Biodiversity (OCR A Level Biology): Flashcards

The diversity of alleles and genes in the genome of a species. Individuals of the same species share the same genes but not necessarily the same alleles for each gene.

By working out the proportion of genes that have more than one form (allele) and how many possible alleles each gene has.

It helps the population adapt to and survive changes in the environment, including:

• Biotic factors such as new predators, pathogens and competition

• Abiotic factors such as temperature, humidity and rainfall

Inbreeding in small, isolated populations leads to a high proportion of individuals being homozygous for many genes, resulting in lower genetic diversity.

Inbreeding raises the proportion of individuals that are homozygous for many genes, lowering genetic diversity. This means genetic diseases caused by recessive alleles are more likely to be expressed and become more common.

True

False — they share the same genes but not necessarily the same alleles.

A method of measuring biodiversity in multiple small areas within a habitat and using this information to estimate and represent the biodiversity of the habitat as a whole.

In large and complex ecosystems it is impossible to find, identify and count every organism, so sampling small areas is used to make an estimate of the biodiversity present.

• Distribution: where organisms live within a habitat\n\n- Abundance: how many organisms are present

A sample must be large enough to eliminate the effects of chance (e.g. missing a species simply because it did not happen to occur at the sites assessed).\n\nThe more samples that are collected, the more likely the data will be representative of the habitat.

In random sampling, sampling sites are selected at random to avoid bias that might result from a researcher choosing the sites.

• Two long tape measures are laid along the outer edges of the habitat to set up a grid system\n\n- A random number generator is used to generate two random numbers\n\n- The numbers are used like graph coordinates, and the sample site is placed at the point of intersection

When a sampling area is reasonably uniform or has no clear pattern of species distribution.

• Opportunistic sampling\n\n- Stratified sampling\n\n- Systematic sampling

The number of random samples taken within each habitat type is proportional to the area covered by that habitat type.\n\nE.g. if 10% of a woodland is grassy clearings, then 90% of sample locations should be under tree cover and 10% in the clear areas.

Samples are taken across a habitat with reference to the changes in habitat conditions. It involves the use of transects.

A square frame placed within the area to be studied to provide a sample; suitable for sampling plants or slow-moving animals, and can be placed randomly or along a transect.

• The number of species present\n\n- The number of individuals of a species (abundance)\n\n- The presence/absence of a species\n\n- The percentage cover of a species (useful where it is hard to tell where one individual ends and another begins)

• Sweep net: swept across vegetation to catch flying insects and insects that live on leaves\n\n- Pitfall trap: a container sunk into the ground to catch ground-dwelling invertebrates (a lid stops it filling with rainwater)\n\n- Pooter: two-tubed container used to suck up small invertebrates for viewing and identification

A line along which samples are taken, used during systematic sampling to assess how the abundance and distribution of organisms is affected by changes in abiotic factors across a habitat.

Line transect:\n\n- Lay a tape in a straight line across the sample area\n\n- At regular distances (e.g. every 1 m) record the identity of organisms that touch the line\n\nBelt transect:\n\n- Lay a tape in a straight line across the sample area\n\n- Place quadrats at regular intervals (or continuously) and record the abundance or percentage cover of each species within each quadrat

Systematic sampling is used where habitat conditions change across an area, e.g. sampling at increasing altitude, increasing distance from the edge of a woodland, or increasing distance from the shore line.

False — a clear gradient calls for systematic sampling using transects; random sampling suits uniform habitats.

True

A square frame of a known area used to sample the abundance and distribution of sessile (immobile) organisms within a defined area.

• Mark up a grid on a map or to-scale drawing of the area and label the grid with coordinates

• Use a random number generator to select a set of coordinates

To avoid sampling bias, which could otherwise lead to over- or under-estimation (e.g. subconsciously choosing areas that are easier to access or that appear to contain more individuals).

• Population density

• Percentage cover

• Species frequency

Calculate the mean number of individuals per quadrat for the first two quadrats, then for the first three, then the first four, and so on.

Continue until there is no further significant change in the mean — this indicates enough quadrats have been sampled.

