Measuring and Modeling Population ChangeSBI4U

Demography• The statistical study of the processes that change the size and

density of a population through time.• Why is Demography important?• Used to predict the growth of a population or develop plans to

protect endangered species.

• What are some factors that would change the size and density of a population through time?• Natality (birth rate), mortality(death rate), immigration, and

emigration are factors that generate changes in a population population dynamics

• How do ecologists record/follow these changes?• Routine sampling

• What are some types of sampling an ecologist would use?

Life Tables• What are some techniques demographers use?• Life table – summarizes the demographic characteristics of a

population• How are Life Tables created?

• Cohort

Population Dynamics• Fecundity is the potential to produce offspring in one lifetime• Varies from species to species

• What conditions could effect a population’s fecundity?• Environmental• Other regulating factors:• Generation time• Sex ratio• Parental care

Population Dynamics• Survivorship curves• Used to depict data collected on a life table• Displays the survival of individuals in a population over the lifespan

of the species.

• There are 3 general survivorship curve types:• I = many survive childhood and die of old age• Large animals with few young and high parental care• Long gestation periods

• II = consistent birth and death rate• Short gestation period, usually prey for

larger animals, feed on Type III

• III = high childhood mortality• Large number of offspring produced

Carrying Capacity• The carrying capacity is the

maximum number of organisms that can be sustained by available resources for a specific amount of time.

• K is the carrying capacity

• Determined by factors in the environment

Calculating Changes

• Open populations• Uses the equation above

• Closed populations• No immigration or emigration

• Biotic potential• The maximum rate of population growth under ideal conditions

Population Growth Models• Geometric growth • Geometric growth is growth

where organisms reproduce at fixed intervals at a constant rate

• Growth is intermittent• See example on page 663

• Exponential growth • Exponential growth is growth

where organisms reproduce at continuously at a constant rate

• Growth is continuous• See example on page 665

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Modeling Logistic Growth

Lag phase

Log phase

Stationary phase

Credits• http://commons.wikimedia.org/wiki/

File:CarryingCapacity_2.jpg• http://commons.wikimedia.org/wiki/

File:Survivorship_Curves.jpg• http://en.wikipedia.org/wiki/File:Population_curve.svg