Population Ecology
Population Ecology is the part of ecology that focuses on the factors influencing the
population size, growth rate, growth forms and distribution of individuals inside a
population.
Important Terminology
Word Definition
Individual A single organism that forms a species.
Species A group of organisms with similar characteristics and produce fertile
offspring.
Population Group of organisms of the same species that are found in a specific
area.
Community Groups of different species occurring in a particular area.
Ecosystem A unit of plant and animal communities in interaction with each other
as well as non-living factors in a particular area.
Environment The external factors, biotic and abiotic surrounding an organism and
influencing its development and survival.
Habitat The specific environment in which a plant or animal species normally
occurs.
Population Size
➔ Population size refers to the total number of individuals in a population
➔ Population density refers to the number of individuals of a population per unit
area.
,Population parameters
Four main factors (Parameters) have an effect on population size:
➔ Natality- The birth rate of a population.
➔ Mortality- The death rate of a population.
➔ Immigration- A one-way movement of organisms into an area.
➔ Emigration- A one-way movement of organisms out of an area.
● Natality and immigration increase population size.
● Mortality and emigration decrease population size.
● A population where immigration and emigration do not take place is known as a
CLOSED POPULATION.
Determining Population Size
, Population size can be determined by direct or indirect techniques. The choice
regarding the technique is determined by:
➔ The size of the organisms.
➔ The mobility of the organisms.
Direct technique
Involves the total count of all individuals in the population. The direct counting is known
as a census. Census methods include:
➔ Direct contact counting of smaller-sized organisms.
➔ Direct counting from vehicle/helicopter/plane of larger organisms.
➔ Counting from aerial photographs taken of larger moving organisms.
Indirect technique
Involves the counting of only part of the population. The tally/count is used as a sample
to determine the total estimated population. It includes the following:
➔ Mark-recapture technique.
➔ Quadrant technique.
Mark-recapture technique
➢ A specific area is demarcated.
➢ A number of individuals are caught, counted and marked as the 1st sample.
○ The marked individuals are released back into the environment.
○ Sufficient time must be allowed in order for the individual to mix with the
population.
➢ Another group is captured and marked as the 2nd sample.
➢ The 2nd sample is counted.
➢ The data is used to estimate the population size
○ Formula:
Population Ecology is the part of ecology that focuses on the factors influencing the
population size, growth rate, growth forms and distribution of individuals inside a
population.
Important Terminology
Word Definition
Individual A single organism that forms a species.
Species A group of organisms with similar characteristics and produce fertile
offspring.
Population Group of organisms of the same species that are found in a specific
area.
Community Groups of different species occurring in a particular area.
Ecosystem A unit of plant and animal communities in interaction with each other
as well as non-living factors in a particular area.
Environment The external factors, biotic and abiotic surrounding an organism and
influencing its development and survival.
Habitat The specific environment in which a plant or animal species normally
occurs.
Population Size
➔ Population size refers to the total number of individuals in a population
➔ Population density refers to the number of individuals of a population per unit
area.
,Population parameters
Four main factors (Parameters) have an effect on population size:
➔ Natality- The birth rate of a population.
➔ Mortality- The death rate of a population.
➔ Immigration- A one-way movement of organisms into an area.
➔ Emigration- A one-way movement of organisms out of an area.
● Natality and immigration increase population size.
● Mortality and emigration decrease population size.
● A population where immigration and emigration do not take place is known as a
CLOSED POPULATION.
Determining Population Size
, Population size can be determined by direct or indirect techniques. The choice
regarding the technique is determined by:
➔ The size of the organisms.
➔ The mobility of the organisms.
Direct technique
Involves the total count of all individuals in the population. The direct counting is known
as a census. Census methods include:
➔ Direct contact counting of smaller-sized organisms.
➔ Direct counting from vehicle/helicopter/plane of larger organisms.
➔ Counting from aerial photographs taken of larger moving organisms.
Indirect technique
Involves the counting of only part of the population. The tally/count is used as a sample
to determine the total estimated population. It includes the following:
➔ Mark-recapture technique.
➔ Quadrant technique.
Mark-recapture technique
➢ A specific area is demarcated.
➢ A number of individuals are caught, counted and marked as the 1st sample.
○ The marked individuals are released back into the environment.
○ Sufficient time must be allowed in order for the individual to mix with the
population.
➢ Another group is captured and marked as the 2nd sample.
➢ The 2nd sample is counted.
➢ The data is used to estimate the population size
○ Formula:
