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I. Population Growth Patterns
1. What is a population?
2. Resources determine how a given population will grow.
Exponential Growth (using algebra):
Exponential Growth (without using algebra): “doubling time”
Exponential Growth (without using algebra): The effect of
“doubling time”
The Emperor’s
Reward to the
Inventor of Chess:
“…give me one grain
of wheat for the first
square, two for the
second and so on,
doubling the grains
for each of the 64
squares of the chess
board.”
• a. EXPONENTIAL GROWTH happens when there are
UNLIMITED RESOURCES available to the population
(usually early in the population’s growth).
• Populations grow when:
birth rate + immigration > death rate + emigration
(# of organisms
moving in)
(# of organisms
moving out)
Can exponential growth
go on forever?
No.
3. Exponential growth is part of a more complete picture of
population growth known as “LOGISTIC GROWTH”. Logistic
growth curves demonstrate the natural (logical)
progression/phases of population growth from slow, to
moderate, to fast, to level or collapse.
STEADY STATE
C,D
GROWTH
LEVELING OFF
B
A
EVENTUALLY THE GROWTH
WILL LEVEL OFF OR
COLLAPSE. THIS ENTIRE
PROGRESSION IS KNOWN
AS LOGISTIC GROWTH.
or COLLAPSE?
E
4. Over time, in real environments, exponential growth can
not be sustained (not enough resources). So…
The population
growth may level
off. This is known
as reaching a
“STEADY STATE”.
This is also sometimes
referred to as an “SCurve”.
4. Over time, in real environments, exponential growth can
not be sustained (not enough resources). So…
The other possibility is
that the population will
COLLAPSE.
This is also
sometimes
referred to as a
“J-Curve”.
5. Reaching steady state or collapse is part of population
logistics because resources are finite. The theoretical
point beyond which a population can no longer be sustained
is known as the CARRYING CAPACITY (K).
Result:
Steady state or…
Collapse
II. Limiting Factors
1. Resources, nutrients (matter) and energy in short
supply, limit how large a population can grow,
therefore resources can be limiting factors.
2. Density-dependent limiting factors control population size
when a population is large and crowded.
a. EXAMPLES : competition, predation, parasitism and
crowding
3. Density-independent limiting factors control population
size regardless of whether a population is large or small.
a. EXAMPLES: natural causes such as geothermal activity,
extreme weather
(Steady
state/
S-curve)
Or not…
Sometimes populations grow beyond the “control” of
limiting factors…
THE END!?
(Collapse/
J-curve)