Biodiversity Introduction and Measurement | A-Level Biology PDF

```markdown ## 4.2 # 1 Biodiversity By the end of this topic, you should be able to demonstrate and apply your knowledge and understanding of: * how biodiversity may be considered at different levels * how sampling is used in measuring the biodiversity of a habitat and the importance of sampl...

```markdown ## 4.2 # 1 Biodiversity By the end of this topic, you should be able to demonstrate and apply your knowledge and understanding of: * how biodiversity may be considered at different levels * how sampling is used in measuring the biodiversity of a habitat and the importance of sampling **KEY DEFINITIONS** **biodiversity:** a measure of the variation found in the living world. **habitat:** where an organism lives. **species:** a group of organisms that can freely interbreed to produce fertile offspring. ## Biodiversity Biodiversity is a measure of all the different plant, animal, fungus and other microorganism species worldwide, the genes they contain, and the ecosystems of which they form a part. Biodiversity is about the structural and functional variety in the living world. We can consider it at a number of levels. ### Habitat biodiversity A habitat is the place where individuals in a species live. The range of habitats in which different species live is known as the habitat biodiversity. Common habitats found in the UK include sand dunes, woodland, meadows and streams. Even in your school grounds or in a local park, there may be a variety of habitats. Carefully manicured lawns, ponds, dark corners between buildings or a small patch of trees are all different habitats. Each habitat will be occupied by a range of organisms. ### Species biodiversity A species consists of individual organisms that are very similar in appearance, anatomy, physiology, biochemistry and genetics. As a result, individuals in a species can interbreed freely to produce fertile offspring (offspring that can breed to give rise to more offspring). The range of organisms found in a habitat contributes to the species biodiversity. However, it is not a simple matter of counting the number of different species. Two habitats may have an equal number of different species, but they may not be considered as equally diverse. For example, a wild meadow might have 25 species of grasses and herbs (see Figure 1(a)). In any small sample you might find most of these species. Compare that with a garden lawn, or a managed cow pasture (see Figure 1(b)). Here there may be 25 plant species, but one or two grass species dominate, with just a few individuals of the other species dotted about. The wild meadow is much more diverse, because the 25 species are more evenly represented. We call the number of plant species the species richness. The degree to which the species are represented is known as the species evenness. These terms are further used in topic 4.2.4. The image shows two fields of plants, the one on the left is a collection of wildflowers and the one on the right is a uniform grass pasture. **Figure 1** A wildflower meadow (left) and a grass pasture (right). ### Genetic biodiversity Genetic biodiversity is the variation between individuals belonging to the same species. This is the variation found within any species that ensures we do not all look identical. Genetic variation can create breeds within a species, as shown by the difference between breeds of cattle or dogs (see Figure 2). The image shows two dogs of different breeds, a dachshund and a dalmatian. Figure 2 Genetic diversity in dogs. ## Using samples to measure biodiversity of a habitat In order to measure the biodiversity of a habitat, you need to observe all the species present, identify them, and count how many individuals of each species there are. Ideally, you should do this for all the plants, animals, fungi, bacteria and other single-celled organisms living in the habitat. Obviously, this is not practical, as it would be impossible to count all the fungi, bacteria and single-celled organisms. One estimate suggests that there may be billions of single-celled organisms per square metre of soil, and possibly hundreds of thousands of mites per square metre! Some microorganisms can be cultured on a nutrient medium in the laboratory to gain an estimate of numbers, but not all will grow like this. ## ## 4.2 **1. Biodiversity** Instead, you can sample a habitat. This means you select a small portion and study that carefully. Then you can multiply up the numbers of individuals of each species found, in order to estimate the number in the whole habitat. It is important that the samples taken are representative of the habitat. There are a number of sampling strategies that can be adopted, and each has advantages and disadvantages **Table 1.