Divide the total area of the habitat by the area of one quadrat, then multiply by the mean number of individuals per quadrat.

• Place a grid quadrat (a frame split into 100 smaller squares) at the coordinate; each small square represents 1% cover

• Count the number of squares in which the species occupies over half the square (e.g. 30 squares = 30% cover)

Because estimating percentage cover is subjective, so the same person should make the estimate for all samples to control this variable.

Count the number of quadrats that contain the species, divide by the total number of quadrats, and multiply by 100.

For example, if bluebells were found in 18 out of 50 quadrats, the species frequency = (18/50) × 100 = 36%.

Together they give a good picture of the distribution of a species across the habitat.

It suggests the species lives in groups in preferred areas of the habitat (e.g. preferring light/dark or wet/dry conditions).

Quadrats (and transects) can only be used for sessile and immobile species, such as plants and slow-moving animals.

It shows how common a species is but does not give information on the estimated number of individuals or the size of the population.

• A first large sample is caught, counted and marked in a way that won't affect survival (e.g. non-toxic paint on a beetle's carapace)

• The marked individuals are returned to their habitat and allowed to randomly mix with the population

• After sufficient time, a second large sample is captured

• The proportion of marked to unmarked individuals is used to estimate the population size

N = (n₁ × n₂) ÷ m₂

• N = population estimate

• n₁ = number of marked individuals released

• n₂ = number of individuals in the second sample (marked and unmarked)

• m₂ = number of marked individuals in the second sample

Step One: Substitute values into the formula

N = (n₁ × n₂) ÷ m₂

N = (236 × 244) ÷ 71

Step Two: Calculate N

N = 57,584 ÷ 71

N = 811 leafhoppers

• Marked individuals have sufficient time to disperse and mix back into the population

• Marking does not affect survival rates (e.g. does not make them more visible to predators)

• The marking remains visible and does not rub off during the study

• The population size stays constant (no significant births, deaths or migration during the study)

A random number generator is used to select sampling coordinates in order to avoid sampling bias, which could lead to over- or under-estimation.

False — quadrats only work for sessile or slow-moving organisms; mark-release-capture is used for mobile animals.

True

A measure of biodiversity in a given area that takes into account both species richness and species evenness.

• Species richness

• Species evenness

A measure of the number of different species within a given area.

A measure of the relative abundance of the different species within a given area.

Because it only counts the number of different species and does not take into account the number of individuals of each species (their relative abundance).

A greater species evenness (and therefore a higher overall species diversity).

Area 1 has the higher species diversity.

Both areas have the same species richness, but Area 1 has a higher species evenness because its species have more similar abundances.

Species diversity takes both richness and evenness into account.

Simply count the number of different species present in the area.

Count the number of different species present and the number of individuals of each species (any sampling method that takes the abundance of each species into account).

Simpson's Index, because it takes into account both species richness and species evenness.

Species evenness is a measure of the relative abundance of the different species within a given area.

Species richness is a measure of the number of different species within a given area.

False — species richness only counts the number of different species; it is species evenness that accounts for relative abundance.

True

A measure of biodiversity that takes into account both the number of different species in an area (species richness) and the evenness of abundance across those species (species evenness).

The number of different species present in an area.

A measure of how even the abundance is across the different species in an area.

To quantify the biodiversity of an area, taking into account both species richness and species evenness.

• n = the total number of organisms of a single species\n\n- N = the total number of organisms of all species

Step 1: Calculate n / N for each species\n\nStep 2: Square each of these values\n\nStep 3: Add the squared values together and subtract the total from 1

D can fall between 0 and 1.

A high level of biodiversity.

A low level of biodiversity.

Values of Simpson's Index of Diversity near 1 indicate high levels of biodiversity.

Species evenness measures how even the abundance is across the different species in an area.

No. The formula is provided in the exam, so you do not need to recall it — but you must know how to use it to calculate D.

False — a value near 1 indicates a high level of biodiversity.

False — species richness is only the number of different species; evenness is measured by species evenness.

The genetic variation that exists within a species.

All of the alleles of all of the genes within a species.

They do not necessarily have the same alleles for each gene, so different alleles occupy the same loci.

