Biodiversity

biodiversity

• Biodiversity can be thought of as the variation that exists within and between all forms of life

• Biodiversity looks at the range and variety of genes, species and habitats within a particular region

• It can be assessed on different scales

  • The number and range of different ecosystems and habitats on Earth

  • The number of species and their relative abundance within a small, local habitat (like a pond)

• Biodiversity is essential for the resilience of ecosystems, in that it allows them to resist changes in the environment

ecosystem or habitat diversity

• Ecosystem diversity refers to the variety of different ecosystems or habitats within a particular area or region

• Each ecosystem provides unique environmental conditions, supporting different communities of organisms

• An area with a large number of distinct habitats (e.g. forests, wetlands, grasslands) has high ecosystem diversity and therefore greater overall biodiversity

  • E.g. A coral reef is a highly diverse ecosystem — it contains a range of microhabitats and ecological niches, supporting a wide variety of species

• In contrast, environments with limited habitat types, such as sandy deserts, have low ecosystem diversity. The relatively uniform conditions support fewer species, resulting in lower overall biodiversity

species richness

• Species richness is the number of species within a community

• Species richness is the simplest way to measure species diversity

• A community with a greater number of species will have a greater species richness score

  • For example, a tropical rainforest has a very high number of different species, so it would be described as species-rich

why can species richness be misleading

• Species richness can be a misleading indicator of diversity, as it does not take into account the number of individuals of each species

  • For example, habitat A has 10 plant species (1 individual each), while habitat B has 7 species but over 20 individuals per species

  • Although habitat A is more species-rich, habitat B has greater abundance and evenness

  • This highlights the limitation of species richness — it doesn’t account for population size or distribution

• Conservationists often favour the use of an index of diversity as it takes into account species number and evenness

index of diversity

• An index of diversity describes the relationship between the number of species in a community and the number of individuals in each species

• It gives a numerical measure of species diversity in a community and takes into account both:

  • species richness – how many different species are present

  • species evenness – how evenly individuals are distributed among those species

• Using species richness alone can be misleading

conservation ad farming

• After the Second World War there was a massive change in how food was produced

• There was a need to produce more food, at a quicker rate and farmers needed to produce a higher yield

• It was then that modern farming practices began:

  • Farms became more specialised, so they grew only one crop or raised one type of livestock (monoculture)

  • There was a switch to growing cereal crops rather than vegetables

  • Fields were made bigger to accommodate machinery via the removal of hedgerows and stonewalls

  • More land was made arable by draining wetlands and filling in ponds

  • The use of pesticides and fertilisers increased

modern farming practices and biodiversity

• Biodiversity looks at the range and variety of genes, species and habitats within a particular region

• Biodiversity of insect, animal and plant species is often measured and studied within a farming context

• Modern farming aims to maximise yield (e.g. crops, livestock), often using methods that reduce biodiversity

  • For example:

    • fast-growing grass is essential for raising healthy livestock, but this is limited in floral species, reducing species richness

    • sowing crops in the autumn instead of spring so the gap between harvesting and ploughing is very short - one or two weeks, reducing the time available for local birds to benefit from ploughing of fields

    • monoculture of crops reduces plant diversity for bumblebee habitats, contributing to the very rapid decline in bumblebee numbers in recent years (bumblebees are essential for the pollination of wildflowers and valued crops such as oilseed rape and peas

• These practices increase productivity but often destroy habitats, reduce species diversity, and disrupt ecosystem services (e.g. pollination, nutrient cycling).

• Conservationists have made strong efforts to try to maintain or improve biodiversity around farmlands

• Conservation of habitats and ecosystems is important because:

  • it maintains biodiversity, including wild species that may have future value (e.g. in medicine or agriculture)

  • ecosystem stability is supported

  • there are ethical, aesthetic, and cultural reasons to maintain biodiversity

  • it helps combat climate change through carbon storage (e.g. in woodland and peatland)

conservation and farming

• The aim is to maintain or improve biodiversity while still producing enough food

• Conservation measures may reduce short-term yield or increase costs to the farmer

• Farmers may be reluctant to adopt changes unless they receive financial or policy support

