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

• A group of interbreeding individuals of the same species that live in a particular area at a defined time.

Natality

• Number of births per 1000 people per year

births per yearcrude birth rate = total population X 1000

Mortality

• Number of deaths per 1000 people per year

deaths per yearCrude death rate = total population

X 1000

Density

• 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• Only a few animals per

unit area• Highly territorial,

solitary animals

High Density• Individuals crowded

together• Colonial organisms

Distribution

• How individuals are spaced in an area• 3 types of distribution

1. Random2. Clumped3. Uniform

Distribution - Random• Presence of one individual does not directly

affect the location of another individual. • Uncommon in animals • Often seen in plants

Distribution - Clumped

• Individuals are grouped in patches, sometimes around a resource

• The presence of one individual increases the probability of finding

another• E.g. Herding or highly social species (buffalo)

Distribution - Uniform

• Individuals are evenly spaced• Presence of one individual decreases the

probability of finding another close by

Pair Share Class

1. Describe why some organisms may exhibit a clumped distribution because of

a. Resources in the environmentb. A group social behaviour

Pair Share Class

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

Pair Share Class

3. Describe the type of environment that would encourage uniform distribution

Pair Share Class

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

a. Clumpedb. Randomc. Uniform

Age structure and Survivorship Curves

Survivorship• 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.

Survivorship

Your Task:

Biozone exerciseSurvivorship curves

286

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 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

An Expanding Population

A Stable Population

A Diminishing Population