Biodiversity (AQA A Level Geography)
Revision Note
Written by: Jacque Cartwright
Reviewed by: Bridgette Barrett
Defining Biodiversity
Biodiversity is defined by the Convention on Biological Diversity (1992), as ‘the variability among living organisms from all sources including terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are a part; this includes diversity within species, between species and of ecosystems.’
In other words, biodiversity is the amount and assortment of biological life forms; that are found in a particular area; and its changes over time
It includes variety within, and between, species and ecosystems
Ecosystems are communities of living organisms (biotic - plants and animals), sharing the environment, with the non-living (abiotic - light, water, soil etc.) components
Each ecosystem is unique at a local level
Biodiversity varies on a local scale:
Natural habitats will have higher biodiversity than agricultural land
Biomes are very large ecosystems on a global scale; such as tropical rainforests, savannahs, deserts etc.
Each biome share similarities but differ at the local level
Tropical rainforests share general features such as climate and overall appearance
However, each tropical rainforest's biodiversity will differ, along with its composition and interactions
Ecosystems are dynamic systems and develop through distinct succession from a 'sterile' area to a climatic climax community
Plant succession affects food chains, biomass, species diversity and size of organisms
Measuring biodiversity
Biodiversity is measured through:
Indicator species
Certain species are used as an indication of environmental conditions
Often used as evidence in planning and conservation of an area
Species richness
Provides a direct link between biodiversity and the number of species
Measures the total number of the species in a community
Difficult to produce a complete inventory of all the species present in a location as living organisms are dynamic and areas change
Living Planet Index (LPI)
This measures the state of the world's biological diversity - the health the world's ecosystems
Based on average changes in the population of vertebrate species from terrestrial, freshwater and marine habitats
Population number
The amount of a genetically distinct population within a particular species
E.g. Butterflies as a species, but Red Admiral as a genetically distinct population
Evenness indices
Shows how evenly spread individuals are in a community of different species
Genetic diversity
This is the total amount genetically different information found within a species
Genetic differences allow species to adapt to its changing environment
Also known as natural selection
Examiner Tips and Tricks
Biodiversity is vital to the healthy functioning of ecosystems and is the foundation to a healthy life on Earth
Make sure you can relate the concept of biodiversity at a local and global scale
Distribution of biodiversity
Biodiversity is not equally distributed within ecosystems or biomes
Biodiversity decreases further away from the equator (north and south)
Approximately 50% of global biodiversity lives within tropical rainforests
This is due to the climate being wetter, warmer, with little seasonal variation; making it a reasonably stable climate that supports continuous plant growth
Which, in turn, supports greater biodiversity along the food chain
Worked Example
Explain the link between global ecosystems (biomes) and biodiversity.
[4 marks]
Show the examiner that you understand what biodiversity and biomes mean
Answer:
Biodiversity is the amount, variety and differences of living organisms [1] in and amongst species in a particular area known as an ecosystem. [1] Ecosystems are part of the global system that make up biomes. [1] The link is that biodiversity shows how changes occur from one location to another. [1]
Trends in Biodiversity
Global scale
Overall biodiversity is declining at both local and global levels
Very few global ecosystems are untouched by human activity
Extinction rates have increased a 100 fold compared to natural background extinction rates
Scientists believe we are in a 6th period of mass extinction - due to human activity
Biomes with the highest rates of degradation are tropical, temperate, flooded grasslands/savannahs and tropical deciduous forests (aka monsoon forests or tropical dry forests)
The WWF's Living Planet Index (LPI), shows a general decline of the world's biodiversity:
1970 - 2002 approx. 40%
The decline rose to 58% by 2012
The latest report shows a 69% decline of the world's biodiversity from 1970 - 2018
Freshwater populations have been hit the hardest with an average decline of 83% since 1970
Biodiversity Decline by Region in Descending Order
Region | Percentage | Species Hardest Hit |
|---|---|---|
Latin America and the Caribbean | 94% | Freshwater fish, reptiles and amphibians |
Africa | 66% | Freshwater fish and mammals |
Asia and Pacific | 55% | All groups |
North America | 20% | Overall decline but also shows signs of stabilising |
Europe and Central Asia | 18% | Amphibian, reptile and freshwater fish, although shows signs of stabilising |
Local scale
The UK’s National Ecosystem Assessment (NEA, published in 2011) presented a thorough account of the ecosystem services provided by biodiversity that are essential for national social and economic wellbeing
The NEA showed the value of biodiversity to the UK, for example;
The value of inland wetlands for water quality
The value of pollination to agriculture
The UK also has habitats and species of global significance:
Approximately 13% of the world’s blanket bog
20% of Europe’s lowland heathland
Important collections of mosses, liverworts and lichens
The UK’s estuaries are a crucial migratory links for waders and wildfowl
Blanket bog
These bogs are extensive and widespread in the wetter, flat or gently sloping uplands of west and north UK
