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
crude birth rate =
births per year
total population
X 1000
Mortality
• Number of deaths per 1000 people per year
Crude death rate =
deaths per year
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. Random
2. Clumped
3. 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 environment
b. 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. Clumped
b. Random
c. Uniform
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 exercise
Survivorship 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