Covers the entire section on population ecology. Includes notes from the textbook, as well as additional class, video and research information, diagrams and practice questions.
Applicable to all IEB Grade 12s.
Written by a 90% < candidate.
Population ecology
Definitions:
Ecology: The study of the interactions of organisms with their physical and biological
. environments and how these determine the distribution and make up of
. populations within an ecosystem.
Population ecology: The fluctuations in the size of a population and the physical and social
. factors that regulates these fluctuations.
Organism: An individual form of life, such as a bacterium, fungus, protect plant or
. animal, composed of a single cell or a complex of cells that are capable of
. growing and reproducing.
Individual: A single organism capable of independent existence.
Species: A group of closely related organisms that are very similar to each other and
. are usually capable of interbreeding and producing fertile offspring.
Population: A group of organisms of the same species that occupy the same area and
. can breed freely with each other.
Community: A group of different species that inhabit and interact in a particular area.
Ecosystems: Made up of groups of different species of organisms that interact with each
. other and with the environment.
Biosphere: The part of earth where living organisms are found.
Demography: The statistical study of populations. It is used to predict how the size of a
. population will change.
Ecological niche: All conditions and resources necessary for survival.
Habitat: A type of place or part of an ecosystem occupied by an organism.
Niche: The specific functional role of an organism.
. The way it goes about living its life (what the organism does, and what is
. (done to the organism)
, Key features of a population:
1. Size
= is the total number of individuals in a population.
Has an important effect on the ability of the population to survive.
Example: A small population is more likely to become extinct:
- In the case of random events or natural disaster
- Due to inbreeding where the population is more genetically alike
- With reduced variability it is harder to adapt to changes
2. Density
= the number of individuals in a given area.
If the individuals are too far apart they may only rarely encounter one another resulting in
little reproduction.
Too close together, disease can be easily spread.
3. Dispersion
= the way in which the individuals are arranged.
(Effects mating and the land)
Example: penguins - uniform
Example: Seeds dispersed by wind - random
Example: Elephant herds - clumped
Population size
= the total number of individuals in a population
It can increase or decrease over time with a change in one or more of the following.
Population parameters:
1. Natality - birth rate in animals or the production of seeds in plants
2. Mortality - death rate
3. Immigration - individuals move into a population and stay
4. Emigration - individuals leave a population and do not return
Population size = (Natality - Mortality) + (Immigration - Emigration)
Note: For humans, natality and mortality are measure in the number of births or deaths per
1000 people in a year
A population will:
- Grow when natality and immigration exceed mortality and emigration
- Decline when mortality and emigration exceed natality and immigration
- Remain stable when natality and immigration approximately equal natality and emigration
In a closed population, with no immigration or emigration, the only parameters affecting any
change in population size will be natality and mortality.
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