RAS question
In ecology, 'Indicator species' refers to:
Correct answer: (D) Species whose presence/absence indicates environmental conditions.
In ecology, indicator species are species whose presence or absence indicates environmental conditions.
Explanation
Indicator species are used because living organisms respond to the conditions around them, so their presence, absence or behaviour can signal the state of an environment. Option D is right because it defines indicator species through that ecological signal: the species is not the condition itself, but evidence of it. Examples show the idea clearly. Lichens indicate air quality because they are sensitive to sulphur dioxide, caddisfly larvae indicate clean water, and tubifex worms point towards pollution. United Nations Environment Programme describes a bio-indicator as a species whose presence, absence or behaviour gives information about environmental conditions.
Why the other options are wrong
- (A) A weather phenomenon is a physical atmospheric event, whereas an indicator species is a living organism used to read environmental conditions.
- (B) A type of pollution is an environmental problem itself, while an indicator species only signals conditions such as pollution or cleaner water.
- (C) A conservation technique is a method of protection or management, but an indicator species is evidence used to understand environmental quality.
Concept
Bio-indicators and environmental monitoring connect basic ecological terms with applied examples such as air quality, clean water and pollution in RAS preparation.