3.2 Human impact on biodiversity

Learning objectives

• Distinguish between direct and indirect human influences on biodiversity, with named examples of each.

• Explain why several human impacts acting together cause more damage than each would alone.

• Design an investigation of human impact using a transect perpendicular to a footpath, and calculate Simpson’s reciprocal index from the results.

• Explain how invasive alien species reduce local biodiversity, and evaluate the management of a named invasive species.

• Outline how the IUCN assigns conservation status and how the Red List is used by governments, organisations and individuals.

• Describe, for three named species, the causes and consequences of their decline and the success of conservation measures.

• Explain the tragedy of the commons and apply it to an overharvested resource and a polluted environment.

• Explain why biodiversity hotspots and key biodiversity areas are threatened and why they are priorities for conservation. (HL)

• Evaluate the conflict between palm oil production, development and conservation in Malaysia and Indonesia. (HL)

• Discuss the threats to traditional Indigenous land management and the environmental justice issues raised by conservation. (HL)

• Evaluate the claim that human-caused extinctions could push the Earth system past a tipping point. (HL)

Introduction

Human activities are reducing biodiversity, the variety of life at the levels of habitats, species and genes, faster than at any time in human history. Forests are cleared for farms, fish are taken faster than they can reproduce, species are moved around the world, and the climate is changing. These losses matter because biodiversity supports the ecosystem services on which societies depend, such as pollination, clean water and food from fisheries.

Biodiversity loss is a question of systems, because each threat changes the flows and storages of an ecosystem and threats interact through feedback. It is a question of perspectives, because a forest that a conservation scientist sees as irreplaceable may be a source of land, jobs and income to a farmer or a government. It is also a question of sustainability, because many of the resources at risk are shared, and no single user has a reason to protect them.

Direct and indirect threats to biodiversity

Every human influence on biodiversity works in one of two ways. Some activities kill or remove organisms themselves: a fisher catches a fish, a poacher shoots an elephant, a trader takes a parrot from its nest. Others change the conditions that species depend on, so that populations decline even though nobody sets out to harm them. The first group are called direct influences and the second indirect influences.

Indirect influences act through the habitat, the climate, the chemistry of air, soil and water, or the community of other species. They are usually harder to see and harder to control, because they come from many small decisions made far away, such as buying food grown on cleared forest land or burning fossil fuels.

Direct influences

Overharvesting is the taking of a wild population faster than it can replace itself by reproduction. It applies to fish, timber, medicinal plants and wild meat. A harvest is sustainable only when it is no larger than the population’s net growth, so overharvesting causes the population to shrink year after year until it collapses or becomes too small to be worth harvesting.

Poaching targets species that have a high market value, and the rarer a species becomes, the higher the price of its parts can rise. This creates a dangerous positive feedback: scarcity makes each animal more valuable, which makes poaching more profitable. Large, slow-breeding animals such as rhinoceroses, elephants and great apes are especially vulnerable, because they cannot replace losses quickly.

The illegal wildlife trade moves live animals, plants and animal parts across borders for pets, food, traditional medicine, ornaments and collections. Pangolins, scaly anteaters of Africa and Asia, are believed to be the most trafficked mammals in the world. More than a million were estimated to have been poached in the decade before 2014, mainly for their scales, used in traditional Chinese medicine, and their meat, which is eaten as a luxury in parts of China and Vietnam. In 2016 all eight pangolin species were moved to Appendix I of CITES, which bans their international commercial trade.

Sources: IUCN SSC Pangolin Specialist Group estimates, via Wikipedia “Pangolin trade” (2026).

Indirect influences

Habitat loss is the conversion of a natural habitat into a different land use, such as farmland, plantations, mines, roads or cities, so that it can no longer support the species that lived there. It is the largest single cause of biodiversity loss on land. Habitat degradation is a milder form, in which a habitat remains but loses quality, for example a forest that has been selectively logged or a river that has been polluted.

Habitat fragmentation harms biodiversity even when the total area of habitat lost is modest. Small patches support only small populations, which are more likely to die out through chance events and inbreeding. Animals that need large territories, such as tigers or jaguars, cannot survive in them at all. Patches also have a larger proportion of edge, where wind, light and predators from outside penetrate, so conditions inside differ from those in the interior of a large forest.

Climate change shifts the temperature and rainfall that each species is adapted to. Species can respond by moving towards the poles or uphill, but many cannot move fast enough, or have nowhere to go: mountain-top species and species on low islands are trapped. Pollution adds toxic substances, nutrients or plastics to ecosystems; examples include pesticides that kill insects other than pests, nitrates that cause eutrophication in lakes, and plastic debris that entangles seabirds and turtles. Invasive species are a further indirect influence and are taught separately.

These influences do not carry equal weight. A global assessment by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), published in 2019 by 145 experts from 50 countries, ranked the direct drivers of loss in this order: changes in land and sea use, direct exploitation of organisms, climate change, pollution and invasive alien species. The same assessment estimated that about one million animal and plant species are threatened with extinction.

Sources: IPBES Global Assessment Report on Biodiversity and Ecosystem Services (2019).

What drives the drivers

Behind each threat lie social and economic pressures: a growing human population, rising consumption per person, global trade that links consumers in one country to land use in another, poverty that leaves rural people few alternatives to hunting or clearing land, and weak governance that fails to enforce laws. A full explanation of biodiversity loss in a particular place therefore includes both the ecological mechanism and the human reasons behind it.

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Multiple impacts that amplify each other

Most ecosystems are under several human pressures at once. A coral reef may be warmed by climate change, enriched with nutrients from farmland, fished heavily and damaged by boat anchors, all in the same decade. These impacts do not simply add up. Very often, one pressure lowers the resilience of an ecosystem, its capacity to resist and recover from disturbance, so that a second pressure does more damage than it would on its own.

Climate change and invasive species provide a common example of a synergistic effect. A forest weakened by drought or heat stress has fewer healthy native plants competing for space, so an invasive plant spreads more easily. Warmer winters also allow pests and pathogens to survive in places where frost used to kill them. The invasive species then has more impact than it would have in a healthy ecosystem, and the loss of native species reduces resilience further.

The Bramble Cay melomys (Melomys rubicola), a small rodent, lived only on about 2 hectares of vegetation on Bramble Cay, a low coral island in the Torres Strait at the northern tip of the Great Barrier Reef. Repeated flooding by storm surges on top of rising sea level destroyed the vegetation it fed and sheltered in.

