What Is Biodiversity?

HSC Biology | Free Study Notes

In this lesson

• what biodiversity means

• the difference between genetic, species and ecosystem diversity

• why biodiversity matters

• how biodiversity links to ecosystem balance

What is biodiversity?

Biodiversity means the variety of life.

It can be considered at different levels, including:

• genetic diversity

• species diversity

• ecosystem diversity

A useful exam-style idea is that biodiversity is not just the number of organisms. It is the variety of genes, species and ecosystems.

HSC marking materials define biodiversity as the variety of species present in an ecosystem as well as the genetic diversity of those species. 

Genetic diversity

Genetic diversity is the variation in genes or alleles within a species.

What this means

Individuals of the same species are not genetically identical. Different alleles create variation within the population.

Why genetic diversity matters

Genetic diversity is important because it:

• increases variation in a population

• gives populations a better chance of adapting to environmental change

• reduces the risk of all individuals being affected in the same way by a disease or selection pressure

Example

Humans are one species, but individuals differ in characteristics such as eye colour, height and blood group because of genetic variation.

Species diversity

Species diversity is the variety of different species in an area or ecosystem.

What this means

An ecosystem with many different species has higher species diversity than one with only a few species.

Why species diversity matters

Species diversity is important because:

• different species play different roles in food webs

• interactions between species help maintain ecosystem balance

• loss of species can affect other organisms in the ecosystem

Example

A rainforest usually has high species diversity because it contains many different plants, animals, fungi and microorganisms.

Ecosystem diversity

Ecosystem diversity is the variety of ecosystems, habitats or environments in a region.

What this means

Different ecosystems have different abiotic and biotic conditions.

Examples include:

• forests

• grasslands

• wetlands

• deserts

• coral reefs

Why ecosystem diversity matters

Ecosystem diversity matters because different ecosystems support different communities of organisms. The more varied the habitats, the greater the range of life that can be supported.

Why biodiversity matters

Biodiversity is important to balance Earth’s ecosystems. 

Ecosystem balance

Biodiversity helps maintain balance because:

• food webs are more complex and stable

• species interactions support ecosystem function

• ecosystems are often better able to cope with change

Adaptation and survival

Biodiversity matters because variation gives organisms and populations a greater chance of surviving changing conditions.

Human importance

Biodiversity is also important to humans because it supports:

• food sources

• medicines

• ecosystem services

• environmental stability

At this level, the key point is that biodiversity supports healthy ecosystems and helps living things persist over time.

Comparing the three levels of biodiversity

Level of biodiversity	What varies?	Example
Genetic diversity	Genes within a species	Different alleles in a possum population
Species diversity	Different species in one area	Many plant and animal species in a rainforest
Ecosystem diversity	Different ecosystems in a region	Forests, wetlands and grasslands in one country

Worked example

Exam-style question

Explain the difference between genetic diversity and species diversity.

Worked answer

Genetic diversity is the variation in genes or alleles within a single species, while species diversity is the variety of different species in an ecosystem or area. Genetic diversity compares individuals within one species, whereas species diversity compares the number and variety of species present.

Why this works

This answer:

• defines both terms clearly

• shows the difference directly

• keeps the comparison focused

Common mistakes

• Saying biodiversity only means the number of species.

• Mixing up genetic diversity and species diversity.

• Forgetting that ecosystem diversity is also part of biodiversity.

• Describing biodiversity as just “lots of organisms” without mentioning variety.

• Explaining why biodiversity matters without first defining it clearly.

Quick quiz

1. What does biodiversity mean?

2. What is genetic diversity?

3. What is species diversity?

4. What is ecosystem diversity?

5. Why is biodiversity important for ecosystem balance?

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