Biodiversity and Conservation

Biodiversity is under threat from human activities. In this lesson you will learn why biodiversity matters, what threatens it, and how conservation efforts work to protect species and ecosystems.

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What is Biodiversity?

Biodiversity is the variety of all the different species of organisms on Earth, or within a particular ecosystem.

Biodiversity can be measured at different levels:

Level	Description
Species diversity	The number of different species AND the abundance of each species in an area
Genetic diversity	The variation of genes within a species
Ecosystem diversity	The range of different ecosystems in an area (e.g. forests, wetlands, grasslands)

A high biodiversity means there is a wide variety of species with good population sizes.

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Why Biodiversity Matters

Reason	Explanation
Ecosystem stability	Ecosystems with high biodiversity are more resilient — if one species declines, others can fill its role; food webs have more connections so are less likely to collapse
Food sources	Humans depend on a diversity of plants and animals for food; genetic diversity in crops protects against disease wiping out entire harvests
Medical discoveries	Many medicines are derived from organisms — e.g. aspirin from willow bark, penicillin from fungi, anti-cancer drugs from plants; undiscovered species may hold future cures
Ecosystem services	Biodiversity provides clean air, clean water, pollination of crops, decomposition of waste, flood prevention, climate regulation
Aesthetic and cultural value	Natural areas provide recreation, tourism income, inspiration, and cultural significance
Economic value	Tourism, fishing, timber, and other industries depend on healthy, biodiverse ecosystems
Ethical reasons	Many people believe all species have a right to exist, regardless of their usefulness to humans

Exam tip: If asked why biodiversity is important, give at least THREE different reasons from the table above. Examiners want breadth — do not just focus on one reason.

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Threats to Biodiversity

Human activities are the main cause of biodiversity loss. Global biodiversity is declining at an alarming rate.

1. Habitat Destruction

Activity	How it reduces biodiversity
Deforestation	Removes trees that provide habitat for countless species; destroys food webs; reduces photosynthesis (less CO₂ absorbed)
Urbanisation	Building towns, cities and roads destroys natural habitats; creates barriers that fragment populations
Agriculture	Clearing land for farming; hedgerow removal reduces wildlife corridors; monoculture (growing a single crop) drastically reduces plant species diversity
Mining and quarrying	Destroys habitats; creates pollution; alters water drainage

2. Pollution

Type of pollution	Effect on biodiversity
Air pollution (e.g. SO₂, NOₓ)	Acid rain damages forests and acidifies lakes, killing aquatic organisms
Water pollution (e.g. sewage, fertiliser runoff)	Eutrophication: excess nutrients → algal bloom → algae block light → plants die → bacteria decompose dead matter → bacteria use up oxygen → fish and invertebrates die
Land pollution (e.g. pesticides, herbicides)	Kills non-target species; bioaccumulation — toxins build up along food chains

3. Climate Change

• Rising global temperatures alter habitats — some species cannot adapt or migrate fast enough
• Coral bleaching — warmer seas cause corals to expel their symbiotic algae, leading to death of coral reefs (extremely biodiverse ecosystems)
• Changes in rainfall patterns affect water availability
• Sea level rise floods coastal habitats
• Timing of seasonal events changes (e.g. flowers blooming before pollinators are active)

4. Invasive Species

• Species introduced (accidentally or deliberately) to new environments where they have no natural predators
• They can outcompete native species for resources
• Example: grey squirrels outcompeting native red squirrels in the UK

5. Overexploitation

• Overfishing — catching fish faster than they can reproduce
• Overhunting — reducing populations below sustainable levels
• Over-harvesting of plants (e.g. deforestation for timber or palm oil)

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Impact of Human Activities in Detail

Deforestation

When forests are cut down:

• Habitats destroyed — animals lose homes, nesting sites and food sources
• Food webs disrupted — removal of producers affects all trophic levels
• Soil erosion — tree roots no longer hold soil in place; rain washes soil into rivers
• Flooding increases — trees no longer intercept and absorb rainfall
• CO₂ increases — fewer trees means less photosynthesis; burning wood releases CO₂
• Biodiversity plummets — tropical rainforests contain the highest biodiversity on Earth

Agriculture and Monoculture

Monoculture is the practice of growing a single crop over a large area. While efficient for food production, it:

• Drastically reduces plant diversity (and therefore insect and animal diversity)
• Makes crops vulnerable to disease (if one plant is susceptible, all are)
• Requires heavy use of pesticides (which kill non-target organisms) and fertilisers (which cause pollution)

Exam tip: When discussing threats to biodiversity, always explain the MECHANISM — do not just name the threat. For example, do not just write "pollution reduces biodiversity." Write "fertiliser runoff causes eutrophication, leading to algal blooms that block light, killing aquatic plants and reducing oxygen levels, which causes fish to die."

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Conservation Methods

Conservation is the protection and management of ecosystems and species to maintain biodiversity.

In-Situ Conservation (Protecting in Natural Habitat)

Method	Description
National parks	Large protected areas where land use is regulated; wildlife habitats preserved
Nature reserves	Areas set aside specifically for wildlife; human activity restricted
Marine conservation zones	Protected areas of sea where damaging activities (e.g. dredging, certain fishing) are restricted
Wildlife corridors	Strips of habitat (e.g. hedgerows, green bridges) connecting fragmented habitats, allowing animals to move between areas and maintaining genetic diversity
Legislation	Laws protecting endangered species (e.g. making it illegal to hunt, trade or disturb them); CITES (Convention on International Trade in Endangered Species)

Ex-Situ Conservation (Protecting Outside Natural Habitat)

Method	Description
Seed banks	Seeds from rare and endangered plants stored in controlled conditions; preserves genetic material for future use
Captive breeding programmes	Endangered species bred in zoos or breeding centres; aims to increase population size
Reintroduction programmes	Captive-bred animals released back into their natural habitat; e.g. red kites and beavers in the UK
Botanical gardens	Collections of living plants including rare species; research and education

Advantages and Disadvantages

Approach	Advantages	Disadvantages
In-situ	Protects the whole ecosystem; maintains natural behaviour and interactions; protects habitat for many species at once	Difficult to enforce; habitats may still be affected by pollution or climate change
Ex-situ	Can save species from immediate extinction; allows controlled breeding to increase genetic diversity	Expensive; animals may lose natural behaviours; limited capacity; does not protect the habitat

Exam tip: The best conservation strategies combine both in-situ and ex-situ methods. Captive breeding without habitat protection is ineffective — there must be a suitable habitat to release animals into.

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Sustainable Development

Sustainable development means meeting the needs of the present population without compromising the ability of future generations to meet their own needs.

Maintaining Fish Stocks

Overfishing is a major threat to marine biodiversity. Methods to maintain fish stocks sustainably include: