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The Prickly pear cactus introduced into ...

The Prickly pear cactus introduced into Australia in the early 1920's caused havoc by spreading rapidly in to millions of hectares of rangeland qbecause -

A

There is no competitor

B

Due to less intra specific competition

C

Absence of natural predator

D

Availability of high nutrient

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**Step-by-Step Solution:** 1. **Introduction of Prickly Pear Cactus**: The prickly pear cactus was introduced to Australia in the early 1920s. It is an exotic species that was not native to the region. 2. **Rapid Spread**: After its introduction, the prickly pear cactus spread rapidly across millions of hectares of rangeland in Australia. This rapid spread can be attributed to several ecological factors. 3. **Lack of Competitors**: One of the main reasons for the cactus's rapid spread is the absence of natural competitors. The endemic species of plants in Australia were not able to compete effectively with the prickly pear cactus, which allowed it to thrive. 4. **Low Intra-specific Competition**: Intra-specific competition refers to competition among individuals of the same species. In this case, since the prickly pear cactus was the only species introduced, there was minimal intra-specific competition, allowing it to grow and spread without significant limitations. 5. **Absence of Natural Predators**: Another critical factor contributing to the cactus's spread was the absence of natural predators. In its native habitat, the prickly pear cactus would have had predators that kept its population in check. However, in Australia, these natural predators were not present, leading to unchecked growth. 6. **Impact on Endemic Species**: As the prickly pear cactus spread, it negatively impacted the native or endemic species of plants. The resources available to these endemic species were diminished, leading to a decline in their populations. 7. **Conclusion**: The combination of a lack of competitors, low intra-specific competition, and the absence of natural predators allowed the prickly pear cactus to spread rapidly and cause significant ecological disruption in Australia. **Final Answer**: The prickly pear cactus caused havoc in Australia by spreading rapidly due to the absence of natural predators, lack of competitors, and low intra-specific competition. ---
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