Summary Environmental studies Gr 12 IEB & DBE notes
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Module
Life Sciences
Institution
12th Grade
Detailed notes of Gr 12 environmental studies section.
Including:
Definitions
Changes in population
Density independent and density dependent factors
Territoriality
Population growth forms
Carrying capacity
Sampling methods
Random sampling
Predator-prey relationships
Food webs...
, Population
Definitions
ecology
Species: a group of organisms that share similar characteristics, are
able to interbreed, produce viable & fertile offspring
Population: a group of organisms of same species, living in same
habitat & capable of random interbreeding
Community: a group of different populations living together in the same habitat.
Ecosystem: where all the biotic (living) components of an environment interact with each
other & with the abiotic (non-living) components.
Changes in a population
Population parameters, factors affect size of population. Availability of food, disease & habitat.
Factors can cause populations to either get bigger or smaller.
Population growth = [(natality + immigration) – (mortality + emigration)]
Populations increases, positive growth. Decreased population, negative growth.
Natality (birth rate) Mortality (death rate)
Rate at which new individuals are added to Rate at which new individuals are lost to
population though reproduction. Number of new population through death. Number of
individuals in a certain time period. Unit of time deaths in certain time period. Deaths occur
depends on rate of reproduction. Per second by disease, predation, parasitism, old age,
(bacteria), per month (rats), per year (humans). hunting, fishing, culling & harvesting.
Immigration (move into area) Emigration (move out of area)
Rate at which new individuals join Rate at which individuals from a
a population from somewhere else, population leave to go somewhere else.
permanent one-way movement into Permanent one-way movement of
population area. Leads to increase individuals out of population area. Leads
in population size in that area. to decrease in population size in that area.
, Seasonal & annual changes in population size
Population size fluctuates seasonally & annually depending on resources available.
In years of drought, have fewer young as not enough water & grazing larger population.
Migration = Population moves from original habitat, but returns later, driven by food availability.
The size of a population may fluctuate seasonally or annually, depending on environmental
factors and available resources.
Seasonal fluctuations: European swallow, during cold European winter, fly to southern
Africa, where temp more favourable & food plentiful. Also breed in Africa.
Annual fluctuations: migration of wildebeest annually in East Africa, for seasonal grazing.
Dependent on rainfall, spend wet season on grassy plains of southeast & dry season in
woodlands of northwest. Young between Jan & March, when grazing is plentiful.
Limiting factors on a population growth
Density independent factors
Factors not related to population density, same effect on a population regardless of size.
density-independent factors can Climate
lead to a drastic drop in
population, see graph below. Severe storms, sudden temperature
changes, usually permanent.
Numbers
Disasters
Floods, fires, drought, earthquakes, volcanic eruptions,
sea currents changes. Not permanent, possibility for
Time (years) populations to multiply & stabilize carrying capacity.
Density dependent factors Greater demand for food/water, increased competition.
Factors that take effect when population size/ Decrease in living space, reduced reproduction, stress.
Shelter shortage, exposure to bad weather conditions &
density increases. Bigger the population,
predators.
bigger the effect of these factors. Increase in predation because more food available.
The more individuals there are the more will Easier spreading of diseases & parasites, increase in
excretion, may poison the environment.
die or fail to reproduce.
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