The two populations may occupy slightly different ranges in their habitat.\n\nThis means they are subject to slightly different selection pressures, which affect the allele frequencies in each population, adding different alleles to the overall gene pool.

It creates a larger gene pool, which helps the population to adapt and survive changes in the environment.\n\nThese changes may be:\n\n- Biotic factors e.g. new predators, pathogens and competition with other species\n\n- Abiotic factors e.g. temperature, humidity and rainfall

• The proportion of polymorphic gene loci (loci with two or more alleles)\n\n- The proportion of the population that is heterozygous for a specific gene locus\n\n- Allele richness (the number of different alleles that exist for specific genes)

The number of different alleles that exist for specific genes.

For some genes, each different allele produces observable differences when expressed in the phenotype of an individual.\n\nHowever, for other genes different alleles do not produce an observable change, so the DNA sequences or the protein products of the alleles must instead be examined and compared.

When there are two or more alleles present at a single locus, where the rarest allele has a frequency greater than a chosen threshold (e.g. 1% or 5%).

A monomorphic locus is one that does not have multiple alleles.

P = number of polymorphic gene loci ÷ total number of loci investigated

P = number of polymorphic gene loci ÷ total number of loci investigated\n\nP = 59 ÷ 100\n\nP = 0.59

P does not illustrate the allele richness of a species.\n\nTwo loci can both be polymorphic (counting equally towards P) yet have very different numbers of alleles, e.g. all loci polymorphic (P = 1) but the number of alleles per locus varying from 2 to 11.

• Comparing the amino acid sequences of proteins (useful for investigating allozymes — slightly different forms of the same enzyme coded for by different alleles)\n\n- Comparing DNA base sequences (in nuclear DNA and mitochondrial DNA)

The genetic code is degenerate, so two alleles can code for the same amino acid sequence but still have different DNA base sequences.

Comparing base sequences therefore reveals differences that protein comparison would miss, which is why nearly all genetic diversity assessment is now done at the level of base sequences.

False — a polymorphic locus has two or more alleles; it is a monomorphic locus that does not have multiple alleles.

True

• Improved technology leading to an abundance of food, which increases the birth rate

• Improved medicine and health care, which decreases the death rate

As the population increases and countries become more economically developed, the demand for natural resources (land, water, wood, fossil fuels) increases.

Meeting these human needs damages aquatic and terrestrial ecosystems, the atmosphere and climate, which negatively impacts the species and habitats within them.

• Habitat destruction

• Overexploitation

• Hunting

• Agriculture

• Climate change

Habitat loss: plants and animals completely lose their habitats when land is cleared.

Habitat fragmentation: habitats are divided into small, separated areas. Populations in these fragments are more likely to suffer from inbreeding or local extinction.

Forest habitats often have the highest levels of biodiversity, so their destruction results in the loss of a very large number of species and habitats.

The use of natural resources faster than they can be replaced, for example removing trees or fish stocks more quickly than they can regrow or replenish.

Many wild, non-farmed species are hunted and removed more quickly than their wild populations can be replenished.

An example is the hunting of animals for 'bush meat' in developing countries, including primates such as monkeys and chimpanzees.

• Monoculture (growing one crop or raising one type of livestock) supports much lower biodiversity than natural habitats

• Removal of hedgerows to make bigger fields destroys habitats for insects, small mammals and birds

• Draining wetland and filling in ponds removes habitats

• Increased use of fertilisers and pesticides

Fertilisers can leach into waterways, causing eutrophication, which can lead to the death of many aquatic invertebrate and fish species.

Pesticides such as insecticides used on crops kill insect pests but also kill many non-target species, including important pollinators like bees.

• Monoculture of crops reduces plant diversity, lowering the supply of pollen and nectar in bumblebee habitats

• Pesticides can have a negative effect on bumblebees even though they are not the target species

Practices that maintain or increase biodiversity can be expensive, labour- and time-intensive, and can reduce yield.

For example, stopping pesticide use increases bumblebee numbers but also increases pest numbers, reducing crop yield and profit in a very competitive market.

