Population is defined as the total number of organisms of the same species living together in a given area at a particular time in an ecosystem, the community is made up of many populations of different species.

Factors Affecting Population

Factors which may affect the population of organisms in a given habitat include :
  • Birth rate 
  • Mortality (death rate)
  • Immigration 
  • Availability of food
  • Seasonal climatic changes 
  • Breeding periods 
  • Natural disasters examples earthquake, volcano etc. 

Population Studies By Sampling 
   Population studies can easily be carried out in a habitat especially in a terrestrial habitat by sampling into making use of an instrument called a Quadrant or Transects. 
A Quadrant is a square frame made from thick wire used for determining the population of organisms per unit area of land or water. 

Population Size

This refers to the total number of the same kind in a given area or habitat.  Sarge population stands a better chance of surviving dangerous and unfavorable conditions such as fire, diseases etc. 


Choose and locate sample plot and identify the plant species in the plot measure the area using a measuring tape to know the area of the habitat throw or toss the quadrant randomly at intervals for up to 10 times or above. After each throw or toss record the number in area of quadrant, the total number of each species obtained from several throws (10times) divided by the number of the species per quadrant. The average when multiplied by the total area of the habitat and then divided by the area of quadrant gives the population size of the species.
Population density X Area of habitat habitat = p size.


     Population density is defined as the number of individual organism per unit area or volumes of the habitat. 
Mathematically it can be calculated as frequency of species = X
Numbers of toss or throws = Y
Therefore population density of species = Z/area of quadrant.