Correct option is D
The correct answer is (d).
Introduction
Alien or exotic species are organisms introduced into an ecosystem outside their natural geographic range.
When introduced unintentionally often via global trade or transport these species lack natural predators in their new environment.
Consequently, they frequently multiply uncontrollably, turning invasive and severely disrupting the local ecological balance.
Information Booster
- Invasive Alien Species (IAS) are considered one of the primary drivers of global biodiversity loss.
- Because they lack natural checks like specific predators or diseases in the new ecosystem, their populations explode.
- They aggressively compete with indigenous (native) species for vital resources such as food, water, light, and space.
- Classic examples in India include the introduction of Lantana camara, Water Hyacinth, and Parthenium, which devastated native flora.
- They can alter fundamental ecosystem processes, including soil chemistry, water cycles, and fire regimes.
- In many cases, alien predators (like rats or feral cats on islands) have directly caused the extinction of native bird species.
- The Convention on Biological Diversity (CBD) identifies invasive species as a critical threat requiring global mitigation efforts.
- Option A (Decrease of alien species): While some introduced species fail to survive in a new habitat, the core environmental concern addressed in ecological studies is when they thrive and become a threat.
- Option B (Increase in habitat): Alien species do not create or expand natural habitats; rather, they degrade existing ecosystems and diminish the functional habitat available for native fauna and flora.
- Option C (They turn invasive and cause increase species): Invasive species reduce biodiversity; they do not increase the overall species count in a healthy, sustainable manner.
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