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

Aim

Our aim is to study plant population frequency by quadrat method.

Theory

In ecology it is useful to know the frequency of certain plant species in a certain place, or at a certain time. Frequency can be defined as the degree of uniformity of the occurrence of individuals of a species within a plant community.  However, finding the frequency of plant species is very difficult for a large populations or extensive habitats. A widely used method for plant frequency sampling is by quadrat method.

Quadrat Method

Scientists usually calculate the plant population frequency using the quadrat method. A quadrat is a sample plot of a specific size used for the study of population or a community. Quadrats are used in many different scientific disciplines like vegetation assessment, including plant density, plant frequency and plant biomass. Frequency is highly influenced by the size and shape of the quadrats used. The area that is chosen for study must not be so big that it cannot be sampled adequately, or so small that the habitat is difficult for sampling. For herbaceous vegetation a metre square quadrat is normally used.

Frequency

Determining plant population frequency using quadrat method has become popular primarily because it is relatively simple and objective. Frequency indicates the number of times a plant species is present within a given number of sample quadrats. It is measured by noting the presence of a species in random sample areas which are distributed as widely as possible throughout the area of study. Once analyzed, the sample data enables the scientist to calculate population frequency of the entire population by the following method:
%Frequency=(Number of sampling units in which the species occurs)/(Total number of sampling units employed for the study)*100

How to calculate population frequency?

The image below depicts a plot which is divided into seven quadrats.

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

Observe the presence sunflower plant in each quadrat.  In this case, sunflowers are present in five quadrats among the seven.

Hence, the percentage frequency of sunflower is:

%Frequency=5/7*100=71.42

Variations in Plant Distribution

Variation in distribution is caused by several factors like soil conditions, vegetative propagation, quantity and dispersal of seeds, grazing or other biotic activities and predation by insects or diseases. Some species abundantly spread all over the area have a chance of occurring in all the sampling quadrats and therefore, its frequency will be 100. The plants with high frequency are wide in distribution.

Learning Outcomes:

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

Materials Requires

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

Real Lab Procedure

  • In the selected site of study, hammer the nails firmly in the soil 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.     
  • Select the plant species for study of the population frequency.
  • Observe the presence of species “A” in the first quadrat and mark it in the table.
  • Similarly, check for the presence of species “A” in other quadrats respectively and record the data in the table.
  • Observe the presence of species “B” in all quadrats and mark it in the table.
  • Repeat the same procedure for species C and record the data in the table.
  • We can calculate the frequency of plant populations by this equation:
  • Percentage Frequency=(Number of sampling units in which the species occurs)/(Total number of sampling units employed for the study)*100

Observations

Plant Species
Quadrats employed in the study
Number of quadrats in which the species is present (N)
Percentage Frequency F=N/Q*100
 
I
II
III
IV
V
VI
VII
VIII
IX
X
 
 
A
P
P
 
P
 
 
P
 
P
 
5
50%
B
 
 
 
 
P
 
 
 
 
 
1
10%
C
 
P
 
P
 
P
 
 
 
P
4
40%

Frequency value indicates the number of times a plant species is present within a given number of sample quadrats.

Simulator Procedure (as performed through the Online Labs)

  • Click on the popup corresponding to each quadrat to enlarge the view.
  • You can select the environment for study from the ‘Select the environment’ drop down list.
  • Observe the presence plant species in the quadrat.
  • Enter 'Y’ in the worksheet if a particular plant species is present or ‘N’ if it is not present.
  • Click on the back button to show normal view of the quadrat.
  • Based on the values entered, the worksheet gives the plant population frequency for each species.
  • You can redo the experiment by clicking on the ‘Reset’ button.
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FAQs on Theory & Procedure, Study of Plant Population Frequency by Quadrat Method - Additional Study Material for NEET

1. What is the quadrat method of studying plant population frequency?
Ans. The quadrat method is a technique used to study the distribution and abundance of plant populations in a given area. It involves selecting a square or rectangular frame called a quadrat and placing it randomly or systematically within the study area. The number of individuals of each plant species within the quadrat is then counted, providing an estimate of the plant population frequency.
2. How is the quadrat method useful in studying plant populations?
Ans. The quadrat method allows researchers to gather quantitative data on plant populations, such as the number of individuals of each species in a given area. This information can be used to analyze the spatial distribution, density, and diversity of plant communities. It also helps in monitoring changes in plant populations over time and assessing the impact of environmental factors on their distribution.
3. What is the procedure for conducting a plant population study using the quadrat method?
Ans. The procedure for conducting a plant population study using the quadrat method involves the following steps: 1. Select the study area and determine the size and number of quadrats. 2. Randomly or systematically place the quadrats within the study area. 3. Count the number of individuals of each plant species within each quadrat. 4. Repeat the process for multiple quadrats to obtain a representative sample. 5. Analyze the data to calculate population density, frequency, and other relevant parameters.
4. How can the quadrat method help in conservation efforts?
Ans. The quadrat method can be useful in conservation efforts by providing valuable information on the distribution and abundance of plant populations. This data can help identify areas of high biodiversity and prioritize conservation efforts accordingly. It can also assist in monitoring the success of conservation interventions and assessing the impact of habitat restoration projects on plant populations.
5. Are there any limitations to the quadrat method in studying plant population frequency?
Ans. Yes, there are some limitations to the quadrat method. Firstly, the accuracy and representativeness of the data collected can be influenced by the size and number of quadrats used, as well as the placement method. Secondly, the quadrat method may not be suitable for studying plants with large or highly mobile individuals. Additionally, the method may not account for all plant life stages, such as seeds or germinating individuals, which could affect population frequency estimates.
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