Analyse the natural and human-induced causes of change to ecosystems and biodiversity, including the HIPPO framework and the role of climate change; refer to the IUCN Red List and named threatened species

Note: This page is part of the HSC Geography 11-12 (2022) syllabus, first examined in HSC 2025. The legacy 2009 syllabus "Ecosystems at Risk" content is preserved in sibling folders.

What this dot point is asking

This dot point asks you to identify, explain and evaluate the drivers of biodiversity loss. You need a framework to organise the drivers (the HIPPO acronym is widely taught), a way to talk about the role of climate change as a cross-cutting amplifier, and a working knowledge of the IUCN Red List as the global authority on extinction risk. Strong responses use named Australian examples (Australia has the highest modern mammal-extinction rate of any continent) alongside global examples. The geographical concepts to lean on are interconnection (drivers interact), scale (local clearing plus global climate change) and change (the pace and direction of biodiversity loss).

The answer

The HIPPO framework

The HIPPO acronym, popularised by E.O. Wilson, summarises the major direct drivers of biodiversity loss:

• H - Habitat loss and degradation. Deforestation, agricultural expansion, urbanisation, mining, infrastructure. The single largest driver of terrestrial biodiversity loss globally.
• I - Invasive species. Introduced species that outcompete, prey on, or carry diseases against native species. Particularly devastating on islands and in isolated continental systems such as Australia.
• P - Pollution. Nutrient runoff (nitrogen and phosphorus driving eutrophication), pesticides, plastic, heavy metals, sediment, light and noise pollution.
• P - Population (human) growth and consumption. The indirect driver behind the other four; rising demand for food, water, energy, materials and space.
• O - Overharvesting and overexploitation. Overfishing, hunting, poaching, illegal wildlife trade, logging beyond regeneration rates.

Climate change as a cross-cutting driver

Climate change is usually treated as a fifth direct driver alongside HIPPO. It acts both alone (temperature shifts pushing species beyond their tolerance, ocean warming bleaching coral) and as a multiplier on the other drivers (drier conditions intensifying fire-driven habitat loss; warmer waters helping invasive species spread). The IPCC and IPBES jointly identify climate change as projected to become the dominant driver of biodiversity loss in many ecosystems by mid-century if current warming trajectories continue.

The interaction is what matters. Mass coral bleaching is driven by ocean warming, but the reef's resilience is reduced by water-quality decline (pollution from agricultural runoff) and by Crown-of-Thorns starfish outbreaks (linked to nutrient enrichment). No single driver explains the change on its own.

The IUCN Red List

The International Union for Conservation of Nature (IUCN) Red List of Threatened Species is the global standard for assessing extinction risk. Each assessed species is placed in a category based on population size, trend, geographic range and threats:

• Extinct (EX). No reasonable doubt that the last individual has died.
• Extinct in the Wild (EW). Surviving only in captivity or as cultivated populations.
• Critically Endangered (CR). Extremely high risk of extinction in the wild.
• Endangered (EN). Very high risk.
• Vulnerable (VU). High risk.
• Near Threatened (NT). Close to qualifying for a threatened category.
• Least Concern (LC). Lowest risk; widespread and abundant.
• Data Deficient (DD). Inadequate information to assess.

The Red List is updated continuously. Australia's federal Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) maintains a separate national list of threatened species that often aligns with, but is not identical to, the IUCN list.

Drivers of biodiversity loss in Australia

Australia is the canonical case study because the drivers are concentrated and well-documented.

Habitat loss. Land clearing for agriculture and urban expansion has stripped a large share of original native vegetation across the Murray-Darling Basin, the Cumberland Plain, parts of Queensland and the wheatbelt of Western Australia. Queensland has been a national focus for clearing rates, though state-level legislation has tightened in recent years.

Invasive species. Australia's record is severe because of long evolutionary isolation:

• European red fox (Vulpes vulpes). Introduced for sport hunting in the nineteenth century; implicated in many small-mammal extinctions.
• Feral cat (Felis catus). Widely distributed; significant predator of small native mammals, birds and reptiles.
• Cane toad (Rhinella marina). Introduced to Queensland in 1935 to control sugarcane beetles; spread north and west; toxic to native predators that try to eat them, including quolls and goannas.
• European rabbit (Oryctolagus cuniculus). Caused widespread habitat degradation; biocontrols (myxomatosis, rabbit haemorrhagic disease) have had partial success.
• Weeds (lantana, buffel grass, prickly pear). Transform fire regimes and outcompete natives.

