Threats to Biodiversity

Biodiversity faces threats from both human-caused and natural factors. While natural threats have always existed, the scale and rate of current biodiversity loss is driven overwhelmingly by human activities, operating synergistically to amplify each other’s effects.

The ‘HIPCC’ Framework of Threats

Conservation biology commonly uses the acronym HIPCC to summarise the primary human-caused threats:
- Habitat loss and fragmentation
- Invasive species
- Pollution
- Climate change
- Consumption (overexploitation)

Habitat Loss and Fragmentation

The single greatest driver of species loss globally:
- Clearing for agriculture, urban development and infrastructure
- Creates habitat islands — small, isolated patches surrounded by inhospitable matrix
- Fragments previously connected populations, reducing gene flow
- Smaller patches support fewer species (species-area relationship: $S = cA^z$)
- Edge effects: increased exposure to wind, predators, nest parasites and weed invasion at habitat edges

Overexploitation

• Hunting, fishing, logging and collection beyond sustainable yield
• Particularly impacts large-bodied, slow-reproducing species (whales, elephants, sharks)
• Combined with habitat loss, pushes species into extinction
• Bushmeat trade and illegal wildlife trade (valued at USD\$23 billion/year) are major drivers

Invasive Species

• Introduced species that establish and spread in a new range, causing harm
• Compete with native species for food, shelter and water
• Predate on native species that lack evolved defences
• Alter habitats (e.g. carp muddying waterbodies, rabbits overgrazing)

Australian examples: Cats, foxes, rabbits, cane toads, common myna, blackberries — Australia has some of the world’s worst invasive species problems.

Pollution

• Bioaccumulation and biomagnification concentrate persistent pollutants in organisms (see next KK)
• Nutrient pollution (eutrophication) from agriculture collapses aquatic biodiversity
• Plastic pollution entangles and is ingested by marine megafauna
• Pesticides kill non-target species including pollinators and aquatic invertebrates
• Noise pollution disrupts breeding behaviour

Climate Change

• Shifting temperature and rainfall patterns alter species’ ranges
• Phenological mismatches: breeding/flowering times drift out of synchrony with food availability
• Ocean acidification threatens calcifying marine organisms
• Coral bleaching events increase in frequency
• Melting ice loss threatens polar and alpine species

Non-Human Threats

• Volcanic eruptions, large storms, droughts
• Disease outbreaks (chytrid fungus has driven >90 amphibian extinctions or declines globally)
• Natural range contractions driven by climate cycles (ENSO)

These become more serious when populations are already reduced by human-caused threats — a small population has little buffer against natural catastrophes.

Synergistic Effects

Threats rarely operate alone:
- Habitat loss isolates populations → reduced gene flow → inbreeding → reduced disease resistance → disease outbreak finishes the species off
- Climate change dries out habitats → increased fire frequency → kills remaining individuals in already small populations

KEY TAKEAWAY: While multiple threat categories exist, VCAA exam scenarios typically require you to identify which specific threat is operating, explain its mechanism, and link it to biodiversity outcomes. Avoid vague answers — be mechanistic.