Q.Alien species invasion is a threat to endemic species - substantiate this statement.

(a) Introduced non-native species can invade and disrupt ecosystems, threatening native biodiversity. (b) Organisms handle unfavourable abiotic conditions by regulating, conforming, migrating, or entering dormancy.

(a) When a species is introduced -- intentionally (for ornamental, agricultural or aquaculture purposes) or accidentally -- into a region outside its natural range, it may find itself free of the predators, parasites and competitors that kept its population in check in its native habitat; under these conditions, such an 'invasive' or 'exotic' species can multiply rapidly and spread aggressively, outcompeting native species for food, space and other resources, altering habitat structure, and in some cases causing the local decline or extinction of native species. Well-known examples in India include water hyacinth (Eichhornia crassipes), which chokes lakes and ponds and depletes oxygen for aquatic life, and the introduction of exotic fish species that can prey on or outcompete native fish populations -- making invasive species one of the major recognised threats to biodiversity loss, alongside habitat destruction and over-exploitation. (b) Because environmental conditions such as temperature, water availability and salinity are rarely constant, organisms have evolved four broad strategies to cope with unfavourable abiotic stress. Regulators actively maintain a relatively constant internal environment regardless of external fluctuations, through physiological (e.g., sweating, shivering) or behavioural means -- birds and mammals regulating body temperature (homeothermy) are the classic example, at a significant energetic cost. Conformers, in contrast, let their internal body condition passively change along with the external environment -- most plants, and 'cold-blooded' (poikilothermic) animals like fish, amphibians and reptiles, allow their body temperature to track the surrounding temperature. Some organisms instead migrate, temporarily moving away from the unfavourable area to a more hospitable habitat and r …