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
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
