Human Impact on Biodiversity Revision Notes | GCSE AQA Higher Biology

1. Why Biodiversity Matters for Human Survival

Imagine waking up tomorrow to find no bees, no forests, and no fish in the oceans. This isn't science fiction — it's the direction we're heading if biodiversity continues to collapse at current rates.

Biodiversity isn't just about saving cute animals. It's about human survival. We depend on other species for food, medicine, clean air, and stable climate. When species disappear, entire ecosystems can collapse, taking their life-supporting services with them.

Think of biodiversity like a giant web. Remove too many threads and the whole structure falls apart. Each species plays a role — predators control prey populations, decomposers recycle nutrients, and plants produce oxygen. Lose key species and the system breaks down.

2. How Human Activities Destroy Biodiversity

Humans are causing the sixth mass extinction in Earth's history. But unlike asteroid impacts or volcanic eruptions, this one is entirely our doing. Let's examine the main culprits.

Deforestation is the biggest threat. We're clearing forests for agriculture, urban development, and logging. Tropical rainforests are particularly vulnerable — they contain 50% of Earth's species but cover only 6% of land surface.

Pollution poisons ecosystems. Pesticides kill beneficial insects alongside pests. Plastic waste chokes marine animals. Chemical runoff creates dead zones in rivers and oceans where nothing can survive.

Climate change is shifting habitats faster than species can adapt. Coral reefs bleach in warming oceans. Arctic species lose their ice habitat. Weather patterns change, disrupting migration and breeding cycles.

Overfishing and hunting remove species faster than they can reproduce. Large predators like sharks and tigers are particularly vulnerable because they reproduce slowly and need large territories.

Invasive species introduced by human transport outcompete native species. Without natural predators, they can devastate local ecosystems. Think grey squirrels pushing out red squirrels in the UK.

3. The Domino Effect: When Ecosystems Collapse

Ecosystems are like house of cards — remove the wrong species and everything tumbles down. This cascading effect makes biodiversity loss particularly dangerous.

Worked example: Ecosystem Collapse: The a habitat Wolf Example

Trace what happened when wolves were removed from a habitat National Park, then reintroduced 70 years later.

1. Hunters killed all wolves in a habitat — Wolves were seen as dangerous predators to eliminate
2. Without predation pressure, deer numbers increased dramatically — No natural predator to control deer population
3. Excessive deer grazing destroyed young trees and shrubs — Too many deer eating all available plant material
4. Birds lost nesting sites, beavers lost food sources, rivers changed course — Loss of vegetation had cascading effects throughout ecosystem
5. 25 wolves released back into a habitat — Attempt to restore natural predator-prey balance
6. Deer behaviour changed, vegetation recovered, other species returned — Wolves restored the natural balance and ecosystem health

Answer: Removing one species can affect other species and change the balance of a community.

This example shows how losing just one species can transform an entire landscape. Some species have a large effect on other species and the balance of a community.

4. Conservation: Fighting Back Against Extinction

The good news? We're finally taking action. Conservation efforts are showing that we can reverse biodiversity loss when we commit resources and political will.

Protected areas like national parks and marine reserves give species safe spaces to recover. The key is making them large enough and connected by wildlife corridors.

Captive breeding programmes save species from extinction by maintaining populations in zoos and wildlife centres. Success stories include the California condor and Arabian oryx — both brought back from the brink.

Habitat restoration repairs damaged ecosystems. Reforestation projects plant native trees. Wetland restoration filters water and provides wildlife habitat. Even urban green spaces help by creating stepping stones for wildlife movement.

Countries can cooperate to protect habitats, reduce pollution, and conserve endangered species.

5. Balancing Human Needs and Conservation

The challenge is meeting human needs while protecting biodiversity.

Renewable energy reduces carbon dioxide emissions and can help protect habitats.

Responsible agriculture produces food without destroying ecosystems. Organic farming avoids harmful pesticides. Crop rotation maintains soil health. Agroforestry combines trees with crops, providing habitat while producing food.

Reusing and recycling materials reduces waste and can help protect habitats.

6. Exam Technique: Biodiversity Questions

Biodiversity questions often test your ability to link human activities to their ecological consequences. Here's how to tackle them effectively.

Common mistakes to avoid: Don't confuse conservation with preservation (conservation involves active management). Don't assume all human impact is negative — some activities like rewilding can increase biodiversity. Always consider the scale — local vs global impacts.

Remember: examiners want to see that you understand the complex relationships between human activities and ecosystem health. Show your understanding of cause-and-effect chains, and always support your points with specific examples.