** A summary of sampling strategies | Type of sampling | How sampling is carried out | Advantages | Disadvantages | | :--------------- | :----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | :-------------------------------------------------------- | :------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | | Random | Sample sites inside the habitat are randomly selected. You can do this by deciding where to take samples before you study any area in detail. This can be achieved by using randomly generated numbers as coordinates for your samples, or possibly selecting coordinates from a map and using GPS to find the exact position inside the habitat. | Ensures that the data are not biased by selective sampling. | May not cover all areas of a habitat equally. Species with a low presence may be missed, leading to an underestimate of biodiversity. | | Non-random Opportunistic | This is when the researcher makes sampling decisions based on prior knowledge or during the process of collecting data. The researcher may deliberately sample an area that he or she knows (or can see) contains a particular species. | Easier and quicker than random sampling. | The data may be biased. The presence of large or colourful species may entice the researcher to include that species. This may lead to an overestimate. | | Stratified | Dividing a habitat into areas which appear different, and sampling each area separately. For example, patches of bracken in heathland might be sampled separately from the heather or gorse patches. | Ensures that all different areas of a habitat are sampled and species are not under-represented. | There is a possibility that this may lead to over-representation of some areas in the sample i.e a disproportionate number of samples are taken in small areas that look different. | | Systematic | This is when samples are taken at fixed intervals across the habitat. Line transects and belt transects are systematic techniques. | Particularly useful when the habitat shows a clear gradient. | Only the species on the line or within the belt can be recorded. Other species may be missed, leading to an underestimate of biodiversity. | **Questions** 1. Make a list of the habitats found in your school/college or in a local park. 2. Describe what is meant by the means 'species richness' and 'species evenness'. 3. Explain why it is important to sample a habitat in order to estimate the biodiversity. 4. Why should sampling be as random as possible? 5. Explain why opportunistic sampling may lead to an overestimate of biodiversity. 6. Describe what type of sampling would be best to sample a field such as the wild meadow in Figure 1. ## ## 4.2 **2 Sampling plants** By the end of this topic, you should be able to demonstrate and apply your knowledge and understanding of: * practical investigations collecting random and non-random samples in the field #### Sampling a habitat Preparation It is important to be properly prepared for any fieldwork. Your planning should include: * suitable clothing - this will depend upon the type of habitat and the expected weather conditions * suitable footwear * apparatus needed to carry out the sampling * clipboard, pen and paper to record your observations. * appropriate keys to identify plants * camera or smartphone to record specimens and grid location. Ideally, you will have considered the number of samples that you will collect, and you will have prepared a results table ready to record your observations. It is important that you can recognise all species correctly, so that you do not record several different species as one. Plants can be identified using a dichotomous key. Before heading out to the sample site, you should be familiar with using this type of key. At some times of year, some plants may be visible only as a leaf or two (or not even visible at all). Features such as shape and size of leaf, hairs and colour will all help to identify it. Some plants look different at different times of year in spring only a few small leaves may be visible. It may be necessary to visit a site several times to get a full estimate of biodiversity. At the site When visiting a site to measure its biodiversity, it may be best to use a range of techniques. Random sampling is important, but it may be helpful to modify the sampling technique if the habitat is not homogeneous (even). Moving some of the sample sites into areas that look different would be classed as opportunistic sampling (as you are making decisions during the sampling process) and also stratified sampling (as you are treating parts of the habitat differently). It may also be helpful to combine random sampling with systematic sampling, as described below for the point frame. One important aspect of your work should be to consider the effect your presence will have on the habitat. Any sampling should cause as little disturbance as possible. Trampling, picking flowers, placing quadrats, etc. will all cause some