It was last seen in 2009 and was declared extinct by the Queensland government in 2016 and by the Australian government in 2019. A Queensland report concluded that it probably represents the first recorded mammal extinction caused by human-induced climate change. Its tiny range made it unable to survive a pressure that a widespread species could have absorbed.

Sources: Queensland Government and University of Queensland report (2016), via Wikipedia “Bramble Cay melomys” (2026).

Measuring human impact with a transect

The effect of a human activity on biodiversity can be measured directly in the field. A common approach is to sample species diversity along a transect that runs at a right angle (perpendicular) away from a site of human interference, such as a footpath, a road, a car park, a drain outlet or the edge of a field. If the activity reduces diversity, diversity should be lowest next to the source and rise with distance from it until it levels off at the value of the undisturbed habitat.

Method

1. Choose a site where the human impact forms a clear gradient, such as a footpath through grassland, and state a hypothesis: species diversity increases with distance from the path.

2. Lay a tape measure at right angles to the edge of the path. Place a quadrat (for example 0.5 m × 0.5 m) at fixed intervals along it, such as every 2 m, which is systematic sampling.

3. In each quadrat, identify every plant species with a key or an identification app and count the number of individuals of each (or estimate percentage cover where individuals cannot be separated).

4. Repeat the transect at least three times at randomly chosen points along the path, so that a single unusual patch does not distort the result.

5. Calculate Simpson’s reciprocal index for each distance and plot it against distance from the path.

6. Record abiotic factors that might explain the pattern, such as soil compaction (with a penetrometer), soil moisture and light.

A second design compares diversity in the same place before and after an activity, for example sampling a meadow with randomly placed quadrats within transects before a new car park is built and again a year later. Both designs aim to isolate the effect of the human activity by keeping everything else, such as the type of habitat and the season, the same.

Simpson’s reciprocal index combines richness (the number of species) and evenness (how similar their populations are) into one number. Its lowest possible value is 1, when a sample contains only one species, and it rises as richness and evenness increase.

In the formula, $N$ is the total number of individuals of all species in the sample and $n$ is the number of individuals of each species.

The table gives a student’s counts of plants in quadrats at 0 m and 10 m from the edge of a footpath across a grassland (hypothetical data).

Invasive alien species

People have always carried plants and animals with them, deliberately as crops, livestock, pets and garden plants, and accidentally in ships’ ballast water, on muddy boots or inside timber and soil. A species living outside its native range because of human action is an alien species. Most alien species cause little harm: many die out, and others settle into a small niche. A minority spread rapidly and damage the ecosystems they enter; these are called invasive.

The difference matters, because only a small share of alien species go on to cause serious harm.

How alien species arrive and why some become invasive

An alien species has to pass through several stages before it becomes invasive. It must survive transport, be released or escape, establish a breeding population and then spread. At each stage most species fail: they die in transit, the climate is unsuitable, they cannot find mates, or native predators and competitors keep them in check. Only the few that pass every filter become invasive.

The species that do become invasive tend to share certain features, and they often meet favourable conditions in their new home:

• No natural enemies. The predators, parasites and diseases that limit the species in its native range were left behind, so its death rate falls (often called enemy release).

• High reproductive rate. Many invasive species mature quickly and produce many offspring, the traits of an r-strategist, so their numbers can grow exponentially.

• Broad tolerance and a generalist diet. They can live in many habitats and eat many foods.

• Naive native species. Native prey have not evolved defences against the new predator, and native predators may not recognise a new prey as dangerous or toxic.

• Disturbed habitats. Land that has been cleared, burned or polluted offers open space and fewer competitors.

With these advantages and few limiting factors, an invasive population can follow a J-curve of exponential growth for years before it approaches the carrying capacity of its new environment, and by then it may have spread over a whole continent.

How invasive species reduce biodiversity

Example: cane toads in Australia

In June 1935, 102 cane toads (Rhinella marina), native to Central and South America, were brought from Hawaii to Gordonvale in Queensland to control two native beetles whose larvae damaged sugar cane. About 62,000 young toads bred in captivity were released by March 1937. There is no evidence that they ever reduced the beetles they were introduced to control.

Instead, the toads spread. They covered most of Queensland’s east coast by 1959, reached the Northern Territory border in 1984, entered Kakadu National Park in 2001 and reached Kununurra in Western Australia by 2011. The western invasion front moved about 40 km a year in 1994 and about 60 km a year by 2014, and the population was estimated at over 200 million by 2011. The acceleration happened partly because toads at the front evolved to move further and faster than those behind them.

Cane toads have poison glands in their skin. Australian predators evolved without toads, so many die after eating one. Northern quolls (small marsupial predators) and large monitor lizards declined sharply after toads arrived, with yellow-spotted monitor numbers falling by up to 90% in some areas. Some native species have adapted: red-bellied black snakes have become more resistant to the toxin, and some birds and water rats have learned to eat toads while avoiding the poisonous skin.

Management and how well it works

• Physical removal: trapping adults and community “toad-busting” events, such as Townsville’s annual Toad Day Out, which collected 143.6 kg of toads in 2015. These reduce numbers locally, but cleared areas are quickly reinvaded and traps also catch native animals.

• Tadpole traps: traps baited with a chemical lure from adult toads catch cane toad tadpoles but not native tadpoles; they became commercially available by 2024.

• Fencing water sources: in dry areas toads must reach water to survive, so toad-proof fences around farm dams can stop them spreading across arid land.

• Conditioned taste aversion: baits made of toad meat with a nausea-causing chemical were trialled in the Kimberley to teach quolls to avoid toads, but field research by 2023 found that they had not reduced quoll declines.

• Genetic approaches: researchers are developing northern quolls that carry a gene for resistance to the toxin, and other genetic controls of the toads themselves have been proposed but not tested at scale.

No method has stopped the spread. Management now aims mainly to protect the most vulnerable native species and keep toads out of high-value sites, such as islands, rather than to eradicate them. The case shows how hard it is to remove an invasive species once it is established, which is why preventing introductions in the first place, through quarantine, border inspection and laws on the import of live animals, is the most effective strategy.

Sources: Wikipedia “Cane toads in Australia” and sources cited there (2026).

The cane toad is itself a failed attempt at biological control. Biological control can work well when the control agent is host-specific, as when two species of weevil were released to control water hyacinth on Lake Victoria. The risk is that a poorly tested agent becomes an invasive species in its own right.

The IUCN Red List

Conservation money and effort are limited, so they must be directed to the species in greatest danger. The International Union for Conservation of Nature (IUCN), founded in 1948, is a union of governments, government agencies and non-governmental organisations, supported by thousands of volunteer scientists. Since 1964 it has published the IUCN Red List of Threatened Species, which assesses the conservation status of species worldwide: how likely each is to become extinct.

