Biodiversity

Biodiversity is an indication of the variety of different species living in a particular place. Human activity has made the planet less diverse so now conservation strategies are being employed to try and reverse some of the mess we’ve made.

Biodiversity

Biodiversity is defined as the variety of living organisms in a particular habitat. Habitats such as a tropical rainforest, which host an abundance of plant and animal life, have higher biodiversity compared to desert or arctic habitats. Biodiversity can be defined in different ways:

• Species diversity - the variety of different species living in an area

• Habitat diversity - the number of different habitats within an area

• Genetic diversity - the number of different alleles within a population

Endemism

A species is described an ‘endemic’ if it is found in one location only. For example, the Malabar climbing frog is endemic because there is just a single population living in India. Endemic species are vulnerable to extinction because if a natural disaster or some other threat to their survival wipes out the population, there will be no other individuals remaining. This means that conservation programmes are particularly important for endemic species.

Heterozygosity Index

Genetic diversity is a measure of the number of different alleles within a population. It can be measured using something called the Heterozygosity Index which calculates the extent of genetic diversity by determining the proportion of heterozygotes (genotypes with two different alleles) within a population. The higher the number of heterozygotes, the higher the genetic diversity. The Heterozygosity Index is measured using the equation below:

Index of Diversity

Species diversity can be measured by calculating the Index of Diversity (D) of a particular habitat. It takes into account both the number of different species and the abundance of each species. The larger the value for the Diversity Index, the more biodiverse the habitat is. It is calculated using the following equation:

You should be given this formula in the exam so there is no need to memorise it! But you do need to remember what each component of the equation represents. N is the total number of organisms of all species living in that habitat and n is the number of organisms of a single species. Look at the example below to see how the Index of Diversity is calculated:

The table below shows the species present in a woodland habitat and their population size.

When calculating the Index of Diversity, the best way to organise your answer is to add another column to the table to work out n (the population size of each species) x n-1. We will then add all of these values together to work out the sum of n(n-1). We also need to add together the population sizes of all the species to get a value for N, which is then multiplied by N-1. Our N(N-1) value will be divided by the Σn(n-1) value to calculate the Index of Diversity (D). A value of 1 means there is no diversity at all (i.e. only one type of species is living in the habitat). As biodiversity increases, D also increases.

Conserving Biodiversity

Over the past few hundred years, biodiversity has decreased because of human activities. Hunting, deforestation and pollution have already caused some species to become extinct. Human beings have a moral duty, along with economic incentives, to maintain biodiversity for future generations - this is mostly done through conservation. Conservation involves the protection and management of endangered species. Zoos carry out conservation work to protect animals from extinction and seedbanks conserve biodiversity by storing seeds of endangered plants. Zoos and seedbanks are also important for educating the public about the importance of conserving biodiversity and valuable scientific research takes place at these institutions, enabling us to learn more about different animal and plant species to help conservation efforts.

Seedbanks

Seedbanks are places which store a variety of different seeds from different plant species. They try to store seeds from plants with different phenotypes so that they have a stock of lots of different alleles which may prove useful in the future. They help protect plants from extinction because if a plant becomes extinct in the wild, the seedbank can grow new plants to replace it from the seeds in its collection. In order to keep a stock of viable seeds, the seedbank needs to keep conditions cold and dry. However, seeds do not stay healthy indefinitely, so every so often the seeds need to be planted and new seeds taken from the growing plant.

The reasons seeds are stored rather than fully grown plants are that seeds take up less space and require less maintenance, which makes conservation cheaper because less labour is needed. Growing plants from lots of different parts of the world would require replicating lots of different climates and the plants would be more vulnerable to damage or disease.

Reintroducing organisms into the wild

Sometimes animals bred in captivity or plants grown in seedbanks can be reintroduced into the wild. For example, storks have been reintroduced into their natural habitat in the UK after being bred in captivity - they had been extinct as breeding pairs in Britain since 1416. Reintroducing organisms into their wild habitat can boost population numbers and protect them from becoming extinct. It will also have an impact on the other organisms in the food chain which prey on these animals. However, reintroduction can be problematic since animals that have been brought up in captivity haven’t learned how to survive in the wild. Reintroduced organisms can also bring new diseases into habitats, infecting wild populations.

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