CIE A Level Biology复习笔记18.3.5 Controlling Invasive Species

• A species that has moved into an ecosystem where it was previously unknown is an invasive species
• An invasive species can occur naturally as a result of a species migrating or expanding their habitat but most recorded incidents of invasive species have been caused by humans
• In the past humans have:
  • Knowingly collected and traded species between countries via ships
  • Unknowingly provided transport for invasive species to a new ecosystem
  • Introduced alien species deliberately as biological control for pests
• Japanese knotweed is the UK’s most invasive non-native plant species
  • There are several natural population controls that exist for Japanese knotweed in its natural habitat in Japan. The irregular climate and the deposits of volcanic ash over the ground limit its growth
  • A German botanist brought the plant to the UK in the 19th century because he admired its beauty
  • As the UK does not possess the same environmental factors the plant was able to grow unchecked. Since the 1800s it has spread across the UK and become a major problem
  • It grows at a rapid rate, breaking up tarmac and blocking out all sunlight for the native plant species

Problems with invasive alien species

• The biological process of evolution often brings balance to an ecosystem
• Through evolution the environment a species lives in strongly influences the adaptations that the species evolve to live in that environment
• A non-native invasive species will have evolved adaptations for survival in different environmental conditions so when they are introduced into the new ecosystem this can upset the balance
• In a new ecosystem invasive species will have little or none of the natural population controls that existed in their previous ecosystem:
  • They will have no natural predators or competitors
• As a result they are able to increase in number at a rapid rate
• This can affect the processes within an ecosystem
  • Competition may occur between invasive species and native species that occupy a similar niche with the native species getting displaced or pushed to extinction. It could be competition for things such as prey, soil nutrients, light and space
  • Many invasive species can be over successful predators causing a massive decline in their prey species
  • Invasive species can introduce new diseases, to which the native species have no natural immunity
  • The biodiversity of an ecosystem is negatively impacted which reduces its productivity
• Humans can also feel the knock on effects of an invasive species taking over an ecosystem
  • The spread of novel diseases and irritants of the skin / respiratory system directly affect human health
  • The economy of a country can be severely impacted by the costs of trying to control invasive species and their negative effects
  • In the past travel has been brought to a standstill by invasive species, with some plant species prone to blocking up waterways

The Cane Toad in Australia

In the early 1900s, there was a major problem with the sugarcane crop in Australia. An insect pest was destroying the crop and causing major economic losses for many farmers. It was decided that the non-native cane toad (from Hawaii) should be introduced so that it could act as a biological control. After a short period of time the numbers of cane toads increased rapidly due to a lack of natural predators and they spread into other habitats outside of the sugarcane plantations. This had a knock on effect on other species:

• The cane toad is toxic when eaten. The northern quoll, which is an endangered marsupial carnivore, declined steeply in numbers as they preyed on the cane toad
• Other amphibian species face increased competition for food and resources
• The eggs of ground-nesting birds are often eaten by cane toads