Gina Brown
Environmental Studies
Strand 1 – Paper 1
Matric 2022
Population Ecology
Population A group of organisms of the same
species living in the same definable area
or habitat such that random interbreeding
can occur
Species A category used in the classification of
organisms that consists of a group of
individuals with similar characteristics that
can breed among themselves and
produce fertile offspring
Individual A single organism capable of
independent existence
Community Different populations that interact with
one another
Ecosystem Refers to the interactions between a
community of organisms (as the biotic
factors) and the abiotic/physical factors in
that locality
Ecological niche The particular combination of abiotic and
biotic factors that determine where a
species can survive and reproduce
Population size
Population Ecology: the study of factors affecting the sizes of different populations
Population Size: refers to the number of individuals in a population; also deals with the
interactions between individuals in a population & interactions between different
populations
- When tracking population movements, it’s useful to refer to the density (no. of
individuals in a unit area) of a population
- Populations very seldom stay the same size, but vary both seasonally and
annually depending on resource availability
- Availability of resources affect the 4 parameters that result in changes in
population size
1
, Gina Brown
4 Parameters affecting population size
1. Natality
- natural ability of a population to increase as shown by the birth rate in animals
and the production of seeds in plants
- % Increase of the population per unit time
- humans: expressed as the number of births per 1000 persons per year
Reproductive strategies:
R – strategy K – strategy
- produce large numbers of offspring - produce only a few offspring
- lack parental care - high level of parental care
- only few of the offspring survive - have a good chance of survival
(high juvenile mortality)
- often pioneer species (first to - climax species found with a
inhabit a new area) which invade population density that is close to
habitats rapidly and rely on carrying capacity of habitat
reproducing quickly to exploit
natural resources before
competitors come
Type 3 – concave survivorship curve Type 1 – convex survivorship curve
Fish, insects, frogs, bacteria Birds and mammals
2. Mortality
- rate at which individuals of a population die
- humans: number of deaths per 1000 individuals per year
- each species has a particular pattern of mortality and can be
plotted on a graph of the no. of deaths per 1000 individuals
over time (survivorship curve)
Survivorship Curves
Type I – convex - most offspring survive to adulthood
survivorship curve - mostly the old individuals that die
- K-strategists
Type III – concave - Few offspring reach adulthood
survivorship curve - Mostly young individuals that die and as th
offspring age, there is a decrease in morta
- R-strategists (when the young are older an
better able to fend for themselves, there is
improvement in life expectancy)
Type II – straight line - Young individuals are as likely to die as old
survivorship curve - Songbirds/ white stinkwood/ hydra
2
, Gina Brown
3. Immigration (into)
Refers to individuals entering an area from another area; occurs especially when a
population colonizes a favourable new habitat
4. Emigration (exit)
Refers to individuals leaving an area; occurs especially when an area becomes
overpopulated, resulting in a lack of food/space
Closed population No movement of animals into or out of population, therefore
only affected by mortality and natality
i.e., fenced nature reserves
Open populations Most natural populations allow individuals to enter and leave
the population. Immigration and Emigration are seasonal
events and may occur as seasons change and resources
become scarce.
Population density may change annually depending on the
relative ability of resources in different areas
Estimating population size
A. Direct Techniques: techniques here an effort is made to count every individual in a
community; no statistical calculations involved. Organisms must be stationary, sessile,
slow-moving, or very big.
1. Census
- Estimate human population and large mammals
2. Aerial photography
- Airplane flies in straight line, backwards and forwards over a whole area, taking
photographs of the whole area
- Photographs developed and placed together to form an aerial picture of the area
and individuals are then counted
- Depends on:
o Terrain type (not very hilly)
o Vegetation type (tall trees)
o Individual type
3
Environmental Studies
Strand 1 – Paper 1
Matric 2022
Population Ecology
Population A group of organisms of the same
species living in the same definable area
or habitat such that random interbreeding
can occur
Species A category used in the classification of
organisms that consists of a group of
individuals with similar characteristics that
can breed among themselves and
produce fertile offspring
Individual A single organism capable of
independent existence
Community Different populations that interact with
one another
Ecosystem Refers to the interactions between a
community of organisms (as the biotic
factors) and the abiotic/physical factors in
that locality
Ecological niche The particular combination of abiotic and
biotic factors that determine where a
species can survive and reproduce
Population size
Population Ecology: the study of factors affecting the sizes of different populations
Population Size: refers to the number of individuals in a population; also deals with the
interactions between individuals in a population & interactions between different
populations
- When tracking population movements, it’s useful to refer to the density (no. of
individuals in a unit area) of a population
- Populations very seldom stay the same size, but vary both seasonally and
annually depending on resource availability
- Availability of resources affect the 4 parameters that result in changes in
population size
1
, Gina Brown
4 Parameters affecting population size
1. Natality
- natural ability of a population to increase as shown by the birth rate in animals
and the production of seeds in plants
- % Increase of the population per unit time
- humans: expressed as the number of births per 1000 persons per year
Reproductive strategies:
R – strategy K – strategy
- produce large numbers of offspring - produce only a few offspring
- lack parental care - high level of parental care
- only few of the offspring survive - have a good chance of survival
(high juvenile mortality)
- often pioneer species (first to - climax species found with a
inhabit a new area) which invade population density that is close to
habitats rapidly and rely on carrying capacity of habitat
reproducing quickly to exploit
natural resources before
competitors come
Type 3 – concave survivorship curve Type 1 – convex survivorship curve
Fish, insects, frogs, bacteria Birds and mammals
2. Mortality
- rate at which individuals of a population die
- humans: number of deaths per 1000 individuals per year
- each species has a particular pattern of mortality and can be
plotted on a graph of the no. of deaths per 1000 individuals
over time (survivorship curve)
Survivorship Curves
Type I – convex - most offspring survive to adulthood
survivorship curve - mostly the old individuals that die
- K-strategists
Type III – concave - Few offspring reach adulthood
survivorship curve - Mostly young individuals that die and as th
offspring age, there is a decrease in morta
- R-strategists (when the young are older an
better able to fend for themselves, there is
improvement in life expectancy)
Type II – straight line - Young individuals are as likely to die as old
survivorship curve - Songbirds/ white stinkwood/ hydra
2
, Gina Brown
3. Immigration (into)
Refers to individuals entering an area from another area; occurs especially when a
population colonizes a favourable new habitat
4. Emigration (exit)
Refers to individuals leaving an area; occurs especially when an area becomes
overpopulated, resulting in a lack of food/space
Closed population No movement of animals into or out of population, therefore
only affected by mortality and natality
i.e., fenced nature reserves
Open populations Most natural populations allow individuals to enter and leave
the population. Immigration and Emigration are seasonal
events and may occur as seasons change and resources
become scarce.
Population density may change annually depending on the
relative ability of resources in different areas
Estimating population size
A. Direct Techniques: techniques here an effort is made to count every individual in a
community; no statistical calculations involved. Organisms must be stationary, sessile,
slow-moving, or very big.
1. Census
- Estimate human population and large mammals
2. Aerial photography
- Airplane flies in straight line, backwards and forwards over a whole area, taking
photographs of the whole area
- Photographs developed and placed together to form an aerial picture of the area
and individuals are then counted
- Depends on:
o Terrain type (not very hilly)
o Vegetation type (tall trees)
o Individual type
3