• Conservation efforts require education, subsidies, and long-term thinking from parties involved

conservation strategies - maintaining hedgerows

Provides habitats and wildlife corridors for birds and insects

conservation strategies - planting wildflower strips

Supports pollinators and natural predators of pests

conservation strategies - crop rotation

Reduces soil depletion and supports soil biodiversity

conservation strategies - using organic fertilisers

Reduces eutrophication risk and supports soil health

conservation strategies - agri-environment schemes

Offer financial incentives to farmers who adopt wildlife-friendly practices

biodiversity vs profit

• High yield and profit are essential for economic farming

• However, conservation-friendly practices can be costly, time-consuming, and may reduce yield

• For example, avoiding pesticides can boost bumblebee populations but also allow pests to thrive, lowering crop yield and profit

• Farmers may then need to raise prices

• Balancing farming and conservation is challenging, but EU grants help by subsidising environmentally friendly practices to offset losses

measuring genetic diversity

• A species can be defined as

  • a group of organisms that can interbreed and produce fertile offspring

• Members of one species are reproductively isolated from members of another species

• In reality, it is quite hard to define ‘species’, and the determination of whether two organisms belong to the same species is dependent on investigation

• Individuals of the same species have similar behavioural, morphological (structural) and physiological (metabolic) features

• A common example used to illustrate this concept is mules: the infertile offspring produced when a male donkey and a female horse mate

genetic diversity

• Genetic diversity is the number of different alleles of genes

• Genetic diversity within and between species can be measured by looking at the following:

  • Displays of measurable characteristics

  • The nucleotide base sequence of DNA

  • The nucleotide base sequence of mRNA

  • The amino acid sequence of proteins

measurable and observable characteristics

• Comparing characteristics of different individuals is usually the quickest but least reliable form of determining genetic diversity

  • The genetic differences between individuals can only be implied using this technique

• This method was used successfully to classify organisms into the taxonomic hierarchy for hundreds of years before DNA sequencing

• The problem with this method is that it is not precise enough if only one characteristic is looked at, for example, many animals have four legs

• It can be useful if a species has unique characteristics

• Often, if two species cannot be distinguished from their observable characteristics, measurable characteristics will give a better understanding of the similarities and differences

characteristics that could be measured

• number of legs

• number of seeds in a berry

• number of petals

• number of leaf indentations

characteristics that could be measured

• colour

• patterns on fur/scales/feathers

• habitat

• presence of hair/wings/fins

DNA analysis and comparison

• DNA sequence analysis has replaced using characteristics as a means of determining genetic diversity

• DNA is extracted from the nuclei of cells taken from an organism

  • DNA can be extracted from blood or skin samples from living organisms or fossils

• The extracted DNA is processed, analysed, and the base sequence is obtained

• The base sequence is compared to that of other organisms to determine evolutionary relationships

  • The more similarities there are in the DNA base sequence, the more closely related (in that the less distant the species separation) members of different species are

  • Computers can be used to highlight matches between the DNA samples

  • Two groups of organisms with very similar DNA will have separated into separate species more recently than two groups with less similarity in their DNA sequences

• DNA sequence analysis and comparison can also be used to create family trees that show the evolutionary relationships between species

mRNA analysis and comparison

• mRNA is often easier to isolate from cells than DNA, as it is found in the cytoplasm and there are usually multiple copies of the same mRNA

• Collected mRNA from an individual can be used as a template to produce cDNA (complementary DNA)

  • The first strand of cDNA produced is complementary to the mRNA (the same as the template strand of the DNA)

  • The first strand is then used to produce a second cDNA strand, which is the same as the coding strand of DNA

  • Unlike the original DNA in the nucleus, the cDNA contains only the coding regions of the gene (exons) and no introns

• It is important to compare the same mRNA between samples

  • mRNA for a known, universal protein is often used and compared, for example, cytochrome-c (from the electron transport chain)

  • Primers can be used that bind to specific sequences

amino acid sequence analysis and comparison

• Similarly to mRNA, proteins are often easier to isolate from the cell than DNA

• The sequence of amino acids of the same protein can be compared between individuals

  • The protein chosen must be found in all the individuals/species being compared e.g. haemoglobin is used for many animals

• Amino acid sequences can also be determined from mRNA sequencing if the 'frame' is known (the correct start codon is determined)

