BiodiversityWhat do we understand by species diversity?

How is Simpson’s Diversity Index used as a measure of species diversity?

Saturday 22 April 2023

Biodiversity Species diversity: the number of different

species and the number of individuals of each species within any one community.

Genetic diversity: the variety of genes possessed by individuals that make up any one species

Ecosystem diversity: the range of different habitats within a particular area

Species Diversity Can be used to measure biodiversity

Two components:• Number of different species in a given

area• The proportion of the community that is

made up of an individual species

Measuring species diversity

Species found Number in habitat X

Number in habitat Y

A 10 3B 10 5C 10 2D 10 36E 10 4No. of species 5 5No. of individuals

50 50

Measuring species diversity

The table on the previous slide does not show us much about the differences in the two habitats.

In both cases the number of species and individuals are the same

If we now calculate species diversity, then we get a different picture.

Measuring species diversity

d= N(n-1) .

Σn(n-1)

Where: d = species diversity indexN = total number of organisms of

all speciesn = total number of organisms of

each speciesΣ= sum of

Calculate the species diversity index of each habitat from the table on the previous slide.

d= N(n-1) .

Σn(n-1)

Species n in habitat X

n(n-1) n in habitat Y

n(n-1)

A 10 3B 10 5C 10 2D 10 36E 10 4

Σn(n-1) Σn(n-1)

Species n in habitat X

n(n-1) n in habitat Y

n(n-1)

A 10 10(9)=90

3 3(2)= 6

B 10 10(9)=90

5 5(4)= 20

C 10 10(9)=90

2 2(1) = 2

D 10 10(9)=90

36 36(35)= 1260

E 10 10(9)=90

4 4(3)= 12

Σn(n-1) 450 Σn(n-1) 1300

Use this to calculate the species diversity index

Now we can calculate the species diversity index:

Habitat Xd = 50 (49) = 4250 = 5.44

450 450 Habitat Y

d = 50 (49) = 2450 = 1.881300 450

The higher the value, the greater the species diversity

Species Diversity & human activities

What is the influence of deforestation and the impact of agriculture on species diversity?

Saturday 22 April 2023

The impact of agriculture

Impact of agriculture Natural ecosystems develop from complex

communities

Agricultural ecosystems are carefully controlled by humans

Farmers select crops that are more productive.

The frequency of alleles is reduced

For economic reasons, the crop yield needs to be large.

Any one area can only support a certain amount of biomass – if most of this area is taken up by a crop, then there is little area left for anything else

Crops are sprayed with pesticide and man made fertiliser.

This further disadvantages and excludes species that the farmer does not want

This all acts to reduce species diversity

Impact of deforestation

Impact of deforestation Forests contain many varied and different

habitats = high species diversity

Permanent clearing of the forest leads to loss of habitats and in turn loss of biodiversity

What might you want to clear a forest for?

You should be able to… Explain what we mean by species diversity.

Explain how Simpson’s Diversity index is used to compare habitats

Calculate Simpson’s Diversity when given the formula

Outline the effects of agriculture and deforestation on species diversity