Transcript Biotic Potential

Population = all members of same species
(interbreeding organisms) within an
ecosystem.
Populations can grow
exponentially...
...If each organism has
multiple offspring.
For Example
• 1 fly lays about 120 eggs
• In one year, that one fly has
about 5 x 1012 great, great,
great, great grandchildren.
• This fly population is
meeting its Biotic Potential
because it is increasing at
the maximum rate possible.
Biotic Potential
• Maximum rate at which a population can increase
in ideal conditions.
Biotic Potential is affected by the organism’s
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Lifespan
Age at first reproduction
Frequency of reproduction
Clutch size (how many offspring produced)
• Length of reproductive capability
Exponential growth of 2 organisms
with different biotic potentials
• Bacteria divide every 20
minutes; it takes 220
minutes to reach a
population of about 2000.
• Eagles reproduce once a
year starting at age 4 (red)
or age 6 (green). It takes
about 23 years (red) or 32
years (green) to reach
2000 individuals.
Reality Check: There are limits
to exponential growth !
Population growth is limited by“environmental resistance”
Density - Dependent Factors (tend to be biotic)
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Limited resources (food, space, light for photosynthesizers)
Competition
Predation - increased prey means increased predation
Parasitism - spread more easily in high density pops
Density- Independent Factors (tend to be abiotic)
• Weather (e.g. plants, insects sensitive to extreme hot, cold)
• Natural disasters - fire, hurricanes, earthquake, volcanos
Some populations expand until they
reach equilibrium at their limit
• Exponential growth under
favorable conditions: food,
space available, little to no
predation, parasitism or
competition.
• Once the population size
matches the carrying
capacity of the ecosystem, its
growth slows and reaches
equilibrium.
Carrying Capacity
•Is the maximum population size that can be supported by an
ecosystem over the long term
•Is typically limited by the resources available in that ecosystem
What happens if a population
exceeds carrying capacity?
• Some populations
grow too fast…
• Population overshoots
resources…
• Population crashes
• E.g. Gypsy Moth
caterpillars can defoliate
the trees they live on so
quickly that their larvae
have nothing to feed on!
Sometimes they overshoot but
are able to stabilize
Predator - Prey relationships can
cause cyclical population curves
• When prey populations increase, more predation occurs
because- (1) predators encounter prey more often and
(2) more prey support a bigger predator population.
• When predators get too numerous, they reduce the prey
population, thus depleting their food supply.
• A change in the prey population illicits change in the
predator population and vice versa.
Predator-Prey population trends
Human Population Growth:
When will we hit carrying capacity?
Advances have increased the earth’s carrying capacity and pop size