Before you can argue about how to protect nature, you need to be able to say why it is worth protecting. Examiners ask this constantly, and the students who lose marks are the ones who only give one kind of reason. There are five, and they are not the same thing.
📚 What you need to know
There are five kinds of reason for preserving biodiversity: aesthetic, ecological, economic, ethical and social.
Ecological reasons are about the jobs nature does — pollination, clean water, climate control, soil.
A more diverse ecosystem is usually more stable and more resilient, so it recovers better after a shock.
Keystone species have an effect far bigger than their numbers suggest. Lose them and you get knock-on effects.
Economic reasons include natural capital, genetic resources for crops and medicines, and income from ecotourism.
Ethical reasons rest on intrinsic value — the idea that a species is worth something even if it is no use to us.
You need a named example for each type. That is what turns a 1-mark point into a 2-mark point.
The five reasons at a glance
Think of these as five different arguments you could make to five different people. A poet, an ecologist, an economist, a philosopher and someone who just likes walking in the woods would all defend the same forest for different reasons.
Questions that say “justify the preservation of biodiversity” want more than one column. Two well-chosen reasons with examples beat five vague ones.
Aesthetic reasons
This is the simplest one: people find the living world beautiful, and beauty is worth something. Wild places feed photography, painting, music, poetry and film. A landscape that has been stripped down to one crop species does not do that.
It sounds soft, but it is a real argument, and it is often the one that gets ordinary people to care in the first place. That matters, because public support is what keeps conservation funded.
Ecological reasons
This is the strongest argument in an ESS answer, because it links straight to systems thinking. Species and habitats run ecological processes and provide ecosystem services that we would otherwise have to pay for: pollination of crops, purification of water, regulation of climate, formation and holding of soil.
Diversity gives stability and resilience
The more species an ecosystem has, the more ways it has of doing each job. If one species cannot cope with a change, another one probably can, so the system keeps functioning.
Take a species-rich lake that warms up because of climate change. Some fish species cannot handle the higher temperature. But others tolerate it or adapt, keep feeding and breeding, and the food web carries on. In a lake with only two fish species, losing one is close to losing everything.
Careful with the words.Stability means the system does not swing about much. Resilience means it bounces back after it has been knocked. Diversity helps with both, but they are not the same idea, and examiners notice when students swap them.
Keystone species
Some species matter far more than their numbers suggest. A keystone species has a disproportionate effect on the structure and functioning of its ecosystem. Take it out and the whole thing rearranges itself.
Definition
A keystone species is a species whose effect on ecosystem structure and function is much larger than you would expect from its abundance or biomass.
Bush elephants in the African savannah are the classic example, and it is worth knowing properly because it feels backwards at first.
The odd part is that the “damage” is the point. Elephants destroying vegetation is what stops one plant species dominating and what creates space for everything else.
Students often write that elephants are important because they are big and rare. That gets nothing. The mark is for the mechanism: they change the physical structure of the habitat, and that structure is what other species depend on.
Economic reasons
Money is not a dirty word in ESS. A lot of conservation only happens because someone can show it pays.
Natural capital
Natural ecosystems supply timber, fish, fresh water and fertile soil. Treat these as capital — a stock that generates income — and it becomes obvious why running it down is bad economics. Keep the stock healthy and it keeps paying out.
Genetic resources
Wild relatives of crop plants carry genes for drought tolerance, pest resistance and disease resistance. Plant breeders and biotechnologists go back to those wild populations again and again. Lose the wild population and those genes are gone permanently, which is a direct threat to future food security.
Medicines
A large share of the drugs in use today started life in a plant, fungus or bacterium. The cancer drug paclitaxel comes from yew trees, including the Pacific yew and the Himalayan yew. The Himalayan yew has itself declined because it has been over-harvested for fuel and medicine, which is a neat example of how easily we can destroy the thing we depend on.
