Measures of Biodiversity

This lesson covers: 

1. Key biodiversity terminology and the different levels of biodiversity
2. Species richness and species evenness
3. The diversity index
4. How to compare genetic diversity

Defining biodiversity

Biodiversity refers to the variety of organisms in an area.

Levels of biodiversity:

• Ecosystem diversity - The number of habitats.
• Species diversity - The number of species and the number of individuals in each species.
• Genetic diversity - The variation in alleles within a population of a species.

High genetic biodiversity allows for better adaptation to a changing environment and resistance to disease.

Key terms related to biodiversity:

• Habitat - The place where a species lives within an ecosystem.
• Community - The living organisms of all species found in a particular ecosystem at a particular time.
• Ecosystem - A relatively self-contained, interacting community of organisms and their environment.

Species richness and species evenness

Species richness and species evenness are measures of biodiversity.

Species richness:

• The total number of different species in a habitat at a given time.
• It is quantified by taking random samples and counting the species present.
• A higher species richness indicates greater diversity.

Species evenness:

• A comparison of the numbers of individuals of each species in a community.
• It is measured by taking samples and counting individuals of each species.
• More even abundances mean higher species evenness and diversity.

The diversity index

The index of diversity equation considers species number and abundance to quantify biodiversity.

It is calculated as:

d =∑n(n−1)N(N−1)​

Where:

• N = total individuals of all species.
• n = number of individuals of each species.

Higher values of d indicate greater diversity.

Worked example - Calculating the diversity index

A biologist is assessing the biodiversity of two fields. Field A contains 150 individual plants, consisting of 85 daisies, 35 buttercups, and 30 clovers. Field B contains 150 individual plants, consisting of 55 daisies, 45 buttercups, and 50 clovers.

Calculate and compare the diversity indices for each habitat.

Step 1: Equation

d=∑n(n−1)N(N−1)​

Step 2: Construct a table to calculate ∑n(n−1) for field A

Step 3: Substitution and correct evaluation for field A

diversity of field A =9,200150(150−1)​

diversity of field A =9,200150(149)​

diversity of field A =9,20022,350​

diversity of field A =2.43

Step 4: Construct a table to calculate ∑n(n−1) for field B

Step 5: Substitution and correct evaluation for Field B

diversity of field B =7,400150(150−1)​

diversity of field B =7,400150(149)​

diversity of field B =7,40022,350​

diversity of field B =3.02

Step 6: Interpretation of result

as the diversity index for field A is 2.43 and for field B it is 3.02, this indicates that field B has a higher species diversity compared to field A

How to compare genetic diversity

Genetic biodiversity can be assessed by calculating the percentage of gene variants (alleles) in a genome within isolated populations. A high genetic biodiversity means there is a large variety of alleles in the population's gene pool.

Measuring genetic diversity also allows quantification of diversity within and between species.

Genetic diversity can be compared by:

1. Comparing the frequency of measurable or observable characteristics.
2. Comparing the base sequence of DNA.
3. Comparing the base sequence of mRNA.
4. Comparing the amino acid sequence of the proteins encoded by DNA and mRNA.