Biodiversity (AQA A-Level Geography): Revision Notes

Biodiversity

What is biodiversity?

Protecting biodiversity isn't only the responsibility of governments and international organisations. The private sector and every individual person has a role to play in changing harmful attitudes and ending destructive behaviours.

All these elements form part of the global ecosystem - Earth's complete collection of living organisms and their environment. Ecosystems provide the foundation for life support systems, including food provision, clean air and water, climate regulation, disease control and many other services. Biodiversity underpins healthy ecosystems.

Measuring biodiversity

Why is measurement challenging?

From the broad definition above, it becomes clear that no single measurement can fully represent biodiversity. This is because measuring biodiversity involves two key components:

• The number of entities (for example, the number of individual organisms, the number of species, or the number of different habitats)
• The degree of difference (dissimilarity) between those entities

Measurements are commonly used to provide evidence for conservation needs or for general planning purposes. Often indicator species are used to assess biodiversity.

This method can be very useful, but it introduces an element of how we value different components of biodiversity. For example, we are more likely to use the abundance of birds or butterflies on a farm as a measure of biodiversity than the richness of microbes in the soil.

Species richness

Advantages of species richness:

• It has proven to be measurable in practice - it is a doable measure
• Extensive information already exists on patterns in species richness, which has been made available in scientific literature, allowing comparisons over time
• Species richness serves as a proxy measure for many other types of variation in biodiversity. Generally, greater numbers of species indicate more genetic diversity (through a greater diversity of genes in populations), more species diversity, and greater ecological diversity
• It is commonly viewed as the unit of practical management and is most easily applied to legislation and political debate. For a wide range of people, variation in biodiversity is pictured as variation in species richness

Disadvantages of species richness:

• There is a lack of agreement about what actually constitutes a species. For example, it is not an adequate method for defining single-cell organisms
• Some assemblages of organisms may be very closely related (for example, two species of rat), whilst others are highly diverse (for example, a species of rat and a species of snail)

Living Planet Index (LPI)

A more recently developed measure of biodiversity is the Living Planet Index (LPI). The LPI measures trends in thousands of vertebrate species populations and provides information on changes in the abundance of the world's vertebrates. It can quickly convey information about which habitats or ecosystems have species that are declining most rapidly. This information can be used to define the impact humans are having on the planet and for guiding actions to address biodiversity loss.

Global trends in biodiversity

Historical perspective

Over Earth's geological history, global biodiversity has gradually increased from when life began around 550 million years ago. During that time, there have been five episodes of mass extinctions (for example, the end of the dinosaurs approximately 65 million years ago).

Current decline statistics

Population sizes of animal species measured by the LPI have declined overall by 60 per cent between 1970 and 2014. This decline has continued rapidly since then.

Biodiversity is declining in both temperate and tropical regions, but the decline is greater in the tropics - particularly in South America (with a fall of 89 per cent). Key statistics include:

• The tropical LPI showed a 56 per cent reduction in 3,811 populations of 1,638 species from 1970 to 2010
• The 6,569 populations of 1,606 species in the temperate LPI declined by 36 per cent over the same period
• Latin America shows the most dramatic decline of 83 per cent

The LPI for freshwater species shows an average decline of 83 per cent. The main threats to freshwater species are habitat loss and fragmentation, pollution and invasive species. Changes to water levels and freshwater system connectivity - for example, through irrigation and hydropower dams - have a major impact on freshwater habitats.

Marine species declined by more than half between 1975 and 2015. The period from 1970 through to the mid-1980s experienced the steepest decline, after which there was some stability, before another period of decline. The steepest declines can be seen in the tropics and the Southern Ocean - species in decline include marine turtles, many sharks and large migratory seabirds like the wandering albatross.

Threats to biodiversity

Exploitation through hunting and fishing, and habitat degradation and loss are the main causes of decline. Climate change is the next most common primary threat, and is likely to put more pressure on populations in the future.

According to the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), since 1900, the average abundance of native land-based species has declined by at least 20 per cent. This trend shows no sign of slowing down. The loss of habitat for human land use - particularly for agriculture, urban development and energy production - continues to be a major threat, made worse by hunting.

Human contributions to biodiversity change

Human activities contribute to changing biodiversity through multiple interconnected pathways:

The diagram illustrates how various human activities create cascading effects on biodiversity:

• Industrial farming increases atmospheric methane and involves nitrogen fixation for fertilisers, which has more than doubled terrestrial fixation rates of gaseous nitrogen into biologically available forms
• Fossil fuel combustion and deforestation increase atmospheric CO₂, leading to increased global temperatures
• Agricultural runoff from urban areas changes the chemical nature of rivers and estuaries
• Land transformation: Humans have transformed 40-50 per cent of the ice-free land surface, changing grasslands, forests and wetlands into agricultural and urban systems
• Water consumption: Humans use 54 per cent of available freshwater, and this is increasing
• Fishing: Fish are harvested from oceanic and freshwater systems, using up to 8 per cent of the potential productivity
• Species transportation: The increased mobility of people has transported organisms across geographical barriers that long kept the biotic regions of Earth separated. Many ecologically important plant and animal species have been introduced to new areas in historic time

Case study: Blanket bog habitat in the UK

What are blanket bogs?

One of the most extensive semi-natural habitats in the UK is blanket bog. It ranges from Dartmoor in the south to Shetland in the north. It is a globally restricted peatland habitat confined to cool, wet, typically oceanic climates. Blanket bogs comprise generally upland peat bogs that are fed by rainfall alone.

Peat is an accumulation of dead organic material, mainly plant remains, that is unable to break down because of the wet, acidic and cold conditions in which it is found. These peat bogs take thousands of years to form and support mosses, insects, rare birds and even carnivorous plants. Peat depth is very variable, with an average of 0.5-3 metres being fairly typical.

Kinder Scout, Derbyshire

One area of blanket bog is Kinder Scout, Derbyshire. Kinder Scout is an area of moorland and National Nature Reserve in the Dark Peak of the Derbyshire Peak District in England. Part of the moor, at 636 metres above sea level, is the highest point in the Peak District. The 7,000-year-old blanket peat bog sits on top of a plateau, formed from horizontal layers of an impermeable sandstone called Millstone Grit. The land is owned and managed by the National Trust.

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