Measuring Biodiversity at the Species and Ecosystem Levels

Biodiversity or biological diversity refers to the variation of plants and animals within a given area. If the population of a particular species suddenly drops, there is loss of biodiversity. If a given area supports only two or three different species, there is very little biodiversity even when the population of such species are large. Thus, from the perspective of ecologists, biodiversity is characterized by two aspects. These are species richness and relative abundance. Species richness refers to the number of species. A high number is usually desirable but may sometimes reflect loss of biodiversity. For example, a surge in the population of rats meant that the area has significantly lost the population of snakes or other predators of rats. Relative abundance, on the other hand, refers to how the numbers of species varies from one place to another. Also known as equitability, relative abundance tells ecologists the spread of species. This is why a rainforest is considered more biologically diverse than a grassland. The analysis of the relationship of species richness and relative abundance provides a clearer picture of the state of biodiversity of a given area.

The importance of biodiversity is underlined by the many levels at which biodiversity is measured. It can be analyzed at a genetic level, at a species level, at an ecosytem level, and at a larger biome level. The majority of efforts towards the conservation of biodiversity utilized number estimates from measurements at the species level and at the ecosystem level. Measuring biodiversity at the species level is known as "alpha-diversity." Between the two previously described aspects of biodiversity, species richness takes greater importance at the species level. Determining the number of species in a given area is often a time-consuming tasks for field ecologists. Given a specific small area, the field ecologists count the number of different species. Obviously, such counting is not always possible and covering an entire ecosystem is impractical. This is why indices were formulated. The two commonly used indices are the Simpson Index and the Shannon Index.

The Simpson Index compares the number of a species to the total population of a given area. The simplest formula is D=∑(n/N)2. The small letter n refers to the total number of a particular species while the capital letter N refers to the total number of all species. The formulafor the Shannon Index, on the other hand, is more complicated and takes into consideration four factors, which are the number of species, the abundance of species, the relative abundance of species, and the total number of individuals.

Measuring biodiversity at the ecosystem level is essentially comparing the biodiversity of two or more ecosystems. This type of biodiversity is called beta-diversity. For example, the species richness of a particular plant in a savannah is compared to the species richness of the same plant in a grassland. The results of the comparisons will provide insights into the survival of the said plant and can prevent further loss of diversity. The species richness of a particular organism in one area can also be compared at different periods of time. This comparison can reveal whether the identified organism is facing stresses or possible extinction.