Q.What do you understand by 'exotic species'?

An exotic species is one that is introduced, deliberately or accidentally, into a habitat where it does not naturally occur. It arrives from outside its native range, often through human activity such as trade, travel, or agriculture.

Once in a new environment, an exotic species may fail to survive, or it may thrive. The danger arises when it thrives too well. Because the new habitat lacks the natural predators, competitors, or diseases that kept it in check back home, the species can spread rapidly and outcompete native organisms. …

Think of a forest that has stood for centuries. Every tree, insect, bird, and fungus there has carved out a role through long, slow co-evolution. Now imagine someone drops a new player into that forest — a plant from another continent, a fish from a distant river. That newcomer is an exotic species. It has no shared history with the soil, the predators, or the competitors around it. It is, quite literally, a stranger in a strange land.

The key word is introduced. A species is exotic not because of what it looks like or how it behaves, but because of where it comes from relative to where it now lives. A mango tree is native to South Asia, but if you plant it in the Amazon rainforest, it becomes exotic there. The same tree, back in its original home, is simply a native. So the label is always relative to a particular ecosystem, never absolute.

Most introductions are not accidental. Humans have carried species across oceans and mountains for thousands of years — for food, for decoration, for sport, or simply by accident in the ballast of ships or the soil on a boot. Some of these arrivals fail to survive. Others survive but stay harmless. A small number, however, do something far more dangerous: they thrive, spread aggressively, and begin to outcompete the native species that have no defence against them.

The real trouble begins when an exotic species turns invasive. Because it left behind its natural enemies — the predators, parasites, and diseases that kept it in check back home — it can multiply without restraint. It may eat the food that native animals depend on, crowd out native plants for sunlight and water, or even prey on species that have never encountered anything like it. The result is often a cascade: one introduced species can push several native ones toward extinction, and the entire food web wobbles.