• Amino acid sequences of proteins evolve much more slowly than DNA, especially if the protein is of high importance

  • Therefore, it is likely that closely related species (e.g. humans and chimpanzees) will have the same amino acid sequence even though these species split from their common ancestors millions of years ago

  • This is because the shape, and therefore function and specificity, of a protein is determined by the amino acid sequence, as the position of amino acids determines the intermolecular forces between R groups

mean

• A mean value is what is usually meant by “an average” in biology

mean = sum of all measurements ÷ number of measurements

• Problems with the mean occur when a dataset contains extreme, or outlying values, which can make the mean too high or too low to represent the data

• The mean is sometimes referred to as X̄ in calculations

standard deviation

• The mean is a more informative statistic when it is provided alongside standard deviation

• Standard deviation measures the spread of data around the mean value

  • It is useful when comparing consistency between different data sets

• The mean must be calculated before working out the standard deviation

quantitative investigations of variations

• Quantitative investigations of variation can involve using measures of central tendency such as the mean values and their standard deviations

  • A mean value describes the average value of a data set

  • Standard deviation is a measure of the spread or dispersion of data around the mean

    • A small standard deviation indicates that the results lie close to the mean (less variation)

    • A large standard deviation indicates that the results are more spread out

relationships between organisms

• Before recent advances in gene technology, which allow us to directly investigate DNA sequences, investigating genetic diversity used to occur through inferring differences in the DNA from measurable characteristics such as

  • size

  • mating processes

  • fruit production

  • observable characteristics

• The use of DNA sequencing technologies has allowed us to assess and track genetic diversity more accurately

comparing DNA base sequences

• DNA found in the nucleus, mitochondria and chloroplasts of cells can be sequenced and used to show evolutionary relationships between species

• DNA base sequences can be compared directly between organisms to determine genetic similarity

• The more similar the base sequences, the more closely related the organisms are

• Differences in base sequences arise from mutations over time: the greater the difference, the more distant the common ancestor

• DNA sequencing allows precise comparisons at the molecular level, within or between species

• DNA sequence analysis and comparison can also be used to create family trees that show the evolutionary relationships between species

comparing amino acid sequences

• Differences in DNA codes for amino acid sequences may lead to differences in proteins

• Comparing amino acid sequences (e.g. in cytochrome C or haemoglobin) provides insight into evolutionary relationships

• Fewer differences in amino acid sequences mean a closer evolutionary relationship

• Amino acid comparisons are less precise than DNA because:

  • The genetic code is degenerate

  • Some mutations are silent (they don't change the amino acid)

interpreting sequence data

• Sequence comparisons help determine evolutionary relationships between organisms by analysing DNA or protein similarities

• As a general rule, the fewer the differences, the more recent the common ancestor, whereas more differences may mean a longer time since divergence

interpreting sequence data - how the data may be presented

• DNA or amino acid sequence alignments:

  • Lines of base or amino acid letters lined up to show matching positions

  • The number of differences or mutations can be counted

• Comparison tables:

  • A comparison table often shows the number of base or amino acid differences between pairs of species

  • This helps identify which species are most similar and therefore most closely related

• Phylogenetic trees (cladograms):

  • These are branching diagrams that represent evolutionary relationships

  • Organisms with fewer differences cluster closer together on the tree and can help identify closely related species

  • Branch length may reflect the amount of genetic change or time since divergence

interpreting sequence data - from observable traits to molecular methods

• Older methods of assessing genetic diversity are based on

  • observable phenotypes (e.g. flower colour, leaf shape)

  • measurable traits (e.g. enzyme activity, protein structure)

  • protein structure – inferred from things like antibody–antigen reactions (e.g. in immunological comparisons)

• These methods assumed that observable differences were caused by genetic variation

• However, phenotypes are influenced by both genes and the environment, which can make results misleading:

  • For example, two genetically identical plants may look different if grown in different light or soil conditions.

• Modern methods directly examine the genetic material itself (DNA or amino acid sequences)

• Techniques include:

  • DNA sequencing, which determines the exact order of nucleotide bases

  • comparing base sequences of genes between individuals or species

  • comparing amino acid sequences in proteins encoded by those genes