What is biodiversity, why does it matter, and how is it measured?
Biodiversity defined at the species, genetic and ecosystem levels; the importance of biodiversity for ecosystem services and human wellbeing; biodiversity hotspots; and how biodiversity is measured and indicated.
An SQA National 5 Environmental Science answer on biodiversity, covering the species, genetic and ecosystem levels of diversity, why biodiversity matters for ecosystem services and people, what a biodiversity hotspot is, and how biodiversity is measured using indicator species and sampling.
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What this dot point is asking
The SQA wants you to define biodiversity at three levels (species, genetic and ecosystem), explain why biodiversity matters for ecosystems and for people, say what a biodiversity hotspot is, and describe how biodiversity is measured, including the use of sampling and indicator species.
What biodiversity means
It is not just a count of species. Scientists describe biodiversity at three connected levels, and a question often asks you to name and describe all three.
The three levels of biodiversity
- Species diversity is the number and variety of different species found in an area. An area with many different species has high species diversity.
- Genetic diversity is the variety of genes (alleles) within a single species. It is what makes individuals of the same species slightly different from one another, and it lets a species adapt to change.
- Ecosystem diversity is the variety of different habitats or ecosystems within a wider region, such as woodland, wetland, grassland and coast all occurring in one area.
Why biodiversity matters
High biodiversity is valuable for two main reasons that the SQA expects you to explain.
1. Ecosystem services. Healthy, diverse ecosystems provide free services that people depend on:
- Provisioning such as food, timber, fresh water and medicines.
- Regulating such as pollination of crops by insects, purification of water, control of pests and diseases, and regulation of the climate (for example by carbon storage).
- Supporting and cultural such as soil formation, nutrient cycling, and the value of nature for recreation, tourism and wellbeing.
2. Stability and resilience. A more diverse ecosystem is more stable: it can keep functioning and recover more easily after a disturbance such as disease, fire or drought, because if one species declines another can take on a similar role.
Biodiversity hotspots
To be classed as a hotspot a region must hold a large number of unique (endemic) plant species and must already have lost a large proportion of its original natural habitat. Hotspots are conservation priorities because protecting them safeguards a great deal of biodiversity in a small area. They are often in places with rapid development and growing human populations, which is part of why they are threatened.
How biodiversity is measured
Scientists cannot count every organism, so they sample an area and use the results to indicate the biodiversity present.
- Counting species and abundance. Using quadrats (for plants and slow-moving animals) or other sampling methods, scientists record how many different species are present and how many of each there are. Greater variety indicates higher biodiversity.
- Indicator species. Some species are sensitive to particular conditions, so their presence or absence indicates the state of a habitat. For example, certain freshwater invertebrates only survive in clean, well-oxygenated water, so finding them indicates low pollution; lichens are sensitive to air pollution and indicate air quality.
Examples in context
Example 1. Lichens and air quality. Lichens are sensitive to sulfur dioxide pollution. A wide variety of lichens on tree bark indicates clean air, while bare bark with few lichens near a busy road indicates higher air pollution. This makes lichens a simple, low-cost indicator of air quality.
Example 2. Genetic diversity and crop disease. A field planted with a single genetically identical crop variety has very low genetic diversity, so if a new disease can attack that variety, the whole crop is at risk. Maintaining genetic diversity in crops and their wild relatives gives a reserve of resistance, showing why genetic diversity matters to people.
Try this
Q1. Name the three levels at which biodiversity is described. [1 mark]
- Cue. Species diversity, genetic diversity and ecosystem diversity.
Q2. Explain why a freshwater invertebrate can be used as an indicator species for water quality. [2 marks]
- Cue. It is sensitive to pollution and only survives in clean, well-oxygenated water, so its presence indicates low pollution and its absence indicates poorer water quality.
Exam-style practice questions
Practice questions written in the style of SQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
SQA N5 style3 marksBiodiversity can be described at three levels. Name the three levels and give a brief description of each.Show worked answer →
A 3-mark name-and-describe answer needs all three levels, each with a short description, so plan one mark per level.
Species diversity: the number and variety of different species living in an area.
Genetic diversity: the variety of genes (alleles) within a single species, which gives differences between individuals.
Ecosystem diversity: the variety of different habitats or ecosystems within a region.
Markers reward each level correctly named and described. Naming a level without describing it, or describing it without the correct name, may lose the mark, so always pair the two.
SQA N5 style4 marksExplain why maintaining high biodiversity is important, giving two reasons, and describe one method scientists use to measure biodiversity.Show worked answer →
This combines importance with method, so plan two reasons (2 marks) plus a method described well enough to score the remaining marks.
Reason 1. High biodiversity supports ecosystem services that humans rely on, such as pollination of crops, water purification and climate regulation.
Reason 2. A more diverse ecosystem is more stable and resilient, so it is better able to recover from disturbances such as disease or drought.
Method. Scientists sample organisms (for example using quadrats for plants) and count the number of different species and how many of each are present. The variety found indicates the level of biodiversity. Indicator species can also be used: the presence or absence of a pollution-sensitive species shows the health of the habitat.
Markers reward valid reasons and a correctly described sampling or indicator method. A vague reason such as "it is good for nature" without a service or stability point may not score.
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