How a status is assigned

Experts gather all the available data on a species and test it against five quantitative criteria. A species is placed in the highest-risk category for which it meets any one criterion. The factors considered are:

• Population size: the number of mature individuals.

• Rate of decline: how fast the population has fallen, measured over 10 years or three generations, whichever is longer.

• Geographic range: the area over which the species occurs, and whether that area is fragmented or shrinking.

• Breeding potential: how quickly the species can reproduce and how many individuals are of breeding age.

• Known threats: the pressures acting on the species and the probability that they will cause extinction.

Because the criteria are numerical and the same for all species, a fish, a fern and a frog can be compared on one scale. The categories run from Least Concern (LC) to Extinct (EX).

Critically endangered is the highest category for living species, and the other categories have similar precise definitions. Endangered species face a very high risk of extinction in the wild and Vulnerable species a high risk. Near threatened species are close to qualifying for a threatened category, and Least concern species are widespread and abundant. A species that survives only in captivity, in cultivation or outside its native range is Extinct in the wild; the Arabian oryx was once in this category. Data deficient species lack enough information to be assessed, which does not mean they are safe.

In 2025 the Red List contained assessments of 172,620 species, of which 48,646 (28%) were classed as threatened. The share varies greatly between groups. Amphibians, corals and conifers have very high shares of threatened species, partly because of specific threats: a fungal disease (chytridiomycosis) has spread through amphibians worldwide, and corals are bleached by marine heatwaves.

The Red List Index for birds, mammals, amphibians, corals and cycads has fallen over recent decades, which shows that more species have moved into higher-risk categories than have moved out of them. The index is one of the indicators used to track progress towards the global biodiversity targets.

How the Red List is used and who uses it

Assigning a status publicises a species’ vulnerability. A move into a threatened category often attracts media attention, which can bring public pressure and funding. The status also lets different groups decide where to spend their effort, although they do so from different perspectives and with different priorities.

These uses are not free of tension. A government might delay protecting a species if a valuable project is planned in its habitat, while an NGO might campaign for that species above others that are more threatened but less appealing. More ecocentric groups argue that every threatened species deserves protection for its own sake, whereas more anthropocentric decision-makers tend to prioritise species with economic or cultural value. A further limitation is coverage: in 2025 only about 172,000 of the roughly two million described species had been assessed, and assessments of tropical insects, fungi and plants lag far behind those of birds and mammals.

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Three species and what happened to them

Named species show how the causes of decline, its consequences and the response to it play out in real cases. Three are compared here: one made extinct by human activity, one critically endangered, and one whose status has improved because of conservation.

Extinct: the passenger pigeon

The passenger pigeon (Ectopistes migratorius) was once the most abundant bird in North America, with a population of around 3 billion, and possibly up to 5 billion. It lived in the deciduous forests east of the Rocky Mountains and fed on acorns, beech nuts and chestnuts. It nested in huge colonies: the largest recorded, in central Wisconsin in 1871, covered 2,200 km² and held an estimated 136 million birds.

Causes of decline. From the mid-nineteenth century passenger pigeons were hunted on a commercial scale and sold as cheap meat in eastern cities; railways carried the birds to market and the telegraph spread news of where flocks were nesting. At the same time, the forests that supplied their food were cleared for farmland.

The decline was slow from about 1800 to 1870 and then collapsed between 1870 and 1890. The species depended on huge colonies to breed successfully, so once numbers fell below a certain level, the remaining birds could no longer reproduce effectively. The last confirmed wild bird was shot in 1902, and the last captive bird, Martha, died in 1914.

Impacts. The extinction removed a species that had shaped eastern North American forests. The flocks ate vast quantities of seeds, deposited thick layers of dung that fertilised the soil at roosts, and broke branches that opened the canopy. Some researchers suggest that the loss of the pigeon helped red oaks, whose acorns the pigeons ate in large numbers, to become more dominant than white oaks.

Response. No conservation action came in time. The extinction did, however, become a widely cited warning that even an extremely abundant species can be driven to extinction, and it helped build support for early wildlife protection laws in the United States.

Sources: Wikipedia “Passenger pigeon” and sources cited there (2026).

Critically endangered: the vaquita

The vaquita (Phocoena sinus) is the smallest living cetacean, a porpoise up to 1.5 m long found only in the northern end of the Gulf of California, Mexico. It has been listed as Critically Endangered since 1996 and is the most endangered marine mammal in the world. The first comprehensive survey, in 1997, estimated 567 vaquitas; there were about 150 in 2007, fewer than 19 in 2018, and a 2024 survey counted a minimum of 6–8, with a possible maximum of 9–11.

Causes of decline. Vaquitas drown when caught as bycatch in gillnets. Many of these nets are set illegally for the totoaba, a large fish that is itself endangered, whose dried swim bladders sell for high prices on the black market, largely in China, where they are used in traditional medicine. Legal gillnet fishing for shrimp has also caught vaquitas. The decline therefore links a local fishing community to an international illegal trade.

Impacts. The vaquita is a predator of fish, squid and crustaceans on the sea floor, and its loss would remove a unique evolutionary lineage. The decline also affects people. Fishing communities around the upper Gulf depend on shrimp and fish, and restrictions to protect the vaquita have cut their incomes.

Conservation strategies and their success. Mexico banned gillnets in part of the vaquita’s range in 2015 and made the ban permanent in 2017, and offered fishers compensation and alternative gear. In 2017 an attempt to capture vaquitas for a protected breeding programme was abandoned after one of the two captured animals died of shock.

Since 2020 a zero-tolerance fishing area has been enforced with naval patrols and, from 2022, concrete blocks on the sea floor that snag and destroy illegal nets. The decline has slowed, and calves are still being seen, but the population is so small that a few illegal nets could still cause extinction. The case shows that strategies fail when they do not address the economic needs of local people and the demand that drives illegal trade.

Sources: Wikipedia “Vaquita” and sources cited there, including the 2024 survey (2026).

Status improved: the mountain gorilla

The mountain gorilla (Gorilla beringei beringei) lives in two areas of montane forest: the Virunga volcanoes, shared by Rwanda, Uganda and the Democratic Republic of the Congo, and Bwindi Impenetrable National Park in Uganda. A census in 1981 estimated only 254 gorillas in the Virunga population. The most recent counts found 604 gorillas in the Virunga Massif in 2015–2016, more than twice the 1981 figure, and at least 459 in the Bwindi–Sarambwe area in 2018, a total of 1,063. In 2018 the IUCN moved the subspecies from Critically Endangered to Endangered.

