Biodiversity (Module 4, Section 2)


1. Investigating Biodiversity


1. Habitat diversity: Habitat diversity is the number of different habitats  in an area. It includes physical factors like the soil and temperature range and living (biotic) factors like availability of food and presence of predators. E.g. Coastal area could cotain many different habitats - beaches, sand dunes, mudflats,salt marshes, etc. 

2. Species diversity: Species diversity is the number of different species (species  richness) and the abundance of each species (species evenness). Species = group of siimilar organisms able to reproduce to give fertileoffspring. E.g. A woodland could contain many different species of plants, anials and insects.

3. Genetic diversity: Genetic diversity is the variation of alleles within a species or a population of a secies. E.g. Human blood type is determined by a genewith three different alleles.

Collecting data on biodiversity:

Finding out the number of different species in a habitat or number of individuals in each species. In most cases, its too time consuming to count every individual so a sample of  the population is  taken. Estimates about whole habitat are based on the sample. 

1 of 13

1. Investigating Biodiversity

Random sampling: To make sure a sample is not biased, should be random sampling. E.g. Splitting a field into a grid and using a rando number generator for the coordinates. This makes sure that each sample site has same probability of being chosen. To ensure any variation is not due to chance, it's important to analyse  results statistically. This allows you to be more confident with the results. Therefore a true reflecion of what's going on in the whole population.

Non-random sampling: Sometimes it is necessary for non-random sapling. E.g. When there's alot of variety in thee distribution of species in the habitat and you want to make sure that all different areas or species are sampled. Three types:

1. Systematic sampling: When samples are taken at fixed intervals, often along a line. E.g. If looking at plant species in a field, quadrats could be placed along a transect (a line) from area of shade in corner to middle of  field. Each quadrat would be a sample site.

2. Opportunistic sampling: When samples arechosen by investigator. Simple to carry out but data will be biased.

3. Stratified sampling: When different areas in a  habitat are identified and sampled separately in proportion to their part of the habitat as a whole. E.g. Heathland may have patches of gorse in it - heath and gorse areas would be sampled separately according to how much of each there was in that habitat.

2 of 13

1. Investigating Biodiversity

Estimating Biodiversity:

1. Choose site to sample. 2. Record number of different secies or number of individuals of each species. For plants = use quadrat (0.5m by 0.5m). For ground insects, use pitfall trap. For flying insects, use a sweepnet. For aquatic animals, use a net. 3. Take as many samples as possible. 4. Number of individuals for whole habitat can be estimated by calculating mean for data in each sample and multiplying by size of whole habitat. 5. When sampling and comparing different habitats, use same sampling technique.

Species richness and species evenness:

Species richness: is the number of diferent species in an area. The higher the number, the greater richness. Measured by random samping and counting number of species.

Species evenness: Measure of relative abundance of each species in an area. The more similar the population size of each species, the greater the evenness. Measured by random sampling and counting nuber of species,

The greater the species richness and evenness in an area, greater the biodiversity. (vice  versa).

3 of 13

1. Investigating Biodiversity

Tip: A low species evenness means that one or two species dominate a habitat - other species present arein low numbers or not at all.

Tip: Abundance is the number of individuals. Distribution means where the individuals are found.

Simpson's Index of Diversity: 

Species present in habitat in small numbers shouldn't be reated same as those with bigger numbers. Use Simpson's Index of Diversity (D) :

D = 1 - ([sum of] (n÷N)2)

n = total number of organisms in one species. N = total number of all organisms. D =  Dominance.

D is always between 0 and 1. Closer to 1 = more diverse and greater ability to cope with change as well as greater species richness and evenness.

4 of 13

2. Genetic Diversity

GD = Measure of diversity within a species. Important to help us understand the survivability of different species. Greater GD is linked to greater ability to adapt and survive.

Importance of Genetic diversity (GD): If population has low genetic diversity, may not be able to adapt to change in environment, whole population could be wiped out by 1 event. E.G. Disease.

Polymorphism: Alleles are different versions of a gene. Alleles of same gene are found at same point (called a locus) on a chromosome. Polymorphism describes a locus that has 2 or more alleles. 

Assessing Genetic Diversity:

Genetic polymorphism is used to measure GD. Working out th proportion of polymorpic gene loci in a population gives you a measure of GD. 

Proportion of polymorphic gene loci = Number of polmorhic gene loci ÷ total number of loci

5 of 13

3. Factors affecting Biodiversity

Human population growth:

1. Habitat loss: More land needed for housing and to produce food, destroying habitats.

2. Over-exploitation: Resources are being used quicker than they can be replenished. Destroying habitats or even affecting a species directly.

3. Urbanisation: can isolate species meaning populations are unable to interbreed and GD is decreased.

4. Pollution: High levels can kill species or destroy habitats.

Monoculture: Large areas of land are devoted to Monoculture - the growing of a single variety of a single crop. Leading to decline in biodiversity because of...

1. Habitat loss: Both Land and sea. Habitats lost as land is cleared.

2. Loss of local plants and animals: local and naturally occurring plants and animals seen as weeds and pests so are destroyed with pesticides and herbicides, reducing species diversity.

