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Threats to biodiversity

3.2.1 Biological diversity is being adversely affected by both direct and indirect influences.

Direct threats include overharvesting, poaching and the illegal pet trade. Indirect threats include habitat loss, climate change, pollution and invasive alien species.

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Human activity threatens biodiversity in many ways, but not all threats operate in the same manner. Some are direct: they involve the deliberate removal or killing of organisms. Others are indirect: they alter the conditions in which species live, making survival harder.

Direct threats

Direct threats involve the intentional targeting of organisms:

Overharvesting occurs when organisms are removed from an ecosystem faster than the population can replace itself. This applies to fisheries, forestry and the collection of wild plants.

Poaching is the illegal hunting or killing of wildlife. It is driven by demand for products such as ivory, rhino horn and tiger bones.

The illegal pet trade involves the capture and sale of wild animals for private ownership. This affects species such as parrots, reptiles and primates, and can severely reduce wild populations.

Indirect threats

Indirect threats alter ecosystems in ways that make them less suitable for the species that live there:

Habitat loss is the single largest driver of biodiversity decline globally. Conversion of forests, wetlands and grasslands for agriculture, urbanisation and infrastructure destroys the environments species depend on.

Climate change alters temperature and precipitation patterns, shifts growing seasons, and changes the distribution of species. Some species cannot adapt or migrate quickly enough.

Pollution introduces harmful substances into ecosystems. This includes chemical pollutants in waterways, air pollution, light pollution and noise pollution.

Invasive alien species are non-native organisms that, once established, outcompete, prey upon or introduce diseases to native species. They are the focus of this lesson.

Distinguish between a direct and an indirect threat to biodiversity. Give one example of each.
Explain why habitat loss is considered an indirect rather than a direct threat.

[Source]

A species of slow loris is captured from forests in Southeast Asia and sold online as a pet. Identify the type of threat and explain the likely impact on the wild population.

Multiple impacts and amplification

3.2.2 Most ecosystems are subject to multiple human impacts.

These impacts are increasing and their effects are amplified when combined. For example, when the impact of climate change has reduced resilience, other threats, such as invasive alien species, have more impact than if they were acting alone.

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In reality, ecosystems rarely face a single threat in isolation. Most are subject to multiple human impacts acting simultaneously, and these impacts are increasing in both number and intensity.

Critically, the effects of multiple threats are amplified when combined. This means that the total impact is greater than the sum of the individual impacts acting alone. When one threat reduces the resilience of an ecosystem, it becomes more vulnerable to additional threats.

Example: climate change and invasive alien species

Consider a lake ecosystem. Climate change raises water temperatures, disrupts seasonal mixing patterns and reduces dissolved oxygen in deeper water. The ecosystem's resilience is reduced: it is less able to absorb further disturbance.

Now add an invasive filter-feeding mussel. Under normal conditions, the lake might absorb the impact of the invader. But with resilience already lowered by climate change, the invasive species has a far greater impact than it would have had acting alone. The warmer water may even favour the invader, accelerating its reproduction.

This is exactly what is happening in Lake Geneva.

Explain what it means for the effects of multiple threats to be "amplified when combined".
Using the lake example, explain how climate change can reduce the resilience of an ecosystem, making it more vulnerable to invasive species.
Suggest why a single threat acting alone might have a relatively small impact on biodiversity, but the same threat combined with others could push the ecosystem towards a tipping point.

🎒 Base knowledge and understanding

✅ Tasks

🌿 Content

🔑 Key terms

🎯 Context

Threats to biodiversity

Distinguish between a direct and an indirect threat to biodiversity. Give one example of each.

Explain why habitat loss is considered an indirect rather than a direct threat.

A species of slow loris is captured from forests in Southeast Asia and sold online as a pet. Identify the type of threat and explain the likely impact on the wild population.

Multiple impacts and amplification

Explain what it means for the effects of multiple threats to be "amplified when combined".

Using the lake example, explain how climate change can reduce the resilience of an ecosystem, making it more vulnerable to invasive species.

Suggest why a single threat acting alone might have a relatively small impact on biodiversity, but the same threat combined with others could push the ecosystem towards a tipping point.

Invasive alien species