disturbance. #### Sampling plants Large plants such as trees in a wood or in a field van be identified and counted individually. However, many plants may be too small or too numerous. In this case it may be best to calculate a value percentage ground cover occupied by each species. #### Using random quadrats A quadrat is A square frame used to define the size of the sample area. A quadrat may be any size, but it often Measures 50cm or 1m on each side. For random sampling, you can generate random ## ## 4.2 **Biodiversity ** numbers and then use these numbers as coordinates to place the quadrats within the habitat. A tape measure will help with placing the quadrat accurately. Alternatively, counting even paces will help to locate the correct coordinates. Inside the quadrat you will need to identify the plants found and then calculate the percentage over as a measure of their abundance. * It may be possible to estimate the percentage cover of each species, although most students tend to underestimate. Some quadrats have a grid of string that divides the quadrat into a number of smaller squares (usually 100). This grid can help to make your estimates more accurate. * You can measure percentage cover using a point frame (see Figure 1). This is A frame holding A number of long needles or pointers. You lower The frame into the quadrat and record any plant touching the needles. So each plant recorded as touching the needle will have 1% cover. As one needle may touch several plants, it is possible to find you have 300-400% cover in some habitats. Don't forget to record bare ground. It is Easy to bias your readings by using the point frame non-randomly within the quadrat. Therefore, it may be best to use the point frame at regular intervals across the quadrat (systematic sampling within the randomly placed quadrat). The image shows a quadrat point frame **Figure 1** A point frame. #### Using a transect A transect is A line taken across the habitat. You stretch a long string or tape measure across the habitat and take samples along the line. In a large habitat, you might use A line transect. In this case you would record the plants touching the line at set intervals along it. You may also decide to use A quadrat at set intervals along the line. This is called An interrupted belt transect. This will provide quantitative data at intervals across the habitat. Alternatively, you may use a continuous belt transect. In this case you place a quadrat beside the line, and move it along the line so you can study a band or belt in detail. You should study each quadrat as desribed above. This will provide quantitative data in A band or belt across the habitat. the image shows a person conducting a line transect experiment **Figure 2** A line transect. **Questions** 1. Describe How you would sample A meadow to find out what plants live there. 2. Explain why it is necessary to take samples. 3. Describe The ways That sampling A habitat may disturb That habitat. 4. When would you use A belt transect. 5. Explain why sampling in spring may give A very different measure of plant biodiversity when compared with sampling in summer. 6. Why should you always use a key to identify plants. ## ## 4.2 **3 Sampling animals** By the end of this topic, you should be able to demonstrate and apply your knowledge and understanding of: * practical investigations collecting random and non-random samples in the field #### Sampling animals by observation Many animals are not easy to spot and are more difficult to count. Larger animals can detect the presence of humans before we see them, and will hide away. Small animals will also hide, and often move too quickly to count accurately. Therefore, obtaining quantitative data on animals isdifficult. You can note the presence of many larger animals by careful observation - looking for signs that they have left behind. For example, owls deposit pellets of undigested food; rabbits have obvious burrows; and deer damage the park of trees in a particular way. Ecologists often rely on these signs to estimate population sizes. Recent advances allow scientist to use DNA sequencing to distinguish drippings from different individuals. This provides a more accurate way to calculate the population size. #### Collecting samples of live animals Preparation for A site visit Is described in the previous topic. Planning Should include bringing along Appropiate apparatus For the Chosen Sampling techniques. #### Catching invertebrates * The technique of sweep netting involves walking through the habitat with a stout net. You sweep the net through the vegetation in wide arcs, Any small animals such as insects, will Be caught In the net. Then you can empty The contents on to A white sheet To identify Them. You need To be Careful, As many Of the animals May Crawl Or fly away As soon As you release Them From the net. You CAN use