Question

Introduction of prickly pear cactus in Australia in the year 1920, caused havoc by spreading rapidly into wide range of lands because

• A. the invaded land did not have its natural predators
• B. they formed new mutualistic relationships with the native species of cactus
• C. of the presence of coevolved herbivores
• D. they drained soil of all nutrients

Answer 1

The correct option is A the invaded land did not have its natural predators

Predation plays an important role in transferring energy across trophic levels, checking prey population under control and many more reasons. Whenever certain exotic species are introduced into a geographical area they become invasive and start spreading fast as the invaded land does not have its natural predators.
Such a case happened in Australia in the year 1920 when a species of prickly pear cactus was introduced, it started spreading rapidly covering millions of hectares of land. It was later countered by introduction of cactus feeding moths as predators.
Basically this rapid growth and spread of the cactus in the new land was due to absence of natural predators which resulted in the havoc. And also there were no coevolved herbivores to eat the prickly pear cactus and no other environmental factors that resisted the spread of it in Australia.