Quick questions on Threats to biodiversity and extinction (habitat loss, invasive species, overexploitation, pollution): VCE Environmental Science Unit 3

A useful memory aid is HIPPO: Habitat loss, Invasive species, Pollution, Population (human) growth and Overexploitation. Climate change increasingly cuts across all of these.

Fragmentation matters because it does more than just remove habitat. It isolates populations, which reduces gene flow between patches and lowers genetic diversity. Small isolated populations are vulnerable to inbreeding and to local extinction from a single fire, flood or disease outbreak, with no nearby population to recolonise. Wildlife corridors (strips of vegetation linking patches) are one management response that reconnects fragmented habitat.

Extinction is the permanent loss of a species when its last individual dies. A local extinction (extirpation) is the loss of a species from one area while it survives elsewhere. Extinction is a natural process (background extinction), but human pressures have raised the rate far above background levels, which is why scientists describe a current biodiversity crisis.

Clearing native vegetation for agriculture, mining and urban growth is the single largest driver of biodiversity loss. Fragmentation breaks a large continuous habitat into small isolated patches. Smaller patches support smaller populations (more vulnerable to chance events), have more edge effect (drying winds, weeds and predators penetrating from the boundary), and block the movement of animals between patches.

Introduced species can outcompete, prey on, or bring disease to native species that did not evolve alongside them. Australia is a global hotspot for this threat. Foxes and feral cats have driven declines and extinctions of small native mammals such as bandicoots and bilbies.

Harvesting a species faster than it can reproduce drives population collapse. Historic overhunting drove the Tasmanian tiger (thylacine) toward extinction (helped by bounties), and overfishing has depleted stocks such as orange roughy and southern bluefin tuna in Australian waters.

Nutrients, chemicals, plastics and sediment degrade habitats. Fertiliser runoff causes algal blooms that deoxygenate waterways; sediment from land clearing smothers seagrass and coral on the Great Barrier Reef.

Rising temperatures, altered rainfall, sea-level rise and more frequent extreme events shift the conditions species depend on. Marine heatwaves have caused repeated mass coral bleaching on the Great Barrier Reef. Species that cannot move or adapt fast enough decline.