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BIOLOGY, M3 EQ-Bank 5

Describe the potential changes in native species populations as an introduced species becomes established and its population grows. In your answer, consider both direct and indirect effects on the ecosystem.   (4 marks)

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Cane toads:

  • As cane toad populations grew, many native predators such as quolls, goannas, and certain snake species experienced rapid declines due to poisoning when they attempted to eat the toxic toads.
  • This direct effect led to a decrease in these predator populations, which in turn caused indirect effects on their usual prey species.
  • For example, with fewer predators, some native frog and small mammal populations initially increased.
  • However, the cane toads also compete with native species for food and habitat, potentially leading to declines in some native insect and small animal populations over time. 

Rabbits:

  • As rabbit populations exploded, they caused significant damage to vegetation through overgrazing, reducing food and habitat for native herbivores such as kangaroos and wallabies.
  • This direct competition led to declines in these native species.
  • The changes in vegetation also indirectly affected other species; for example, small ground-dwelling animals lost protective cover, making them more vulnerable to predation.
  • In some areas, vegetation loss and rabbit burrowing has led to increased soil erosion, further altering habitats.
  • Over time, some native predators like dingoes and wedge-tailed eagles may have benefited from the abundant rabbit population as a new food source, potentially leading to complex changes in predator-prey dynamics.
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Answers could include one of the following.

Cane toads:

  • As cane toad populations grew, many native predators such as quolls, goannas, and certain snake species experienced rapid declines due to poisoning when they attempted to eat the toxic toads.
  • This direct effect led to a decrease in these predator populations, which in turn caused indirect effects on their usual prey species.
  • For example, with fewer predators, some native frog and small mammal populations initially increased.
  • However, the cane toads also compete with native species for food and habitat, potentially leading to declines in some native insect and small animal populations over time. 

Rabbits:

  • As rabbit populations exploded, they caused significant damage to vegetation through overgrazing, reducing food and habitat for native herbivores such as kangaroos and wallabies.
  • This direct competition led to declines in these native species.
  • The changes in vegetation also indirectly affected other species; for example, small ground-dwelling animals lost protective cover, making them more vulnerable to predation.
  • In some areas, vegetation loss and rabbit burrowing has led to increased soil erosion, further altering habitats.
  • Over time, some native predators like dingoes and wedge-tailed eagles may have benefited from the abundant rabbit population as a new food source, potentially leading to complex changes in predator-prey dynamics.

BIOLOGY, M3 EQ-Bank 22

Explain how cane toads in Australia have evolved to develop longer legs and an ability to travel faster over greater distances.   (3 marks)

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  • Cane toads have rapidly multiplied to 200 million since there introduction in Australia in 1935. This is largely due to their ability to produce large amounts of offspring all year round and have no predators, as they are extremely poisonous and toxic.
  • As a result, they have not needed to rapidly evolve as there are no significant pressures, but they have been shown to exhibit traits which allow them to travel faster.
  • This trait allows those which exist on the front-line of cane toad communities to outcompete their peers as well as travel further than cane toads at the back, leading to higher reproduction rates and hence a more commonly exhibited trait.
Show Worked Solution
  • Cane toads have rapidly multiplied to 200 million since there introduction in Australia in 1935. This is largely due to their ability to produce large amounts of offspring all year round and have no predators, as they are extremely poisonous and toxic.
  • As a result, they have not needed to rapidly evolve as there are no significant pressures, but they have been shown to exhibit traits which allow them to travel faster.
  • This trait allows those which exist on the front-line of cane toad communities to outcompete their peers as well as travel further than cane toads at the back, leading to higher reproduction rates and hence a more commonly exhibited trait.