chapter 11 p2

Question 1

Estimating animal population size:
p1

Answer 1

As animals are constantly moving through a habitat and others may be hidden, it can be difficult to accurately determine their population size.
A technique known as capture-mark-release-recapture is often used to estimate a population size.
This involves capturing as many individuals of a species in an area as possible.
The organisms are marked and then released back into the community.
Time is allowed for the organisms to redistribute themselves throughout the habitat before another sample of animals is collected.

Question 2

Estimating animal population size:
p2

Answer 2

By comparing the number of marked individuals with the number of unmarked individuals in the second sample, scientists can estimate population size.
The greater the number of marked individuals recaptured, the smaller the population.
The species evenness in an area can then be calculated by comparing the total number of each organism present. Populations of plants or animal that are similar in size or density represent as even community and hence a high species evenness
Species evenness can also be expressed as a ratio between the numbers of each organism present.

Question 3

Measuring abiotic factors:

Answer 3

Abiotic factors are the non-living conditions in a habitat.
They have a direct effect on the living organisms that reside there. Examples are the amount of light and water available.
To enable them to draw conclusions about the organisms present and the conditions they need for survival, scientists normally measure these conditions at every sampling point.

Question 4

Table 1 summarises the ways in which common abiotic factors can be measured:

Answer 4

Question 5

Many abiotic factors can be measured quickly and accurately using a range of sensors, which are advantageous for a number of reasons:

Answer 5

Rapid changes can be detected.
Human error in taking a reading is reduced.
A high degree of precision can often be achieved.
Data can be stored and tracked on a computer.

Question 6

chapter 11.4 - Calculating biodiversity

Answer 6

Ecologists, such as those working for the Environment Agency, often perform calculations using specific formulae to determine the biodiversity of an area.
One such calculation is a measure of the species diversity.

Question 7

The diversity of the organisms present in an area is normally proportional to the

Answer 7

stability of the ecosystem, so the greater the species diversity the greater the stability.
The most stable communities have large numbers of fairly evenly distributed species, in good-sized populations.

Question 8

what reduces biodiversity

Answer 8

Pollution often reduces biodiversity. As a result of harsh conditions, a few species tend to dominate.
If corrective steps are taken to improve environmental conditions, biodiversity levels usually increase.
Monitoring biodiversity is therefore a useful tool in successful conservation and environmental management.

Question 9

How to calculate biodiversity:

Answer 9

The simplest way to measure biodiversity is to count up the number of species present - the species richness.
However, this measure does not take into account the number of individuals present.
Therefore in a meadow containing two daisies and 1000 buttercups, the daisies have as much influence on the richness of the area as 1000 buttercups.
A community dominated by one or two species is considered to be less diverse than one in which several different species have a similar abundance.

Question 10

Simpson’s Index of Diversity (D)

Answer 10

is a better measure of biodiversity as it takes into account both species richness, and species evenness.

It is calculated using the formula:

Question 11

When using a technique such as Simpson’s Index of Diversity

Answer 11

scientists normally have to estimate population size using a variety of sampling techniques, such as using a quadrat to estimate the population of a plant species in an area.
Simpson’s Index of Diversity always results in a value between 0 and 1, where 0 represents no diversity and a value of 1 represents infinite diversity.
The higher the value of Simpson’s Index of Diversity, the more diverse the habitat.

Question 12

What do low and high biodiversity values tell us about a habitat:

Answer 12

Although some habitats of low biodiversity are unable to support a large species diversity, those organisms that are present in the habitat can be highly adapted to the extreme environment of the habitat.
These organisms may not survive elsewhere. It is therefore important to conserve some habitats with low biodiversity, as well as those with high biodiversity, in order to conserve rare species that may be too specialised to survive elsewhere.

Question 13

Answer 13

Question 14

worked example p1

Answer 14

Question 15

worked example p2

Answer 15

Question 16

Chhpater 11.5 - Calculating genetic biodiversity

Answer 16

Maintaining genetic biodiversity is essential to the survival of a species. In isolated populations, such as those present within a captive breeding programme, genetic biodiversity is often reduced.
This means that the individuals may suffer from a range of problems associated with in-breeding.
Scientists can calculate the genetic biodiversity of a population of a species (sometimes referred to as the gene pool) to monitor the health of the population and ensure its long-term survival.

Question 17

The importance of genetic biodiversity: p1

Answer 17

Within a species, individuals have very little variation within their DNA.
All members of the species share the same genes. However, they may have different versions of some of these genes.
The different ‘versions’ of genes are called alleles.
The differences in the alleles among individuals of a species creates genetic biodiversity within the species, or within a population of the species.
The more alleles present in a population, the more genetically biodiverse the population.

