Measuring Biodiversity

Measuring Biodiversity
How Biodiversity Varies.

High Biodiversity is seen in:
• Very stable ecosystems,
• Areas where there are high levels of productivity (when photosynthetic rates are
very high), and,
• Areas where organisms can grow and reproduce rapidly.
High biodiversity vs low biodiversity
High Biodiversity Low Biodiversity

• When an environment has extreme conditions, the
biodiversity is low.
• Any changes in the extreme environment has a big
impact on the population number.
• This type of ecosystem is usually unstable and very
susceptible to change.
• In less hostile environments, biodiversity can be

very high.
• This results in a very stable ecosystem, because a
new species moving in or out will have almost no
effect.
Biodiversity within a species.
• Biodiversity within a species is also a very important concept.
• The gene pool of a species is all the genes in the genome, including all the
different variants of each gene.
Gene and allele frequency
• Mutations are changes in the DNA sequence.
• Many mutations have no effect at all on the phenotype, while others may have useful, or damaging or
lethal effects.
• Increases gene pool of a population → Increases number of different
alleles.
• The relative frequency of a particular allele in a population is called the

Allele Frequency.
• If mutation is advantageous → Allele will be selected.

Therefore, frequency in population increases.
• If mutation is disadvantageous → May become advantageous if

conditions change.
May lead to the evolving of a new species.
THE DIVERSITY INDEX
DIVERSITY INDEX IS A WAY OF MEASURING
THE BIODIVERSITY OF A HABITAT.
THIS METHOD OF MEASURING
BIODIVERSITY CONSIDERS THE SPECIES
RICHNESS AND SPECIES ABUNDANCE.
LIKE ALMOST ALL METHODS OF MEASURING
BIODIVERSITY, THIS TOO MAY HAVE
LIMITATIONS.
Measuring genetic biodiversity
• Genetic variation within a population is an important measure of biological health and well-being – without
genetic variation a population becomes vulnerable.
• We can build up a model of genetic diversity of a population by analyzing DNA and comparing regions for
similarities and differences.
• Scientists look at the proportion of heterozygous animals (animals with two alleles for a given feature) in a
population.
• This can be used to calculate a ‘Heterozygosity Index’ which is a useful measure of genetic diversity in a
population.
• High heterozygosity index → High levels of genetic variation and a potentially healthy population.
• Low heterozygosity index → Low levels of genetic variation and is in trouble.

High heterozygosity pertains to excessive genetic variability. Low
heterozygosity pertains to less genetic variability in a population.
The Hardy-Weinberg
Equilibrium
The Hardy-Weinberg Equilibrium theory states that in a population that is not
evolving,
the allele frequencies in the population will remain stable from one generation to
the next if there are no other evolutionary influences
1) Selection Pressure
• For Hardy-Weinberg equilibrium to occur, all alleles would have the same level of
reproductive advantage or disadvantage.
• Many alleles are neutral in their effect.
• If the environment conditions change, a new selection pressure will be exerted.
• As a result, alleles which used to be neutral will become advantageous or

disadvantageous.
• Some individuals will now have an advantage and may survive and pass on the
beneficial allele.
• The genetic make-up of the population will change over time.
• This is natural selection in progress.
• Selection pressure drives speciation as environments change

2) Mutations
• For the allele frequency to remain stable in a population, no mutations
must occur.
• Why?
Mutations involve changes in the genetic materials, so the
alleles are changed.
• Mutations in the somatic cells of organisms will not be passed on to

their offspring and may or may not affect the individual themselves.
3) Isolation
• If the Hardy-Weinberg genetic equilibrium is to be
maintained, the population must exist in isolation.
• No migration into or out of the population must occur.
• When the gene flow between two populations is reduced,

they become effectively isolated, and this is when speciation
is more likely to occur.
• 4) Populations of varying sizes
• The Hardy-Weinberg equation is only valid if the population
is large- at least several thousand individuals.
• Why? Because maintaining genetic equilibrium depends on a

random assortment of the alleles.
• Larger the population, bigger the chance of a potentially

useful allele being maintained. This is one reason why large,
genetically diverse populations are needed to maintain
biodiversity.
5) Non- random mating
• One of the most important requirements for a gene pool to
remain in equilibrium is for random mating to occur.
• Random mating means the likelihood of any two individuals
in a population mating is independent of their genetic make-
up.
• If mating occurs randomly, the frequency of the alleles in the
population will stay the same.
• Non-random mating (common among people) occurs when

some feature of the phenotype affects the probability of two
organisms mating- and as a result natural selection occurs.
• In every human culture, value judgements are used in the

selection of a partner, by the individual or the family or
social groups to which the individual belongs.
• Population:
It is a group of individuals of the same species

occupying a particular habitat and a particular niche within that
habitat
• Habitat:
It is the place where an organism lives and includes

both physical and biological elements of the surrounding
Population Genetics
Gene pool is the sum of all the alleles in a population at a given time.
It can be millions or even billions of genes!
Evolution can be considered as a permanent change in

allele frequencies within a population
Allele frequencies
• The frequency of alleles is not fixed.
• So, the frequency of different alleles changes as the

environment changes, through the process of natural
selection and adaptation.
• The number of individuals carrying a certain allele in a

population determines the allele frequency.
Selection Pressure is seen when a change occurs in an
environment.
Some individuals will have alleles which give them an

advantage in the new conditions
The End!

Measuring Biodiversity

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Measuring Biodiversity

How Biodiversity Varies.

High Biodiversity Low Biodiversity

• In less hostile environments, biodiversity can be

• Biodiversity within a species is also a very important concept.

• Mutations are changes in the DNA sequence.

• The relative frequency of a particular allele in a population is called the

• If mutation is advantageous → Allele will be selected.

• If mutation is disadvantageous → May become advantageous if

• Low heterozygosity index → Low levels of genetic variation and is in trouble.

• Many alleles are neutral in their effect.

• If the environment conditions change, a new selection pressure will be exerted.

• As a result, alleles which used to be neutral will become advantageous or

• The genetic make-up of the population will change over time.

• This is natural selection in progress.

• Selection pressure drives speciation as environments change

• Mutations in the somatic cells of organisms will not be passed on to

• No migration into or out of the population must occur.

• When the gene flow between two populations is reduced,

• Why? Because maintaining genetic equilibrium depends on a

• Larger the population, bigger the chance of a potentially

• Non-random mating (common among people) occurs when

• In every human culture, value judgements are used in the

It is a group of individuals of the same species

It is the place where an organism lives and includes

Evolution can be considered as a permanent change in

• So, the frequency of different alleles changes as the

• The number of individuals carrying a certain allele in a

Some individuals will have alleles which give them an

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