Theory & Procedure, Study of Plant Population Density by Quadrat Method | Additional Study Material for NEET PDF Download

Aim

Our aim is to study plant population density by the quadrat method.

Theory

A population is a group of individuals of the same species which inhabit a particular space at a particular time. The number of individuals in a population never remains constant. It may increase or decrease due to many factors like birth rate, death rate and migration. The number of individuals of the species in any unit area at a given time is its population density. The unit area may be as small as 5 square centimeters to as large as 10 square metres, depending on the size and nature of the plant community under study.

Let’s understand the Quadrat Method.

Counting all individuals in a population is the most accurate way to determine its size. However, this approach is not usually feasible, especially for large populations or extensive habitats. Scientists usually calculate plant populations with the quadrat method. A quadrat is a square that encloses an area within a habitat.  For herbaceous vegetation, a metre square quadrat is normally used.

Once analyzed, the sample data enables the scientist to calculate the population size and population density for the entire population. Population density is calculated by counting all the individuals present at a given time in a given space, divided by the number of units of area or space.

Population density is calculated as follows:

Density   = (Total no.of individuals of the species in all the sampling unit (S))/(Total number of sampling units studied (Q))

Learning Outcomes:

• Students understand the term quadrat method.
• Students understand how to calculate plant population density.
• Students do the experiment better in the real lab having gone through the animation and simulation.

Materials Requires:

Real Lab Procedure

• In the selected site of study, hammer the nails firmly without damaging the vegetation.
• Fix four nails to make a square.
• Tie each end of the nails using a thread, to make a 1 m X 1 m quadrat.
• Similarly make nine more quadrats randomly in the site of study.     
• Count the number of individuals of a species “A” present in the first quadrat.
• Record the data in the table.
• Similarly count the number of individuals of the species “A” in other quadrats respectively and record the data in the table.
• Count the number of individuals of a species “B” present in the all quadrat.
• Record the data in the table.
• Repeat the same procedure for species C and record the data in the table.
• We can calculate the density of plant population by this equation:
• Density =Total number of individuals of the species in all the sampling  unit (S) / Total number of sampling units studied (Q)

Observations

The density value thus obtained is then expressed as number of individuals per unit area.

Simulator Procedure (as performed through the Online Labs)

• You can select the environment for study from the ‘Select the environment’ drop down list.
• Click on the popup corresponding to each quadrat to enlarge the view.
• Count the number of individuals of a species present in each quadrat and enter in the worksheet.
• Click on the back button to show normal view of the quadrat.
• Based on the values entered, the worksheet gives the plant population density for each species.
• You can redo the experiment by clicking on the ‘Reset’ button.