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Population. Learning outcomes for today. Define a population and describe the attributes that make up that population Describe the 3 types of population distribution Work in a pair to learn about survivorship curves and age structure. Definition.

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learning outcomes for today
Learning outcomes for today
  • Define a population and describe the attributes that make up that population
  • Describe the 3 types of population distribution
  • Work in a pair to learn about survivorship curves and age structure
  • A group of interbreeding individuals of the same species that live in a particular area at a defined time.
  • Number of births per 1000 people per year

births per year

crude birth rate = total population

X 1000

  • Number of deaths per 1000 people per year

deaths per year

Crude death rate = total population

X 1000

  • Number of individuals of a population per unit area of habitat at a specific time.
    • E.g. Pine trees per hectare of the Urewera forest in 2007
    • E.g. Diatoms per cubic metre of sea water taken of Raglan beach in 2006
Low Density

High Density

Individuals crowded together

Colonial organisms

  • Only a few animals per unit area
  • Highly territorial, solitary animals
  • How individuals are spaced in an area
  • 3 types of distribution
    • Random
    • Clumped
    • Uniform
distribution random
Distribution - Random
  • Presence of one individual does not directly affect the location of another individual.
  • Uncommon in animals
  • Often seen in plants
distribution clumped
Distribution - Clumped
  • Individuals are grouped in patches, sometimes around a resource
  • The presence of one individual increases the probability of finding


  • E.g. Herding or highly social

species (buffalo)

distribution uniform
Distribution - Uniform
  • Individuals are evenly spaced
  • Presence of one individual decreases the probability of finding another close by
pair share class
Pair Share Class
  • Describe why some organisms may exhibit a clumped distribution because of
    • Resources in the environment
    • A group social behaviour
pair share class1
Pair Share Class

2. Describe a social behaviour found in some animals that may encourage a uniform distribution

pair share class2
Pair Share Class
  • Describe the type of environment that would encourage uniform distribution
pair share class3
Pair Share Class

4. Give an example of each of the following types of distribution patterns

  • Clumped
  • Random
  • Uniform
  • There are three types of survivorship curves
    • Type I
      • Mortality is very low in the infant and juvenile years, and throughout most of adult life. Mortality increases rapidly in old age.
    • Type II
      • Mortality is relatively constant through all life stages (no one age is more susceptible than another)
    • Type III
      • Mortality is very high during early life stages, followed by a very low death rate for the few individuals reaching adulthood.
your task
Your Task:

Biozone exercise

Survivorship curves


population age structure
Population Age Structure
  • The age structure of a population refers to the relative proportion of individuals in each age group in the population.
  • The population is usually divided into three groups
    • Pre-reproductive
    • Reproductive
    • Post-reproductive
population age structure1
Population Age Structure
  • This is usually shown as a age pyramid. The shape of the pyramid show different things
    • True pyramid – an expanding population
    • Bell shaped – a stable population
    • Urn shaped – a diminishing population