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Summary Grade 12 Life Science: environmental studies notes
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detailed notes and diagrams on population ecology, social organisations, environmental studies
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GRADE 12POPULATiON
ECOLOGY
SUMMARY
, Population ecology
Population Size
Refers to the total number of individuals in a population
Population density refers to the number of individuals of a popular per unit area
Birth Rate Is the one way movement of organic into
↳ number of live births per thousand per year an area where they become established
Natality Immigration
-
Mortality’
-* Population Size
Emigration Does not occur in
Death Rate
One way moment of organisms out closed population
↳ number of deaths per 1000 individuals of an area to become established
ECOLOGY : The study of the interactions of organisms with their physical and biological environments.
Population Ecology: The fluctuations in the size of a population and the factors (physical and social) that regulates these fluctuations.
Environmental Resistance: The total number of factors that stop a population from reproducing at its maximum rate.
↳ Limiting factors build up this.
Eventually a balance is reached: Population stabilises. This is the carrying capacity.
Population fluctuates around carrying capacity = self-regulating.
Carrying Capacity: The population density that the environment can support. The pop fluctuates around the carrying capacity.
T Physical factors eg. rainfall, temperature, humidity, acidity
- Catastrophic events eg. flood, fire, drought, volcano
7 Density Independent 7
LIMITING FACTORS: Build up environmental resistance ~
Density Dependent 7
- Competition
>
- Predators
>
- Disease.
STABLE AND UNSTABLE POPULATIONS
Stable: numbers decrease when size exceeds carrying capacity and increase when numbers fall below capacity
• Unstable: Population exceeds carrying capacity:
- rapid deterioration of population & habitat
- cant, support population = extinction
Direct
DETERMINING To choose which technique consider : size and mobility
Indirect
POPULATION SIZE
7 Direct contact counting of smaller organisms or humans
DIRECT TECHNIQUES
Involves the total count of individuals in the population & Direct counting from a vehicle / helicopter/ plane of larger organisms
Direct counting is known as a census S Counting from an aerial photograph taken of larger moving organisms
INDIRECT TECHNIQUES
Counting only a part of the population
Used as a sample to determine total estimated population ONLY VALID
Mark Recapture Method ⦾ MARKINGS : visible and not harm the individuals and
↳ a specific area is demarcated affect their movements
↳ a number of individuals are caught, counted and marked -> 1st sample ⦾ 1st sample should be allowed enough time to mix w/ rest
↳ first sample re.eased back into the environment of population
↳ sufficient time for first sample to mix with the rest of the population ↳ period between markings should be sufficient so no
↳ another group of individuals are caught and counted -> 2nd sample deaths or births occur
↳ this data is used to determine estimated population size:
⦾ has to be in closed population
total # Of
animals
1n
1st sample
total #
↳of animals BIG XBIG
P =
und
mXS
in
sample
estimatea P
SMALL
-
> =
Size
t - total marked
individuals 2nd
in
sample
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