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

Options

A. There is no competitor
B. Due to less intra specific competition
C. Absence of natural predator
D. Availability of high nutrient

Answer

**Step-by-Step Solution:**

1. **Understand the Context**: The question refers to the introduction of the prickly pear cactus in Australia during the early 1920s and its rapid spread across rangelands.

2. **Identify the Problem**: The prickly pear cactus caused significant ecological disruption by spreading uncontrollably. We need to determine the reason for this rapid spread.

3. **Analyze the Options**:
- **Option 1**: No competitor due to less interspecific competition.
- **Option 2**: Absence of natural predator.
- **Option 3**: Availability of high nutrients.

4. **Evaluate Each Option**:
- **Option 1**: While competition can affect growth, the primary issue here is not just competition but the lack of control over the cactus population.
- **Option 2**: The absence of natural predators means that there are no organisms to keep the cactus population in check, allowing it to spread rapidly.
- **Option 3**: High nutrient availability can support growth, but it does not explain the uncontrolled spread.

5. **Conclusion**: The most logical explanation for the rapid spread of the prickly pear cactus in Australia is the **absence of natural predators**. Without natural enemies to limit its growth, the cactus proliferated unchecked.

6. **Final Answer**: The prickly pear cactus introduced into Australia in the early 1920s caused havoc by spreading rapidly into millions of hectares of rangeland because of the **absence of natural predators**.

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