The prickly pear cactus became unusually abundant after its introduction in Australia, because it- .

Options

A. Had no coevolved herbivore
B. Had no secondary compounds
C. Formed new mycorrhizal association
D. Lost its thorn

Answer

**Step-by-Step Solution:**

1. **Introduction of Prickly Pear Cactus**: The prickly pear cactus was introduced to Australia in the early 20th century, specifically around the 1920s. It was brought in to support the dye industry and later for agricultural purposes.

2. **Lack of Natural Predators**: Upon its introduction, the prickly pear cactus thrived because it did not have any natural predators in Australia. Since it was not a native species, the herbivores and insects that typically feed on it in its native habitat were absent.

3. **Rapid Population Growth**: The absence of natural predators allowed the prickly pear cactus to grow uncontrollably. It spread rapidly across millions of hectares of land, leading to an unusual abundance of the species.

4. **Introduction of Natural Predators**: Eventually, to control the overpopulation of the prickly pear cactus, a natural predator (a specific moth) was introduced to Australia. This predator helped to manage the cactus population, but initially, the cactus flourished due to the lack of co-evolved herbivores.

5. **Conclusion**: The prickly pear cactus became unusually abundant in Australia primarily because it had no co-evolved herbivores to keep its population in check.

**Final Answer**: The prickly pear cactus became unusually abundant after its introduction in Australia because it had no co-evolved herbivore.

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