Causes of decline. Forest was cleared for farming and settlement in one of the most densely populated regions of Africa. Gorillas were caught in snares set for antelopes, infants were captured for the pet and zoo trade, and diseases such as respiratory infections passed to them from humans. Civil war and refugee camps in the region added further pressure.

Conservation strategies and their success. Anti-poaching patrols remove snares, and veterinarians treat injured and sick gorillas. National parks protect the remaining forest, and the three countries cooperate across their borders. Gorilla tourism pays for much of this work, and part of the permit revenue is shared with surrounding communities, so local people gain from living gorillas rather than seeing them as competitors for land. The population is still small and confined to two areas, so a single disease outbreak or renewed conflict could reverse the gains.

Sources: UC Davis Mammalian Ecology and Conservation Unit (2019); Wikipedia “Mountain gorilla” (2026).

The tragedy of the commons

Many of the resources that support biodiversity are not owned by anyone in particular. Fish in the open ocean, the atmosphere, a lake shared by three countries, or grazing land used by a whole village are available to many users at once. Shared resources like these face a particular risk: each user has a reason to take more, even when everyone can see that the resource is being destroyed.

Where nobody controls access at all, a common-pool resource is an open-access resource. The economist William Forster Lloyd described the problem in 1833 using the example of cattle on a shared pasture, and the ecologist Garrett Hardin gave it the name tragedy of the commons in an essay, “The Tragedy of the Commons”, published in the journal Science in 1968.

Why individual choices lead to collective ruin

Hardin imagined a pasture open to all herders. Each herder asks whether to add one more animal. The herder receives all the benefit of that animal (its milk, meat or sale price), but the cost, a little less grass for every animal on the pasture, is spread across all the herders. For each individual, adding the animal is a gain. Because every herder reasons in the same way, the pasture is overgrazed and eventually supports far fewer animals than before.

The process includes a positive feedback loop. As the pasture degrades, each animal produces less, so herders who want to keep their income add even more animals, which degrades the pasture faster. Restraint by one user does not help: if a single herder keeps fewer animals, the others simply use the grass that is left. Hardin argued that appeals to conscience therefore fail, and he called for “mutual coercion, mutually agreed upon”, meaning rules that all users accept and that are enforced.

An overharvested resource: Grand Banks cod

The cod stocks of the Grand Banks off Newfoundland, Canada, were for centuries one of the richest fisheries on Earth. They behaved as a commons: boats from many countries fished them, and no single fleet had a reason to leave fish in the water for the future. The catch peaked in 1968 at about 810,000 tonnes, as factory trawlers from Europe and elsewhere joined the fishery.

When Canada declared a 200-nautical-mile exclusive economic zone in 1976 and excluded foreign trawlers, Canadian vessels filled the gap, and the stock kept falling. By 1992 the northern cod population was about 1% of its historic level, and the government closed the fishery, putting about 37,000 fishers and plant workers out of work. Limited commercial fishing for northern cod reopened only in 2024.

Sources: Wikipedia “Collapse of the Atlantic northwest cod fishery” and sources cited there (2026).

The cod case shows that dividing a commons between countries is not enough. Within Canada’s zone the fish were still shared by many boats, and the quotas were set too high because scientists overestimated the stock and politicians feared job losses. The full story of the collapse, and the maximum sustainable yield that the quotas were meant to protect, belongs to fisheries management.

A contaminated commons: plastic in the Great Pacific Garbage Patch

The tragedy of the commons also applies to pollution. Here the resource is a clean environment that can absorb waste, and each user gains by dumping waste rather than paying to dispose of it safely. The open ocean is an extreme case, because most of it lies outside any country’s jurisdiction and is shared by everyone.

Floating plastic is carried by currents into the centres of the great rotating ocean currents, the oceanic gyres. The largest accumulation, the Great Pacific Garbage Patch, lies in the North Pacific gyre roughly between Hawaii and California. A 2018 study estimated that it covers about 1.6 million km² and holds 45,000–129,000 tonnes of plastic in about 1.8 trillion pieces. Most pieces are microplastics, but most of the mass is larger objects, and synthetic fishing nets make up nearly half of it. More than 40 animal species have been found living on the debris, and seabirds and turtles eat or are entangled by it.

Sources: Lebreton et al., _Scientific Reports (2018), via Wikipedia “Great Pacific garbage patch” (2026)._

No single country, company or fishing fleet is responsible, and none has a strong reason to pay for clean-up, because the benefit of a cleaner ocean would be shared by all. Each user saves money by discarding nets or failing to manage plastic waste, while the cost, damage to marine life and fisheries, falls on everyone. This is why marine plastic pollution is so difficult to solve without international agreements.

Escaping the tragedy

Several ways of managing a commons have been proposed, and each reflects a different view of people and the environment:

Hardin’s pessimism has been challenged. The political scientist Elinor Ostrom, who received the Nobel Memorial Prize in Economic Sciences in 2009, studied commons around the world, such as Swiss Alpine pastures managed by farmers since 1517, and found that communities often manage shared resources sustainably without either privatisation or government control. Hardin himself later accepted that his argument applied to a commons without rules, not to every shared resource. The cause of overuse is therefore unrestricted access, not shared ownership as such.

The tragedy of the commons also shows the tension at the heart of sustainable development: the short-term self-interest of each user conflicts with the long-term shared benefit of keeping the resource healthy. A more technocentric response looks to monitoring technology, such as satellite tracking of fishing vessels, to enforce rules; a more ecocentric response stresses reducing demand and protecting areas from use altogether.

Case study: the Nile perch in Lake Victoria

Context

Lake Victoria, in East Africa, is the largest lake in Africa, with an area of 59,947 km². It is shared by Tanzania (49% of the area), Uganda (45%) and Kenya (6%), and about 45 million people live in its catchment. It is shallow for its size, with an average depth of about 40 m and a maximum of 81 m.

Until the mid-twentieth century the lake held one of the most remarkable concentrations of fish species on Earth. More than 500 species of haplochromine cichlids, almost all endemic to the lake, had evolved in it, making up about 90% of its native fish species. They filled almost every niche, feeding on algae, detritus, insects, snails, zooplankton and other fish. Small-scale fishers from lakeside communities caught them, and women dried and sold them in local markets.

