Biodiversity

Biodiversity

 

• Biodiversity refers to the number of different ecosystems and habitats in an area, the number of species within those ecosystems, and the genetic variation within each species 

• Rio Convention: ‘Biological diversity means the variability among living organism from all sources including terrestrial, marine and other aquatic ecosystems and ecological complexes of which they are apart of’

  • It includes the different ecosystems present in a habitat, the different species present and the genetic variation within these species 

 

Species Diversity: 

• One definition of species is ‘A group of organisms that interbreed to give rise to fertile offspring and are reproductively isolated from other species. If the organisms do breed species these offspring must be sterile.’

• This definition is often too vague as it cannot be applied to many species, a more complete definition, and what is actually used, is the outward appearance/morphology of the species and the anatomy.

  • We can thus use the definition: ‘A group of organisms that share many physical features that distinguish them from other species’

 

• We also use a large degree of genetic analysis to assess genetic similarities to classify a species 

• Taxonomic diversity is an important consideration in a habitat/ecosystem as we need to consider the relationship of species to each other

• A greater taxonomic diversity indicated there are more types of species present and thus more biodiverse (typically) 

 

Genetic diversity:

• This refers to the genetic variation within a species. 

• It occurs due to gene variants and different allele expression in the human gene pool 

• It is this diversity which is involved in selective breeding, wwe utilise selective breeding of plants and livestock to optimise their appearance and the energy we can claim from them as well as economic gain 

• When species evolve from a small select number of organisms, like cheetahs, the degree of genetic diversity is limited, in rice for example where the are thousands of different grains 

• Some different species may have many genes which are similar as a result of having similar cells and enzymes but each species will overall have a unique combination of genes 

• The position that the differentiating gene is in within the chromosome is called the locus 

• Alleles are different forms of the same gene, the gene pool has a multitude of different alleles 

• Different forms of an enzyme which have different primary sequences are known as allozymes and these different alloenzymes affect phenotype 

• We can use electrophoresis to separate out allozymes 

• The amino acid sequence of an allozyme are altered as they have different sequence of nucleotides and this sequence can be analysed by sequencing 

• Genetic diversity is limited in small populations hence why inbreeding causes genetic disease to become more common as the gene pool reduces

 

Assessing Genetic Diversity:

• To assess diversity we must assess 

  • the proportion of gene loci that have two or more alleles (gene variants)  that is, the proportion that show genetic polymorphism (different forms) 

  • the proportion of the population that are heterozygous (eg. Aa) for any particular gene locus

  • the number of different alleles for certain genes which is known as allele richness.

• To measure genetic diversity involves finding out whether there are different alleles of each gene locus. In some cases, all the alleles of a gene locus are expressed in the phenotypes of different individuals

• When it is not obvious the way in which a gene is expressed we can examine the protein products of the alleles/sequence the DNA to gain an idea of diversity 

 

Calculating the proportion of polymorphic gene loci:

• Genetic polymorphism is the existence of different alleles of a gene, where the rarest allele has a frequency that is either more than 1% or more than 5%

  • A polymorphic locus is one where the most common allele has a frequency that is less than 95%

• To calculate the percentage of alleles in the population, it is assumed that each individual contributes. two alleles.

• Gene loci that do not have alleles are described as monomorphic.

• The proportion can be calculated using number of polymorphic gene loci/total loci

• Though this mechanism works, determining the amino acid sequence of the proteins reveals more genetic variation. This measure of genetic diversity is particularly suitable when investigating allozymes.

• Using sequencing we can also assess whether the genetic code is degenerate (more than one triplet code for each amino acid) and thus is more accurate 

 

Habitat Diversity:

• Habitat - place where one species lives. Habitats provide the resources that organisms need. Plants require light, carbon dioxide, water and mineral ions; animals require food, water, shelter and somewhere to breed.

  • Can be confused with Biome and Ecosystem:

    • Biome - refers to a region of the world that has a dominant type of vegetation that is associated with the climate.

    • Ecosystem - areas that support communities of organisms that interact with each other and with their surroundings.

