Explain the major causes of biodiversity loss, including habitat change, introduced species and disease, and describe their effects on Tasmanian ecosystems.

What this dot point is asking

This dot point asks you to explain why biodiversity is declining and to describe the main causes, with particular attention to introduced species, habitat change and disease. You should be able to outline each driver, explain how it reduces biodiversity, and support your answer with Tasmanian examples.

The main drivers of biodiversity loss

Scientists group the causes of biodiversity decline into a handful of major drivers, which usually act together.

• Habitat destruction, degradation and fragmentation is generally the biggest driver. Clearing land for agriculture, forestry and development removes the places species need, while fragmentation isolates populations and reduces gene flow.
• Invasive species compete with, prey on or spread disease to native species that did not evolve alongside them.
• Climate change shifts conditions faster than many species can adapt or move.
• Overexploitation removes species faster than they can reproduce, through overfishing, overhunting or overharvesting.
• Pollution poisons or smothers organisms and degrades habitats.

Because these drivers interact, their combined effect is often greater than any one alone.

Introduced species in Tasmania

Tasmania's isolation means many native species evolved without certain predators or competitors, leaving them highly vulnerable to introductions. Feral cats and the establishment risk from foxes threaten ground-dwelling mammals and birds, which have few defences against fast, efficient mammalian hunters. European rabbits compete with native herbivores and damage vegetation, and gorse and other weeds crowd out native plants.

In the sea, the long-spined sea urchin (Centrostephanus rodgersii) has spread south as waters warm, grazing kelp forests down to bare urchin barrens that support far fewer species. Marine pests such as the northern Pacific seastar also disrupt seafloor communities.

Disease as a driver

Disease can devastate populations with low genetic diversity. Devil Facial Tumour Disease is a transmissible cancer that has killed a large proportion of wild Tasmanian devils since the 1990s. Because devils have low genetic diversity, many individuals cannot mount an immune response, so the disease spreads readily through biting. The decline of this top predator can in turn allow feral cats and other species to increase, showing how the loss of one species ripples through the community.

Why these losses matter

Each driver reduces biodiversity at one or more levels. Losing populations cuts genetic diversity, losing species cuts species diversity, and degrading or clearing habitat cuts ecosystem diversity. As diversity falls, functional redundancy is lost, so the ecosystem becomes less resilient and more likely to shift into a degraded state, such as a kelp forest becoming an urchin barren.

Bringing it together

To answer this dot point well, list and explain the major drivers of biodiversity loss, then focus on the Tasmanian context with introduced species such as cats and urchins, habitat change from clearing, and disease such as Devil Facial Tumour Disease. Link each driver back to the level of biodiversity it reduces and to the loss of ecological function and resilience.