Human impact on biodiversity

· Biodiversity loss is driven by both direct threats and indirect threats.
· Direct threats: overharvesting, poaching, illegal pet trade.
· Indirect threats: habitat loss, climate change, pollution, invasive alien species.
· In exams, always link cause → mechanism → impact on biodiversity → impact on ecosystems/societies.
· Remember: biodiversity loss reduces resilience, making ecosystems less able to resist disturbance and more likely to approach a tipping point.

This diagram shows habitat fragmentation, one of the main indirect human threats to biodiversity. It helps explain how human land use breaks continuous habitat into smaller patches, reducing population size and increasing extinction risk. Use it to explain why habitat loss often has long-term effects on species survival. Source

Multiple human impacts acting together

· Most ecosystems face more than one human impact at the same time.
· Combined impacts are often amplified rather than simply added together.
· Example: climate change can reduce ecosystem resilience, making ecosystems more vulnerable to invasive species, disease, or pollution.
· Good exam phrasing: “Human impacts interact synergistically, increasing the overall rate of biodiversity loss.”
· If asked to discuss severity, explain that compound pressures can push systems past critical thresholds.

Invasive alien species

· Invasive alien species are non-native species that spread and cause harm in a new ecosystem.
· They reduce local biodiversity through:
· Competition for limited resources.
· Predation on native species.
· Introduction of diseases or parasites.
· They often increase rapidly because they may have few natural predators, high reproductive rates, and disturbed habitats to colonize.
· Ways they arrive: shipping, trade, tourism, released pets, agriculture, aquaculture.
· A strong named example is useful, such as zebra mussels in North America or brown tree snakes in Guam.
· Management strategies may include physical removal, biological control, chemical control, quarantine, and prevention of introduction.
· Evaluation point: prevention is usually more effective and cheaper than eradication after establishment.

IUCN Red List and conservation status

· The IUCN Red List assesses the global conservation status of species.
· Status is based on population size, population trend, breeding potential, geographic range, and known threats.
· Conservation categories range from Least Concern (LC) to Extinct (EX).
· Why it matters: it publicizes vulnerability, guides conservation priorities, and helps governments/NGOs decide management strategies.
· In essays, explain that different stakeholders may prioritize differently:
· Governments may weigh economic development and policy feasibility.
· NGOs may prioritize species protection and advocacy.
· Individuals may respond through consumer choices, donations, activism, or local conservation.

This infographic summarizes how species are grouped by conservation risk. It is useful when revising the IUCN-style logic of threat categories and when explaining why some species require urgent intervention. Use it to reinforce the idea that conservation status depends on evidence, not just rarity. Source

Required named species examples

· You must know three named species:
· One species made extinct by human activity.
· One critically endangered species.
· One species whose status improved through intervention.
· For each species, revise:
· Causes of decline.
· Ecological impacts of decline or disappearance.
· Societal impacts.
· Conservation strategies used.
· Whether intervention was successful or unsuccessful.
· Strong example set: Passenger pigeon (extinct), Vaquita (critically endangered), Giant panda or Bald eagle (improved with intervention).
· In higher-mark answers, always connect species decline to food webs, ecosystem services, and human values/perspectives.

Tragedy of the commons

· The tragedy of the commons describes overuse of a shared resource when individuals act in self-interest rather than for long-term sustainability.
· It causes overexploitation, resource decline, and biodiversity loss.
· The key tension is individual short-term gain versus collective long-term benefit.
· ESS examples:
· Overharvested fish stocks such as the Grand Banks cod fishery.
· Plastic pollution in ocean gyres as contamination of a shared global commons.
· Management responses include quotas, permits, protected areas, international agreements, and community-based regulation.
· Excellent evaluation point: commons can be protected if there is effective governance, monitoring, and shared responsibility.

This NOAA infographic shows how unsustainable fishing damages ecosystems and reduces biodiversity. It is useful for explaining the tragedy of the commons because a shared marine resource can be depleted when harvesting is poorly managed. It also links biodiversity loss to human food security and livelihoods. Source

Biodiversity loss: impacts on ecosystems and societies

· Biodiversity loss can destabilize food webs and reduce ecosystem resilience.
· It can lower the quality or reliability of ecosystem services, such as pollination, soil protection, water regulation, and fisheries.
· Societal impacts include loss of food sources, livelihoods, tourism income, cultural value, and genetic resources for medicine or agriculture.
· Loss of one species can trigger cascading effects, especially if it is ecologically important.
· In evaluation questions, distinguish between ecological impacts and social/economic impacts.

Environmental justice and conservation

· Environmental justice must be considered in conservation.
· Biodiversity loss often affects indigenous peoples and marginalized communities most severely.
· Conservation can also create injustice if communities are excluded or forcibly relocated from land they depend on.
· Named example: the Maasai and conflicts linked to conservation in the Serengeti/Ngorongoro region.
· Strong exam argument: conservation is most effective when it is socially just, includes local participation, and respects land rights.
· Traditional indigenous land management is often more sustainable, but may face pressure from population growth, economic development, climate change, and weak legal protection.

This map shows the global distribution of biodiversity hotspots. It is useful for explaining why conservation priorities are often spatially focused and why many high-priority regions are in tropical areas under strong human pressure. Use it to support HL discussion of hotspots, KBAs, and competing land-use pressures. Source

Exam-ready links and phrases

· “Biodiversity loss reduces ecosystem resilience and increases vulnerability to further disturbance.”
· “Human impacts are often synergistic, so combined pressures produce greater biodiversity loss.”
· “Invasive alien species can outcompete native species, prey on them, or introduce disease.”
· “The IUCN Red List helps prioritize conservation by identifying species at greatest risk of extinction.”
· “The tragedy of the commons shows how shared resources can be degraded without effective governance.”
· “Conservation strategies must consider environmental justice as well as ecological effectiveness.”
· “The planetary boundary for loss of biosphere integrity has been crossed.”