Population = all members of same species (interbreeding organisms) within an ecosystem.

1
Population Growth

• Population all members of same species
  (interbreeding organisms) within an ecosystem.

2
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.

3
Biotic Potential

• Maximum rate at which a population can increase
  in ideal conditions.
• Biotic Potential is affected by the organisms
• Lifespan
• Age at first reproduction
• Frequency of reproduction
• Clutch size (how many offspring produced)
• Length of reproductive capability

4
Exponential growth of 2 organisms with different
biotic potentials

• Some algae divide every 20 minutes it takes 220
  minutes to reach a population of about 2000.
• Osprey 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.

5
Reality Check There are limits to exponential
growth !

• Population growth is limited byenvironmental
  resistance
• Density - Dependent Factors (tend to be biotic)
• 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

6
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.

7
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

8
What happens if a population exceeds carrying
capacity?

• Some populations grow too fast
• Population overshoots resources
• Population crashes

9
Sometimes they overshoot but are able to stabilize
10
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.

11
Predator-Prey population trends
12
Human Population GrowthWhen will we hit
carrying capacity?
Advances have increased the earths carrying
capacity and pop size