What happened

The Nile perch (Lates niloticus), a large predatory fish that can grow to 2 m and 200 kg, is native to the Nile and other African rivers but not to Lake Victoria. Fishery officers in colonial Uganda released it above Murchison Falls in 1954 and into Lake Kyoga in 1955, intending to turn the small cichlids into a large, valuable fish that would support a commercial fishery. The perch reached Lake Victoria by the late 1950s, more were added in 1962–63, and by 1970 it had spread through the whole lake.

For about twenty years the perch remained rare. In the early 1970s it made up only about 0.15% of the fish biomass. Then its population grew explosively, following the exponential pattern typical of an invasive species with abundant prey and no predators. In the Jinja area of Uganda its share of the commercial catch rose from 13.4% in 1981 to 75.1% in 1982, while the catch rate of research trawlers fell from 797 kg per hour in 1968–71 to 360 kg per hour in 1982–83 as the cichlids disappeared.

The perch ate the cichlids, and it is now estimated that at least 200 species, about 40% of the haplochromines, have become extinct. Earlier estimates of up to 65% were later revised down when some species were found to have survived. Once the cichlids were scarce, the perch switched to eating a freshwater shrimp, small fish and young perch.

Several impacts at once

The introduction did not act alone. Over the same decades, the lake received more nutrients from farm run-off, sewage and soil eroded from cleared land in the catchment, which caused algal blooms. With the algae-eating and detritus-eating cichlids gone, more dead organic matter sank and decomposed, using up oxygen in the deep water. In 1961 oxygen concentrations below 1 mg L⁻¹ occurred only below 50 m, but by 1990–91 they occurred as shallow as 40 m. Deep water, which had once been a refuge for cichlids, became uninhabitable.

From 1993 the floating water hyacinth spread across bays, shading the water and blocking boats and landing sites, until it declined by the end of 2001 after two species of weevil were released as biological control agents and mats were removed by mechanical harvesting.

The fish also changed life on land. Cichlids could be dried in the sun, but Nile perch is oily and must be smoked to stop it spoiling, which increased the demand for firewood in a region already losing forest. Soil eroded from cleared land added to the nutrients washing into the lake.

Data

The perch fishery grew into the largest inland fishery in Africa. Nile perch landings peaked in the early 1990s at about 500,000 tonnes a year and then declined. By 2015 the lake produced an estimated 876,547 tonnes of fish, with about 219,900 fishers working from about 76,900 canoes at 1,535 landing sites. Nile perch is exported to more than 50 countries, 60% of it to Europe, earning about US$400 million a year. Its sales to the European Union alone reached €169 million in 2003.

The perch stock itself is now under pressure from the fishery that it created. Hydroacoustic surveys estimated the Nile perch stock at 1.23 million tonnes in 2014 and 0.85 million tonnes in 2016. In 2017, 96% of the perch were below the minimum legal size of 50 cm, which shows that most fish are caught before they can breed. Between 2006 and 2016 the number of illegal monofilament nets on the lake rose from 2,293 to 72,101, and the number of fish-processing factories fell from 41 to 17 as supplies dropped.

Sources: Wikipedia “Lake Victoria” and “Nile perch” (2026); FAO CIFA Technical Paper 17 (1988); Tumwebaze, Lake Victoria Fisheries Organization, in FAO User Rights proceedings (2018).

Management and responses

• Regional cooperation. Kenya, Uganda and Tanzania manage the fishery through the Lake Victoria Fisheries Organization, with lake-wide management plans since the early 2000s. These set a slot size for Nile perch (only fish from 50 cm to 85 cm may be caught, protecting both young fish and large breeding adults), minimum mesh sizes for gillnets, protected breeding areas, and, in 2018, a cap on the number of fishing canoes.

• Co-management. Beach Management Units, committees of fishers and traders at each landing site, check that boats carry legal gear before they are licensed, collect catch data and settle disputes. This gives local users a role in managing their commons.

• Enforcement. Patrols confiscate illegal nets; Uganda deployed its army on the lake to enforce fishing rules.

• Treatment of the invader. Uganda classes the Nile perch as an invasive alien species to be controlled, while the export industry wants it protected as a valuable fishery.

• Water hyacinth control by biological control and harvesting (largely successful).

Evaluation

From the point of view of the colonial fishery planners and the governments that followed, the introduction achieved its aim: it created a large, export-earning fishery, jobs in fishing and processing, and foreign currency. From the point of view of biodiversity, it was a disaster that destroyed a unique evolutionary radiation that cannot be recreated.

Many people around the lake fall between these positions. Some fishers earned far more from perch than they ever had from cichlids, but others were pushed out because the strong nets and larger boats needed for perch were expensive, and much of the most valuable fish now leaves the region rather than feeding local people. Fish processing and small-scale trading around the lake were almost entirely women’s work, so the switch from sun-dried cichlids to smoked perch and export factories changed who earned money from the catch.

Eradicating the perch is neither possible nor wanted by most people who now depend on it. The management goal has therefore become to make the perch fishery itself sustainable. Here the lake shows the tragedy of the commons at work: the fishery is shared by three countries and hundreds of thousands of fishers, and each has a reason to use illegal nets and catch undersized fish before someone else does.

The rapid rise in illegal gear despite enforcement suggests that rules alone are not enough without fair access, alternative incomes and trust between fishers and authorities. Hydroacoustic surveys also show haplochromine numbers rising over the decade to 2017 as the perch has been fished down, which suggests that a reduced perch population could allow part of the native community to return.

What it shows

Lake Victoria shows how an alien species becomes invasive when it meets abundant, defenceless prey and no predators, and how it reduces biodiversity through predation. It shows that human impacts combine: the perch, nutrient pollution, deforestation and water hyacinth amplified each other. It shows that biodiversity loss affects societies as well as ecosystems, and that the same change creates winners and losers. Finally, the perch fishery itself has become a commons at risk of overharvesting, so the case connects invasive species with the tragedy of the commons.

Threats to biodiversity hotspots (HL only)

Biodiversity hotspots are regions with an exceptional number of endemic species that have already lost most of their original vegetation. Under the definition first proposed by Norman Myers in 1988 and refined in 2000, a hotspot must contain at least 1,500 endemic species of vascular plants and must have lost at least 70% of its primary vegetation. The 36 recognised hotspots cover only about 2.4% of the Earth’s land surface but hold nearly 60% of the world’s species of plants, birds, mammals, reptiles and amphibians, a high proportion of them found nowhere else.

Because hotspots are defined partly by the habitat they have already lost, every hotspot is by definition under threat. The danger is that the remaining fragments are lost too, and because so many of their species are endemic, each hectare lost in a hotspot causes more extinctions than a hectare lost elsewhere.

