Ecology: Ecosystem, biome and biosphere

NCERT calls an ecosystem a functional unit of nature in which organisms interact among themselves and with the physical environment. Forests, grasslands and deserts are terrestrial examples; ponds, lakes, wetlands, rivers and estuaries are aquatic examples. Crop fields and an aquarium are given as man-made ecosystems, because people create and maintain them, yet they still have producers, consumers, decomposers and abiotic parts.

Charles Elton, the British ecologist, described food chains, the 'food cycle' (now called the food web) and the pyramid of numbers in 'Animal Ecology' (1927); ecological pyramids are therefore often called 'Eltonian pyramids'. A.G. Tansley coined the term 'ecosystem' in 1935, Lindeman developed the trophic-dynamic concept and the 10 per cent law in 1942, and Eugene Odum popularised ecosystem ecology through his textbooks.

Mesopredator release describes the rise of mid-sized predators (mesopredators) once a larger predator that suppressed them is lost. The classic study by Crooks and Soulé (1999) in the fragmented canyons of southern California showed that where coyotes were absent, cats and other mesopredators increased and scrub-breeding birds declined. It is a form of trophic cascade and an argument for conserving apex predators.

Statements 1 and 2 are correct. Gyps vultures are extremely sensitive to diclofenac; residues in carcasses of treated cattle cause visceral gout and kidney failure, which drove declines of over 95 per cent in some species from the 1990s. India banned veterinary diclofenac in the 2000s. Statement 3 is wrong: the Health Ministry's notification S.O. 3448(E) of 31 July 2023 prohibited the manufacture, sale and distribution of ketoprofen and aceclofenac and their formulations for animal use only, under section 26A of the Drugs and Cosmetics Act, 1940.

Three portions are not passed on. Energy in uneaten grass goes to the detritus pathway; energy in faeces (egested, never assimilated) also goes to decomposers; energy spent in respiration is lost as heat. Only the energy stored in the rabbits' new tissue (their secondary production) is available to a predator, which is why only a small fraction — on average about 10 per cent — moves up each trophic level.

Statements 1 and 3 are correct. In a climax, gross production is roughly balanced by community respiration (P/R close to 1), so energy captured and energy used are in near equilibrium. The community is self-perpetuating: its species replace themselves, so composition stays steady while the environment is unchanged. Statement 2 is wrong: Odum (1969) showed that net community production (the yield) is high in young, developing stages and small or close to zero at maturity, because almost all production is used up in maintaining the large biomass.

A parasitoid is an organism, usually an insect such as a wasp or a fly, whose larva develops in or on a single host and eventually kills it — unlike a true parasite, which usually does not kill its host. Trichogramma species are egg parasitoids mass-reared in India (for example under ICAR–NBAIR guidance) for biological control of lepidopteran pests such as sugarcane borers and cotton bollworms.

Statements 1 and 2 are correct. Lantana camara forms dense, often fire-prone thickets in disturbed Indian forests; its shade, competition and allelopathic chemicals suppress the seedlings of native trees and grasses, so regeneration stalls, which matches the inhibition model of succession. Prosopis juliflora, introduced for fuel and to check desertification, forms near-monocultures that crowd out native species; UPSC asked about this in 2018. Statement 3 is wrong: invasives often arrest or deflect succession rather than speed it up.