An in-depth summary of Population Ecology, including definitions, factors that affects a population, the methods of calculating the size of a population, the relationships between different species, ecological succession and social organization. These notes are summarized from the grade 12 Mind Act...
POPULATION ECOLOGY
Definition of individual, population, community and ecosystem
Size of population affected by immigration, emigration, mortality and births
Population ecology: the study of the interactions of organisms with their physical and
biological environments
Individual: a single organism capable of independent existence
Organism: an individual form of life composed of a
single cell or complex of cells that are capable of
growing and reproducing
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
Ecosystem: made up of groups of different species of organisms that interact with each
other
Biosphere: the part of the earth where living organisms are found
Population size: the total number of individuals in a population
What affects the size of a population?
- Natality: birth rate in animals/ production of seeds in plants
- Mortality: death rate
- Immigration: individuals moving into a population
- Emigration: individuals exit a population and do not return
Population will therefore:
Increase when birth & immigration exceed death & emigration
Decrease when death & emigration exceed birth and immigration
In a closed population (no immigration and emigration):
Only parameters affecting any change in population numbers will be birth and
deaths
, How is growth of a population regulated?
Few individuals: no resource shortage and no
predators = individuals increase exponentially
Many individuals: more demand for resources =
builds up environmental resistance with causes
birth rate/ immigration to decrease & death
rate/ emigration to increase
Environmental resistance: the total number of factors
that stop a population from reproducing at its
maximum rate
Eventually balance is reached & the population
stabilises at a particular size or number = carrying capacity
Carrying capacity: the population density that the environment can support
Population size fluctuates seasonally and annually depending on available resources
The population size of an ecosystem is self-regulating. All negative-feedback
mechanisms are examples of this self-regulation
Limiting factors:
Limiting factors: factors that help to regulate the growth of a population
Density independent factors: natural factors
- -physical factors. E.g. rainfall, temperatures
- Catastrophic factors. E.g. floods, fire
Density dependent factors: when population density is high
- Competing
- for resources
- More easily found by predators
- Spreading disease
Stable and unstable populations:
Stable: numbers decrease when size exceeds the carrying capacity but increase
again when numbers fall below the carrying capacity
Unstable: population far exceeds the carrying capacity. This results in the habitat:
- Deteriorating rapidly > leads to lowering carrying capacity
- Eventually not being able to support the population > possibly become extinct
How is population size estimated?
1. Direct methods: counting every individual (census)
Can only be used:
- Organisms are large enough to be seen
- The area is not too large
- When individuals are slow moving
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