Question

In some cases, measuring population density by counting individuals may not be feasible. Mention two other parameters that can be used and justify their use with suitable examples.

Hint:

Use percent cover and biomass, with the Parthenium and banyan tree examples.

Answer 1

Step 1: Why counting can fail:
Population density is the number of individuals per unit area. But sometimes counting is not practical, or the number alone gives a wrong picture of the population. So we use other measures.

Step 2: Parameter 1: Biomass:
Biomass is the total dry weight (or living weight) of the organisms per unit area.
Example: in an area there may be 200 small Parthenium plants but only one huge banyan tree. The count makes the banyan look unimportant. Biomass shows the true size of the banyan population.

Step 3: Parameter 2: Percent cover:
Percent cover is the percentage of the area covered by a species.
Example: in an area with a huge number of small Parthenium plants, counting every plant is time-consuming. Measuring the percent cover of Parthenium is easier and more meaningful.

Step 4: Other indices:
For shy or secretive animals, indirect signs can be used instead. For instance, tiger census uses pugmarks and faecal pellets as an index of the population.

Final Answer:
Two parameters are biomass and percent cover (relative indices such as pugmarks are also accepted), each justified by the example above.