Why tropical hotspots are under such pressure

Most hotspots are in tropical forests, which are the most species-rich biomes on Earth. They are under pressure from the expansion of farming and plantations (oil palm, soy, cattle, cocoa), logging, mining, road building and fire. Sundaland, the hotspot that includes Borneo, Sumatra, Java and the Malay Peninsula, is an example. Its lowland rainforests have been cleared on a large scale for timber and oil palm, and the Bornean orangutan (Pongo pygmaeus), now Critically Endangered, lost more than 100,000 individuals between 1999 and 2015.

Sources: Voigt et al., _Current Biology (2018), via Wikipedia “Social and environmental impact of palm oil” (2026)._

Why conservation is harder in lower-income countries

Many tropical hotspots lie in lower- and middle-income countries, which makes effective conservation harder for several connected reasons:

• Development needs. Governments are under pressure to create jobs, earn export income and repay debts, and selling timber or opening land for plantations does all three quickly.

• Rural poverty. Many rural households depend directly on land and forest for food, fuel and income, and have few alternatives to clearing land or hunting.

• Limited funding and capacity. Protected areas need rangers, equipment and scientists; where budgets are small, parks may exist on paper only.

• Governance. Unclear land ownership, corruption and weak enforcement of laws allow illegal logging and land grabs.

• Global demand. Much of the clearing serves consumers in other countries, so the pressure comes from outside the country even when the damage happens inside it.

This last point means that hotspot loss is not only a problem of the countries where it happens. Wealthier countries consume many of the products grown on cleared land, and they cleared most of their own forests long ago. From an environmental justice perspective, it is unfair to expect lower-income countries to bear the full cost of protecting biodiversity that benefits the whole world. This is why international funding, such as payments for avoided deforestation, is part of most proposed solutions.

Key biodiversity areas (HL only)

Hotspots are very large regions, often covering several countries, so they cannot tell a government exactly which forest, wetland or reef to protect. Key biodiversity areas (KBAs) work at a much finer scale. Each is a specific site, with a boundary on a map, that is identified as being of international importance for the persistence of biodiversity.

How KBAs are identified

KBAs are identified using the Global Standard for the Identification of Key Biodiversity Areas, published by the IUCN in 2016. It extends earlier site networks, such as BirdLife International’s Important Bird and Biodiversity Areas, to all groups of organisms. A site qualifies if it meets at least one of eleven criteria grouped into five categories:

More than 16,000 KBAs have been identified, covering about 21 million km². They include Alliance for Zero Extinction sites, places that hold the last remaining population of a highly threatened species. KBAs have no legal status of their own; their value is that they tell governments, companies, banks and conservation organisations where action matters most. Many governments use them to choose new protected areas, and some lenders require companies to avoid them.

Sources: Wikipedia “Key Biodiversity Area” (2026); KBA Partnership, keybiodiversityareas.org (2026).

Two key biodiversity areas

Batang Toru, North Sumatra, Indonesia. The Batang Toru forest covers about 1,768 km² of mountainous rainforest, of which only about 8.5% lies inside protected areas. It is a KBA under criteria A1 and B1 because it contains 99.3% of the range of the Tapanuli orangutan (Pongo tapanuliensis), a species described only in 2017. Fewer than 800 Tapanuli orangutans survive, making it the rarest great ape, and it is listed as Critically Endangered.

Threats listed for the site include hunting, mining, smallholder farming and a hydroelectric dam that could affect up to 10% of the orangutan’s habitat and cut the forest corridors linking its populations. In December 2025 floods and landslides after Cyclone Senyar were estimated to have killed between 6% and 10% of the remaining orangutans, showing how a species confined to one site can be devastated by a single event.

Makira Natural Park, north-east Madagascar. Makira covers 3,725 km² of humid forest and was formally protected in 2012. It is a KBA and an Alliance for Zero Extinction site, and is thought to hold the highest lemur diversity of any protected area in Madagascar, with 17 species, including the Critically Endangered silky sifaka and indri. About 90,000 people live in around 120 villages within or next to the area and depend on rice, cassava, vanilla and cloves. The main threat is tavy, slash-and-burn clearing for rain-fed rice, along with hunting for meat and small-scale illegal logging.

Makira is managed by the Wildlife Conservation Society on behalf of the government. In 2013 it became the first government-owned project in Africa to sell carbon credits on the voluntary market for avoided deforestation (a REDD+ project), with part of the revenue going to local communities. About 80 local associations manage more than 3,500 km² of forest around the park under contracts, and farmers are supported to grow cash crops such as vanilla and cocoa in agroforestry systems instead of clearing new land. Makira therefore tests whether conservation of a KBA can pay for itself and benefit local people at the same time.

Sources: KBA Partnership, Batang Toru factsheet (2021); Wikipedia “Tapanuli orangutan” and “Makira Natural Park” (2026).

A KBA designation does not protect a site by itself. Protection depends on national law, for example declaring the site a national park, and on international agreements such as the Kunming-Montreal Global Biodiversity Framework, under which governments aim to protect areas of particular importance for biodiversity.

Conflict in key biodiversity areas: palm oil in Malaysia and Indonesia (HL only)

Palm oil comes from the fruit of the oil palm (Elaeis guineensis), a tree native to West Africa that grows best in the hot, wet lowlands of the tropics, the same places where rainforest grows. It is used in cooking oil, margarine, processed foods, soap, cosmetics and biodiesel. Indonesia and Malaysia together produced 65.6 million tonnes of palm oil in 2023, about 82% of the world total of 79.6 million tonnes.

Why oil palm plantations have spread

• High yield. Oil palm produces far more oil per hectare than other oil crops; it supplied about 38% of the world’s vegetable oil from 6% of the land used for vegetable oil crops.

• Rising global demand. Population growth, rising incomes and the spread of processed food increase demand for cheap vegetable oil, and government targets for biofuel have added further demand.

• National development. Palm oil is a major export, earning foreign currency and tax revenue, and governments have promoted it as a route out of poverty for rural areas.

• Jobs and smallholders. An estimated 1.5 million small farmers grow oil palm in Indonesia, and smallholders manage 35–40% of the planted area in the two countries.

• Land availability and weak regulation. Large areas of forest were available, sometimes with unclear ownership, and logging the forest first earned money that helped pay for planting.

