Ecology

Choose the Correct Answer

Correct Answer : Option b

Explanation
Pair 1 is correct: In a forest ecosystem, large sized trees are the producers, which are less in number and so form a narrow base. The trees support a large number of herbivores like insects, birds, frogs, etc. including several species of animals that feed upon leaves, fruits, flowers, bark, etc. of the trees. They are larger in number than trees and hence form a middle broad level. The secondary consumers like predatory birds (hawks, eagles, etc.), foxes, snakes, lizards, etc. are less in number than herbivores while top carnivores like lion, tiger, etc. are still smaller in number making the pyramid gradually narrow towards apex. So the pyramid assumes a spindle shape with narrow on both sides and broader in the middle.

Pair 2 is correct: In a parasitic food chain, for example, the producers like a few big trees offer food to quite a lot of frugivorous birds which are the herbivores and more in number than trees. The birds harbor and sustain a good number of ecto-parasites like lice, bugs, etc., while a greater number of hyperparasites like bugs, fleas, microbes, etc. feed upon them. This when graphically represented form an inverted pyramid.

Pair 3 is not correct: In contrast, in a pond ecosystem, the pyramid of biomass is inverted as the standing crop of phytoplanktons, the major producers, at any given time make up less biomass than the consumers, such as fishes and insects. As with inverted pyramids of numbers, the inverted biomass pyramid is not due to a lack of productivity from the primary producers, but results from the high turnover rate of the phytoplankton. The phytoplanktons are consumed rapidly by the primary consumers, which minimizes their biomass at any particular point in time. However, since phytoplanktons reproduce quickly, they are able to support the rest of the ecosystem. One problem with pyramids of biomass is that they can make a trophic level appear to contain more energy than it actually does. For example, all birds have beaks and skeletons, which despite having mass are not typically digested by the next trophic level.