What Is Biodiversity?

Biodiversity means the variety of living things in an area.

It includes more than just the number of species. Biodiversity can be considered at several levels, including variation:

• within a species
• between different species
• between different ecosystems

A rainforest, coral reef, grassland, pond, and even a school garden can all contain biodiversity.

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A Simple Definition

A useful definition is:

Biodiversity = the variety of life in a particular area

An area with many different species and habitats usually has high biodiversity.

An area with very few species usually has low biodiversity.

However, biodiversity is not only about counting species. Scientists also consider genetic diversity and ecosystem diversity.

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The Three Main Levels of Biodiversity

Biodiversity can be studied at three main levels:

Genetic diversity

Variation within a species.

Species diversity

The variety of species in an area.

Ecosystem diversity

The variety of habitats and ecosystems in a region.

These levels are connected.

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Genetic Diversity

Genetic diversity refers to differences in genes among individuals of the same species.

Members of a species are similar, but they are not genetically identical.

For example, individuals may differ in:

• size
• colour
• disease resistance
• tolerance to heat or cold
• growth rate
• other inherited characteristics

A population with greater genetic variation may be better able to survive environmental changes.

For example, if a disease appears, some individuals may have genetic traits that make them more resistant.

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Example of Genetic Diversity

Consider a population of wild rabbits.

Some rabbits may:

• have slightly different fur colours
• be larger or smaller
• tolerate cold better
• resist certain diseases more effectively

These differences represent genetic diversity within one species.

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Species Diversity

Species diversity refers to the variety of different species in an area.

For example, a forest might contain:

• trees
• mosses
• fungi
• insects
• birds
• mammals
• reptiles
• microorganisms

The more different species present, the greater the species richness.

Scientists may also consider how evenly individuals are distributed among species.

An ecosystem dominated almost completely by one species may be considered less diverse than one containing similar numbers of many species.

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Example: A Coral Reef

Coral reefs often contain very high species diversity.

They can support:

• corals
• fish
• crustaceans
• molluscs
• algae
• sponges
• sea stars
• microorganisms

Many organisms interact through complex food webs and ecological relationships.

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Ecosystem Diversity

Ecosystem diversity refers to the variety of ecosystems and habitats found in a region.

For example, a large area may contain:

• forests
• wetlands
• rivers
• lakes
• grasslands
• coastal habitats

Each ecosystem provides different environmental conditions and supports different organisms.

A region containing many different habitat types therefore has greater ecosystem diversity.

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Comparing High and Low Biodiversity

Imagine two ecosystems.

Ecosystem A

Contains:

• 25 plant species
• 15 insect species
• 8 bird species
• 6 mammal species
• several fungi and microorganisms

Ecosystem B

Contains:

• 2 plant species
• 1 insect species
• 1 bird species

Ecosystem A clearly has greater species biodiversity.

However, biodiversity comparisons can become more complicated when abundance and genetic variation are also considered.

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High-Biodiversity Ecosystems

Examples of ecosystems that often contain high biodiversity include:

• tropical rainforests
• coral reefs
• wetlands
• some tropical forests and mangroves

These environments may contain many species occupying different ecological niches.

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Lower-Biodiversity Ecosystems

Some environments naturally support fewer species.

Examples may include:

• very cold polar environments
• extremely dry deserts
• high mountain environments

Low biodiversity does not mean an ecosystem has no ecological value.

Organisms living in extreme environments may have unusual adaptations and play important ecological roles.

Human activities can also reduce biodiversity by simplifying habitats.

For example, replacing a natural forest with a large area containing only one crop can greatly reduce the variety of species present.

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Why Is Biodiversity Important?

Biodiversity is important because organisms are connected through ecological relationships.

Different organisms may perform roles such as:

• producing food through photosynthesis
• pollinating plants
• decomposing dead organisms
• cycling nutrients
• controlling populations
• providing food for other species
• creating habitats

Removing species can therefore affect many other parts of an ecosystem.

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Biodiversity and Food Webs

High biodiversity often produces more complex food webs.

Consider a simple ecosystem containing:

Grass → Rabbit → Fox

If the rabbit population disappears, the fox may lose its main food source.

Now imagine a more diverse ecosystem in which a predator can feed on:

• rabbits
• rodents
• birds
• insects

If one prey population decreases, other food sources may remain.

This can sometimes make ecological communities more resilient to disturbances.

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Biodiversity and Ecosystem Stability

Ecosystems experience disturbances such as:

• drought
• storms
• disease
• fires
• temperature changes
• introduction of new species

Greater biodiversity can sometimes increase an ecosystem's ability to continue functioning after disturbance because several species may perform overlapping ecological roles.

This ability to recover or continue functioning is called resilience.

However, the relationship between biodiversity and stability can be complex and depends on the ecosystem and type of disturbance.

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Biodiversity Provides Ecosystem Services

Humans depend on healthy ecosystems for many benefits called ecosystem services.

These include:

Food

Plants, animals, fungi, and microorganisms provide food.

Pollination

Insects, birds, and other animals pollinate many plants.

Water Purification

Wetlands and microorganisms can help remove pollutants and nutrients from water.

Soil Formation

Decomposers break down dead material and contribute to soil development.

Nutrient Cycling

Microorganisms and other organisms recycle important elements.

Climate Regulation

Forests and oceans influence carbon cycling and climate.

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Biodiversity and Medicine

Living organisms can also provide useful chemical compounds.

Many medicines have been developed from or inspired by substances produced by:

• plants
• fungi
• bacteria
• animals

Loss of biodiversity could therefore mean losing species before their potential medical or scientific value is understood.

