Life at three sizes: Biodiversity is the total diversity of living systems. It exists at three levels: the places things live, the kinds of living things, and the genes inside each kind.
The points to remember
- Biodiversity is the total diversity of living systems in an area.
- It exists at three levels: habitat diversity, species diversity and genetic diversity.
- Habitat diversity: the range of different habitats in an area.
- Species diversity: how many species there are and how evenly they are spread.
- Genetic diversity: the range of genes within one species or population.
- It can also be given as the amount of biological diversity per unit area.
Remember it as: Three sizes of variety: places, kinds, genes.
Habitat diversity
- Coral reefs, seagrass meadows, mangroves and sandy islands
- Like a park with ponds, woods and meadows
Species diversity
- More than 1,600 kinds of fish
- Hundreds of kinds of coral
Genetic diversity
- Some coral colonies carry genes for warmer water
- Like the many breeds of one species, the dog
Real example: the Great Barrier Reef, Australia, shows all three levels: many habitats, more than 1,600 kinds of fish, and corals whose genes differ from reef to reef.
Richness is not a level: Asked for 'another level of biodiversity', write genetic or habitat diversity. Richness and evenness are parts of species diversity, not separate levels.
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Species diversity and habitat diversity are the two levels you can see. Each has its own parts.
The points to remember
- Species diversity has two parts: richness (how many species) and evenness (how equal their numbers).
- Habitat diversity is the range of habitats in an ecosystem or biome.
- Habitats change along gradients: altitude, latitude, wet to dry, salty to fresh.
- Disturbances such as volcanoes, landslides or floods add new, different habitats.
- More habitats give more niches, food, nursery grounds and shelter from predators, so more species live there.
Species diversity
- Richness: the number of species
- Evenness: how similar their numbers are
- High when many species are all fairly common
Habitat diversity
- The range of habitats in an area
- Set by altitude, latitude and conditions
- Renewed by disturbances such as floods
Real example: on the Great Barrier Reef, the reef crest, the calm lagoon, the seagrass and the mangroves are different habitats. Each has its own fish, so more habitats mean more species.
Say both parts: When you describe species diversity, mention richness AND evenness: ten species where one covers almost everything is less diverse than ten species in equal numbers.
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Genetic diversity is the level inside a species: individuals of one species carry slightly different versions of their genes.
The points to remember
- Genetic diversity is the range of genes in a population or species.
- It shows as variety: breeds of dog, kinds of apple or potato.
- It rises through mutation, sexual reproduction and natural selection in different places.
- Populations cut off from each other build up different genes over time.
- Small populations lose genetic diversity.
Remember it as: Same species, different genes: every dog is a dog.
Real example: farmers in the Andes of Peru and Bolivia grow thousands of kinds of potato, all one species; the International Potato Center in Lima stores more than 4,000 of them. Some survive frost, others drought or disease.
Genes, not species: Genetic diversity is about variety WITHIN one species. 'Many kinds of bird' is species diversity, not genetic diversity.
The three levels are not separate boxes: each one feeds the others. Questions ask you to outline these links.
The points to remember
- More habitats give more niches, so species diversity rises.
- Different habitats set different selection pressures, so genetic diversity rises.
- More genetic diversity helps species survive, adapt and even split into new species.
- Many species build habitats for others (corals build reefs, trees make forest layers).
- Many species share out resources, so each population keeps its variety of genes.
- The converse is true too: lose one level and the others fall.
Real example: on the Great Barrier Reef, corals (species) build the reef (a habitat). Its cracks, caves and lagoons give thousands of niches, so fish diversity is high.
Outline the links: Define each level for up to two points, then give links: 'more habitats, so more niches, so more species'. Say which level causes which.
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Some places hold far more species than others. Data questions ask you to find the reasons in a fact file or a table.
The points to remember
- A range of habitats (mountains to coast) gives many niches.
- Big changes in altitude make zones of different habitat.
- A range of climates in one place: wet and dry, warm and cold.
- Isolation (an island, a mountain range) keeps out competitors and lets new species form.
- Warm, wet, sunny places near the equator are productive, and large protected areas keep species safe.
- Volcanic activity and succession keep making new habitats.
- Comparing two places: habitat loss (clearing for farms) or more surveys can explain a difference.
Real example: Costa Rica covers 0.03% of Earth's land but holds about 5% of its known species: it rises from mangrove coasts to 3,821 m, and has wet and dry sides.
Traps: For plant diversity, 'high rainfall' alone is not enough: say 'a RANGE of climates'. 'Conservation efforts' or 'a large area' do not explain diversity, and nor does 'more resources' alone. Human impacts explain why one place has lost species, but never count as factors that ADD biodiversity. When comparing two places, name the one with more.
Three short data skills come up again and again: telling two places apart, working out a percentage, and saying why a place matters.
The points to remember
- Distinguish = say which one has more, and of what: richness, evenness, habitats.
- Found only here = endemic.
- A percentage: part / total x 100, then round correctly.
- It matters for conservation if it has endemic species, many habitats, high biodiversity or little disturbance.
- Other reasons: legal protection, ecosystem services, cultural value, ecotourism.
- Use the figure's own facts: only the first two answers count.
Distinguish: the meadow has greater richness (8 species against 3) and greater evenness (no species above 14), so higher biodiversity. Real example: Hawaii has about 1,030 native flowering plants and about 920 grow nowhere else: 920 / 1,030 x 100 = 89.3%.
Round as asked: Give the number of decimal places the question asks for, and round the last one correctly: 68.888 is 68.9, not 68.8.
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How this comes up: Paper 1: a fact file about a place. Outline why it is high in plant diversity [2].
Figure 1 is a fact file on the Great Smoky Mountains National Park, USA.
With reference to Figure 1, outline why the park is high in plant diversity.
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