In a field experiment in the rocky intertidal communities of the American Pacific Coast, all the starfish Pisaster were removed from an enclosed intertidal area. Within a year, many species of invertebrates in that area became extinct.
Which role of predators does this experiment show most directly?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Predators help in maintaining species diversity in a community by reducing the intensity of competition among competing prey species.
Predators do several jobs in nature. They pass energy up the food chain, keep prey numbers in check and help keep many species in a community. In the Pisaster experiment, removing the predator starfish led to the loss of more than 10 invertebrate species within a year, because the prey species then competed among themselves and the weaker ones were wiped out.
Option (1) Predators act as conduits for transferring the energy fixed by plants to higher trophic levels. — Incorrect. Predators are indeed ‘conduits’ for energy transfer, but the experiment did not measure energy. What it recorded was species disappearing.
Option (2) Predators help in maintaining species diversity in a community by reducing the intensity of competition among competing prey species. — Correct. With the starfish present, competition among the prey species stays low and many species live together. Once it was removed, interspecific competition drove many species extinct. This shows predators maintaining species diversity.
Option (3) Predators in nature are prudent, since a predator that overexploits its prey may itself become extinct for lack of food. — Incorrect. Prudent predation is about a predator not overexploiting its prey, so that it does not lose its own food supply. The experiment removed the predator; it did not test overexploitation.
Option (4) Predators keep prey populations under control, which is the basis of biological control methods in agricultural pest control. — Incorrect. Controlling prey numbers is a real role, and it is the basis of biological pest control. But the result of this experiment was the extinction of many species, not a rise in the numbers of one prey.
NCERT Extract:
Population Interactions – “… Besides acting as ‘conduits’ for energy transfer across trophic levels, predators play other important roles. They keep prey populations under control. … Predators also help in maintaining species diversity in a community, by reducing the intensity of competition among competing prey species. In the rocky intertidal communities of the American Pacific Coast the starfish Pisaster is an important predator. In a field experiment, when all the starfish were removed from an enclosed intertidal area, more than 10 species of invertebrates became extinct within a year, because of interspecific competition.”