Science That Scares…
What are your inalienable rights?
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#5 Right to enjoy natural beauty
#4 Right to decent shelter
#3 Right to breathe clean air
#2 Right to drink pure water And
• #1 Right to eat well
T.H. Malthus
• “There Should Be No
More People In A
Country Than Can
Enjoy Daily A Glass
of Wine and A Piece
of Beef For Dinner”
– T.H. Malthus
The Malthusian “Iron Law”
• Food resources grow
arithmetically with
increasing technology
• Population sizes grow
exponentially due to
nature’s tendency to
overproduce
• Yet, population sizes
eventually remain
constant
The Iron Law
How is the Malthusian Iron Law Supported by
the 1st Law of Thermodynamics?
J-Curves
• If populations were not
bound by the Iron Law,
then populations would
grow exponentially in a
“J” curve
• Any population allowed
to do this would reach
its BIOTIC POTENTIAL
Lag Phase
• All population
growth starts out
slowly, in an
arithmetic
progression
• This initial period of
slow growth is called
a LAG PHASE
Why does population growth always start
with a lag phase?
Log Phase
• Once a population has
enough reproductive
members, a period of
exponential growth
occurs
• This is known as the
LOG PHASE (or logistic
growth)
FACTORS AFFECTING RATE OF POPULATION
GROWTH
• NATALITY
• MORTALITY
• IMMIGRATION
• EMIGRATION
NATALITY
• Def: # of live births
in a given amt. of
time
• Natality is also
determined by two
additional factors
– Fecundity
– Age Structure
FECUNDITY
• Def: The number of
offspring born to an
individual during the
course of its lifetime
• Fecundity is correlated
with lifespan and other
abiotic factors
Factors Affecting Fecundity
AGE STRUCTURE
• Def: The relative
portions of each
population that are:
– Pre-Reproductive
– Of Reproductive Age
– Post-Reproductive
ANY PREDICTIONS?
MORTALITY
• Def: The number of
deaths in a population
in a given amt. of time
IMMIGRATION
• Def: Individuals of one
species entering a
habitat of a species over
a given amount of time
EMIGRATION
• Def: Number of
individuals of a species
leaving a given area
within a certain length
of time
Doubling Time
• Def: The amount
of time it takes for
a given population
size to double
• In the LOG PHASE,
the doubling times
get shorter
BIOTIC POTENTIAL
• Biotic potential is reached when a population
is allowed to reproduce at its maximum rate
without increasing numbers of deaths
• To reach biotic potential, populations require
unlimited space and resources
• Instead of reaching biotic potential,
populations are affected by limiting factors
LIMITING FACTORS
• Def: Any biotic or abiotic condition that
negatively affects the rate of population
growth
• Limiting factors may be density-dependent or
density independent.
Density Dependent Limiting Factors
• Def: A limiting factor
that is caused by
increasing population
density
• Examples: famine,
disease, parasitic
infections, pollution
Density Independent Limiting Factors
• Def: Limits on
population growth are
not due to increasing
numbers/density of the
population
• Examples: Violent
Weather, Natural
Disasters
S-Curves
• Populations rarely ever
reach biotic potential
• Competition and other
limiting factors cause
growth rates to slow
• The resulting growth
pattern looks like an S
Lag 2
• As density dependent
factors begin to affect
the rate of reproduction
and survival, the growth
rate may slow
• ENVIRONMENTAL
RESISTANCE
• This time of slowing
growth is LAG 2
How does the cause and rate of growth in
Lag 1 differ from Lag 2?
CARRYING CAPACITY (K)
• Every ecosystem has a
limit to how many
organisms in a
population can be
supported.
• This limit is determined
by the biotic and abiotic
composition of the
ecosystem
FLUX
• When populations
exceed the carrying
capacity of the
environment, the
population must
eventually decline
• Populations tend to
overproduce, once
again exceeding K.
Lab: Assessing Population Dynamics of
Saccharomyces cerevisiae
• Purpose: To assess the relationship between
concentration of limiting factors on the carrying
capacity of microorganism populations.
• Methodology: Spectrophotometry
• Hypothesis: How will the percentage of fructose
impact the changes in the size of the
Saccharomyces cerevisiae population? Which
populations do you expect to grow and
stabilize? Which populations will fail to thrive?
Saccharomyces cerevisiae
• “Brewer’s Yeast”
• Kingdom Fungi
• Utilize fructose and
other simple sugars as
the basis of their
metabolism
• Reproduce via binary
fission (asexual
reproduction)
Spectrophotometry
• Indirectly measures
population size of
microorganism culture
• The greater the percent
transmittance, the
smaller the population
Protocol
• 1) CLEAN YOUR TEST TUBES
• 2) Suspend each of the five cultures of
Saccharomyces cerevisiae with the stirring rod
• 3) Using a graduated dropper, transfer 1mL of
culture to a clean test tube
• 4) Dilute the culture sample with 8mL of tap
water (this should fill the test tube to the top)
• 5) Mix/invert and bring to instructor when that %
is called to be assessed
• 6) Determine % transmittance with the
spectrophotometer
• 7) Repeat steps 2-6 for all percentages