3. Loss of heritage varieties: Heritage/traditional plants don't make enough money so are not planted anymore, reducing species diversity. 

6 of 13

3. Factors affecting Biodiversity

Climate change and global biodiversity:

Greenhouse gases cause global warming. Causing climate change. Climate change can affect biodiversity by:

1. Changing environment conditions: Most species need a particular climate to survive, so a change in climate may mean that an area that was previously inhabitable becomes uninhabitable. (Vice versa). This may cause increase or decrease in range of some species. Increase or decrease biodiversity (globally). May force some species to migrate resulting in change in species distribution. If there isn't a suitable place to migrate to, species is a plant, or change is too fast, species may become extinct, decreasing biodiversity.

7 of 13

4. Biodiversity and Conservation

Ecological reasons to maintain biodiversity:

All down to complex relationships between organisms and their environments.

Protecting species: An ecosystem is all the organisms living in an area and all non-living conditions. Organisms in an ecosystem are interdependent - depend on each other to survive. Loss of one species can have drastic effects on an ecosystem:

  • Disruption of food chains.
  • Disruption of nutrients cycles.

There are some species which many of others in ecosystem depend and without, ecosystem would drastically change = Keystone species. Tend to have a relatively low population size but huge effect on environment. Often predators, keeping population of prey in check. Keystone species can also be modifiers - maintaining environment needed for ecosystem (E.G. beavers building dams), or hosts - plants that provide a particular environment, (E.G. palm trees). 

Maintaining genetic resources: Any material from plants, animals or microorganisms, containing genes, that we find valuable. Need to maintain for several reasons: 

  • GR provide us with a variety of everyday products like food, clothing, drugs, fuels...
  • GR also allow us to adapt to changes in the environment.
8 of 13

4. Biodiversity and Conservation

Economic reasons to maintain biodiversity: Products derived from plant and animal species are traded on local and global scale, other reasons such as:

Reducing soil depletion: Continuous monoculture (when harvested, more of the same are planted) causes soil depletion because nutrients required by the crop are gradually used up. Economic costs - Increased spending on fertilisers (to artificially replace nutrients) and decreased yield ( in long run and if fertilisers not used). 

Aesthetic reasons to maintain biodiversity: Areas rich in biodiversity provide pleasant, attractive landscapes. By maintaining biodiversity, we protect the beautiful landscapes. More/greater diversity, more visitors likely = economic advantages. Example, National Trust.

Maintaining biodiversity through conservation: Important to ensure survival of endangered species. A species that is critically endangered is likely to become extinct because it's population size is too small.

1. In situ conservation: Conservation on site - protecting species in their natural habitat. Methods include:

  • Establishing protected areas - nature reserves, marine conservation. 
  • Controlling/preventing introduction of species that threaten local biodiversity.....
9 of 13

4. Biodiversity and Conservation

  • ...Protecting habitats.
  • Restoring damaged areas.
  • Promoting particular species - protecting local food source/nesting area.
  • Giving local protection to endangered species.

Advantage: Often both species and habitat are conserved meaning larger populations can be protected. Less disruptive as it is in the natural habitat. Greater recovery than Ex-situ.

Disadvantage: Can be difficult to control some factors that are threatening a species.

2. Ex situ conservation: conservation off site - protecting a species by removing part of population from threatened habitat to new location. Often a last resort. Methods include: 

  • Relocating an organism to a safer area. 
  • Breeding in captivity then reintroducing into the wild when strong enough. 
  • Botanic gardens.
  • Seed banks.

Advantage: Controlled environment, predation and hunting is controlled. Competition for resources is reduced and it's possible to check health and treat disease. Breeding can be manipulated. Can be used to reintroduce species that have left the area....


10 of 13

4. Biodiversity and Conservation

...Disadvantage: Only a small number of animals can be cared for. Expensive and difficult to create environment. Less successful. 

Conservation and international cooperation:

Rio convention on biological diversity  (CBD): Conservation is everyone's responsibility.  International agreement that aims to develop international strategies in conservation of BD and how to use animal and plant resources in a sustainable way.

CITES agreement: (Convention on International Trade in Endangered Species) Designed to increase international cooperation in regulating trade in wild animals and plants specimens.

Countryside Stewardship Scheme (CSS): Local agreement to conserve wildlife and BD by promoting specific management techniques to land-owners.

11 of 13


Here are potential equations you need to know:

D = 1 - ( sum of (n/N))

(n = total number of organisms in species 1, N = total number of organisms, D = Dominance, (sum of) is shown as a symbol. )

Proportion of polymorphic gene loci = Number of polymorphic gene loci / total number of loci

( as well as basic maths, especially when working with quadrats,  etc)

12 of 13


Side notes: (You should colour code too)

1: Check the OCR specification to make sure you have covered everything.

2: Practice questions and test papers!

3: Find pictures to correspond to each of the processes to help your understanding.  Drawing them yourself may help you to remember more!

4: I could not add pictures so I do recommend finding or drawing some and stapling them to the flashcard.

All notes have been taken from the OCR Biology AS Yr 1 textbook.

Thank you!

13 of 13


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Ecology, ecosystems and environmental biology resources »