Biodiversity Loss and Introduced Species - TCE Environmental Science (Tasmania)
“Explain the major causes of biodiversity loss, including habitat change, introduced species and disease, and describe their effects on Tasmanian ecosystems.”
Biodiversity loss is driven by several interacting causes, often summarised as habitat destruction, invasive species, climate change, overexploitation and pollution. In Tasmania, habitat change from clearing, the spread of introduced species such as feral cats and the long-spined sea urchin, and wildlife disease such as Devil Facial Tumour Disease are major threats. These drivers reduce genetic, species and ecosystem diversity, weakening ecological function and resilience.
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.
An invasive species is a non-native organism that establishes and spreads in a new environment, causing harm to native species, ecosystems or human interests because local species lack defences against it.
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.
Real biodiversity loss rarely has a single cause. Warming seas (climate change) helped the long-spined urchin (invasive species) destroy kelp forests (habitat loss). In your answers, show how drivers interact and reinforce one another, because that systems thinking is what distinguishes a high-level response.
Data questions often give species or habitat measures before and after a disturbance and ask you to describe and explain the change. Work through it in order.
Compare the matched figures
State the before and after values for each measure (such as kelp cover and species richness) and give the size of the change, ideally as a percentage loss or gain.
Identify the drivers
Name the drivers at work and, crucially, how they interact. A range-extending invasive species enabled by warming water is two interacting drivers, not one.
Explain the mechanism
Connect the driver to the data: overgrazing by the urchin removes the habitat-forming kelp, so the species that depend on that structure lose shelter and food and disappear.
Link to biodiversity levels and function
Conclude that the loss cuts species diversity and, by removing functional redundancy, lowers the ecosystem's productivity and resilience.
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.
Avoid attributing biodiversity loss to a single villain such as climate change or one introduced animal. Examiners look for recognition that multiple drivers interact. Name several drivers and explain how they combine, rather than treating one as the sole explanation.
Exam-style questions
Questions in the style of TASC exam questions on this dot point, each with a worked answer. They are written by ExamExplained unless tagged "Past paper"; the year shows the paper a question is modelled on.
Practice7 marksReef surveys recorded kelp cover and species richness before and after the long-spined sea urchin arrived at a Tasmanian east-coast site. Before: kelp cover , species. After: kelp cover , species. Using the data, describe the change and explain how an introduced species combined with warming seas caused it.Show worked answer →
A 7 mark data-and-explain question rewards a quantified change and interacting drivers.
- Describe the change using the data
- Kelp cover collapsed from to and species richness fell from to species, roughly a loss of species. Quote both figures.
- Explain the cause
- Warming seas (climate change) let the long-spined sea urchin (an introduced/range-extending species) survive and spread south. The urchins overgraze the kelp, turning a structured forest into a bare urchin barren. Losing the habitat-forming kelp removes shelter and food, so most associated species disappear.
- Show the interaction
- Neither driver acts alone: warming enabled the urchin, and the urchin destroyed the habitat. Markers reward showing how climate change and the invasive species combined.
Practice6 marksExplain why island ecosystems such as Tasmania are especially vulnerable to introduced species, using one example.Show worked answer →
A 6 mark explain question wants the vulnerability mechanism plus an example.
The vulnerability. Island species often evolve in isolation without certain predators, competitors or diseases, so they lack defences (such as anti-predator behaviour) against introduced organisms. Small, isolated populations also cannot easily be replenished from elsewhere.
An example. Ground-dwelling native mammals and birds have few defences against feral cats (and the establishment risk from foxes), efficient mammalian hunters they did not evolve alongside, so predation can drive sharp declines.
Markers reward the evolved-in-isolation mechanism and a relevant Tasmanian example.