Biology · Organisms and Populations · NEET
No. This is the most common mistake. Darwinian fitness has nothing to do with muscle, speed, or size. Fitness is measured only by reproductive success, that is, the number of offspring that survive to reproduce. A small mouse that leaves 20 surviving pups has higher fitness than a strong lion that leaves 1. NCERT says natural selection favours whatever life history traits give the highest reproductive fitness.
Semelparity means breeding only ONCE in a lifetime (semel = once). The organism puts all its energy into one big reproductive event and often dies after, for example Pacific salmon and bamboo. Iteroparity means breeding MANY times over the lifespan (itero = repeat), for example most birds and mammals. Both are strategies shaped by natural selection to maximise fitness in their particular habitat.
No. NCERT is clear that these traits evolved under natural selection over many generations. An individual does not decide to have many small babies or few large ones. The habitat and pressures 'select' the strategy that leaves the most surviving offspring, and that strategy becomes common in the population.
They are closely linked but not identical terms. r-selected species (living in unstable habitats) tend to produce a large number of small offspring, which fits the semelparous pattern of one big brood. K-selected species produce few, large offspring and are usually iteroparous. For NEET, remember: many small offspring = r-selected, few large offspring = K-selected.
It is a trade-off. Energy is limited, so a parent can make either many small offspring or a few large ones, not both. In harsh or unpredictable habitats, many small offspring raise the chance that at least some survive. In stable habitats, few large well-cared-for offspring survive better. Nature picks whichever trade-off gives higher fitness.
Which of the following is correct for r-selected species?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is the number of surviving offspring an organism leaves behind. Higher offspring count = higher fitness.
Pacific salmon fish and bamboo species. They reproduce only once, invest heavily in that single event, and then die.
Most birds and mammals, which breed several times across their lifespan.
Neither is universally better. It is a trade-off decided by natural selection based on the habitat. Both strategies exist because both can maximise fitness in different conditions.
Many small offspring (semelparous) is typical of r-selected species; few large offspring (iteroparous) is typical of K-selected species.
