Which of the following statements about competition in nature are correct?
A. The Abingdon tortoise in the Galapagos Islands became extinct within a decade after goats were introduced on the island.
B. A species whose distribution is restricted by a competitively superior species expands its distributional range dramatically when the competing species is experimentally removed.
C. In interference competition, the feeding efficiency of one species is reduced by the presence of the other species because food and space are in short supply.
D. Competitive exclusion is easy to demonstrate in laboratory experiments, and the evidence for it occurring in nature is just as conclusive.
Choose the correct answer from the options given below.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A and B only
Competition is an interaction in which the fitness of one species is lowered in the presence of another. It can occur between related or unrelated species. Gause’s competitive exclusion principle says that two closely related species competing for the same limited resources cannot co-exist for long; the weaker one is eliminated.
Statement A: The Abingdon tortoise in the Galapagos Islands became extinct within a decade after goats were introduced on the island. — True. The goats were better at browsing, so they took over the food of the tortoise. This is one of the book’s cases of circumstantial evidence for competition in nature.
Statement B: A species whose distribution is restricted by a competitively superior species expands its distributional range dramatically when the competing species is experimentally removed. — True. This is called competitive release. In Connell’s experiments on the rocky coasts of Scotland, the larger barnacle Balanus kept the smaller barnacle out of the intertidal zone.
Statement C: In interference competition, the feeding efficiency of one species is reduced by the presence of the other species because food and space are in short supply. — False. In interference competition the feeding efficiency drops because of the interfering and inhibitory presence of the other species, even if food and space are abundant. Resources need not be limiting for this kind of competition.
Statement D: Competitive exclusion is easy to demonstrate in laboratory experiments, and the evidence for it occurring in nature is just as conclusive. — False. The first half is right: Gause and others showed it in the laboratory. But the book says the evidence for competitive exclusion in nature is not always conclusive.
NCERT Extract:
Population Interactions – “… 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. … It is relatively easy to demonstrate in laboratory experiments, as Gause and other experimental ecologists did, when resources are limited the competitively superior species will eventually eliminate the other species, but evidence for such competitive exclusion occurring in nature is not always conclusive. … The Abingdon tortoise in Galapagos Islands became extinct within a decade after goats were introduced on the island, apparently due to the greater browsing efficiency of the goats. Another evidence for the occurrence of competition in nature comes from what is called ‘competitive release’. A species whose distribution is restricted to a small geographical area because of the presence of a competitively superior species, is found to expand its distributional range dramatically when the competing species is experimentally removed.”