Question 18

The importance of genetic biodiversity: p2

Answer 18

Species that contain greater genetic biodiversity are likely to be able to adapt to changes in their environment, and hence are less likely to become extinct.
This is because there are likely to be some organisms within the population that carry an advantageous allele, which enables them to survive in the altered conditions.
For example, when a potentially fatal new disease is introduced to a population, all organisms will be killed unless individuals carry resistance to the disease.
Those organisms are likely to survive the disease, and therefore be able to reproduce - leading to the survival of the species.

Question 19

Factors that affect genetic biodiversity:

Answer 19

For genetic biodiversity to increase, the number of possible alleles in a population must also increase.
This can occur through:
- mutation(s) in the DNA of an organism, creating a new allele.
- interbreeding between different populations. When an individual migrates from one population and breeds with a member of another population, alleles are transferred between the two populations.
This is known as gene flow.

Question 20

In order for genetic biodiversity to decrease, the number of possible alleles in a population must also decrease.
This can occur through:

Answer 20

selective breeding (also known as artificial selection)

captive breeding programmes

rare breeds

artificial cloning (asexual reproduction

natural selection.

genetic bottlenecks

the founder effect

genetic drift

Question 21

selective breeding

Answer 21

(also known as artificial selection), where only a few individuals within a population are selected for their advantageous characteristics and bred.
For example, the breeding of pedigree animals or of human food crops

Question 22

captive breeding programmes

Answer 22

captive breeding programmes in zoos and conservation centres, where only a small number of captive individuals of a species are available for breeding.
Often the wild population is endangered or extinct

Question 23

rare breeds

Answer 23

where selective breeding has been used historically to produce a breed of domestic animal or plant with characteristics which then become less popular or unfashionable, so the numbers of the breed fall catastrophically.
When only a small number of individuals of a breed remain and are available for breeding and all of these animals will have been selected for the specific breed traits, the genetic diversity of the remaining population will be low.
This can cause serious problems when trying to restore numbers yet maintain breed characteristics, for example, a Gloucester Old Spot pig must have at least one spot on the body to be accepted into the registry of this rare breed

Question 24

artificial cloning

Answer 24

(asexual reproduction), for example using cuttings to clone a farmed plant

Question 25

natural selection.

Answer 25

As a result, species will evolve to contain primarily the alleles which code for advantageous characteristics.
Over time, alleles coding for less advantageous characteristics will be lost from a population, or only remain in a few individuals.

Question 26

genetic bottlenecks

Answer 26

where few individuals within a population survive an event or change (e.g., disease, environmental change or habitat destruction), thus reducing the ‘gene pool’.
Only the alleles of the surviving members of the population are available to be passed onto offspring

Question 27

the founder effect

Answer 27

where a small number of individuals create a new colony, geographically isolated from the original.
The gene pool for this new population is small.

Question 28

genetic drift,

Answer 28

due to the random nature of alleles being passed on from parents to their offspring, the frequency of occurrence of an allele will vary.
In some cases, the existence of a particular allele can disappear from a population altogether.
Genetic drift is more pronounced in populations with a low genetic biodiversity.

Question 29

Measuring genetic biodiversity:

Answer 29

One way in which scientists quantify genetic biodiversity is by measuring polymorphism.
Polymorphic genes have more than one allele.
For example, different alleles exist for the immunoglobulin gene, which plays a role in determining human blood type - this is therefore defined as a polymorphic gene. The three alleles are:

Question 30

For example, different alleles exist for the immunoglobulin gene, which plays a role in determining human blood type - this is therefore defined as a polymorphic gene. The three alleles are:

Answer 30

Question 31

Answer 31

(The locus (plural - loci) of a gene refers to the position of the gene on a chromosome.)
The greater the proportion of polymorphic gene loci, the greater the genetic biodiversity within the population.

Question 32

Worked example: Measuring genetic biodiversity

Answer 32

Gel electrophoresis is a technique used to separate fragments of DNA based on their size.
In this technique restriction enzymes are used to cut DNA into smaller pieces, which are then placed in a gel.
The gel is placed between positive and negative electrodes, which cause the negatively charged DNA to move towards the positive side.
The smaller the fragment of DNA, the further the movement through the gel.
The pattern produced, known as a banding pattern, can be used to compare DNA samples from different individuals.
The following section of data was collected from the gel electrophoresis of five genetic loci within 20 individuals in an ibex (mountain goat) population. The five loci studied were labelled V, W, X, Y, and Z.

