What does endemic mean?

Found naturally in one geographical area only, and nowhere else in the world.

Why are endemic species especially vulnerable to human activity?

They have no other populations, so if their one habitat is destroyed the whole species is lost.

What is species richness?

The number of different species in a habitat.

What is the main limitation of species richness?

It takes no account of how many individuals there are of each species.

How is biodiversity within a species measured?

By its genetic diversity, for example using the heterozygosity index.

Write the heterozygosity index formula.

H = number of heterozygotes ÷ number of individuals in the population.

Write the formula for the index of diversity.

D = N(N − 1) ÷ Σn(n − 1), where N is the total number of individuals and n is the number of each species.

What does a high value of D show?

Greater biodiversity: there are many species and the individuals are spread fairly evenly between them.

Why does one dominant species give a low D?

It gives a large Σn(n − 1), the denominator, so D is small.

Name three human activities that threaten biodiversity.

Habitat destruction, over-exploitation (such as overfishing), pollution, climate change or invasive species.

Why does a small, isolated population have low genetic diversity?

Few individuals breed, so alleles are lost and there is no gene flow to bring in new ones.

Biodiversity and its measurementEdexcel A-Level Biology A: Flashcards

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What is biodiversity?

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What is biodiversity?: The variety of life: the number of species in a habitat and the genetic variation within each species.
What does endemic mean?: Found naturally in one geographical area only, and nowhere else in the world.
Why are endemic species especially vulnerable to human activity?: They have no other populations, so if their one habitat is destroyed the whole species is lost.
What is species richness?: The number of different species in a habitat.
What is the main limitation of species richness?: It takes no account of how many individuals there are of each species.
How is biodiversity within a species measured?: By its genetic diversity, for example using the heterozygosity index.
Write the heterozygosity index formula.: H = number of heterozygotes ÷ number of individuals in the population.
A sample of 40 individuals has 12 heterozygotes. What is H?: H = 12 ÷ 40 = 0.30.
Write the formula for the index of diversity.: D = N(N − 1) ÷ Σn(n − 1), where N is the total number of individuals and n is the number of each species.
What does a high value of D show?: Greater biodiversity: there are many species and the individuals are spread fairly evenly between them.
Why does one dominant species give a low D?: It gives a large Σn(n − 1), the denominator, so D is small.
Name three human activities that threaten biodiversity.: Habitat destruction, over-exploitation (such as overfishing), pollution, climate change or invasive species.
Why does a small, isolated population have low genetic diversity?: Few individuals breed, so alleles are lost and there is no gene flow to bring in new ones.

Exam questions on Biodiversity and its measurement

A botanist surveys the forest on a remote island. She records 42 plant species in total. Nine of these grow naturally on the island and nowhere else in the world; the other 33 also occur on the nearby mainland.
Suggest why endemic species are more at risk of extinction from human activity than species that also occur elsewhere.2 marks
A conservation geneticist studies one gene locus in two populations of a rare orchid. In population A, 35 of the 50 plants sampled are heterozygous at the locus. In population B, 6 of the 40 plants sampled are heterozygous at the locus.
Calculate the heterozygosity index for population B and state which population has the greater genetic diversity at this locus.2 marks
A student compares the beetles living in two habitats using pitfall traps. In the meadow she catches 50 beetles belonging to 5 species, in numbers of 20, 15, 10, 4 and 1. In the hedge bank she catches 50 beetles belonging to 3 species, in numbers of 40, 8 and 2. She uses the index of diversity, D = N(N − 1) / Σn(n − 1), where N is the total number of individuals and n is the number of individuals of each species.
Calculate the index of diversity for the meadow. Show your working.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).