A device Called A pooterTo Collect The animals Before They fly Away. This Type Of Sampling Is SuitableFor Low Vegetation That Is Not Too Woody. You Can Use A Similar The image shows scientists conducting a sweep net experiment **Figure 1** Using sweep nets. The image shows a pooter device **Figure 2** A pooter. * Collecting From trees Using A sweep Net Is Unlikely To Work Well here It Is Better To Spread out under A Branch, And knock The branch With A Stout Stick. The Vibrations dislodge Any Small animals, Which Then Drop on To The sheet. Again, You Will need To be Quick To Identify And Count The animals Before They Crawl or Fly Away. * A pitfall trap is A trap Set In The Soil To Catch Small animals. It Consists Of A Small Container Buried In The Soil So That Its Rim is Just Below The Surface. Any animals Moving Through The plants Or Leaf Litter On The Soil Surface Will fallInto the Container. The trap Should Contain A Little Water Or Scrunched paper To StopThe animals Crawling Out Again. The image shows a pitfull trap **Figure 3** A pitfall trap. * A Tullgren funnel is A device For Collecting Small animals From Leaf Litter. You place Them Leaf Litter in A funnel. A Light AboveThe Litter DrivesThe animals Downwards As The Litter Dries Out And Warms Up. They Fall through Them ## ## 4.2 **Biodiversity** Light ( 100W) Funnel Ring Stand Screen Collecting Jar Figure 4 A Tullgren funnel. A light trap can be used to collect flying insects at night. It consists of an ultraviolet light that attracts the insects. Under the light is a collecting vessel containing alcohol. Moths and other insects attracted to the light eventually fall into the alcohol. Trapping small animals Small animals can be trapped and population estimates calculated. The technique that you use will depend on the habitat and the type of animals you are hoping to catch. Beware though, you may need a licence to trap some animals, and care should also be taken not to harm the animals in any way. Small mammals can be trapped using a Longworth trap. This is a humane trap that does not harm the animal. These traps must be monitored regularly to release any trapped animals. Trapping with a Longworth trap enables the population size to be calculated using the mark-and-recapture technique. * First, you need to capture a sample of animals. * Mark each individual in some way that causes it no harm. The number captured will be $C_1$. * Release the marked animals and leave the traps for another period of time. * The number captured on this second occasion will be $C_2$. The number of already marked animals captured on the second occasion is $C_3$. You can then calculate the total population using the formula: $$Total\ Population=\frac{C_1 \cdot C_2}{C_3}$$ However, the estimate calculated can be affected by animals that learn that the trap is harmless and contains food, or by animals that do not like the experience and therefore keep away from traps after the first capture. It is also possible to calculate the size of some insect populations(such as grasshoppers) by the mark and recapture technique. Populations of birds can be estimated by using e ringing technique to identify individuals, and some larger mammals can be tagged. These techniques require skill and experience, and should only be carried out with a suitable permit issued by the relevant authority (the British Trust for Ornithology issues permits to ring birds for research purposes). Questions 1 Describe how you might sample animals from (a) a meadow,and (b) under a hedge. 2 Plan an investigation to determine whether sweet chestnut treessupport a higher biodiversity than hazel. Describe how you wouldcarry out the investigation. 3 How could owl pellets be useful in determining what animals live in a habitat? 4 How could you mark a small mammal, causing no harm to it? 5 How would animals that like to be trapped affect the estimatedsize of the population when using the mark-and-recapturetechnique? ### ## 4.2 ## 4 Calculating biodiversity By the end of this topic, you should be able to demonstrate and apply your knowledge and understanding of: * how to measure species richness and species evenness in a habitat * the use and interpretation of Simpson's index of diversity (D) to calculate the biodiversity of a habitat * how genetic diversity may be assessed, including calculations **KEY DEFINITIONS** **allele or gene variant:** a version of a gene. **locus:** the position of that gene on a chromosome. **polymorphic gene locus:** a locus that has more than two alleles **Simpson's index of biodiversity:** a measure of the diversity of a habitat. **species evenness:** a measure of how evenly represented the species are. **species richness:** a measure of how many different species are present. Estimating biodiversity **Measuring biodiversity within a habitat** When measuring biodiversity, we have to consider