GCSE · Geography · AQA · Spec 8035

Biodiversity issues in hot deserts

Under 250 mm of rain a year, scorching days, freezing nights — yet some life manages here. So why so few kinds, and why can people do so much damage?

Build the web

What keeps desert life so thin?

Seven factors, one question: which factor makes which one happen — or makes it worse? Add every link you can justify, then check yours against the lesson's web.

Very little rain (under 250 mm a year)
Climate change: hotter, drier, longer droughts
Growth in tourism
Overgrazing by livestock
Scarce water for plants and animals
Nutrient-poor soil
Few plants, so few animals: low biodiversity (outcome)

Add a link

This factor……made this happen or worse

No links yet.

Exam line: A strong explanation follows each cause all the way through: cause → what it does to water, soil or plants → fewer plants → fewer animals → lower biodiversity.

What do you think?

Adapted — but is it rich in life?

A hot desert gets less than 250 mm of rain a year and has very hot days and very cold nights. Yet some plants and animals live there, each with special adaptations to these conditions.

Which of these is closest to what you think right now?

Deserts are basically empty. Nothing can really live somewhere that harsh.If so many desert species have clever adaptations, the desert must be full of different kinds of life.Some specially adapted species live there, but there aren't many different kinds — the variety is low.

How sure are you?

I'm sureI think soI'm guessing

Deserts are basically empty. Nothing can really live somewhere that harsh.

This is a common misconception

Not quite — a range of plants and animals do live in hot deserts. They're the ones with special adaptations. An adaptation is an evolutionary change that improves an organism's chance of survival in its environment. So the desert isn't empty: it's that most species can't survive there, and only the adapted ones can.

If so many desert species have clever adaptations, the desert must be full of different kinds of life.

This is a common misconception

This is the trap. Being adapted lets a species survive there — it doesn't mean there are lots of species. Biodiversity means the variety of different types of life in an area, and in hot deserts it's naturally low compared with most other large ecosystems. The conditions are so extreme that only a few species can cope.

Some specially adapted species live there, but there aren't many different kinds — the variety is low.

This matches the evidence

Spot on. Biodiversity is the variety of different types of life in an area. Hot deserts do have a range of adapted plants and animals, but because the conditions are so extreme, few species can survive — so biodiversity is naturally low.

An ecosystem is a community of living organisms and their interactions with their environment. In a hot desert that community is real — but it's made of few kinds of life, because only specially adapted species can survive the extremes.

Exam line: Say both halves: a range of adapted species live there, AND biodiversity is naturally low. Either half on its own is only half the picture.

Natural or human?

Sort the pressures

Is each one a physical (natural) cause of low biodiversity, or a human threat to it?

Still to sort

Physical cause (0)

Part of the desert's natural conditions — why biodiversity has always been low.

Where the line is: A physical cause is simply how the desert is. If it's something people do, or a change on top of the desert's natural state, it belongs in the other column.

Human threat (0)

A change linked to human activity that is pushing biodiversity lower.

Where the line is: Don't be fooled by weather words: low rainfall is the desert's normal state, but longer droughts from climate change are a change making things worse.

8 of 8 still to sort.

Two kinds of pressure act on desert life. Decide which kind each one is.

Watch out: Low rainfall and climate change both mean less water — but only one of them is the desert's natural state.

Why fragile?

Reason it through

Why can human activity do so much damage to a hot desert?

Link 1 of 4

First link · your turn

Most plants and animals can't survive the lack of rain and the extreme heat. So which ones do live here?

Locked — reveal the link above first

Your turn to write

Explain it in your own words

Explain why biodiversity in hot deserts is naturally low, and how one human activity threatens it. [6 marks]

Your answer

0 words · your answer stays on this page and is not sent anywhere.

The mark scheme

Biodiversity is naturally low because conditions are extreme, so only the species specially adapted to them survive. (1 mark)
A physical cause with its effect: e.g. very little rain (under 250 mm a year), so few plants can survive. (1 mark)
A second physical cause: e.g. nutrient-poor soil that cannot sustain much life, or very hot days and cold nights that very few species can cope with. (1 mark)
Fewer plants (producers) means fewer animals (consumers) can be supported. (1 mark)
Names a human activity and what it does: e.g. overgrazing damages plants and reduces soil cover; tourism over-extracts water; urbanisation fragments ecosystems; climate change brings longer droughts. (1 mark)
Links that activity to lower biodiversity: e.g. eroded, degraded soil or less water means fewer plants, and so fewer animals. (1 mark)

Model answer

Hot deserts are extreme environments, so only species specially adapted to the conditions can survive there, which keeps biodiversity naturally low. Rainfall is under 250 mm a year, so few plants can survive. The soils also lack nutrients and cannot sustain much life. With fewer plants (producers), the ecosystem can support fewer animals (consumers). Overgrazing makes this worse: livestock damage plants and reduce soil cover, so the soil erodes and soils already low in nutrients are degraded. That means even fewer plants can grow, fewer animals can be supported, and biodiversity falls further.