Question 33

Maintaining biodiversity is essential for

Answer 33

preserving a balanced ecosystem for all organisms.
As species are interconnected within an ecosystem, the removal of one species can have a profound effect on others.
For example, it could lead to a loss of another species’ food source or shelter.
As part of the human population you rely on biodiversity for many of the materials you need to survive, such as food, wood, and oxygen.
However, humans are the leading cause of loss of biodiversity

Question 34

Human influence on biodiversity:

Answer 34

The human population is growing at a dramatic rate.
There are now over seven billion people living in the world, over double the number alive in the 1960s and over seven times more than in 1800.
This increasing growth rate is linked to improvements in medicine, hygiene, housing, and infrastructure, which enable people to live for longer.
To create enough space for housing, industry, and farming to support the increasing population, humans are severely disrupting the ecology of many areas.

Question 35

To create enough space for housing, industry, and farming to support the increasing population, humans are severely disrupting the ecology of many areas.

The main problems are occurring as a result of:

Answer 35

deforestation - the permanent removal of large areas of forest to provide wood for building and fuel (known as logging), and to create space for roads, building and agriculture.

agriculture - an increasing amount of land has to be farmed in order to feed the growing population.
This has resulted in large amounts of land being cleared and in many cases planted with a single crop (monoculture).

climate change - there is much evidence that the release of carbon dioxide and other pollutants into the atmosphere from the burning of fossil fuels is increasing global temperatures.

Other forms of pollution result from industry and agriculture, such as the chemical pollution of waterways.
The improper disposal of waste and packaging is a form of environmental pollution called littering.

Question 36

Deforestation:

Answer 36

Deforestation can occur naturally, for example as a result of forest fires caused by lightning or extreme heat and dry weather.
However, most deforestation now occurs deliberately as a result of human action.
Some areas of forest have also been destroyed indirectly by humans through acid rain, which forms as a result of pollutants being released into the atmosphere.

Question 37

Deforestation affects biodiversity in a number of ways. For example:

Answer 37

• It directly reduces the number of trees present in an area.
• If only a specific type of tree is felled, the species diversity is reduced. For example, rosewood is often extracted from rainforests (it is used in the manufacture of furniture and guitars), but less useable trees may be left intact.
• It reduces the number of animal species present in an area as it destroys their habitat, including their food source and home.
  This in turn reduces the number of other animal species that are present, by reducing or removing their food source.
• Animals are forced to migrate to other areas to ensure their survival.
  This may result in the biodiversity of neighbouring areas increasing.

In some areas forests are now being replaced.
Although this helps to restore biodiversity, generally only a few commercially viable tree species are planted.
Therefore, biodiversity is still significantly reduced from its original level.

Question 38

Agriculture:

Answer 38

In general, farmers will only grow a few different species of crop plants, or rear just a few species of animals.
Farmers often select the species based on characteristics that give a high yield (high levels of production), for example, wheat that produces the most grain or dairy cows that produce the most milk.
The selection of only a few species greatly reduces the biodiversity of the area.
In order to be economically viable, once the farmers have selected their desired species, a number of techniques are used to produce as many of the desired species as possible, maximising food production.

Question 39

Unfortunately many of these techniques lead to a reduction in biodiversity, for example:

Answer 39

Deforestation

Removal of hedgerows

Use of chemicals such as pesticides and herbicides.

Herbicides are used to kill weeds

Monoculture

Question 40

Deforestation

Answer 40

to increase the area of land available for growing crops or rearing animals.

Question 41

Removal of hedgerows

Answer 41

as a result of mechanisation, farmers remove hedgerows to enable them to use large machinery to help them plant, fertilise, and harvest crops. It also frees up extra land for crop growing.
This reduces the number of plant species present in an area and destroys the habitat of animals such as blackbirds, hedgehogs, mice and many invertebrates.

Question 42

Use of chemicals such as pesticides and herbicides.

Answer 42

Pesticides are used to kill pests that would eat the crops or live on the animals.
This reduces species diversity directly as it destroys the pest species (normally insects), and indirectly by destroying the food source of other organisms.

Question 43

Herbicides are used to kill weeds

Answer 43

A weed is any plant growing in an area where it is not wanted.
Weeds are destroyed as they compete with the cultivated plants for light, minerals, and water.
By destroying weeds, plant diversity is reduced directly, and animal diversity may also be reduced by the removal of an important food source.

Question 44

Monoculture

Answer 44

many farms specialise in the production of only one crop, with many acres of land being used for the growth of one species.
This has an enormous local effect in lowering biodiversity as only one species of plant is present.
As relatively few animal species will be supported by only one type of plant, this results in low overall biodiversity levels.
The growth of vast oil palm plantations is one of the leading causes of rainforest deforestation, leading to a loss of habitat for critically endangered