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Biodiversity and Agriculture

Agriculture also depends on biodiversity.

Useful organisms include:

• pollinators
• soil microorganisms
• natural predators of crop pests
• genetically diverse crop varieties

Genetic diversity in crops can be especially valuable.

If all plants in a crop are genetically very similar, a single disease might affect most of them.

Greater genetic diversity can provide more variation in resistance.

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Examples of Biodiversity in Nature

Biodiversity can be observed almost anywhere.

Forest

May contain:

• trees
• shrubs
• insects
• mammals
• birds
• fungi
• bacteria

Pond

May contain:

• algae
• aquatic plants
• insects
• fish
• amphibians
• microorganisms

Rocky Shore

May contain:

• algae
• barnacles
• crabs
• molluscs
• fish
• sea stars

Soil

Even a small amount of soil may contain enormous numbers of:

• bacteria
• fungi
• microscopic animals
• plant roots

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Biodiversity Can Exist at Small Scales

You do not need to visit a rainforest to investigate biodiversity.

A school campus might contain:

• several grass species
• trees
• flowering plants
• ants
• butterflies
• birds
• spiders
• fungi

Students could compare biodiversity between:

• a maintained lawn
• a garden
• a wooded area
• a pond
• an unused field

Different habitats may support very different communities.

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Comparing Two Ecosystems

Suppose students investigate two areas.

Area A: Maintained Lawn

They identify:

• 2 plant species
• 2 insect species
• 1 bird species

Area B: Natural Garden

They identify:

• 12 plant species
• 9 insect species
• 5 bird species
• 3 spider species

Based only on species richness, Area B has much higher biodiversity.

A strong conclusion would be:

Area B has greater observed species diversity because more different species were recorded there.

A scientific comparison should always use evidence rather than simply saying one area "looks more diverse."

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Threats to Biodiversity

Biodiversity can decrease when populations or habitats are damaged.

Major threats can include:

• habitat destruction
• pollution
• overharvesting
• invasive species
• climate change
• disease
• habitat fragmentation

When a species becomes extinct, its genetic information and ecological role are permanently lost.

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Protecting Biodiversity

Humans can help conserve biodiversity through actions such as:

• protecting habitats
• restoring damaged ecosystems
• reducing pollution
• controlling invasive species
• managing hunting and fishing sustainably
• maintaining wildlife corridors
• protecting endangered species
• preserving genetic diversity

Conservation aims not only to protect individual species but also the ecosystems and ecological relationships that support them.

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Worked Example

Two forests are surveyed.

Forest A

Contains:

• 18 tree species
• 30 insect species
• 12 bird species

Forest B

Contains:

• 5 tree species
• 8 insect species
• 3 bird species

Which forest has greater recorded species biodiversity?

Forest A

Why?

Because it contains a greater number of different species in all three groups sampled.

We should be careful, however, because a complete biodiversity assessment would also consider factors such as:

• abundance
• genetic variation
• habitat diversity

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Levels of Biodiversity Together

Consider a large rainforest.

Genetic Diversity

Individuals within a monkey species have different genes.

Species Diversity

The rainforest contains thousands of plant, animal, fungal, and microbial species.

Ecosystem Diversity

The larger region may contain rivers, forest canopy, forest floor, wetlands, and other habitats.

These levels interact to create the overall biodiversity of the region.

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Common Misconceptions

Biodiversity does not simply mean "lots of animals."

Plants, fungi, microorganisms, and other organisms are also part of biodiversity.

Biodiversity is not only the number of species.

It also includes genetic and ecosystem diversity.

A large number of organisms does not necessarily mean high biodiversity.

A field containing 10,000 plants of one species has many organisms but low species diversity.

Low natural biodiversity does not mean an ecosystem is unimportant.

Extreme environments may naturally support fewer but highly specialised species.

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Did You Know?

A huge amount of Earth's biodiversity is extremely small.

Soil, seawater, and even surfaces of plants and animals contain enormous communities of bacteria, fungi, and other microorganisms.

Many of these species are difficult to identify using traditional observation, so scientists increasingly use DNA analysis to investigate microbial biodiversity.

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Key Terms

Biodiversity – The variety of life in an area.

Genetic diversity – Variation in genes within a species or population.

Species diversity – The variety of species within an ecosystem.

Species richness – The number of different species present.

Ecosystem diversity – The variety of ecosystems and habitats in a region.

Ecosystem – A community of organisms interacting with each other and their physical environment.

Resilience – The ability of an ecosystem to withstand or recover from disturbance.

Ecosystem service – A benefit humans obtain from natural ecosystems.

Conservation – Protection and management of biodiversity and natural resources.

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Key Takeaways

• Biodiversity is the variety of living things in an area.
• Biodiversity can be studied at three major levels: genetic, species, and ecosystem diversity.
• Genetic diversity describes variation within a species.
• Species diversity describes the variety of different species present.
• Ecosystem diversity describes the variety of habitats and ecosystems in a region.
• Ecosystems such as tropical rainforests and coral reefs often have very high biodiversity.
• Some extreme environments naturally have fewer species.
• Biodiversity supports important ecological processes including pollination, decomposition, food webs, and nutrient cycling.
• Humans depend on biodiversity for food, medicines, clean water, agriculture, materials, and other ecosystem services.
• Biodiverse ecosystems may be more resilient to some environmental disturbances.
• Biodiversity can be reduced by habitat loss, pollution, invasive species, overharvesting, and climate change.
• Biodiversity can be investigated even in small local habitats such as gardens, ponds, fields, and school campuses.
• Comparing biodiversity should be based on evidence, such as the number and distribution of species observed.