Why is population density sometimes measured in terms of biomass rather than in terms of number?

Both options (a) and (b).

a-It provides a more meaningful measure when the considered organisms vary greatly in size.

b-It is a more convenient option when the population is large and counting individuals is impractical or time-consuming

c-It provides a relatively constant measure of population density.

d-Both options (a) and (b).

The measurement of population density is typically done by counting the number of individuals within a given area. However, in some cases, using biomass as a measure of population density is more appropriate.

Option (a) states that measuring population density in terms of biomass is more meaningful when the considered organisms vary greatly in size. This is because using biomass takes into account the weight or mass of the organisms, which can vary significantly even if the number of individuals is the same. For example, in a population of trees, using biomass would provide a better understanding of the overall biomass production and energy flow within the ecosystem, considering the different sizes of the trees.

Option (b) suggests that measuring population density in terms of biomass is more convenient when the population is large and counting individuals becomes impractical or time-consuming. This is especially true for populations that are difficult to observe directly or those that exist in vast areas. Instead of counting each individual, biomass can be estimated through sampling or indirect methods, making the measurement process more efficient.

For example: If there are 200 carrot grass plants but only one large banyan tree with a substantial canopy. If we solely consider the total number of individuals, it would appear that the population density of the banyan tree is much lower compared to that of the carrot grass. However, this would underestimate the important role played by the banyan tree in the community.

In such cases, alternative measures such as percent cover or biomass become more meaningful. Percent cover refers to the proportion of the area covered by a particular organism, while biomass represents the total weight or mass of the organisms. These measures take into account the spatial extent or the amount of resources utilized by an organism, providing a more comprehensive understanding of its ecological significance.

Using percent cover or biomass as measures of population size becomes particularly relevant when the population is large and counting each individual is impractical or time-consuming. In these situations, estimating the coverage or biomass through sampling or indirect methods allows for a more efficient assessment of population density.

Option (c) implies that using biomass as a measure of population density provides a relatively constant measure. Unlike counting the number of individuals, which can vary due to factors such as migration, birth, and death, biomass provides a more stable and reliable measure over time.

Therefore, both options (a) and (b) are correct as they highlight the advantages of using biomass as a measure of population density in certain situations.