The pricky pear cactus became unusually abundant after its introduction in Australia, because it

Options

A. had no coevolved hebivores
B. formed new mycorrhizal association
C. lost its thorns
D. all of these

Explanation

**Step-by-Step Solution:**

1. **Introduction of the Prickly Pear Cactus**: The prickly pear cactus (Opuntia) is originally native to America and was introduced to Australia.

2. **Alien Species**: Upon its introduction, the prickly pear cactus became an alien species in Australia, meaning it was not part of the native flora and fauna of that ecosystem.

3. **Absence of Natural Predators**: In its native habitat, the prickly pear cactus co-existed with specific herbivores that had evolved to feed on it despite its defenses (like thorns). However, in Australia, there were no such herbivores or natural predators that could control the population of the prickly pear cactus.

4. **Rapid Population Growth**: Due to the absence of these natural predators, the prickly pear cactus was able to multiply rapidly. Without any limiting factors, such as herbivory, its population grew unchecked.

5. **Invasive Species**: As a result of this unchecked growth, the prickly pear cactus became an invasive species in Australia, spreading over large areas and outcompeting native plants.

6. **Conclusion**: The prickly pear cactus became unusually abundant in Australia primarily because there were no co-evolved herbivores to feed on it and keep its population in check.

**Final Answer**: The prickly pear cactus became unusually abundant after its introduction in Australia because there were no co-evolved herbivores who could feed on this plant and check its population.

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