Population ecology
- ecology = study of interactions of organisms with their physical and biological
environments
- Fluctuations in population ecology
- Population = group of organisms of the same species found in an area close
enough to interbreed
- Different populations form a community
- Communities and abiotic factors form an ecosystem
- A species is a group of closely related organisms that can produce fertile
offspring
Definitions
Biosphere = part of the earth where living organisms are found
Ecosystem = made up of groups of different species that interact with each other
and the abiotic factors
Organism = an individual form of life or an animal composed of a single cell or
complex of cells that are capable of growing and reproducing
Community = group of different species that inhabit and interact in a particular area
Species = closely related group of organisms that are very similar and are capable
of interbreeding and producing fertile offspring. Have the same number of
chromosomes and similar karyotype
Individual = single organism capable of independent existence
4 population parameters:
- natality (increase) (birth rate)
- Mortality (decrease) (death rate)
- Immigration (increase) (movement of individuals into a population)
- Emigration (decrease) (movement of individuals exiting a population)
- stable population (immigration and natality = emigration and mortality)
- Increased population (immigration and natality > emigration and mortality)
- closed population = no immigration or emigration (eg. Fish in a fish pond)
, - Open population = all 4 parameters
Regulating the growth of a population
- no shortage or resources and no predators will cause the individuals to
increase exponentially
- As numbers increase, more demands are made which builds up
environmental resistance
- Population stabilises around the carrying capacity
- Carrying capacity = the population density an environment can support
- Population fluctuates depending on resources
- Population size of ecosystem is self regulating
Limiting factors
- Environmental resistance
- the organism most adapted will survive
- Factors help regulate growth of population
Density independent factors
- limit the growth of a population as result of natural factors
- Physical factors like rainfall, global warming, earthquakes
- Volcanoes, floods, drought or habitat disruption
Density dependent factors
- have greater effect when population density is high
- When organisms get more crowded they need more resources, easier to find
by predators and spreads disease and parasites faster
- Disease, competition, predators, parasites or food
Stable population = population numbers fluctuates around carrying capacity with no
drastic increase or decrease
Unstable population = population numbers exceed carrying capacity which ends up
lowering the carrying capacity
Determining population size
- direct and indirect methods
- Direct is more accurate
Direct methods
- census
- Count every individual in a population
- For large, slow or stationary animals
- Better in small areas
- If area is large, aerial photos can be taken
, - Or helicopters can be used
Problems with a census
- People may not be home
- People may lie about income to avoid tax or about number of people in a
house
- Some places are hard to get to
Indirect methods
- sample number
Quadrat method
- total population = N
- N = (number in sample x whole habitat) / size of 1 quadrat
- Method:
- Measure size of total area/habitat
- Distribute quadrats at random
- Count individuals in each quadrat and get an average (used as number in
sample)
- Random sampling used to achieve true reflection of distribution
Mark-recapture method
- a known number of individuals is caught and marked, then released
- Suitable for mobile or hard to see animals
- N = estimated population
- N = (total number of marked animals x total number of animals caught in
second sample) / number of recaptured animals in second sample
- Method
- Mark out well defined area
- Capture and mark as many animals as possible
- Release back into environment and wait for them to mix
- Recapture as many as possible
- Count total caught and how many of them were recaptured
- Precautions: short time passes (no births/deaths), repeated several times, no
damage to animal, closed population
- ecology = study of interactions of organisms with their physical and biological
environments
- Fluctuations in population ecology
- Population = group of organisms of the same species found in an area close
enough to interbreed
- Different populations form a community
- Communities and abiotic factors form an ecosystem
- A species is a group of closely related organisms that can produce fertile
offspring
Definitions
Biosphere = part of the earth where living organisms are found
Ecosystem = made up of groups of different species that interact with each other
and the abiotic factors
Organism = an individual form of life or an animal composed of a single cell or
complex of cells that are capable of growing and reproducing
Community = group of different species that inhabit and interact in a particular area
Species = closely related group of organisms that are very similar and are capable
of interbreeding and producing fertile offspring. Have the same number of
chromosomes and similar karyotype
Individual = single organism capable of independent existence
4 population parameters:
- natality (increase) (birth rate)
- Mortality (decrease) (death rate)
- Immigration (increase) (movement of individuals into a population)
- Emigration (decrease) (movement of individuals exiting a population)
- stable population (immigration and natality = emigration and mortality)
- Increased population (immigration and natality > emigration and mortality)
- closed population = no immigration or emigration (eg. Fish in a fish pond)
, - Open population = all 4 parameters
Regulating the growth of a population
- no shortage or resources and no predators will cause the individuals to
increase exponentially
- As numbers increase, more demands are made which builds up
environmental resistance
- Population stabilises around the carrying capacity
- Carrying capacity = the population density an environment can support
- Population fluctuates depending on resources
- Population size of ecosystem is self regulating
Limiting factors
- Environmental resistance
- the organism most adapted will survive
- Factors help regulate growth of population
Density independent factors
- limit the growth of a population as result of natural factors
- Physical factors like rainfall, global warming, earthquakes
- Volcanoes, floods, drought or habitat disruption
Density dependent factors
- have greater effect when population density is high
- When organisms get more crowded they need more resources, easier to find
by predators and spreads disease and parasites faster
- Disease, competition, predators, parasites or food
Stable population = population numbers fluctuates around carrying capacity with no
drastic increase or decrease
Unstable population = population numbers exceed carrying capacity which ends up
lowering the carrying capacity
Determining population size
- direct and indirect methods
- Direct is more accurate
Direct methods
- census
- Count every individual in a population
- For large, slow or stationary animals
- Better in small areas
- If area is large, aerial photos can be taken
, - Or helicopters can be used
Problems with a census
- People may not be home
- People may lie about income to avoid tax or about number of people in a
house
- Some places are hard to get to
Indirect methods
- sample number
Quadrat method
- total population = N
- N = (number in sample x whole habitat) / size of 1 quadrat
- Method:
- Measure size of total area/habitat
- Distribute quadrats at random
- Count individuals in each quadrat and get an average (used as number in
sample)
- Random sampling used to achieve true reflection of distribution
Mark-recapture method
- a known number of individuals is caught and marked, then released
- Suitable for mobile or hard to see animals
- N = estimated population
- N = (total number of marked animals x total number of animals caught in
second sample) / number of recaptured animals in second sample
- Method
- Mark out well defined area
- Capture and mark as many animals as possible
- Release back into environment and wait for them to mix
- Recapture as many as possible
- Count total caught and how many of them were recaptured
- Precautions: short time passes (no births/deaths), repeated several times, no
damage to animal, closed population
