HOW CAN THE BIODIVERSITY OF A LOCALITY BE MEASURED? - BIOLOGY - 2025

The biodiversity of a locality can be measured by knowing the taxonomic diversity and the levels of biodiversity -alpha, beta and gamma-, although there is no single measure that captures the concept of biodiversity in a value.

However, there are a number of empirical measurements that have allowed biologists to characterize and compare sites of interest. The best known indices are the species richness, the Simpson index and the Shannon index.

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Biodiversity is a term used to refer to the biological diversity of an ecosystem or locality. It can be defined as the sum total of all biotic variation, from the level of genes to that of the ecosystem.

Note that this concept is extremely broad and quantifying diversity has posed a series of challenges for biologists interested in measuring it.

What is biodiversity?

Biodiversity is the variety of life forms that exist within a limited area, call it a study site, ecosystem, landscape, among others. Biodiversity is defined, and quantified, in terms of an attribute that has two components: richness and uniformity.

The first of these, wealth, refers to the number of groups that are genetically or functionally related. In other words, richness is measured based on the number of species and the parameter is called species richness.

In contrast, uniformity is the proportion of species - or other functional groupings - at the site in question. The uniformity increases as the proportion of the species found in similar.

Likewise, a locality with a few very dominant species and a significant number of rare species is a region with low uniformity.

At what level is diversity studied?

Biological diversity can be approached at different levels. At the genetic level, diversity can be understood as the number of species or varieties that inhabit the ecosystem.

Leveling up, we can focus on it based on the forms of life present. If we are interested in studying biodiversity in a forest ecosystem, and we focus on plant life forms, we will be able to distinguish grasses, mosses, ferns, among others.

In a similar way, we can specify different functional groups in the study area. For example, we will group all organisms capable of fixing nitrogen into a single category.

How is biodiversity measured?

Generally, biodiversity is a measure that combines the two parameters mentioned above: richness and uniformity.

There are different indices and parameters used by biologists to quantify biodiversity. Below we will describe the most used and the most popular.

-Taxonomic diversity

If you want to assess community biodiversity in terms of taxonomic diversity, there are several measures to do so:

Species richness

It is one of the easiest and most intuitive ways to measure diversity. It is understood as the number of species that inhabit the community of interest.

To measure it, simply count the species. It is a parameter that does not take into account the abundance or distribution of each of the species.

Simpson index

This index measures the probability that two randomly chosen individuals from a sample are of the same species. It is quantified by taking the table of the proportional abundance of each species, and adding these values.

Shannon index

This index measures the uniformity of the importance values ​​across all the species that exist in the sample. When there is only one species, the index value is zero.

Thus, when all species are represented by the same number of individuals, the value is the logarithm of the total number of species.

-Levels of biodiversity

Biological diversity can be measured or monitored across different spatial scales. In this way, we can distinguish between alpha, beta, and gamma diversity.

Alpha diversity

It is also called species richness (parameter discussed in the previous section). It is the number of species in a particular community and can be used to make comparisons between the number of species in different biological communities or in different geographic areas.

Beta diversity

Refers to the degree of change that exists in terms of species composition along a gradient, whether environmental or geographic

For example, beta diversity would measure the degree of change in the composition of bat species on an altitudinal gradient. If a single bat species inhabits the entire gradient, the beta diversity would be low, while if the species composition changes substantially, the diversity will be high.

Gamma diversity

Applies to regions or geographic areas on a larger scale. For example, it seeks to quantify the number of species in a wide region, such as a continent.

To exemplify the previous measures, let's imagine a region where we have three sub-regions. Species A, B, C, D, E and F inhabit the first; in the second B, C, D, E and F; and in the third A, B, C, D, E, F, G.

In the previous zone, the alpha diversity will be the species per mountain, that is, 6. The gamma diversity will be the species per region, 7. And finally, the beta diversity, which is a relationship between the gamma and the alpha, which in this hypothetical case yields a value of 1.2.

What does high diversity mean?

When we say that an area has a "high diversity", we instantly associate it with positive aspects.

A diverse ecosystem is generally a healthy ecosystem, with high values ​​for stability, productivity and resistance to invasions or other potential disturbances.

However, although it is rarely considered, there are negative aspects linked to high diversity. On some occasions, fragmented sites exhibit high values ​​of diversity. In these regions, much of the richness is due to the presence of disturbed species.

In plant communities, high diversity translates into an ecosystem that is difficult to manage. If you want to implement grazing, it will be a difficult task, since each plant has its specific tolerance to grazing.

References

1. Hawksworth, DL (Ed.). (nineteen ninety five). Biodiversity: measurement and estimation. Springer Science & Business Media.
2. Núñez, EF (2008). Silvopastoral systems established with Pinus radiata D. Don and Betula alba L. in Galicia. Univ Santiago de Compostela.
3. Primack, RB, & Ros, J. (2002). Introduction to conservation biology. Ariel.
4. Purvis, A., & Hector, A. (2000). Getting the measure of biodiversity. Nature, 405 (6783), 212.
5. Whittaker, RH (1972). Evolution and measurement of species diversity. Taxon, 213-251.
6. Willis, KJ, Gillson, L., Brncic, TM, & Figueroa-Rangel, BL (2005). Providing baselines for biodiversity measurement. Trends in Ecology & Evolution, 20 (3), 107-108.