ENVIRONMENTAL STUDIES NOTES:
Individual - a single organism that forms part of a species
Species - a group of organism with similar characteristics, which produce fertile o spring
Population - a group of organisms of the same species that are found in a particular area and
can crossbreed freely
Community - a group of populations occurring in a particular area
Ecosystem - a unit of plant and animal communities in interaction with each other as well as
with the nonliving factors in a particular area
Environment - the external factors, biotic and abiotic, surrounding an organism which
influence its development and survival
Habitat - the specific environment in which a plant/animal species normally occurs
POPULATION SIZE
Population size - total number of individuals in a population
Population density - the number of individuals of a population in a specific area (per unit area)
Population parameters:
Natality - the birth rate of a population, normally expressed as a number of live births per thousand individuals per year
Mortality - the death rate of a population, normally expressed as the number of deaths per thousand individuals per year
Immigration - the one-way movement of organisms into an area where they become established
Emigration - the one-way movement of organisms out of an area to become established
Closed population - a population where immigration and emigration do not occur
Change in population = (Natality + Immigration) - (Mortality + Emigration)
*in a closed colutlation, sub 0 into Immigration and Emigration
DETERMINING POPULATION SIZE:
Can be determined directly or indirectly, this is determined by the
size and mobility of the organisms
Direct techniques: Indirect techniques:
● Involves the total count of all individuals in the population ● Involves the counting of part of the population
● Census - directing counting of individuals ● This tally/count is used as a sample to determine the total
○ Direct contact counting (humans) estimated population size by means of statistical
○ Direct counting from vehicle/plane/helicopter calculations
○ Counting from aerial photographs ○ Mark-recapture technique
○ Quadrat technique
1
, Mark-recapture technique:
● A specific area is demarcated
● 1st sample - a number of individuals are caught, counted and marked
● The marked individuals are released back into their environment
● Su cient time must be allowed for the marked individuals to mix with the rest of the population
● 2nd sample - another group of individuals is caught and counted
● Can be made more accurate when repeated and calculating the average population size
● The data is used to estimate the population size using the following formula:
M ×S P - estimated population size
P = T
M - 1st sample
S - 2nd sample
T - number of marked individuals in 2nd sample
Limitations:
● The marking methods should not injure/damage or a ect the movement/behaviour of the organism
● The marks should be clearly visible
● Allowed for enough time between samples, but brief enough for no deaths/births to occur
● Population must be closed
Quadrats:
● A quadrat is usually a square frame of metal, wood or plastic of known size
● An area where organisms must be counted is demarcated and the surface area is determined
● The quadrat is placed on the ground in the demarcated area and the organisms concerned are counted inside
● This is the number of individuals per unit area
● The process is repeated several times in di erent areas in the demarcated area
● The total number of individuals in the population is determined using the following formula:
Surf ace area of demarcated area
P opulation size = Average number of individuals per quadrat × Surf ace area of quadrat
Limitations:
● Through random sampling, each member of the population has an equal and independent chance of being included
● The exact number of organism in each quadrat must be known
● The surface area of the quadrat and demarcated area must be known
● The quadrat must be placed randomly in the demarcated area
POPULATION GROWTH FORMS
Geometric (J-shaped) growth form:
● A population can reach its full reproductive potential when it has
unlimited resources such as food, water, space and no predators
● These ideal environmental conditions result in the maximum possible
growth rate and population figures increase rapidly
Characteristics:
● Distinctive J-shape
● Initially increase in numbers is slow as there are few individuals
● In time, there is a sharp increase in individuals and the graph rises steeply. Geometric growth takes
place due to optimum environmental conditions
● A sudden standstill often occurs in the growth form when conditions suddenly become unfavourable,
environmental resistance, see density dependent factors of page --
● Once conditions are favourable, the growth pattern can be repeated
2
Individual - a single organism that forms part of a species
Species - a group of organism with similar characteristics, which produce fertile o spring
Population - a group of organisms of the same species that are found in a particular area and
can crossbreed freely
Community - a group of populations occurring in a particular area
Ecosystem - a unit of plant and animal communities in interaction with each other as well as
with the nonliving factors in a particular area
Environment - the external factors, biotic and abiotic, surrounding an organism which
influence its development and survival
Habitat - the specific environment in which a plant/animal species normally occurs
POPULATION SIZE
Population size - total number of individuals in a population
Population density - the number of individuals of a population in a specific area (per unit area)
Population parameters:
Natality - the birth rate of a population, normally expressed as a number of live births per thousand individuals per year
Mortality - the death rate of a population, normally expressed as the number of deaths per thousand individuals per year
Immigration - the one-way movement of organisms into an area where they become established
Emigration - the one-way movement of organisms out of an area to become established
Closed population - a population where immigration and emigration do not occur
Change in population = (Natality + Immigration) - (Mortality + Emigration)
*in a closed colutlation, sub 0 into Immigration and Emigration
DETERMINING POPULATION SIZE:
Can be determined directly or indirectly, this is determined by the
size and mobility of the organisms
Direct techniques: Indirect techniques:
● Involves the total count of all individuals in the population ● Involves the counting of part of the population
● Census - directing counting of individuals ● This tally/count is used as a sample to determine the total
○ Direct contact counting (humans) estimated population size by means of statistical
○ Direct counting from vehicle/plane/helicopter calculations
○ Counting from aerial photographs ○ Mark-recapture technique
○ Quadrat technique
1
, Mark-recapture technique:
● A specific area is demarcated
● 1st sample - a number of individuals are caught, counted and marked
● The marked individuals are released back into their environment
● Su cient time must be allowed for the marked individuals to mix with the rest of the population
● 2nd sample - another group of individuals is caught and counted
● Can be made more accurate when repeated and calculating the average population size
● The data is used to estimate the population size using the following formula:
M ×S P - estimated population size
P = T
M - 1st sample
S - 2nd sample
T - number of marked individuals in 2nd sample
Limitations:
● The marking methods should not injure/damage or a ect the movement/behaviour of the organism
● The marks should be clearly visible
● Allowed for enough time between samples, but brief enough for no deaths/births to occur
● Population must be closed
Quadrats:
● A quadrat is usually a square frame of metal, wood or plastic of known size
● An area where organisms must be counted is demarcated and the surface area is determined
● The quadrat is placed on the ground in the demarcated area and the organisms concerned are counted inside
● This is the number of individuals per unit area
● The process is repeated several times in di erent areas in the demarcated area
● The total number of individuals in the population is determined using the following formula:
Surf ace area of demarcated area
P opulation size = Average number of individuals per quadrat × Surf ace area of quadrat
Limitations:
● Through random sampling, each member of the population has an equal and independent chance of being included
● The exact number of organism in each quadrat must be known
● The surface area of the quadrat and demarcated area must be known
● The quadrat must be placed randomly in the demarcated area
POPULATION GROWTH FORMS
Geometric (J-shaped) growth form:
● A population can reach its full reproductive potential when it has
unlimited resources such as food, water, space and no predators
● These ideal environmental conditions result in the maximum possible
growth rate and population figures increase rapidly
Characteristics:
● Distinctive J-shape
● Initially increase in numbers is slow as there are few individuals
● In time, there is a sharp increase in individuals and the graph rises steeply. Geometric growth takes
place due to optimum environmental conditions
● A sudden standstill often occurs in the growth form when conditions suddenly become unfavourable,
environmental resistance, see density dependent factors of page --
● Once conditions are favourable, the growth pattern can be repeated
2