species richness - Species Richeness can be Measured by Counting all the species The Number OF Species Found In A Habitat, The More number of Species Present The Richer The Habitat, However, richness is not sufficently quantitative to be a present in the habitat. Measuring species evenness is more difficult. For this you need to carry out a quantitative survey. Once a full quantitative survey has been carried out as described in topic 4.2.1 the sata can be used to calculate Measure OF Biodiversity ON ITS OWN. Surveying the frequency of plants It DOES NOT take IN TO ACCOUNT THE individuals IN Each First use the sampling technigues described intopic 4.2.2 SPecies for thIS WE need 10 estimate species evenness survey record the percentage cover plants Species evenness is a meaure of the relative number with large plants area with A Habitat in which Individuals In each species use similar techiques for terrestrial and area Table 1. Results ofa simple survey oftwo fields Measuring the density of animals in ahabitat This means calculaing how many animals of each species Species observed Percentage cover There are per unit oeaof the habitat. Larger animals Cocksfoot grass 57 38 an observation counting by Timothy grass 32 16 sampling techniques described in topic 4.2.3 The population Meadow buttercup 3 14 use a sample of sol and sit though tt white clover 3 22 sampling in waterisimillar process. You can Creeping thistle 1 5 the botom. Then toetimute poputiation site Dandelion 4 5 and danity. Total 100 100 Simple index of diversity Table 1. Results ofasimple survey oftwo fields Simpson's of diversity D=1-ΣN^2 wher n is the number of individuals of a particular species(or thepercentage coverforplants) and N isthetotal number of allindividuals of all species(orthe totalpercentage coverfor plants). ## ##4. 2 Biodiversity measurinf gentic diversty Table 1. Applying slmpson's diversity index to the results for field A interpreting the data A high value A habitat provides aplace for rmany different speciesandmany organisms ivel change the ervionrment may atiect one species. It th speciesis olyas part of that habitat, the number of that allect the Therefore the effect in the whole habitat is all the the habiatstable allow value for diversity ahabitatdominated by a te species change th environmrnt affect one those decy th whal such or samething humans hav done nearby population diversity Isolated populations, such as captive animals in a 200, rare breeds or pedigree animals, may be small(e.g. Przewalski's horses, ses Pigure i (a)). Therefore their genetic diversity may bed limited Assessing their genetic diversity can help to assess the value of thal population asa resourcr for conservation. A simple proportionof polymorphic gene loki numberol polymorphic gene loci total numberiol loi nL 2013 giraffe called Marnuwas delberately killedal Copentagen lo, because the ded noc conbute anyera for Calculate the value for fietd See Table 1 Explain why fkd is likely to be a beter tieid keopa nature why d habitat with higher diverity is more stable than one ow diversity accuratey Why is it important to monitor the genetic diversity of animal oulatons are genetically varations be easy to identify. genetic variations may be easyto identify. ## ## 4.2 **5 What affects biodiversity** By the end of this topic, you should be able to demonstrate and apply your knowledge and understanding of: * the factors affecting biodiversity **KEY DEFINITIONS** **climate change:** significant, long-lasting changes in weather patterns. **monoculture:** a crop consisting of one strain of one species. Current estimates of biodiversity vary, as It is impossible to know how many species currently in existence have not yet been discovered. What is certain is that the number of species is declining, and the genetic diversity of many species is also declining, as a result of human activities. #### Human population growth Several thousand years ago, humans lived as hunter-gatherers in small numbers and had little effect on natural processes. However as the human population grows and we demand more food and consumer goods, we have a greater and greater effect upon other species. * We have learned to use the environment to our advantage. * We alter ecosystems to provid ourselves with food. * We destroy and fragment habitats * We are using more and more of the Earth's resources. * We pollute the atmosphere. As a result of our activities we often harm other species either directly or indirectly, and this can lead to extinction * The image shows a graphic with different curves showing population in billions * The vertical axis is labeled "population". * The horizontal axis is labeled "year". * There are three curves (all similar), - One curve is labeled "less developed countries". - One curve is labeled "more developed countries". - There is a label pointing to a dot