Read the paragraph and answer the Question given below:
There is no natural habitat on earth known that is inhabited just by a single species. For any species, the minimal requirement is one more species on which it can feed. Even a plant species, which makes its own food, cannot survive alone and needs soil microbes to break down the organic matter in soil and return the inorganic nutrients for absorption. It is obvious that in nature, animals, plants and microbes do not and cannot live in isolation but interact in various ways to form a biological community.
The process in which the fitness of one species (measured in terms of its ‘r’, the intrinsic rate of increase) is significantly lower in the presence of another species is known as:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Competition
Option (1) Parasitism — Incorrect. In parasitism one species (the parasite) benefits at the cost of the host, and it lives on or in the host. The definition in the question speaks of no such host.
Option (2) Competition — Correct. The question gives NCERT’s own definition. It covers competition for limited resources and also interference competition, where one species lowers the feeding of another even when food is plenty.
Option (3) Predation — Incorrect. In predation one species kills and eats the other. It is a +/− interaction, judged by the prey being eaten, not by a lowered r of a species living alongside.
Option (4) Commensalism — Incorrect. In commensalism one species benefits and the other is neither harmed nor benefited, so no species has its fitness lowered.
Note: The passage is taken from NCERT. NTA has put lines of the NCERT text together to make it. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.
NCERT Extract:
Population Interactions – “… (ii) Competition: When Darwin spoke of the struggle for existence and survival of the fittest in nature, he was convinced that interspecific competition is a potent force in organic evolution. It is generally believed that competition occurs when closely related species compete for the same resources that are limiting, but this is not entirely true. Firstly, totally unrelated species could also compete for the same resource. For instance, in some shallow South American lakes, visiting flamingoes and resident fishes compete for their common food, the zooplankton in the lake. Secondly, resources need not be limiting for competition to occur; in interference competition, the feeding efficiency of one species might be reduced due to the interfering and inhibitory presence of the other species, even if resources (food and space) are abundant. Therefore, competition is best defined as a process in which the fitness of one species (measured in terms of its ‘r’ the intrinsic rate of increase) is significantly lower in the presence of another species.”