- Variation In Population Size -
Plotting growth curves ⇒ When the population growth is slow over a long period of time then it is possible to plot the recorded numbers on a graph against time.
It's not possible if the population increase was rapid over a short period of time.
Example of this would be microorganisms
Graph A ⇒ shows what the curve will look when attempting to record the increasing population of the microorganism as they reproduce asexually increasing over a short period of time.
Graph B ⇒ shows what the curve will look when using logarithmic scale to represent the number of bacteria.
Population size
All the factors needed for the growth of the population are presented, there are no limiting factors although there are things that change in time which can affect population size including:
- Availability of resources
- Nesting sites
- Shelter
- Predation
- Parasites
- Change in weather/ seasons
As a result the population growth slows possibly ceases altogether and the population size may diminish.
Abiotic factors:
Abiotic conditions that influence the size of the population include:
- Temperature > each species has a different optimum temperature, further away from this optimum, the fewer individuals in a population are able to survive and smaller is the population that can be supported.
- Light > ultimate source of energy for most ecosystem
- pH > this affects the action of enzymes each enzyme has an optimum pH at which it operates most effectively
- Water and humidity > when water is of limited supply populations are small and only consist of species that are well adapted to living in dry conditions. Humidity affects transpiration rates in plants and evaporation of water from the bodies of animals.
Equations:
Population growth = [ births + immigration ] - [ deaths + emigration ]
Percentage population growth rate = population change during the period X 100
[ in a given period ] population at the start of the period
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