How is biodiversity measured?
Why measure biodiversity?
Biodiversity is the variety of living organisms, from genetic level to species to ecosystems. It provides sound information, especially used as environmental health indicators, to determine the status of our biological systems. For example, to identify whether there are changes in water quality in a certain lake, scientists can study the lake’s biodiversity and community structure to confirm if changes happened over a period of time.
However, biodiversity is also a complex concept that can be challenging to measure. How do we then measure a broad concept and make it meaningful? We need to establish representatives and identify measurable concepts. We narrow down the vast array of scope of biodiversity and chunk it down into small, quantifiable units. Take note though, that there are many different ways to quantify biodiversity.
Biodiversity is typically observed within a specific location (spatial) and time frame (temporal). Data collected from the spatio-temporal characteristics are defined according to three components: species diversity, ecosystem diversity and genetic diversity.
We focus on species diversity for the sake of discussion in this article. The two common factors taken into account in diversity measurements or indices are richness and evenness.
Species richness is a measure of the number of species present in an area. An area is called species-rich if there are more species found in it. Just remember, it doesn’t measure the number of individuals in the study area.
The variety of life forms does not only depend on species richness, but also on evenness. Species evenness is a measure of the relative abundance of the different species that consist an area. It compares the similarity of the population size of each species composition.
Diversity indices combine both species richness and evenness in a single number. Several literatures will show you many different ways of computing diversity indices. Two of the most popular formulas used to calculate biodiversity are Simpson’s index of diversity and Shannon – weaver index of diversity. Learn more about their applications here.
Questions on biodiversity, anyone?
Recognizing biodiversity in a particular area of study is the foundation of determining its general ecological health status. Biodiversity can be described and measured in many ways, such as answering queries like: what are the species found; how many of them are present within an area; is there any difference between the past and present population number, quality, morphological characteristics (physical attributes); in what particular substrate are they found; were information recorded in the past?; how is it different from the current status, etc. All of these start by identifying the species within an area at a specific time.
Here are three case studies on how biodiversity is measured and quantified for natural resource management and conservation:
(1) High Density of Tridacna crocea by Conales et al. 2015
The crocus clam, Tridacna crocea, is one of the giant clams in the Philippines found in the Indo-Pacific Region and could be the only remaining living representative species as it may have become extinct already on Guam and Northern Mariana Islands. Although exploitation of giant clams has been prohibited by the law since 2001, illegal activities had been going on and massively reduced the giant clam population. T. crocea’s count, abundance and size were recorded from Tubattaha Reef National Park , Palawan, Philippines. The study calls for protection of the high abundance of T. crocea within the Ranger Station of TRNP. It also calls for inclusion of reviving the giant clam population in reef restoration projects.
(2) Species diversity and spatial structure of intertidal molluscs in Padada by Jumawan JH, et al. 2015
Mollusc diversity in the Philippines is considered to be high, with 22,000 species out of the 70,000 species worldwide. However, there is very little information on Mindanao island. This was the first effort to find out how the molluscs and its community structure are in Padada, Davao del Sur, Philippines. The study covered only living bivalves and gastropods. To describe mollusc diversity in Padada, researchers set sampling areas, identified species and counted individuals. Then they analyzed many biodiversity indices such as species abundance and their spatial structure. They found out that the intertidal mollusc community in the area is highly variable. It meant that the species are rich and diverse, and also abundant across all sampling areas.
(3) Spatial and temporal variation of abundance, biomass and diversity within marine reserves by Anticamara JA, et al. 2010
Is it effective on reef fish diversity to implement no fishing zone over a period of time? This was the question researchers asked about the shore of the Danajon Double Barrier Reef in Bohol, Philippines. And so, they collected monthly data for three years. It included reef fish abundance and size structure, on six marine reserves and two open reef areas (not protected). When they analyzed data on species, diversity and abundance, they found out that the no fishing zone affected the reef fish diversity by allowing the large-bodied species to be more dominant and, by improving the total biomass. Results showed that indeed, diversity was influenced when the fishing pressure was removed within the specific zone.
Measuring biodiversity in specific ecosystems is important in the stewardship of our natural resources. Surveys, inventories and monitoring become urgent, especially when man-made intervention begins to influence the natural habitats. Learning to describe and measure biodiversity are very useful skills that can be practiced not only by researchers. It can be taught as well to local people who have direct access to such resources so they too can understand how the things we do affect nature. It must be taught so we can all be united in taking responsibility in keeping the balance between man and his environment.
Featured Image – Why measure biodiversity? | CC Image courtesy of Gary Peeples/USFWS