Summary
Summary Population and Ecology Grade 12(Matric)/IEB
- Course
- Life Sciences
- Institution
- 12th Grade
Summary of the first section of Population and Ecology, Grade 12 IEB.
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Population and EcologyDefinitions:
• Individual – refers to a single/ separate organism, which may be an animal or
plant that is capable of existing independently.
• Population – refers to a group of individuals which are linked to the same type
of species, enabling them to breed with each other.
• Community – refers to a group which resides in different populations, that are
all living amongst each other and are engaging within a specific area.
• Ecosystem – refers to all organisms which reside within a specific area and
engage with each other as well as the physical environment surrounding them.
Population Size
-
Definition of Population Size:
Is regarded as the total amount of individuals residing within a population. It may
increase or decrease over a certain period depending on a change happening with one
or more of the below factors:
• Natality – regarding the birth rate for animals or the creation of seeds within
plants.
• Mortality – regarding the death rate.
• Immigration – consisting of individuals/groups who relocate into a population
to stay.
• Emigration – consisting of individuals/groups which leave a population to
never return.
Therefore, a population will:
• Increase as the birth and immigration rates exceed the death and emigration
rates.
• Illustrate a decrease or decline in the death and emigration rate as it exceeds
the birth and immigration rates.
• Remain consistent and reach a form of equilibrium once both the birth and
immigration rates are equal to the death and emigration rates.
, • When paying specific attention to a closed population, in which there is no
form of immigration or emigration, the only factors to consider are the birth
and death rates (only two factors which affect it).
• Population size may show signs of fluctuation which occurs seasonally or
annually, this is dependent overall on the number of available resources.
Limiting Factors present:
These consist of factors which focus on helping regulate population growth – known as
Limiting Factors.
These may be:
- Density-independent factors limit a population’s growth because of influencing
natural factors and not due to the density or number of organisms. Ex:
- Physical factors, such as temperature, rainfall, humidity, salinity, and
acidity.
- Catastrophic events, such as floods, storms, droughts, fires, tsunamis,
eruptions of volcanoes and earthquakes.
- Density-dependent factors have a greater effect in terms of when a population's
density is high. This is since when organisms are crowded more, they:
- Compete for more resources such as food, water, light, oxygen, area, and
shelter.
- Can easily be found by predators.
- Can spread diseases and parasites more rapidly among each other.
These limiting factors all summed up together created Environmental resistance.
Definition = Environmental Resistance – the total amount/sum of contributing factors
which stop or disrupt a population from reproducing at its potential maximum rate.
Carrying Capacity:
- Over time a form of balance is reached which enables the population to
stabilize within a particular size or number. This can be described as the
carrying capacity.
- Carrying Capacity – The total maximum population size that the
environment can handle/maintain.
The issues which surround the carrying capacity for a particular group or species:
What is a stable population?
- A population whose numbers are decreased when its size exceeds the
carrying capacity.
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