Galapagos Islands
 Rats, snakes and mongooses on Hawai’I
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Removing Exotic Species
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Very costly to remove exotic species once
they are established
May take a long time for re-establishment of
the original community
May never be the same as before the exotic
species
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Extinction of Species
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Extinction of a species is irreversible.
An extinct species represents a lost resource
of unknown value.
Although the net value of any one species is
virtually impossible to represent in pure
numerical or monetary figures, financial
incentives for conservation of many
individual species can be demonstrated.
Ex: Tropical rain forest plant species that
could be used for medicines can be
conserved by preserving the forest.
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Summary
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Dynamics of Population Growth
 Exponential vs. Arithmetic Growth
 Malthusian vs. Logistic Growth
Population Increase
Population Decrease
Survivorship
Regulating Population Growth
 Density Dependence vs. Independence
Conservation Biology
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