In simple terms
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Life's Rich Library
Biodiversity is the total variety of life on Earth, from the unique genetic code within a single species to the vast array of different ecosystems. We measure this variety to gauge the health of our planet and decide where to focus our conservation efforts most effectively.
Imagine our planet is a giant library. Genetic diversity is like the variety of words and sentence structures used within each book. Species diversity is the number of different book titles on the shelves. Habitat diversity is the number of different sections in the library, like 'Science Fiction', 'History', and 'Poetry'. A healthy, resilient library has a rich collection at all three levels, not just thousands of copies of one book.
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First, grasp the three distinct levels of biodiversity: genetic (variety within a species), species (variety between species), and habitat (variety of ecosystems).
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Next, understand how these levels are linked. For example, a high diversity of habitats provides more niches, which in turn supports a higher diversity of species.
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Then, learn to quantify species diversity. Use the Simpson's Diversity Index to combine species richness (the number of species) and evenness (their relative abundance) into a single, comparable value.
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Finally, apply this knowledge to conservation. Identify why biodiversity hotspots, areas with high numbers of unique species under threat, are critical priorities for protecting global biodiversity.
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Key formulas
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Full topic notes
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The Three Levels of Biodiversity
Biodiversity is not a single, simple measure. It is a complex concept that exists at three distinct, interconnected levels. Understanding each level is essential for a full appreciation of an ecosystem's health.
Genetic Diversity: This is the variety of genes within a species. A large gene pool provides the raw material for adaptation and evolution. For example, the low genetic diversity of cheetahs makes them highly vulnerable to disease.
Species Diversity: This is the variety of species in a given area. It is the most common understanding of biodiversity and is determined by both the number of species (richness) and their relative abundance (evenness). A tropical rainforest has high species diversity, whereas a commercial pine plantation has very low species diversity.
Habitat Diversity: This refers to the range of different habitats within a particular area. A landscape containing woodland, rivers, and meadows has higher habitat diversity than one composed solely of grassland. High habitat diversity generally promotes high species diversity by providing a greater number of ecological niches.
Quantifying Species Diversity: The Simpson's Index
To compare the biodiversity of two different ecosystems, we need a quantitative measure. Simply counting the number of species (richness) can be misleading. A community might have 10 species, but if 99% of the individuals belong to just one of those species, it's not very diverse. A diversity index combines richness and evenness into a single value. The Simpson's Diversity Index is a common tool used for this.
Where:
- D = Simpson's Diversity Index
- N = total number of organisms of all species found
- n = number of individuals of a particular species
- Σ = the sum of
Biodiversity Hotspots and Conservation Priorities
With limited funding and time, conservationists cannot protect everything, everywhere. They must prioritise their efforts. One key strategy is to focus on 'biodiversity hotspots'. These are regions that are both exceptionally rich in life and under severe threat. To be classified as a hotspot, a region must meet two strict criteria: it must have a high percentage of endemic plant life (species found nowhere else) and it must be significantly threatened by human activity.
Criteria: A region must have at least 1,500 endemic vascular plants and have lost at least 70% of its primary native vegetation.
Significance: The 36 recognised hotspots contain over 50% of the world's plant species and 43% of its bird, mammal, reptile, and amphibian species in just 2.4% of the Earth's land surface.
Examples: Famous hotspots include Madagascar, the Atlantic Forest of Brazil, the Philippines, and the Cape Floristic Region of South Africa.
Conservation Strategy: Focusing on hotspots is a form of 'conservation triage', aiming to achieve the greatest species protection with the most efficient use of limited resources.
Worked examples
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An ecologist samples a quadrat in an ancient woodland and records the following numbers of three beetle species:
- Ground Beetle: 15
- Rove Beetle: 12
- Click Beetle: 13
Calculate the Simpson's Diversity Index (D) for this community. Show your working.
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Calculate N (total number of organisms):
Two ponds, Pond A and Pond B, were sampled for invertebrates. The results are shown below. Calculate the Simpson's Diversity Index for each pond and state, with a reason, which pond is more diverse.
| Species | Pond A (n) | Pond B (n) |
|---|---|---|
| Pond skater | 45 | 20 |
| --- | --- | --- |
| Water beetle | 3 | 18 |
| Dragonfly nymph | 2 | 22 |
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How it all connects
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Glossary
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What is biodiversity?
The variety of life on Earth at all levels, from genes to ecosystems. It is commonly considered at three levels: genetic, species, and habitat diversity.
Key takeaways
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Genetic Diversity: This is the variety of genes within a species. A large gene pool provides the raw material for adaptation and evolution. For example, the low genetic diversity of cheetahs makes them highly vulnerable to disease.
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Species Diversity: This is the variety of species in a given area. It is the most common understanding of biodiversity and is determined by both the number of species (richness) and their relative abundance (evenness). A tropical rainforest has high species diversity, whereas a commercial pine plantation has very low species diversity.
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Habitat Diversity: This refers to the range of different habitats within a particular area. A landscape containing woodland, rivers, and meadows has higher habitat diversity than one composed solely of grassland. High habitat diversity generally promotes high species diversity by providing a greater number of ecological niches.
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