Population Dynamics

1
Population Dynamics

• Joohee Kim
• IB Biology
• Sec. II

2
Population

• Group of organisms of the same species
• Live in the same area at the same time
• Collection of inter-breeding organisms

3
Population Dynamics

• Short- and long-term changes in the size and age
  composition of populations
• Biological and environmental processes
  influencing changes

4
History

• Dominant branch of mathematical biology
• History of more than 210 years
• First principle
• exponential law of Malthus, modeled by
  Malthusian growth model

5
Malthusian Growth Model

• Simple exponential growth model
• Based on constant rate of compound interest
• Formula P(t) P0ert
• where P0 Initial Population
• r growth rate, t time

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Changes to Size of Population

• There are four ways in which the size of a
  population can change
• 1. Natality birth
• 2. Mortality death
• 3. Immigration move into area
• 4. Emigration move out of area

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Population Change

• Populations are often affected by all four of
  these things and the overall change can be
  calculated using an equation
• Population Change
• (natality immigration) (mortality
  emigration)

8
Population Growth Curves

• If the size of a population is measured
  regularly, a curve can be plotted.
• When a species spreads into a new area, the
  population growth curve is often sigmoid
  (S-shaped).

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3 Phases of Curve

• The three phases of the curve are explained by
  changes in natality and mortality.
• 1. Exponential Phase
• 2. Transitional Phase
• 3. Plateau Phase

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Exponential Phase

• Population increases exponentially
• Natality Rate gt Mortality Rate
• Resources needed by the population are abundant
• Diseases and predators are rare

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Transitional Phase

• Natality rate starts to fall
• Mortality rate starts to rise
• Still, Natality Rate gt Mortality Rate
• Rise less rapidly

12
Plateau Phase

• Natality Mortality
• Constant population size
• Reached carrying capacity (max population size
  that can be supported by environment)

13
Limiting Factors of Population

• Shortage of resources (food)
• More predators
• More disease or parasites
• Limit population increase because they become
  more intense/crowded as the population rises
• Reduce natality rate
• Increase mortality rate