Biodiversity is important for the stability of ecosystems. Explain why a reduction in biodiversity can have serious consequences for an ecosystem, including the impact on food webs and the long-term survival of species.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
In recent decades, human activities such as deforestation, pollution and overuse of pesticides have caused a significant decline in the number of species found in many ecosystems worldwide.
Model answer (5 marks)
Biodiversity is the variety of species in an ecosystem.
A loss of species breaks food webs: if a prey species disappears, its predators lose food; if a predator disappears, its prey may over‑populate, altering the whole chain.
With fewer species the ecosystem is less stable and more vulnerable to change because there are fewer alternative species that can perform the same ecological roles.
Loss of species also reduces the gene pool and genetic diversity, limiting the ability of remaining species to adapt to environmental change.
Once a species is extinct it is lost permanently, making the loss irreversible and further weakening ecosystem stability over time.
A loss of species breaks food webs: if a prey species disappears, its predators lose food; if a predator disappears, its prey may over‑populate, altering the whole chain.
With fewer species the ecosystem is less stable and more vulnerable to change because there are fewer alternative species that can perform the same ecological roles.
Loss of species also reduces the gene pool and genetic diversity, limiting the ability of remaining species to adapt to environmental change.
Once a species is extinct it is lost permanently, making the loss irreversible and further weakening ecosystem stability over time.
Examiner tips
- Use the word "food web" and explain the chain effect; mention stability and genetic diversity; note irreversibility of extinction.
Common mistakes
- Confusing biodiversity with species richness only; ignoring the role of genetic diversity; failing to mention irreversibility of extinction.
Mark scheme (5 marks)
- Biodiversity refers to the variety of different species found in an ecosystem / area
- Reducing the number of species disrupts food webs because removal of one species affects the organisms that feed on it or are fed upon by it
- A less biodiverse ecosystem is less stable / more vulnerable to change, because there are fewer alternative species to fill ecological roles
- Loss of species reduces the gene pool / genetic diversity available, reducing the ability of species to adapt to environmental change
- Once a species becomes extinct, it is lost permanently, so biodiversity loss is irreversible and further reduces ecosystem stability over time
Key terms in this question
Related
- All Edexcel A-Level Biology A: Salters-Nuffield (9BN0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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