• Because the borders of a species' dwelling region are sometimes difficult to establish, habitat diversity is more difficult to measure than species or genetic variety.However, if species can be accurately recognised, the concept of niche can be used to investigate the many habitats accessible.

  • A Niche is the role of a species in an ecosystem 

 

Local Biodiversity: 

• When investigating local biodiversity, first we must identify the different types of organisms and build a species list using a key to identify the organisms (dichotomous key - using questions to determine a species)

• We can make a species list by using a  timed search. Each member of a group spreads out across the area and finds as many different species as possible. After a set time group members pool their results to give a species list. 

  • Species that cannot be identified can be photographed and the species later identified from the photos. Species that still cannot be identified can simply be called species A, species 

• This gives us an indication of species richness 

• It is challenging to do as we should account for all organisms including microscopic ones and nocturnal animals etc. which is highly time consuming 

 

Species Distribution and Abundance: 

• A species list is qualitative; it does not include the number of species required in order to distinguish between common and rare species.

• The second factor which affects biodiversity is the species abundance 

• We use a quadrat (ref pages for diff types [216]) to assess abundance 

• We can assess species frequency, species density, percentage cover

• We can then record the presence or absence of the species on a species list. Species frequency is then calculated as the percentage of quadrats that included each species. The number of individual organisms within a quadrat can be counted to give the species density, which is usually expressed as numbers per unit area, for example per m².

• Species frequency and species density do not take into account the size of the organisms present. It is often difficult if not impossible to count the numbers of very abundant species such as grass. 

• A quadrat divided into a grid makes it relatively easy to assess the area of the quadrat that is occupied by each species. This value is percentage cove, the percentage of the area of the quadrant in which the plant or animal occurs.

 

Random Sampling: 

• We must sample as often the habitat is too large to take results from everywhere

• In a uniform habitat a percentage of the area should be representative of the whole area and thus to use this small area as a representation of the whole area is valid to provide us with an estimation of biodiversity 

• Random samples must be taken to avoid any bias on the part of the person doing the sampling. Random sampling can be done by placing tape measures at right angles to each other along two sides of the sample area. Random numbers are generated by using an app on a mobile phone to give coordinates where the quadrats can be placed.

• We must record percentage cover to enable comparison and provide a value representative of the whole habitat 

• To record percentage cover, because it is impossible to see individual plants. In that case, you estimate how much of the quadrat encloses each plant and express the answer as a percentage of the area of the quadrat.

• It is difficult to isolate individual plants, so an abundance scale such as ACFOR (abundant, common, frequent, occasional, rare) is used.

• When sampling with animals it is more difficult

• To sample Animals we can use

  • Beating trays: A large white sheet is placed on the ground or supported by struts and held below a tree. The tree is shaken to dislodge the animals. Very small animals can be collected from the beating tray with a pooter.

  • Pooters:  Scientists can use this to suck small animals into the glass or plastic tube.

  • Sweep nets: Large nets are used to catch flying insects and insects that live in long grass.

  • Pond nets: These are stronger nets that can lift volumes of water from ponds or rivers; the water drains through the net to leave vegetation and animals behind.

  • Pitfall traps: Cans or jars are buried in the ground, filled with paper or cardboard to provide shelter, and covered with a lid or stone to keep out the rain; these are useful for collecting ground-dwelling insects, which are often nocturnal

 

Estimating Population sizes of mobile animals:

• To estimate the number of animals in an area we could catch a given number and mark them before releasing them back, we can then repeat this some time later and judge the number of marked vs unmarked individuals. 

• Smaller numbers of marked individuals means the population size is smaller. 

• We can use the Lincoln Index

 

Population size= number in 1st sample x number in 2nd sample

                                            Number marked in 2nd sample 

 

Simpson’s index of diversity: 

• We can use the formula of D=1 - sum (n/N)^2

• Where n is the number of individuals of each species and N is the total number of individuals 

• When the index value is small (near 0) there is low diversity. When the number is high (near 1) there is high diversity.

• Comparisons using this diversity the communities should be similar, and the organisms chosen should also be similar.

