Biodiversity: The index of diversity and agriculture

In a nutshell

Biodiversity refers to the variety of organisms in an area and can be calculated at various scales, from local to global. Local biodiversity is the variety of organisms in a small habitat. In comparison, global diversity is the variety of organisms present on the part of the earth. Diversity is calculated using species population and the number of species through a formula called the index of diversity.

Biodiversity

Definition

Biodiversity refers to all the different kinds of life you will find in one area.

This may vary from plants, animals, fungi and even bacteria and can be calculated locally to globally. The population of a species and the number of species present are required for an accurate calculation of biodiversity.

Local biodiversity

This measures the different amount of species present in a small local habitat.

Example

A small habitat could be a lake or a garden.

Global biodiversity

This measures the different number of species present on Earth. Different locations will have different levels of biodiversity. The closer to the equator, the higher the biodiversity.

Index of diversity

The index of diversity is a calculation used to measure biodiversity. It is calculated using both population size and species richness.

Note: Species richness refers to number of different species within a community.

Example

The United Kingdom is home to over $200$  types of breeding bird species.

Calculating the index of diversity

It is possible to calculate an index of diversity using the following formula.

$d=\dfrac{N(N-1)}{\sum n(n-1)}$

Symbol	Description
$d$	Index of diversity.
$N$	The total number of organisms.
$n$	The total number of one species of organisms.
$\sum$	Sum of multiple terms.

Example

Samples of butterflies were collected from a garden. Use the below table to calculate an index of diversity.

Species	Count
Marsh fritillary	$7$
Glanville fritillary	$3$
Dingy skipper	$6$
Purple emperor	$4$

Calculate the total number of organisms:

$N=7+3+6+4=20$

Calculate $n$ for each species:

Marsh fritillary = $7(7-1)$

Glanville fritillary = $3(3-1)$

Dingy skipper = $6(6-1)$

Purple emperor = $4(4-1)$

Substitute into the formula:

$d=\frac{20(20-1)}{7(7-1)+3(3-1)+6(6-1)+4(4-1)}$

$d=\frac{380}{42+6+30+12}$

$d=\frac{380}{90} = \underline{4.2}$

\underline{Therefore,\ the\ index\ of\ diversity\ for\ this\ garden\ is\ 4.2}

Biodiversity and agriculture

Agricultural farmers use methods that reduce biodiversity.

Method	Description
Woodland clearance	This creates areas for farmlands, however, by removing trees, habitats are directly destroyed which leaves many organisms without shelter or food.
Monoculture	This is when farmers use fields to grow only one type of crop. This reduces biodiversity directly and also indirectly as less organisms will be adapted to living in the monoculture environment.
Pesticides	Pesticides kill organisms that feed on crops, this reduces the number of pests and therefore reduces biodiversity.
Herbicides	Herbicides are chemicals that kill weeds, this directly reduces plant biodiversity.
Removing hedgerows	Removing hedgerows creates space for farming. Many organisms live in hedgerows, therefore destroying them reduces biodiversity.

Protecting biodiversity

Conservationists try to protect biodiversity in a variety of ways.

Legally protecting endangered species.
Creating areas where agriculture is restricted.
Creating the environmental stewardship scheme which rewards farmers who support biodiversity.

Example

The Environmental Stewardship scheme encourages farmers to conserve biodiversity.

Biology; Classification and biodiversity; KS5 Year 12; Biodiversity: The index of diversity and agriculture