on one of the curves "2000, 6.1 billion". Figure 1 The growth of the human population. ### Agriculture Agriculture has a huge effect on the biodiversity of natural habitats. As we clear natural vegetation, we reduce the size of habitats and the population size of any wild species living in those habitats. This reduces the genetic diversity of the species as their population is reduced. This means that the species has less capacity to adapt to changing conditions through evolution. It may also leave isolated and fragmented populations that are too small to serve. Modern agriculture relies upon monoculture and selective breeding to increase efficiency. A monoculture is a crop consisting of one strain of the species - it has very limited genetic diversity. This makes the product easier to harvest. The oil palm, which is grown for palm oil a good example: Rainforests with huge natural biodiversity are cut down at the rate of 150 hectares an hour. These are replaced by huge stands of a single strain of one species. Indonesia's oil palm already cover 9 million hectares and this is set to rise to 26 million hectares of 2025. Selective breeding also increases the efficiency of agriculture is vulnerable to Content characteristics that may diversity of the species Image shows an Aerial shot of tall green trees in rows ### #### Biodiversity Selecting for specific breeds of domesticated plants and animals means that other breeds become rare and may die out. Again, loss of these varieties reduces the genetic diversity of the species - a process known as genetic erosion. Climate change Human activities appear to be altering the climate. Species that have lost their genetic diversity show less variation between individuals. As the climate changes, they are less able to adapt to the changes in temperature and rainfall in the area where they live. The only alternative will be for them to move and follow the climate patterns to which they are most suited. This will mean a slow migration of populations, communities and whole ecosystems towards the poles - plants currently growing in southern Europe many soon grow in northern Europe. However, there will be obstructions to this migration. Possible obstructions include: * major human developments agricultural land * large bodies of water * mountain ranges. DID YOU KNOW? Consider the plight of the golden toad of the Costa Rican cloud forest. This amphibian is already facing extinction due to climate change.As the climate warms, the toad moves uphill to stay in the most suitable habitat. What happens when it reaches the top of the hill? The toad will be faced with naving to migrate through unsuitable habitats to reach another area with a suitable habitat. This is unlikely to nappen. Consider the effect on areas such as national parks, where nunting 1sn0t allowed. As the climate changes, the selected site no longer the animals W migrate to live outside their areas. Domesticated *******and animals are particularly at risk. have selectively bred our the that they nave little for is that Agricultural to disease and We 4 Extinction Exinction occurs when the last living species dieS and inces to over1oo years The rate 265 to Extiction Animals the 1O 000-11000 yearsThise Animals were hunted for food. biodiversityWhy has population risens quickly Why has human population rissen so quickly *Why descrtbe usng monoculture t the use ofmono cultere conributest described how seleetive breedingcontributes to losses describehow seleetlve breedingcontributes losses genetic erosion 4 Whatis meant by geretic erosion 5 desent how gereric erosion occurs Explain descntbe thE effect on Explain how domesticeted speries ofanimal animals are moreatisk ofEvinction than Wild animals ## ## 4.2 **6 Reasons to maintain biodiversity** By the end of this topic, you should be able to demonstrate and apply your knowledge and understanding of: * the ecological, economic and aesthetic reasons for maintaining biodiversity **keystone species:** one that has a disproportionate effect upon its environment relative to its abundance. **soil depletion:** : the loss of soil fertility caused by removal of minerals by continuous cropping. #### Ecological reasons to maintain biodiversity Interdependence of organisms Natural ecosytems are complex they have developed over millions of years as species have evolved to to live with each other And depend upon one another all depend on one another all the organisms in a habitat relationship The deer population increases Figure1 Another species Allowing Biodiversity to Decline means what problems we we need to adapt By carefull selection and breeding of the same way we the same way we we crete ## ## Biodiversity 4.2 diversity we *Why Why id be Kaibab Platea to be W Why deses beconsiserekeystone speces Why Might varietes oftheproblems chimate chang sort of woul dustorms Amencan Figure 3