Great answers are chains, not lists: cause → water, soil or plants → animals → biodiversity.

Exam line: Every point you make should be one clear link. Follow each cause through to plants, animals and biodiversity — don't stop halfway.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

Why so few kinds of life manage here — and why people can so easily tip the balance.

What you need to know

Biodiversity is the variety of different types of life in an area; an ecosystem is a community of living organisms and their interactions with their environment.
Hot deserts are extreme, so only specially adapted species survive and biodiversity is naturally low.
Physical causes of low biodiversity: very little rain (under 250 mm a year), very hot days and very cold nights, nutrient-poor soil and strong winds.
Desert species' adaptations cannot cope with change, so the ecosystem is fragile and vulnerable to human activities.
Human threats: urbanisation, growth in tourism, overgrazing and climate change.

The big picture

Hot deserts are extreme: very little rain, very hot days, very cold nights and nutrient-poor soil. Only specially adapted species survive, so biodiversity is naturally low. Those adaptations can't cope with change, which makes the ecosystem fragile — and urbanisation, tourism, overgrazing and climate change all put pressure on the same scarce water, soil and plants.

Key points

1A range of adapted plants and animals live in hot deserts, but biodiversity is naturally low compared with most other large ecosystems.

2Very little rain means few plants survive — and therefore few animals.

3Very few species have evolved adaptations to cope with both very hot days and very cold nights.

4Nutrient-poor soil cannot sustain much life: fewer producers means fewer consumers can be supported.

5Adaptations cannot cope with changes to the ecosystem, which makes the hot desert ecosystem fragile.

6Urbanisation fragments ecosystems; tourism disturbs habitats, pollutes and over-extracts water; overgrazing erodes and degrades soil; climate change brings hotter, drier conditions and longer droughts.

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Worked example

Problem

Explain how urbanisation threatens biodiversity in a hot desert.

⚠ Watch out

Stopping halfway. "Tourists use lots of water" isn't an explanation yet — finish the chain: less water for plants and animals, so fewer can survive, so biodiversity falls.

🧠

Memory hook

Little rain, poor soil, few plants, few animals — and every human threat pulls on that same thin thread.

✓

Check yourself

Without looking back: can you name the four physical causes of low biodiversity in hot deserts, and follow one human threat all the way through to biodiversity?

Flashcards

(14)

What is biodiversity?

The variety of different types of life found in a particular area.

What is an ecosystem?

A community of living organisms and their interactions with their environment.

What is an adaptation?

An evolutionary change that improves an organism's chance of survival in its environment.

Hot deserts have many adapted species. So why is their biodiversity low?

The conditions are so extreme that most species cannot survive — only the few specially adapted ones do, so biodiversity is naturally low.

How much rain does a hot desert get, and why does that lower biodiversity?

Less than 250 mm a year. So little water means few plants can survive — and therefore few animals.

How do the desert's temperatures limit biodiversity?

Days are very hot and nights very cold, and very few species have evolved adaptations to cope with both extremes.

Why does poor desert soil mean fewer animals, not just fewer plants?

The soil lacks nutrients, so it can't sustain much plant life. Fewer producers means the ecosystem can support fewer consumers.

Name the fourth physical cause of low desert biodiversity, alongside rain, temperature and soil.

Strong winds.

Why is the hot desert ecosystem called fragile?

Its plants and animals are very vulnerable because their adaptations cannot cope with changes to the ecosystem.

How does urbanisation threaten desert biodiversity?

Cities, roads and communications fragment ecosystems, disturbing habitats and leading to wildlife loss.

Give three ways growth in tourism threatens desert biodiversity.

Tourists can disturb habitats, cause pollution and lead to over-extraction of the limited water plants and animals rely on.

How does overgrazing threaten desert biodiversity?

Livestock damage plants and reduce soil cover, causing soil erosion and degrading soils already low in nutrients.

How does climate change threaten desert biodiversity?

Rising global temperatures make deserts hotter and drier with longer droughts, leaving less water for plants and animals.

What is a drought?

A period with no rainfall.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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What keeps desert life so thin?

Adapted — but is it rich in life?

Sort the pressures

Explain it in your own words

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