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OCR Biology AS Level (11)
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Chapter 11: Biodiversity11.1: Biodiversity
The importance of biodiversity
Biodiversity is essential in maintaining a balanced ecosystem for all organisms.
All species are interconnected - they depend on one another.
For example, trees provide homes for animals.
Animals eat plants, which in turn need fertile soil to grow.
Fungi and other micro-organisms help decompose dead plants and animals, returning nutrients to the soil.
In regions of reduced biodiversity, these connections may not all be present, which eventually harms all
species in the ecosystem.
We rely on balanced ecosystems as they provide us with the food, oxygen, and other materials we need to
survive.
Unfortunately, many human activities, such as farming and clearing land for housing, can lead to a reduction
in biodiversity.
Measuring biodiversity
Tropical, moist regions have the most biodiversity.
The UK's temperate climate has less biodiversity. Very cold areas such as the Arctic, or very dry areas such as
deserts, have the least biodiversity.
Generally, the closer a region is to the Equator, the greater the biodiversity.
For example, over 40000 plant species live in the Amazon rainforest, whereas less than 3000 live in Northern
Canada.
Measuring biodiversity plays an important role in conservation.
It informs scientists of the species that are present, thus providing a baseline for the level of biodiversity in
an area.
From this information, the effect of any changes to an environment can be measured.
These may include the effect of human activity, disease, or climate change, for example.
Before a major project is undertaken, such as building a new road or the creation of a new nature reserve,
an Environmental Impact Assessment is undertaken.
This assessment attempts to predict the positive and negative effects of a project on the biodiversity in that
area.
Biodiversity can be studied at different levels:
o habitat biodiversity
o species biodiversity
o genetic biodiversity.
Habitat biodiversity
Habitat biodiversity refers to the number of different habitats found within an area.
Each habitat can support several different species.
Therefore, in general, the greater the habitat biodiversity, the greater the species biodiversity will be within
that area.
The UK is home to large number of habitat types, including meadow woodland, streams, and sand dunes. It
has a large habitat biodiversity
By contrast Antarctica, covered almost entirely by an ice sheet has a very low habitat biodiversity and very
few species live in this region.
On a smaller scale, countryside that is habitat rich, perhaps with a river, woodland, hedgerows, and wild
grassland, will be more species rich than farmed countryside with large, ploughed fields making up a single
uniform habitat.
Species biodiversity
Species biodiversity has two different components:
o species richness - the number of different species living in an area
o species evenness - a comparison of the numbers of individuals of each species living in a community.
Therefore, an area can differ in its species biodiversity even if it has the same number of species.
For example, a cornfield and a grass meadow may both contain 20 species.
However, in the cornfield, corn will make up 95% of the community with the remaining 5% made up of other
organisms including weed plants, insects, mice, and birds.
In the grass meadow the species will be more balanced in their populations.
, Genetic biodiversity
Humans have about 25000 genes, but some species of flowering plants have as many as 400000 genes.
Many of these genes are the same for all individuals within a species.
However, for many genes, different versions exist.
This leads to genetic biodiversity within a species
Genetic biodiversity within a species can lead to quite different characteristics being exhibited.
For example, some genes are the same for all breeds of dog - these genes define the organism as a dog.
Some of the genes have many alleles - they code for the wide variation in characteristics seen between
different breeds of dog, for example coat colour and length.
Greater genetic biodiversity within a species allows for better adaptation to a changing environment and is
more likely to result in individuals who are resistant to disease.
11.2: Types of sampling
What is sampling?
Sampling means taking measurements of a limited number of individual organisms present in a particular
area.
Sampling can be used to estimate the number of organisms in an area without having to count them all.
The number of individuals of a species present in an area is known as the abundance of the organism.
Sampling can also be used to measure a particular characteristic of an organism.
For example, you cannot reliably determine the height of wheat by measuring one wheat plant in a farmer’s
field.
However, if you measure the height of several plants and then calculate an average, your result is likely to be
close to the average height of the entire crop.
After measuring a sample, you can use the results of the sample to make generalisations or estimates about
the number of organisms, distribution of species or measured characteristic throughout the entire habitat.
Sampling can be done in two ways: random and non-random.
Random sampling
Random sampling means selecting individuals by chance.
In a random sample, everyone in the population has an equal likelihood of selection, rather like picking
names out of a hat.
To decide which organisms to study, random number tables or computers can be used.
You are not involved in deciding which organisms to investigate
For example, to take a random sample at a grass verge you could follow these steps:
o Mark out a grid on the grass using two tape measures laid at right angles.
o Use random numbers to determine the x coordinate and the y coordinate on your grid.
o Take a sample at each of the coordinate pairs generated.
Non-random sampling
Non-random sampling is an alternative sampling method where the sample is not chosen at random.
It can be divided into three main techniques:
o Opportunistic
this is the weakest form of sampling as it may not be representative of the population
Opportunistic sampling uses organisms that are conveniently available.
o Stratified
some populations can be divided into several strata based on a particular characteristic.
For instance, the population might be separated into males and females.
A random sample is then taken from each of these strata proportional to its size.
o Systematic
in systematic sampling different areas within an overall habitat are identified, which are then
sampled separately.
For example, systematic sampling may be used to study how plant species change as you
move inland from the sea.
Systematic sampling is often carried out using a line or a belt transect.
A line transect involves marking a line along the ground between two poles and taking
samples at specified points, this can include describing all the organisms which touch the
line or distances of samples from the line.
A belt transect provides more information; two parallel lines are marked, and samples are
taken of the area between the two lines.
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