3.2 Human impact on biodiversityIB Environmental Systems and Societies SL: Revision notes

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

• Direct: the activity itself removes or harms organisms or habitats, e.g. hunting, overfishing, habitat destruction, introducing species.
• Indirect: the activity changes the environment, which then harms organisms, e.g. pollution, nutrient runoff, climate change.

Most ecosystems are subject to multiple human impacts. These combine, and one stress can make an ecosystem less able to cope with the next. Example: the Great Barrier Reef faces warming seas, farm runoff, fishing and tourism together.

An invasive alien species is introduced by humans to an area outside its native range and spreads, harming native species. It can reduce local biodiversity by:

• Competing with native species for limited resources.
• Predation on native species.
• Introducing diseases or parasites to which natives have little resistance.

Example: Burmese pythons in the Everglades, Florida, have been linked to steep declines in native mammals such as raccoons, opossums and bobcats.

The International Union for Conservation of Nature (IUCN) assesses the global conservation status of species and publishes the IUCN Red List. Categories run from Least Concern and Near Threatened through the threatened categories Vulnerable, Endangered and Critically Endangered, to Extinct in the Wild and Extinct. Some species are Data Deficient or Not Evaluated.

Assigning a status publicises vulnerability and helps governments, NGOs and individual citizens select appropriate conservation priorities.

The syllabus requires three named species, each with the cause of its status and (where relevant) the response.

• Extinct through human activity: the thylacine (Tasmanian tiger) was hunted, partly under bounty schemes, and lost habitat; the last known animal died in captivity in 1936. The passenger pigeon (extinct 1914) was hunted commercially on a huge scale and lost forest habitat.
• Critically endangered: the Sumatran orangutan (Pongo abelii), threatened by forest clearance for plantations such as palm oil and agriculture, and by the illegal pet trade.
• Status improved by intervention: the Arabian oryx (Oryx leucoryx) was hunted to extinction in the wild by 1972; captive breeding and reintroduction (from 1982 in Oman) moved it to Vulnerable. The giant panda is another example.

You may use other examples, so long as you can give causes and consequences.

The tragedy of the commons describes the possible outcome when a shared resource is used without restriction. Each user gains the full benefit of taking more, while the cost of depletion is shared by all, so rational individuals overuse the resource and it is degraded or collapses.

Examples: open-access fisheries, shared grazing land, the atmosphere as a sink for greenhouse gases.

Implications for sustainability: unrestricted access leads to overexploitation and biodiversity loss. Solutions include quotas and licences, community management, privatisation or regulation, and international agreements.