Biodiversity consequences

A plantation is a near-monoculture of a single tree species of the same age, with little understorey and frequent use of pesticides. Studies of plantations find only a small fraction of the species of the forest they replaced, and almost none of the forest specialists. In Malaysia, the area under oil palm rose by 2.4 million hectares between 1990 and 2005, to 4.2 million hectares, while more than 1.1 million hectares of rainforest were lost in the same period. Orangutans, Sumatran tigers and other forest species lose habitat, and the forest that remains is fragmented into patches separated by plantations.

The impacts reach beyond biodiversity. Many plantations were planted on drained peat swamp forest; once drained, the peat dries, oxidises and burns. Converting peatland has been estimated to cause 16.6–27.9% of the combined greenhouse gas emissions of Malaysia and Indonesia, and peat fires produce haze that affects human health across South-East Asia. Land conflicts have arisen where plantations were established on land used by Indigenous and local communities.

Sources: Wikipedia “Social and environmental impact of palm oil” and sources cited there (2026).

Responses and their limits

The Roundtable on Sustainable Palm Oil (RSPO), founded in 2004, certifies palm oil grown without clearing primary forest or areas of high conservation value. In 2010, after Norway pledged US$1 billion, Indonesia announced a two-year suspension of new agreements to clear natural forest and peatland. The European Union’s deforestation regulation, adopted in 2023 and due to apply from 30 December 2026 after two postponements, will require companies selling palm oil and other commodities in the EU to show that they are not linked to deforestation.

Critics argue that certification covers only part of production, is hard to enforce, and can allow clearing to move to uncertified suppliers. Boycotting palm oil is not a simple answer either: replacing it with other oil crops would need several times as much land.

The palm oil conflict brings together all three HL lenses. Economically, the price of palm oil does not include the costs of lost biodiversity, carbon emissions and haze, which are externalities borne by others. Legally, the question is whether national laws, moratoria and import rules can be enforced. Ethically, it raises the question of whether species such as the orangutan have intrinsic value that should limit development, and who should pay for protecting them.

Traditional Indigenous land management (HL only)

Many Indigenous peoples have managed their lands for thousands of years using knowledge passed down through generations, often called traditional ecological knowledge. Traditional Indigenous land management practices include rotational farming with long fallow periods, controlled burning, seasonal movement of herds, and rules that limit harvests of certain species or places. Some of the most biodiverse forests on Earth lie on land managed by Indigenous peoples, which suggests that these systems can support people while keeping biodiversity high.

Example: cultural burning in Arnhem Land, northern Australia

Aboriginal Australians have used fire to manage land for thousands of years, a practice often called cultural burning or fire-stick farming. In the tropical savannas of northern Australia, people traditionally lit small, cool fires early in the dry season, when grass is still damp. These burn patchily and go out at night, leaving a mosaic of burned and unburned ground. The patches act as firebreaks that stop the large, hot wildfires of the late dry season, which kill trees, destroy the habitat of small mammals and release large amounts of greenhouse gases. Burning also encourages fresh growth that attracts animals for hunting.

After European colonisation from 1788, Aboriginal people were forced off much of their land, and burning stopped across large areas. Without it, fuel built up and fires became larger and more intense. In parts of the Great Sandy Desert, after people left their country, fires burned 36–50% of a 24,000 km² area.

In western Arnhem Land, traditional owners and Aboriginal rangers revived early dry-season burning on a large scale in the West Arnhem Land Fire Abatement project (WALFA), fully operational from 2005 over 24,000 km². An energy company paid the project to reduce emissions as an offset. In its first seven years, the share of the area burned early in the dry season rose from 7.6% to 20.9% and the share burned late fell from 32% to 10.9%, cutting fire emissions by an average of 37.7% a year compared with 1994–2005.

By 2018, 75 savanna burning projects were registered in Australia’s carbon market, and Indigenous projects accounted for 74% of the potential emissions reductions. Carbon income now pays for ranger jobs in remote communities.

Sources: Lipsett-Moore et al., _Nature Communications (2018); Wikipedia “Fire-stick farming” and “Djelk Indigenous Protected Area” (2026)._

Threats to traditional land management

Traditional systems are often described as more sustainable than industrial land use, but they are under pressure. Some threats come from outside the community and some from within, as societies change and many people aspire to the global model of development.

The Arnhem Land example shows both the value and the vulnerability of traditional management. Combining it with carbon finance and modern satellite mapping has revived it, but the revival depends on outside markets and policies that Aboriginal communities do not control. Treating traditional knowledge as a resource to be used for others’ goals, such as carbon credits, without securing the rights of the people who hold it, risks repeating the injustices of the past.

Environmental justice in conservation (HL only)

The places expected to lose most biodiversity and ecosystem function are often home to large Indigenous populations, many of them low-income and without access to legal support. Conservation that excludes these people from their land can protect species at the cost of human rights, a pattern that raises questions of environmental justice: who bears the costs of conservation, and who gains the benefits.

Fortress conservation was the dominant model for national parks in the twentieth century, beginning with parks in the United States from which Native Americans were excluded. It assumes that people and wildlife cannot share land. Critics argue that it ignores the role many Indigenous peoples have played in creating and maintaining the landscapes that parks now protect.

The Maasai and the Serengeti–Ngorongoro ecosystem

The Maasai are pastoralists who have grazed cattle, goats and sheep alongside wildlife on the plains of northern Tanzania and southern Kenya for centuries. Serengeti National Park was created under British colonial rule, and in the 1950s the Maasai living within it were moved out. In 1959 the Ngorongoro Conservation Area was separated from the park as a multiple land-use area where Maasai could live and graze alongside wildlife. Some colonial and later policymakers, influenced by ideas such as the tragedy of the commons, saw Maasai herding as a cause of land degradation, a view that many anthropologists later challenged.

Inside the conservation area, Maasai livelihoods have been restricted repeatedly. Cultivation was banned in 1975, which forced households to sell animals to buy food, and allowed again in 1992. The Maasai population of the area grew from about 8,700 in 1966 to 93,136 in 2017, and the authorities and the IUCN have raised concerns about overgrazing and the effect of settlement on the area’s World Heritage values.

Since 2021 the government has run a programme to move Maasai from Ngorongoro to Msomera, a village about 600 km away. The government describes the moves as voluntary, but Human Rights Watch reported in 2024 that people were pressured and that their free, prior and informed consent was not obtained.

In June 2022 in neighbouring Loliondo, security forces marked out 1,500 km² of Maasai grazing land as a game-controlled area. Protests followed, about 30 Maasai were reported injured and at least one person was killed. Activists said the area would serve a hunting company linked to the United Arab Emirates, which the company denied.

