Organisms And Populations

The Monarch butterfly is highly distasteful to predatory birds because as a caterpillar it feeds on milkweed (Calotropis) and sequesters cardiac glycoside-type chemicals in its tissues. This is a chemical anti-predator defence: a bird that eats one Monarch experiences a strong unpleasant reaction (physiological disturbance) and subsequently avoids the species. Camouflage is incorrect because the Monarch is brightly coloured (aposematic) rather than concealed against the background. A thorny morphological deterrent applies to plants such as Acacia or cacti, not to a butterfly. Mimicry of a harmless model is the reverse of the situation, since here the Monarch is itself the toxic model that other palatable species may mimic. As described in NCERT Class 12, Chapter 13 (Organisms and Populations), prey species evolve diverse defences against predation, and chemical defence is widespread among insects and plants. Plausibility check: bright warning coloration paired with a stored toxin is internally consistent because conspicuousness only benefits the prey if predators learn to associate the colour with toxicity, confirming chemical defence as the answer.