Question

What are the two methods of determining population density?

Answer 1

Two important measures of a population are

1. population size, which refers to the number of individuals, and

2. population density, which corresponds to the number of individuals per unit area or volume.

To estimate the size and density of populations ecologists use two methods namely

• Quadrats and
• Mark-recapture method.

1.Quadrat method

For immobile organisms (Eg:plants) or for very small and slow-moving organisms—plots called quadrats may be used to determine population size and density. Each quadrat marks off an area of the same size—typically, a square area—within the habitat. A quadrat can be made by staking out an area with sticks and string or by using a wood, plastic, or metal square placed on the ground.

After setting up quadrats, researchers count the number of individuals within the boundaries of each one. Multiple quadrat samples are performed throughout the habitat at several random locations, which ensures that the numbers recorded are representative for the habitat overall. In the end, the data can be used to estimate the population size and population density within the entire habitat.

2. Mark-recapture method

For mobile organisms , like mammals, birds, or fish, a technique called the mark-recapture method is used to determine population density. This method involves capturing a sample of animals and marking them in some way—for example, using tags, bands, paint, or other body markings. Then, the marked animals are released back into the environment and allowed to mix with the rest of the population.

Later, a new sample is collected. This new sample will have some individuals that are marked—recaptures—and some individuals that are unmarked. Using the ratio of marked to unmarked individuals, scientists can estimate how many individuals are in the total population.