Sources: Wikipedia “Ngorongoro Conservation Area” and “Maasai people” and sources cited there, including Human Rights Watch (2024) (2026).

The United Nations Declaration on the Rights of Indigenous Peoples, adopted in 2007, sets out indigenous rights including the right not to be forcibly removed from their lands and the principle of free, prior and informed consent. The Maasai case shows the gap between these principles and practice. It also raises an ethical question that runs through conservation: whether protecting wildlife for the benefit of the nation, tourists and future generations justifies imposing heavy costs on the people who already live there.

Alternatives to fortress conservation include community conservancies, in which local people own or co-manage land and earn income from wildlife, and Indigenous Protected Areas, such as those managed by Aboriginal rangers in Australia. These approaches treat local people as partners rather than threats, and evidence from many regions suggests that secure land rights for Indigenous peoples are often associated with lower deforestation.

Extinction and the planetary boundary for biosphere integrity (HL only)

The planetary boundaries model identifies nine processes that keep the Earth system in the stable state of the Holocene, the period in which human civilisations developed, and proposes a safe limit for each. One of these is change in biosphere integrity, which has two parts. Genetic diversity is measured by the rate of extinction; functional diversity, the capacity of the living world to carry out processes such as photosynthesis, is measured by the share of the planet’s plant production that humans take for their own use.

The extinction rate is measured in extinctions per million species-years (E/MSY): if there are a million species, a rate of 1 E/MSY means one extinction a year. The assumed background rate, the rate before human influence, is about 1 E/MSY. The boundary is set at less than 10 E/MSY, but the current rate is estimated at more than 100 E/MSY.

The functional boundary has also been crossed: humans now take about 30% of the planet’s natural plant production, against a boundary of 10%. Biosphere integrity was judged to be beyond its boundary in the first assessment in 2009 and in every assessment since; in the 2025 and 2026 Planetary Health Checks, seven of the nine boundaries were judged to have been crossed.

Population data show the same trend. The Living Planet Index, which in its 2026 release combined 35,803 monitored populations of 5,790 vertebrate species, fell by an average of 73% between 1970 and 2022. The index measures the average change in population sizes, not the share of animals lost, and it can be strongly influenced by a few rapidly declining populations, so it is best used as a sign of the direction of change.

Sources: WWF and Zoological Society of London, Living Planet Index (2026 data release).

Could extinctions tip the whole Earth system?

Some scientists claim that biodiversity loss could push the Earth system past a tipping point, a threshold beyond which it shifts to a new and less hospitable state that would be very hard to reverse. The claim is debated, and the arguments on each side can be weighed.

A balanced conclusion is that the current extinction rate is far above the safe limit and that biodiversity loss weakens the resilience of the Earth system, making other tipping points more likely. Whether extinctions alone could tip the whole planet is uncertain. Under the precautionary principle, uncertainty about the size of the risk is a reason to act rather than to wait, because extinction cannot be undone.

Exam practice

Human impact on biodiversity appears in every part of the assessment. Paper 2 Section A asks for short explanations, definitions and calculations, such as Simpson’s reciprocal index from transect data. Paper 1 often presents data on a named place, such as a species’ population trend or a land-use change, and asks you to interpret it and evaluate a strategy. Paper 2 Section B essays commonly combine threats, named species and the tragedy of the commons with an extended evaluation.

Paper 2 Section A-style questions

Explanations of invasive species need a chain of reasons, each linked to the next.

Questions on the Red List often test the difference between a scientific assessment and legal protection.

Paper 1-style data question

Resource (hypothetical data). A coastal country has a population of a ground-nesting seabird on one island. A survey counts breeding pairs every five years. Rats arrived on the island by accident in 2005. In 2020 the government poisoned the rats, and the island has been checked for rats every year since.

Paper 2 Section B-style essay

HL question

Summary

• Direct influences (overharvesting, poaching, illegal pet and wildlife trade) remove organisms; indirect influences (habitat loss and fragmentation, climate change, pollution, invasive alien species) change the conditions species need.

• Land and sea use change is the largest driver of biodiversity loss; about one million species are threatened with extinction.

• Multiple pressures often act together, and one pressure can lower resilience so that another does more damage.

• Human impact can be measured by sampling diversity along a transect perpendicular to a source of disturbance and calculating Simpson’s reciprocal index.

• Invasive alien species spread rapidly because they lack natural enemies and reduce native biodiversity through competition, predation and disease; prevention is more effective than eradication.

• The IUCN Red List assigns a conservation status from Least Concern to Extinct using quantitative criteria; it guides priorities but has no legal force itself.

• The passenger pigeon (extinct), the vaquita (critically endangered) and the mountain gorilla (improved) show how causes, impacts and responses differ between species.

• The tragedy of the commons describes how unrestricted shared resources, such as Grand Banks cod or the ocean as a sink for plastic, are overused because gains are private and costs are shared.

• Biodiversity hotspots and key biodiversity areas are priorities for conservation; palm oil expansion in Malaysia and Indonesia shows the conflict between development and conservation within them. (HL)

• Traditional Indigenous land management, such as cultural burning in northern Australia, is threatened by loss of land rights, economic change, lack of support and climate change. (HL)

• Fortress conservation, such as the relocation of the Maasai, shows that conservation must consider environmental justice and Indigenous rights. (HL)

• The extinction rate (more than 100 E/MSY) is far beyond the planetary boundary (less than 10 E/MSY); whether extinctions could tip the whole Earth system is debated. (HL)

Self-check

• To do:

  I can distinguish direct from indirect influences on biodiversity and give an example of each.

• To do:

  I can explain how several human pressures combine to cause greater biodiversity loss.

• To do:

  I can design a transect investigation of human impact and calculate Simpson’s reciprocal index.

• To do:

  I can explain how an invasive alien species reduces biodiversity and evaluate how it is managed, using the cane toad or Nile perch.

• To do:

  I can outline the IUCN Red List criteria and categories and how different groups use them.

• To do:

  I can describe the decline, impacts and conservation of one extinct, one critically endangered and one recovering species.

• To do:

  I can explain the tragedy of the commons and apply it to an overharvested resource and a polluted environment.

• To do:

  I can explain why hotspots and key biodiversity areas are threatened and name two KBAs. (HL)

• To do:

  I can evaluate the conflict between palm oil, development and conservation in Malaysia and Indonesia. (HL)

• To do:

  I can discuss threats to a named traditional Indigenous land management practice and the justice issues of fortress conservation. (HL)

• To do:

  I can use data on extinction rates to evaluate the biosphere integrity boundary and the claim of an Earth-system tipping point. (HL)