• Communities with low diversity are less stable than communities with high basis diversity. These communities with high diversity tend to withstand any pressures on them, such as changes in environmental factors or pollution

 

Non-Random Opportunistic Sampling:

• This is sampling where we locate an area which seems to be appealing or have a high degree of the object we are looking for and use this area to sample within 

• The limitation is that we may choose a location that is representative of the area or w may not 

 

Non-Random Stratified Sampling:

• In some ecosystems, there may be different habitats occupying different proportions of the total area.

• It is best to estimate the fraction of the overall area inhabited by these habitats and then sample accordingly to acquire a good representative of the biodiversity in this ecosystem.

• We split the location into the different habitats within it.

 

Non-Random Systematic Sampling: 

• If there is a region in which there is an abrupt change from one habitat to another or that there is a gradual change in conditions across the area you are studying and that random sampling will not reflect the way plants and animals are distributed we can use systematic sampling. 

• This requires a transect and we must use either a line or belt transect

  • Line Transect: 

    • Simply put, a line transect is a straight line drawn across an ecosystem. A long rope or measuring tape is stretched over an environment like a rocky shore or a sand dune system. The starting point for the line should be chosen at random, although this is not always practicable if there are barriers in the way, for example. Species that come into contact with the line at regular intervals (e.g., every 0.5 m) are identified. They are useful in understanding how communities change along a gradient such as a  slope or even a change in abiotic features. 

  • Belt Transect: 

    • A belt transect is a method of sampling an ecosystem quantitatively. Quadrats are placed along a line that runs through an ecosystem. If the distance between the quadrats is low, they can be positioned in a continuous belt transect. If the distance is long, inserting quadrats continually can be time intensive; nonetheless, placing quadrats at intervals provides sufficient information on population fluctuations.This is an interrupted belt transect. Data from belt transects are presented as kite diagrams.

• The method has issues as it may not be representative and can be biased though set intervals for testing somewhat counter this 

 

Practice Questions:

1. D

2. B

3. D

4. ai) The area being sampled was not a uniform habitat, there were two distinctly different region in the woodland and grassland and thus random sampling would not have given results which were representative of the variation in the habitat

aii) They chose a number of quadrats represent of the proportion of the area occupied by each habitat as they used 15 quadrats in proportion as there were divisions of 240/300 and 60/300 and thus the proportions of 12:3 were logical

b) 25680/300 =86.2 m2

c) Opportunistic 

d) The student's t test could be used assuming the null hypothesis of there is no significant difference between the densities of bluebells in different areas of woodland. They could use the calculated t value and compare this to the critical value of t by using the degrees of freedom for their samples. The critical value of t would be deduced for a probability value such as 5%. If the calculated t value is greater than the critical value then the difference is significant at the 5% probability.

e) H. non scripta clearly contributes largely to the woodland species diversity and if it were to go extinct it would cause a reduction in genetic diversity. It is also likely that other animals such as bees and pollinating insects are dependent upon the H. non scripta and thus removing them from existence would have a long lasting effect on the food chain as we would see decreased numbers of subsequent trophic level organisms and thus eventually reaching us as humans.

1. ai) 0.04

aii) Using values of P is limited by the fact it only accounts for a small degree of genetic diversity which is of those samples in the study, It is always an extrapolation as opposed to being wholly accurate. 

aiii) This enables us to make a comparison and judge how successful selective breeding is in increasing genetic diversity. We have data from a larger and smaller population which also enables us to confirm that the extrapolated data is more accurate and representative of the wild large population.

aiv) The 25 gene loci can be genotyped and the number of homozygous and heterozygous loci for each of the individual loci can be recorded. We can then use the proportion of heterozygous loci over the total number of loci tested to get a value for heterozygosity.

b) Primarily the number of leopards in each sample is too small and there is no constancy in the number of each species sampled. This makes comparison between species difficult. A small number of genes was sampled too, only 25 genes were genotypes which also limits accuracy of the data. We are a;so unaware of what the genes used are for/what they are in control of. We thus have no idea of the significance of these genes and what the phenotype they present will be. Understanding the role of the games would aid us in understanding whether the variation causes significant difference in survival ability which could account for population differences. The location of each of the altered species would also aid us in understanding whether some genetic difference may be adaptive in accordance with the surrounding.