What is biodiversity?
Biodiversity means the variety of living things on Earth. "Bio" means life. "Diversity" means many different kinds.
We look at variety in three ways. Each way is called a level.
Level 1: Species diversity
A species is one kind of living thing. Members of a species can have babies together. A tiger is one species. A peacock is another.
Species diversity is how many species live in a place. A rainforest has thousands. A desert has few. A place with more species is richer in life.
Level 2: Genetic diversity
Genes are tiny instructions inside a living thing. They decide colour, size and many other traits.
Inside one species, individuals have different gene mixes. That is genetic diversity. Think of rice: India grows thousands of rice varieties, some for floods, some for dry land. If a new disease arrives, some varieties may still survive.
Level 3: Ecosystem diversity
An ecosystem is a living community plus its surroundings, such as a forest, pond, desert, coral reef or grassland.
Ecosystem diversity is the number of different ecosystems in a region. Each one has its own plants, animals, soil, water and weather.
How evolution creates diversity
Evolution is change in living things over many generations.
- Variation: babies are a little different from each other (genes mix and sometimes change).
- Struggle: there is not enough food or space for all.
- Selection: individuals whose traits fit the place survive more often. This is natural selection.
- Inheritance: survivors pass those genes to their young.
Over very many generations, groups in different places change in different ways. When they become so different that they can no longer breed together, they are new species. One ancestor splits into many branches. More about this in the lesson Evolution.
Try it
At home: take a handful of rice, beans or leaves. Spread them out and sort them by shape and colour. How many kinds (species diversity)? Now look at one kind: are all the same? (genetic diversity).
In the 3D: in step 5 pick brown soil and green soil. Predict how many beetles survive, then check the number.
Key formulas and definitions
- Biodiversity = genetic + species + ecosystem diversity
- Natural selection = variation + struggle + survival of the fit + inheritance
- More generations of splitting = more species (1 → 2 → 4 → 8 …)
Worked examples
1. A pond has 3 species of fish, 2 of frogs and 5 of plants. How many species in all? Which level of diversity is this?
3 + 2 + 5 = 10 species. This is species diversity.
2. A farmer grows 4 varieties of wheat. Are these different species? Which level is this?
No, they are one species (wheat) with different genes. This is genetic diversity.
3. A district has a forest, a lake, a grassland and a wetland. Which level of diversity is described?
Four different habitats: this is ecosystem diversity.
4. In the beetle game the soil is brown. 4 brown and 4 green beetles start. A bird catches the ones it can see. How many survive and what colour will the next generation mostly be?
Brown beetles hide on brown soil, so 4 survive. The green ones are caught. Their babies are brown, so the next generation is mostly brown. This is natural selection.
5. One species splits into 2 in each generation of splitting. How many species after 4 splits?
1 → 2 → 4 → 8 → 16. After 4 splits there are 16 species.
Common mistakes
- Thinking species diversity and genetic diversity are the same. Species = different kinds. Genetic = differences inside one kind.
- Thinking an animal changes its body on purpose to survive. Change comes from genes in the population, not from wanting.
- Thinking evolution happens in one lifetime. It needs many generations.
- Thinking "survival of the fittest" means the strongest. It means best fitted to that place, such as best hidden.