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BIOLOGY, M3 EQ-Bank 6

"The prickly pear cactus, introduced to Australia in the 1800s, became a significant ecological problem before being brought under control."

Describe two significant changes to the ecosystem caused by the prickly pear invasion and the control method used to manage its population. In your answer, consider the effectiveness of this control measure and its ecological implications.   (4 marks)

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  • The prickly pear outcompeted native vegetation, forming dense thickets that reduced grazing land for livestock and native animals.
  • It also altered habitat structures, displacing native fauna and changing local biodiversity patterns. eg. it harboured pest species like rabbits.
  • To control the prickly pear population, scientists introduced the Cactoblastis moth, whose larvae feed exclusively on prickly pear species.
  • This biological control method proved remarkably effective, with the moths feeding almost exclusively on the prickly pear. As prickly pear numbers reduced, the moths also became rarer.
  • This control measure rapidly reduced prickly pear populations to manageable levels within a decade, restoring native ecosystems and millions of hectares of land for agricultural use.
  • This demonstrates the potential power and risks of biological control agents, as the moth’s effectiveness in Australia led to its introduction in other parts of the world, where it has sometimes become a pest itself.
Show Worked Solution
  • The prickly pear outcompeted native vegetation, forming dense thickets that reduced grazing land for livestock and native animals.
  • It also altered habitat structures, displacing native fauna and changing local biodiversity patterns. eg. it harboured pest species like rabbits.
  • To control the prickly pear population, scientists introduced the Cactoblastis moth, whose larvae feed exclusively on prickly pear species.
  • This biological control method proved remarkably effective, with the moths feeding almost exclusively on the prickly pear. As prickly pear numbers reduced, the moths also became rarer.
  • This control measure rapidly reduced prickly pear populations to manageable levels within a decade, restoring native ecosystems and millions of hectares of land for agricultural use.
  • This demonstrates the potential power and risks of biological control agents, as the moth’s effectiveness in Australia led to its introduction in other parts of the world, where it has sometimes become a pest itself.