Science That Scares…
What are your inalienable rights?
• #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
• 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.
Predation can be a positive influence in
keeping invasive populations in check
around the carrying capacity (K)
Populations without predators often
drastically exceed the carrying capacity,
crash and fail to recover
HOW DOES THIS APPLY TO
HUMAN POPULATIONS?
HUMAN POPULATION GROWTH
Why is the log phase for human
growth so extreme? Or is it?
How big will it get?
• There are three major
prediction models for
the future (2050)
– 7.3 billion
– 9 billion
– 10.7 billion
• Most predictions
depend on the decline
in fecundity
Where will they all live?
Megacities & Suburban Sprawl
What about ZPG?
• Zero Population
Growth is a goal of
many nations
• China and other
nations are pushing
for replacement rate
reproduction
The future
(even with one-child policies)