Threats to biodiversity (ESS HL)

Threats to biodiversity at Higher Level: The same direct and indirect threats as SL, with different real cases: Sumatran orangutans, pangolins, the Atlantic Forest, Florida panthers and Madagascar.

Two ways people harm biodiversity: Biological diversity is being damaged by human activity in two ways. Directly: people take or kill the species itself. Indirectly: people change the places and conditions it lives in.

Remember it as: HIPPO: Habitat loss, Invasive species, Pollution, Population growth, Overharvesting. Then add climate change.

Real example: the Sumatran orangutan, Indonesia, is critically endangered, with about 14,000 left. Its forest is cleared for oil palm and paper plantations (habitat loss), fires spread in dry years, and babies are taken for the pet trade after their mothers are killed.

Name the threat: 'Humans' or 'human interference' is too vague. Name the threat and what it does: 'poaching for ivory removes breeding adults'.

Ask one question: is the species itself being taken or killed on purpose? If yes, the threat is direct. If the harm is a side effect of something else people do, it is indirect.

Real example: pangolins, the scaly anteaters of Asia and Africa, are the most trafficked wild mammal: poached for their scales and meat (direct), while their forests are cleared for farms and plantations (indirect).

Habitat loss is indirect: Clearing a forest can kill animals, but they are not the target, so habitat loss counts as an indirect threat. 'Hunting' is direct; say 'illegal hunting' or 'poaching' when it is against the law.

Taking too much, too quickly: Overharvesting is a direct threat: people remove a living resource faster than it can replace itself.

Remember it as: Take more than it makes, and the stock shrinks.

Real example: orange roughy, a deep-sea fish off New Zealand and Australia, lives for more than 100 years and breeds only at about 30. Heavy trawling in the 1980s and 1990s cut many stocks to under a fifth of their size within 20 years. On land, old-growth forests are logged faster than they can regrow.

Link it to biodiversity: Say what the loss does: fewer individuals, lower genetic diversity, a changed food web and lower resilience. Name your example: 'the Atlantic cod collapse of 1992'.

Poaching and the illegal pet trade are direct threats driven by money.

Real example: pangolins: more than a million were poached between 2000 and 2013 for scales used in medicine and for meat. Slow lorises, small night-time primates of South-East Asia, are caught for the pet trade, often with their teeth cut out so they cannot bite.

Say 'illegal': 'Hunting' alone may be legal and sustainable. For poaching, say it is illegal and what the animal is killed for.

Big idea: Habitat loss removes the space and resources species need to survive. When habitats shrink, biodiversity usually falls.

Habitat destruction is like bulldozing nature's homes: rainforest cut for cattle, wetlands drained for buildings and roads, grassland ploughed for crops.

Real example: Brazil's Atlantic Forest once ran along the coast; about 12% is left, cleared for sugar cane, coffee and cities such as Sao Paulo. The golden lion tamarin, a small orange monkey found only there, fell to about 200 animals in the 1970s.

Name it early, with a place: Write the land use, the place and the effect: 'clearing the Amazon for cattle ranching removes habitat, reduces species richness and lowers the ecosystem's resilience'.

Habitat fragmentation is not the same as destruction. The habitat still exists, but organisms are stuck on separate 'islands'.

Real example: the Florida panther, USA. By 1995 only about 20-30 were left, cut off by highways and towns. Inbreeding caused kinked tails and heart defects, until eight female pumas from Texas were released to bring in new genes; there are now about 200.

Destruction or fragmentation?: Destruction removes the habitat; fragmentation breaks it into pieces that still exist. And a small population is at risk because of its genes, mates and rarity, not simply because it 'does not reproduce fast'.

Climate change is an indirect threat: people burn fossil fuels for other reasons, and the warming changes the conditions species are adapted to.

Real example: the Bramble Cay melomys, a small rodent that lived only on a 4-hectare coral island in the Torres Strait, Australia. Storm surges and rising seas destroyed its plants, and it was declared extinct in 2016: the first mammal lost to climate change.

Change, then effect: Name the change and its effect on the species: 'warmer water makes corals expel their algae, so they bleach and die'.

Two more indirect threats: pollution changes the conditions species live in, and invasive alien species arrive with people and take over.

Real example: in the Baltic Sea, fertiliser run-off and sewage have created low-oxygen dead zones of about 70,000 km², where cod eggs cannot survive. In Australia, cane toads, brought in in 1935 to eat beetles, poison the quolls and lizards that eat them.

'Pollution' alone is too vague: Name the pollutant and where it comes from: 'urban sewage', 'agricultural run-off', 'oil spills from ships'. Invasive species have their own page next.

The same threats hit some groups much harder than others. Data questions ask why one group, such as amphibians or corals, is more threatened, or declining faster, than the rest.

Real example: elkhorn coral, which once built the Caribbean's shallow reefs, has fallen by about 90% since the 1980s through disease, bleaching and storm damage.

Tie each reason to the group: 'Amphibians have permeable skin, so pollutants in the water pass straight into their bodies' scores; 'pollution kills animals' does not. For corals, name the pollution source.