1. Joohee Kim IB Biology Sec. II
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

6. 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

7. 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).

9. 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

10. Exponential Phase Population increases exponentially
Natality Rate > Mortality Rate
Resources needed by the population are abundant
Diseases and predators are rare

11. Transitional Phase Natality rate starts to fall
Mortality rate starts to rise
Still, Natality Rate > 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