• Changing weather patterns and more frequent extreme events may occur too fast for many species to adapt, risking extinction

• Global warming causes species to move towards the poles or higher altitudes, where they may out-compete or be out-competed by existing species, decreasing biodiversity

• Some species (e.g. plants) cannot shift their distribution fast enough and may go extinct

Ocean acidification: more CO₂ dissolves in seawater, decreasing its pH. This harms organisms that need calcium carbonate for shells, such as plankton and coral polyps.

Coral bleaching: higher ocean temperatures cause the organisms living inside corals to leave due to temperature stress, so the corals die and reefs (and the biodiversity they support) are lost.

True

False — monocultures support much lower biodiversity than natural habitats.

A farming practice in which only one crop is grown or one type of livestock is raised, supporting much lower biodiversity than natural habitats.

Excessive nutrient enrichment of a waterway, often from fertiliser leaching, that can lead to the death of many aquatic invertebrate and fish species.

The range and variety of genes, species and habitats within a particular region.

• Genetic diversity

• Species diversity

• Ecosystem diversity

• Ecological

• Economic

• Aesthetic

• Social

• Moral/ethical

• Environmental

• Agricultural

Biodiversity has a major effect on the stability of an ecosystem.

A more diverse ecosystem is better able to survive and adapt to environmental changes or threats, because if some species cannot cope with a change, others can survive, reproduce and continue to contribute to the ecosystem.

A species that has a disproportionately large impact on its ecosystem relative to its abundance; when it is lost there are several knock-on effects on the ecosystem.

• They graze in an extreme way, knocking over and eating several species of tree, and this destruction of vegetation actually helps to maintain the ecosystem

• Their dung provides a habitat for many important fungi and insect species

• When they were legally hunted for ivory, their numbers fell and scientists observed a major negative impact on the savannah

• Many medicines originate from plants, fungi and bacteria (e.g. the cancer drug paclitaxel from Yew trees), and undiscovered drugs may still exist in nature

• Ecotourism is a major source of income, contributing to economies and providing jobs

• Ecosystems contribute to science and technology (e.g. the enzyme used in DNA sequencing came from a thermophilic bacterium in a Yellowstone hot spring)

Humans find joy and pleasure in the beauty of nature, and it provides inspiration for creatives such as photographers, poets, musicians and artists.

Many people believe humans have a moral obligation to prevent the loss of biodiversity caused by human activities.

We share the planet with millions of other species and have no right to cause their extinction; as the most intelligent species, the responsibility to protect and value all organisms falls on humans.

• Plants absorb carbon dioxide, helping to reduce the greenhouse effect and climate change

• Microorganisms break down the organic waste produced by larger organisms

• Transpiration of plants contributes to the water cycle, providing irrigation and drinking water

• Fungi and bacteria drive the nutrient cycle, returning nutrients to the soil for further plant growth

• Plants are producers, acting as a direct and indirect energy source for humans

Most crops are very uniform with low genetic diversity, making them highly susceptible to disease.

The wild relatives of crops provide a source of genetic diversity (alleles) that can be used to rescue crops affected by disease or other disasters, through gene technology or interbreeding.

• All of the world's potato crop comes from a single species, so this lack of species diversity makes it highly susceptible to disease

• Over 100 species of wild potatoes grow in the Andes and act as a source of alleles for disease resistance

• These alleles have been introduced into the potato crop through gene technology and interbreeding

A keystone species has a larger impact on its ecosystem than others, causing several knock-on effects when it is lost.

The wild relatives of crops provide a source of genetic diversity that can be used to rescue crops affected by disease or disaster.

Many people enjoy spending time in nature together through activities such as birdwatching, walking and climbing; these social benefits are lost if such environments are not conserved.

True

False — most crops are very uniform with low genetic diversity, making them highly susceptible to disease.

A species that is being threatened with extinction.

Conservation of a species carried out within its natural habitat, where the support systems it needs to survive already exist.

Conservation of a species carried out outside its natural habitat, e.g. by capturing individuals and placing them in captivity.

Because the species is kept in its natural habitat, where all of the support systems it needs to maintain life already exist.