Pollution

Agricultural runoff (nitrogen, phosphorus, sediment) into the Great Barrier Reef lagoon; plastic pollution in marine systems; mercury and other heavy metals from historical mining; pesticide effects on pollinators.

Overharvesting

Historical hunting of whales, seals and large mammals; some current pressure on shark populations and on commercial fisheries.

Climate change

Marine heatwaves driving repeated coral bleaching on the Great Barrier Reef (2016, 2017, 2020, 2022 and a further event in 2024 reported by the Great Barrier Reef Marine Park Authority); shifts in fire weather contributing to the 2019-20 Black Summer fires; warming-driven range shifts and habitat loss.

Named threatened and extinct species

• Thylacine (Tasmanian tiger), Thylacinus cynocephalus. Extinct; the last known individual died at Hobart Zoo in 1936. Driven by hunting, bounties, habitat loss and possibly disease.
• Christmas Island pipistrelle (Pipistrellus murrayi). Last confirmed in 2009; declared Extinct on the IUCN Red List. Causes are debated but likely include invasive species and habitat change on Christmas Island.
• Koala (Phascolarctos cinereus). Listed as Endangered under Australia's EPBC Act in February 2022 in Queensland, New South Wales and the Australian Capital Territory. Drivers include habitat loss, bushfires (with major losses in the 2019-20 Black Summer), disease (chlamydia) and vehicle strike.
• Northern hairy-nosed wombat (Lasiorhinus krefftii). Critically Endangered; restricted to a small protected area in Queensland.
• Leadbeater's possum (Gymnobelideus leadbeateri). Critically Endangered; dependent on old-growth Mountain Ash forest in Victoria affected by logging and fire.
• Great white shark, southern right whale, marine turtles. Various IUCN categories reflecting global pressures.

Examples in context

Example 1. The koala listing decision (February 2022). In February 2022, the Australian Government listed the koala as Endangered under the EPBC Act across Queensland, New South Wales and the Australian Capital Territory, an upgrade from Vulnerable. Drivers identified included cumulative habitat loss from clearing and urban expansion, severe loss of habitat in the 2019-20 Black Summer bushfires, disease (chlamydia) and vehicle strike. The case illustrates multi-driver interaction (HIPPO plus climate-driven fire), the role of legal listing as a management trigger, and the geographical concept of change at decadal scale. Population counts cited in published assessments vary widely, so strong responses describe the trend (declining) and the listing change rather than inventing specific numbers.

Example 2. Black Summer bushfires (2019-20) and biodiversity. The 2019-20 Australian bushfire season burned an unusually large area of forested land across eastern Australia (figures published by federal and state agencies vary; the commonly cited approximate area is in the tens of millions of hectares including grassland). The Department of Climate Change, Energy, the Environment and Water and CSIRO produced post-fire assessments showing that hundreds of threatened species had a substantial share of their habitat burnt. The case demonstrates climate change as a multiplier of fire risk, fire interacting with prior habitat loss (small remnants suffered proportionally larger impacts), and the speed at which biodiversity status can change.

Try this

Q1. Identify the components of the HIPPO framework with an Australian example for each. [5 marks]

• Cue. Habitat loss (Queensland clearing). Invasive species (fox, cat, cane toad). Pollution (Great Barrier Reef runoff). Population (urban expansion on Cumberland Plain). Overharvesting (historical whaling).

Q2. Explain the role of climate change as a cross-cutting driver of biodiversity loss, with one named example. [6 marks]

• Cue. Direct effects (warming, ocean acidification). Multiplier on other drivers (fire weather, invasive expansion). Example: Great Barrier Reef bleaching events 2016/2017/2020/2022/2024 driven by marine heatwaves.

Q3. Analyse the drivers of decline for a named Australian threatened or extinct species, using the IUCN Red List framework. [8 marks]

• Cue. Choose koala (Endangered, EPBC 2022), thylacine (Extinct, 1936) or northern hairy-nosed wombat (Critically Endangered). Apply HIPPO plus climate. Reference IUCN categories. Reach a calibrated judgement on which drivers dominate.