The wider argument writes itself: if we have already found this many useful compounds, the species going extinct now almost certainly include ones we would have wanted.
Ecotourism
Natural areas pull in visitors, and visitors bring foreign currency, jobs and money for local businesses. National parks in Kenya, Costa Rica and Tanzania earn real income precisely because the wildlife is still there.
Two-way link. Economic value can protect biodiversity, but it can also threaten it — too many tourists damage the thing they came to see. You meet this properly in the ecotourism page.
Ethical reasons
Ethical arguments do not depend on nature being useful to us at all. They rest on intrinsic value: the idea that a species or habitat has worth in itself, whether or not any human ever benefits from it.
From there come two common claims:
We share the planet with millions of other species and have no right to drive them extinct.
Because we are the most powerful species, we carry a responsibility to look after the rest — and an obligation to hand a working planet to future generations.
Intrinsic value is the phrase examiners are hunting for in ethical answers. If you write it, define it in the same breath: worth that is independent of usefulness to humans.
Social reasons
People use nature. Birdwatching, walking, climbing, swimming, camping, community tree planting — these are shared activities that build relationships as well as fitness.
Access to natural space measurably improves mental and physical health. If biodiversity is lost, those spaces become dull or degraded, and the social benefits go with them.
How the five reasons interrelate
The syllabus specifically asks you to understand how these justifications differ and how they interrelate. Do not treat them as five separate boxes.
Ecological health is what makes the economic value possible — no healthy reef, no reef tourism.
Aesthetic and social value build the public support that produces political and financial backing.
Ethical arguments explain why we still protect species that offer no economic return at all.
The honest summary is that the reasons pull in the same direction most of the time, but not always, and the interesting exam questions are exactly where they conflict.
EXAM QUESTION
Outline two different justifications for preserving biodiversity. [4]
Notice the word different — two ecological points would score half marks at best.
Point 1 – ecological
Biodiversity supports ecosystem services such as pollination and water purification;
a more diverse ecosystem is also more resilient, so it recovers faster after a disturbance such as warming.Point 2 – economic
Wild species are a source of genes and medicines;
e.g. paclitaxel, an anti-cancer drug, is obtained from yew trees.Two categories + two examples = 4 marks
EXAM QUESTION
Explain why the loss of a keystone species can reduce biodiversity. [3]
Define it first
A keystone species has an effect on ecosystem structure and function that is far larger than its abundance suggests.
Then give the mechanism
Removing it changes the physical structure or the food web, so conditions change for many other species at once.
Then a named exampleBush elephants keep savannah open by knocking over trees; without them one tree species dominates and habitat variety falls.Definition + mechanism + example
💡 Exam tip
Name the category. Write “an ecological reason is…” rather than launching straight into the point. It shows the examiner you know the framework.
One example each. Elephants (ecological), paclitaxel or yew (economic), Maasai Mara tourism (economic/social) will cover most questions.
If a question says justify or evaluate, give reasons and a counter-argument. Pure cheerleading caps your marks.
Use “intrinsic value” in ethical answers and define it in the same sentence.
Link ecological reasons to services and resilience — these are the syllabus words.
Watch for questions that ask how the reasons interrelate. Show one supporting another.
⚠ Common mix-up
Keystone is not the same as flagship. Keystone = huge ecological effect. Flagship = popular with the public and useful for fundraising. A species can be one, both or neither.
Stability is not resilience. Stability is staying steady; resilience is recovering after a shock.
Intrinsic value does not mean “very valuable”. It means valuable regardless of use to humans.
“Biodiversity is important” is not a reason. Say which category and why.
Ecosystem services are not the same as natural capital. Capital is the stock (the forest); services are the flow of benefits (the clean water it gives).
Do not claim every species is a keystone species. Most are not, and the word loses its meaning if you spread it about.
Up next: Approaches to Conservation — now that you can argue why biodiversity is worth saving, you need the actual toolkit: species-based, habitat-based and mixed strategies.
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