• National parks

• Marine parks

• Human access is strictly controlled

• Industrial activities such as agriculture and building are tightly regulated

• Hunting is limited or completely prohibited

A protected area of water set up for the conservation of endangered marine ecosystems and species.

• Parks attract tourists, which raises money and awareness for conservation

• Involving the local community provides jobs and increases acceptance of the parks

• Profits can improve local health and education standards, showing the benefits of the parks

• Captive breeding programmes breed individuals so offspring can be released into the wild

• They allow scientific research into animals' genetics, behaviour and habitat needs

• They provide education and raise awareness of endangered species

• Captive breeding of small populations can reduce genetic diversity

• Certain species will not breed in captivity

• Not all zoos can provide adequate habitats for animals with specific needs

• They use cuttings and seeds collected from the wild to establish a captive population

• Tissue culturing and cloning can produce large numbers of plants from a small sample

• The captive population can later be used for reintroduction into habitats where the species has become rare

A facility that stores animal genetic material (eggs, sperm, tissue samples) at very low temperatures so it can be kept for a very long time.

A facility that conserves plant diversity by drying and storing seeds in a temperature-controlled environment, so that a species can be regrown if it becomes extinct.

Seeds can only be stored for a limited time. After a certain period the stored seeds are grown into plants, and fresh seeds for storage are taken from those plants.

Conservation carried out within a species' natural habitat is known as in situ conservation.

It has restrictions that help prevent overfishing and pollution.

To maintain the gene pool, preserving genetic diversity within the stored samples.

False — ex situ conservation takes place outside the natural habitat.

True

International cooperation is essential if conservation is to be successful, because many species and their habitats cross national borders.

Several agreements and authorities exist within and between countries with the aim of protecting and conserving species worldwide.

The global authority on the status of the natural world and the measures needed to safeguard it.

One of its key duties is assessing the conservation status of animal and plant species around the world.

The IUCN has its own classification system with several categories and levels.

Which category a species falls into depends on its population numbers and the threats and risks to those populations.

Scientists use data and modelling to estimate which category each species should be in.

The IUCN Red List of Threatened Species is a publicly available list of animals classified according to the IUCN classification system.

It can be viewed online, and scientists continually update and review the conservation status of species.

An international agreement, signed at the Earth Summit in Rio de Janeiro in 1992, committing countries to conserve and sustainably use biodiversity.

• The conservation of biological diversity by use of a variety of different conservation methods

• The sustainable use of biological resources

• The fair and equitable sharing of benefits arising from genetic resources

They agreed to:

• Design and implement national strategies for the conservation and sustainable use of biodiversity

• Organise international cooperation and further international meetings

A global agreement, signed by over 150 countries, that aims to control the trade of endangered species and their associated products (for example, elephants and their ivory tusks).

CITES categorises endangered and vulnerable species into three appendices:

• Appendix I: species that are endangered and face the greatest risk of extinction

• Appendix II: species that are not currently endangered, but will be unless trade is closely controlled

• Appendix III: species included at the request of a country regulating trade to prevent overexploitation

• Appendix I: all trade in the species and their associated products is banned

• Appendix II: trade is only granted if an export permit has been issued by the involved countries

• Appendix III: permits are required for regulated trade, but are easier to come by than for the other appendices

When the trade of an endangered species becomes illegal, its price increases.

This increased economic value of the species can be a major incentive for people to break the law.

The CSS was a scheme dating back to the 1980s that provided funding (a financial incentive) to farmers and private landowners in England who used environmental management strategies to protect and increase the natural biodiversity on their land.

• Provide and protect valuable wildlife habitats such as ponds, hedgerows and buffer zones

• Ensure their land is managed well, maintaining its traditional character

• Protect any natural resources or historic features on their land

• Conserve any traditional crops or livestock present on their land

• Provide visitor opportunities so people can learn about the countryside and its importance in sustaining biodiversity

The Convention on Biological Diversity (CBD) was signed at the Earth Summit in Rio de Janeiro in Brazil in 1992.

It was replaced by the Environmental Stewardship Scheme (ESS) in 2005.

True

False — it is a publicly available list that can be viewed online.