Overview
This lecture explains the history and ecological impact of the cane toad invasion in Australia, examining why cane toads became a destructive invasive species and evaluating potential solutions.
The Cane Toad Introduction
- In the 1930s, Australian farmers introduced cane toads to control cane beetle grubs destroying sugarcane.
- Authorities released 100 cane toads from Hawaii without studying environmental impacts.
- Cane toads quickly multiplied, spreading rapidly and becoming a major invasive species.
Biological and Ecological Consequences
- Cane toads are large, poisonous, and eat almost anything except cane beetles and their larvae.
- Their venom is highly toxic, killing native predators like monitor lizards, snakes, and crocodiles.
- Many native Australian species have been pushed toward extinction due to the toads.
- Both cane toad eggs and tadpoles are poisonous and produced in huge numbers (up to 40,000 eggs per female).
Invasiveness and Rapid Evolution
- Cane toads' toxins make them difficult for native predators to eat or control.
- They have few natural predators in Australia, unlike their native region in South America.
- Cane toads have evolved longer legs, allowing them to move faster and expand their range more rapidly.
- Cannibalism among tadpoles helps reduce their numbers but isn't enough to control population growth.
Defining Invasive Species
- A species is considered invasive only if it causes environmental, economic, or health harm in its new habitat.
- Not all introduced species are invasive (e.g., honeybees, potatoes).
Attempted Control and Solutions
- Eradication efforts include culling, trapping, and encouraging humane killing methods (e.g., freezing).
- Some scientists propose using genetic engineering, such as "W-shredder" gene drives, to produce only male toads and reduce reproductive potential.
- Debates exist about the ethics and risks of genetic interventions in ecosystems.
Key Terms & Definitions
- Invasive Species — A non-native species causing harm to environment, economy, or health in its introduced area.
- Cane Toad (Bufo marinus) — A large, poisonous toad introduced to Australia, now a notorious invasive species.
- Cardiac Glycosides — Toxins in cane toad venom that disrupt heart function in predators.
- Gene Drive — Genetic engineering method designed to spread specific genes quickly through a population.
Action Items / Next Steps
- Review notes on invasive species for upcoming test.
- Research the effectiveness and risks of genetic engineering solutions for invasive species control.
- Watch the recommended cane toad documentary for further context.