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Ecology
By Dr Mamdouh El-Sawi
From John E. Petersen
First lecture
Ecology
Greek Oikos = the home or household
ology = study of
•The study of relationships among
organisms and between organisms and
their environment
levels of ecological
organizations:
• Organisms- a unique individual.
• Populations- group of potentially interbreeding
individuals (i.e., species).
• Communities- all populations within an ecosystem
(i.e., multiple species).
ecosystems - community + physical environment.
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• Biomes.
• biosphere - ecosystems of the Earth.
A scaling hierarchy of natural science
• Hierarchy of matter
• Hierarchy of disciplines
(‘levels of
organization’)
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Biospherics
Environmental science
Systems ecology
Ecosystems ecology
Community ecology
Population biology
Organism biology
Histology
Cellular biology
Molecular biology
Molecular genetics
Chemistry
Subatomic physics
Causality from the
Reductionist perspective
Universe
Galaxies
Solar system
Planets
Earth
Biosphere
Biomes
Ecosystems
Communities
Populations
Organisms
Organ systems
Tissues
Cells
Organelles
Molecules
Atoms
Subatomic particles
Increasing scales of time and space
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5
Population
• Population is a group of individuals
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belongs to a species.
Inhabiting a give location.
They are alike.
They are capable of breeding with
one another.
Examples are: sunfish in a lake,
people in a city.
Population growth:
a) Exponential growth.
b) Limited growth.
• 1- a bacterium can divide by binary
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fission to produce two bacteria in 20min.
2-after another 20 min we’d have 4.
3-after another 20 min we’d have 8 and
so on.
4- after 24 we’d have 4 x 1021 bacteria
In this type of growth the size of
population increases exponentially; look
at fig (1).
Fig (1)
In reality this could never
happen. Because
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Nutrients would get used up.
Space would become scarce.
Waste products would accumulate.
Some members of the population would die.
and the growth curve would flatten out as
the population stabilized. Here, the
maximum population size is limited.