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populations II notes


									No Population Can Continue to
Increase in Size Indefinitely
Population Size

Size governed by:
 Biotic potential – reproductive rate
 Environmental resistance –limiting
 Recruitment – surviving environmental
   resistance and breeding
aka Environmental Resistance
Limiting factors – prevent populations
 from growing forever.
  EX: water, light , temperature, oxygen, space

Optimum levels of all factors are
 necessary for survival.
  Zones of stress - above or below optimum
   levels, organism survives.
  Limits of tolerance - upper and lower limit of
   each factor, organism doesn’t survive.
  Range of tolerance – organism survives.
Limiting Factors

Density dependent limiting factors
  Greater population density, the more the
   limiting factor slows growth.

 The limiting factor is density independent if
  population begins declining rapidly.
  EX: temp., oxygen on insect population size
Logistic Growth

                         When limiting factors
                          limit population
    Carrying capacity    S-shaped curve

       Time (hours)
Logistic Growth of a Sheep Population on
the island of Tasmania, 1800–1925
    Carrying Capacity (K)
•    The number of organisms of one species that an
     environment can support.

•    Affected by limiting factors

 Not fixed

 Reproductive time lag may lead to overshoot
      Dieback (crash)

 Ecosystem damage may reduce area’s carrying
Exponential Growth, Overshoot, and
Population Crash of a Reindeer
Reproductive Strategies

1. R-selection (opportunists) -- high biotic
   potential; low recruitment
   Survive in changing ecosystems
   flies, rabbits, bacteria
2. K-selection (competitors) – low biotic
   potential; high recruitment
   Need stable ecosystems
   Primates, elephants
Positions of r- and K-Selected Species on
the S-Shaped Population Growth Curve
Factors affecting population growth
1. Predator/prey – balance one another; ex:
2. Introduced species – impact native species,
   decreases biodiversity
3. Plant/herbivore – herbivores control plant
4. Overgrazing –plants can’t reproduce fast
5. Plant competition – plants release chemicals
   to inhibit growth of other plants
Population Cycles for the Snowshoe
Hare and Canada Lynx
Predator-Prey Dynamics
                   Lotka-Volterra model -
                    a pair of differential
                    equations that
                    describe predator-
                    prey dynamics
                     Also works for herbivore-
                      plant & parasite-host
                     Developed by Alfred Lotka
                      & Vito Volterra in the
                   Population sizes
                     peak of the predator lags
                      behind the peak of the
Why do we care?

                   Predators and prey
                    influence one
                    another's evolution.
                   Traits that enhance a
                    predator's ability to
                    find and capture prey
                    will be selected for
                   Traits that enhance
                    the prey's ability to
                    avoid being eaten
                    will be selected for.
Humans Are Not Exempt from
Nature’s Population Controls
  Potato crop in 1845

Bubonic plague
  Fourteenth century

  Global epidemic
Case Study: Exploding White-Tailed
Deer Population in the U.S.
1900: deer habitat destruction and
 uncontrolled hunting
1920s–1930s: laws to protect the deer
Current population explosion for deer
  Lyme disease
  Deer-vehicle accidents
  Eating garden plants and shrubs
Ways to control the deer population

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