OCR Biology - Evolution and biodiversity

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Module 3: Biodiversity and Evolution
2.3.1 ­ Biodiversity
Biodiversity ­ The number and variety of living things to be found in the world, in an ecosystem or in a
habitat. The variety of habitat communities and species in an area and the genetic diversity within
populations. It consists of:
Genetic diversity ­ the differences between the genes in a species
Species diversity ­ the number of different species in a community
Ecosystem or habitat diversity ­ the variety of different areas where organisms can live
Habitat ­ The place an organism lives.
Species ­ A group of individual organisms very similar in appearance, anatomy, physiology, biochemistry
and genetics, whose members are able to interbreed freely to produce fertile offspring.
Population ­ the amount of a particular species living in the same habitat
Community ­ all the living things in a particular habitat
Biodiversity considered at different levels:
The range of habitats in which different species live. Each habitat will be occupied by a range of
The differences between species. This includes structural and functional differences.
Genetic variation between individuals belonging to the same species. For example, the variation found
within any species that ensures we do not all look alike.
Select small portion of the habitat and study that carefully
Multiply the numbers of individuals of each species found in that portion, then estimate the
number in the whole habitat
To measure biodiversity would need to observe all the species and the number of them present in
the habitat, but it is impractical
Random sampling ­ studying a small part of the habitat and assuming it contains a representative
set of species that can be applied to the whole habitat. The sample sites must be chosen at random.
Choosing places to sample:
Take samples at regular distances across the habitat
Use random numbers, generated by a computer or a random number table, to plot coordinates within
the habitat
Select coordinates from a map of the area and use portable global positioning satellite system to find
the exact position inside the habitat.
How many:
The number of samples dependant on the size of the habitat and the time available
The number of samples should be sufficient to give an accurate measure of the number of species in
the habitat and their relative abundance (frequency of occurrence)
If comparing two areas as part of the same study the same number of samples in needed in each
Sampling plants
Smaller plants ­ measure percentage of ground cover

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Random sampling ­ can miss plants that occur only infrequently (present species but will no
Visual survey of the habitat will view plants that may have been missed by random sampling
Qualitative data ­ not used in statistical analysis
Using random quadrats:
Quadrat ­ square frame used to define the size of the sample area ­ usually 50cm or 1m on each side
Place the quadrat at random in the habitat
Lay 2 tap measures as if it were a grid and plot random…read more

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Light trap
Collect flying insects at night
Ultraviolet light attracts the insects
Under the light is a collecting vessel containing alcohol
Moths and other insects attracted to the light fall into the alcohol
Species richness
The number of species present in a habitat
More species present -> richer the habitat
Qualitative survey to estimate
Make observations within the habitat and record all species seen
Take samples and visually observe missed species
Species evenness
Measure of the relative numbers or abundance of individuals in each species…read more


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