Why is biodiversity so much greater in the tropics, and why does its uneven distribution matter?
Explain the meaning and measurement of biodiversity, account for its concentration in the tropics, and assess its value
A focused answer to the H2 Geography outcome on biodiversity. Its definition and components, the latitudinal gradient and biodiversity hotspots, the reasons for tropical richness, and the ecological and economic value of biodiversity.
Reviewed by: AI editorial process; not yet individually human-reviewed
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What this dot point is asking
SEAB wants you to define biodiversity and its components, account for its concentration in the tropics (the latitudinal gradient and hotspots), and assess why it matters. The central insight is that biodiversity is not spread evenly: it peaks near the equator for reasons of energy, evolutionary time and habitat complexity, and its value, and the seriousness of its loss, flows from the services and resilience it provides.
The answer
What biodiversity is
Biodiversity is the variety of life, considered at three levels:
- Genetic diversity (variation within a species);
- Species diversity (the number and abundance of different species, often summarised by species richness and evenness);
- Ecosystem diversity (the range of habitats and ecosystems).
It is measured by counting species (richness), by indices that combine richness and evenness, and by mapping habitats.
The latitudinal gradient and hotspots
Species richness is highest near the equator and declines toward the poles, the latitudinal biodiversity gradient. Within this, certain biodiversity hotspots, regions with exceptional concentrations of endemic species under serious threat, hold a disproportionate share of the world's species, such as Sundaland in Southeast Asia.
Why the tropics are so biodiverse
- High, reliable energy and water. The warm, wet, aseasonal climate gives high net primary productivity, supporting more organisms and more trophic links.
- Long-term climatic stability. The tropics escaped the repeated glaciations of higher latitudes, so evolution proceeded uninterrupted, generating and preserving more species over time.
- Niche diversity. The structural complexity of tropical forests (many layers and microhabitats) creates many niches, allowing specialisation and reducing competition.
- Large historic area of warm tropical habitat supports more species.
The value of biodiversity
- Ecological: diverse ecosystems are more resilient and stable, and deliver services such as pollination, water regulation, soil formation and climate regulation.
- Economic: food, timber, fibres, genetic resources, the basis of many medicines, and tourism.
- Scientific and option value: undiscovered species may yield future medicines or crops.
- Intrinsic and cultural value: the right of species to exist and their cultural importance.
Why loss is serious
Extinction is irreversible; loss reduces resilience, making ecosystems more likely to collapse under stress; ecosystem services people depend on degrade; and future resources are lost. Loss is accelerating through habitat destruction, climate change, overexploitation, pollution and invasive species.
Examples in context
Example 1. The Sundaland hotspot. Southeast Asia's Sundaland, covering the Malay Peninsula, Borneo, Sumatra and Java, is one of the world's richest yet most threatened biodiversity hotspots, with vast numbers of endemic species including orangutans and the Rafflesia. Heavy deforestation for oil palm and logging makes it a clear case of exceptional tropical richness under acute threat.
Example 2. Singapore's urban biodiversity. Despite being a dense city-state, Singapore retains notable biodiversity in reserves such as Bukit Timah and Sungei Buloh and pursues a "City in Nature" strategy with ecological corridors and species recovery programmes. It shows both the loss that urbanisation causes and the value of protecting and reconnecting habitat fragments to sustain native species.
Try this
Q1. State the three levels at which biodiversity is measured. [3 marks]
- Cue. Genetic diversity (within a species), species diversity (number and abundance of species), and ecosystem diversity (range of habitats and ecosystems).
Q2. Explain why climatic stability has increased tropical biodiversity. [2 marks]
- Cue. The tropics avoided the repeated glaciations that disturbed higher latitudes, giving species long uninterrupted periods to evolve and diversify, so more species accumulated and persisted.
Q3. Explain why the loss of biodiversity is considered irreversible and serious. [3 marks]
- Cue. Extinction permanently removes a species and its genes; this cannot be undone, reduces ecosystem resilience and services people rely on, and forecloses potential future medicines, crops and resources.
Exam-style practice questions
Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Original10 marksAccount for the greater biodiversity of tropical regions compared with higher latitudes.Show worked answer →
Argument: tropical regions hold more biodiversity because of a combination of climatic, evolutionary and ecological factors that together support more species in more niches.
Factors to explain: the warm, wet, stable, aseasonal climate provides high and reliable energy and water, supporting high net primary productivity that sustains more organisms and more trophic links. Long-term climatic stability (less disturbance from glaciations than higher latitudes) has allowed evolution to proceed uninterrupted, generating and preserving more species over time. The structural complexity of tropical forests (layers, microhabitats) creates many niches, allowing specialisation and reducing competition. Greater area of warm tropical habitat historically also supports more species.
Why the gradient exists: combining high productive energy, long stable evolutionary time and abundant niches explains the latitudinal gradient in which species richness peaks near the equator and declines toward the poles.
Markers reward the energy/productivity argument, climatic stability and evolutionary time, niche diversity from structural complexity, and the link to the latitudinal gradient.
Original12 marksAssess the value of biodiversity and explain why its loss is a serious concern.Show worked answer →
Argument: biodiversity has wide-ranging ecological, economic and intrinsic value, so its loss threatens ecosystem function, human wellbeing and future options.
Values to set out: ecological value, biodiverse ecosystems are more resilient and stable and deliver services such as pollination, water regulation, soil formation and climate regulation. Economic value, biodiversity provides food, timber, fibres, genetic resources and the basis of many medicines, and underpins tourism. Scientific and option value, undiscovered species may yield future medicines or crops. Intrinsic and cultural value, the right of species to exist and their cultural importance.
Why loss is serious: extinction is irreversible; loss reduces resilience, so ecosystems are more likely to collapse under stress; ecosystem services that people depend on degrade; and potential future resources are lost forever. Loss is accelerating through habitat destruction, climate change, overexploitation, pollution and invasive species.
Evaluation: a strong answer ranks the values (ecological resilience and ecosystem services as the most consequential for human survival) and judges that irreversibility makes loss uniquely serious. Markers reward a structured account of value types and a reasoned judgement on why loss matters.
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