Found from 1000m down to sea level on poor draining ground with a peat level of at least 0.5m
Development began during warmer and wetter climates in the UK and further aided through forest clearance which increased waterlogging
Heathers, bog mosses, and cotton grasses have adapted to survive on the acidic and infertile ground
Dwarf shrubs appear in the more drier, eastly regions
With higher altitudes allowing mountain crowberry, bearberry and bog bilberry to grow
Purple moorland grass is dominant on the steeper westerly slopes
Human activity on blanket bogs
Industrial peat extraction destroyed many bogs and tax incentives during the 1980s saw afforestation of vast areas
Drainage resulted in shallow drains being dug across peatlands and over-grazing by livestock
Burning to promote fresh growth for grazing or bird nesting has led to the loss of peat forming mosses, along with shrinkage, desiccation and erosion
Climate change will lead to temperature increases and rainfall variations, which will all impact on the biodiversity of the bogs, although the extent of the change is difficult to evaluate
Changes to a Bog Blanket's Biodiversity in the UK
Cause | Consequences | Impacts |
|---|---|---|
Increased temperatures | Longer growing season | Loss of niche vegetation Increase in invasive bracken at higher altitudes Increase in nitrogen deposits and carbon sequestration |
Hotter and drier summers | Increased evapotranspiration and lowering of water table Drought Wildfires | Change in dominant species Increased wind erosion of exposed peat Changes in agricultural potential and habitat of ground nesting birds |
Wetter winters | Increased overland flows and increased rainfall intensities | Gully erosion Peat stability is lost Increased land slides |
Longer grazing period | Over-grazing | Biodiversity decline |
Access by walkers, ramblers and hikers | Footpath erosion Damage to stabilising vegetation Littering | Peat loss Exposed peat areas subject to drying out, wind and gully erosion Increased pollution and damage to wildlife |
Wildfires | Peat is lost and burning can continue underground for miles | Loss of biodiversity and release of carbon into the atmosphere increasing global warming |
Drainage of peat bog | Water table is lowered | Change of dominant plant species Allows access to invasive plant species Habitats are lost or changed |
Recent trends
Whilst the trend of biodiversity loss is downwards, it is showing signs of slowing
This is due in part to:
Introduction of green spaces in urban areas
Farmers rewilding and planting hedges
International polices on the trade of plants and animals
Education on the value of biodiversity
Adoption of polices to manage invasive alien species - bio-hazard controls
Designation of protected areas - conservation and national parks and sites of special scientific importance etc.
Regulations to support sustainable harvesting, reduction of pollution and habitat restoration
Policies to protect individual species or particular ecosystems
New building regulations that include environmental analysis
Increased recognition of local and indigenous knowledge and community managed areas
Causes & Impacts of Biodiversity Decline
Any decline in biodiversity negatively affects global well-being
Causes and Impacts of Biodiversity Decline
Causes | Impacts |
|---|---|
Exploitation via hunting, harvesting and fishing | Reduces the habitat and population of species |
Habitat degradation, change or loss | Deforestation to make way for agriculture, change of soil nutrients, loss of carbon sequestration and release of CO2 into the atmosphere |
Urban development | Changed land use, loss of habitats and biodiversity, increased CO2 production and changes in river drainage and availability of fresh water. Biological waste material increases further contributing to atmospheric pollution |
Energy production | Fossil fuel combustion increases atmospheric CO2 |
Pollution | Damage to habitats and species through run-off from agricultural chemicals and industrial processes |
Climate change and global warming | Rising sea levels and changes to abundance and distribution of species. Industrial farming of cattle increases atmospheric methane |
Mobility/globalisation | Movement of people have transported organisms across geographical barriers - some can be beneficial others are invasive and destructive (introduction of grey squirrels into the UK or Dutch Elm Disease accidentally imported into the UK from Canada in the late 1960s |
Impacts of biodiversity loss can be viewed as physical or human
Categorising Biodiversity Decline into Physical and Human Impacts
Physical | Human |
|---|---|
Loss of one species may result in the extinction of dependent species | Reduction in food supplies through a loss of pollinating insects and birds carrying seeds |
Fewer plants reduces CO2 uptake and increases greenhouse effect in the atmosphere | Air quality and water purity declines through declining biodiversity which will impact human health |
Loss of vegetation affects the water cycle leading to floods or droughts | Potential sources of medicines are lost |
Bare, exposed soil is vulnerable to erosion, leaving land infertile for growth of crops | Loss of crops through erosion can lead to famine |
Overall, biodiversity loss impacts vulnerability to natural disasters, increases energy and food insecurity, and decreases access to raw materials and potable water
Examiner Tips and Tricks
Remember that impacts can be either positive or negative
When asked to discuss recent trends in biodiversity, the 'trend' is the global view - HDEs are seeing an improvement in biodiversity because of its response in creating national parks and action plans on particular species or land, whereas, LDEs are seeing an increase in biodiversity loss as it endeavours to develop or in response to TNCs from HDEs moving production or needing resources that necessitate deforestation, for example.
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