The notes above provide an incredibly detailed summary of the Population Ecology section of the Life Science syllabus of the IEB curriculum.
The notes above have been used to complete the grade 12 year with ease and confidence.
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:
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