Which of the following statements is not true about "ecological niche" ?
- (a)Dominant species occupy extensive and broader ecological niche.
- (b)Number of species becomes large in ecological niche of natural ecosystem, if resources are sufficient.
- (c)Number of species becomes small in ecological niche, if resources are sufficient.
- (d)Dominance of single species becomes minimum if the resource distribution is equitable in a habitat.
Correct — C, 'Number of species becomes small in ecological niche, if resources are sufficient.' This is the statement that is not true, and the question asks for exactly that. Abundant resources do the opposite of shrinking species numbers: when food, light, water, nesting space and nutrients are plentiful, competition for any single resource is relaxed, no species is forced out, and the resource axes can be finely subdivided among many co-existing species — resource partitioning. That is why species-rich systems such as tropical rainforests, coral reefs and the Terai grasslands of Uttar Pradesh are exactly the systems with high productivity and a long, uninterrupted supply of resources, while resource-poor systems (deserts, high alpine zones, polar regions) carry few species. Statement (c) also contradicts statement (b) word for word, so one of the two must be false; since (b) is the ecologically standard claim, (c) is the untrue one.
- (a)Dominant species occupy extensive and broader ecological niche. — True, so it cannot be the answer. In community ecology a dominant species is one that contributes most of the biomass or abundance and exerts the strongest control on community structure. Such species are typically broad-niched generalists — tolerant of a wide range of conditions and able to use many resources — which is precisely what lets them spread across a large part of the habitat. Narrow-niched specialists, by contrast, are usually restricted and rarely dominant.
- (b)Number of species becomes large in ecological niche of natural ecosystem, if resources are sufficient. — True, so it is not the answer — and it is the direct contradiction of option (c). Where resources are sufficient, competitive pressure eases, niches can be partitioned along more dimensions (feeding height, prey size, time of activity, microhabitat), and more species coexist. This is the standard explanation for the higher species richness of productive, stable, resource-rich ecosystems.
- (d)Dominance of single species becomes minimum if the resource distribution is equitable in a habitat. — True, so it is not the answer. If resources are spread evenly across a habitat rather than concentrated in patches, no single species can monopolise a resource-rich core and convert that advantage into dominance. The community then shows high evenness and low dominance — which is exactly what dominance and evenness indices (Simpson's index, Shannon's index) measure.
An ecological niche is not a place — it is the complete set of conditions and resources under which a species can maintain a viable population, together with the functional role it plays in the community. The classic contrast is that a habitat is a species' 'address' while its niche is its 'profession'. Joseph Grinnell (1917) framed the niche spatially, Charles Elton (1927) framed it functionally as the organism's role in food webs, and G. Evelyn Hutchinson (1957) unified both as an n-dimensional hypervolume, distinguishing the fundamental niche (where a species could live in the absence of competitors) from the realised niche (the smaller space it actually occupies once competitors are present).
This is a 'not true' item, so the instinct to hunt for the most familiar-sounding statement is a trap — you must find the false one. The shortcut is structural: options (b) and (c) make opposite claims about the same condition ('if resources are sufficient'), so the answer is bound to be one of them and options (a) and (d) can be set aside. Then apply the general rule that more resources support more species, not fewer — which makes (c) the false statement. Because two species cannot occupy exactly the same niche indefinitely (Gause's competitive exclusion principle), extra resources are absorbed by adding species and splitting niches, not by squeezing them out.
- Habitat = the physical space a species occupies; niche = its functional role plus the full range of conditions and resources it uses. Grinnell (1917) emphasised the spatial sense, Elton (1927) the functional/trophic sense.
- G. Evelyn Hutchinson (1957) defined the niche as an n-dimensional hypervolume and separated the fundamental niche from the realised niche, which is narrowed by competition.
- Gause's competitive exclusion principle: two species competing for exactly the same limiting resource cannot coexist indefinitely — one is eliminated or the niches diverge.
- Resource partitioning lets competitors coexist by dividing a resource. R. H. MacArthur's classic 1958 study showed five warbler species feeding in different zones of the same spruce trees.
- Generalists have broad niches and wide distributions; specialists have narrow niches, are more vulnerable to disturbance and are the first to be lost when a habitat is degraded.
(b) and (c) are opposite claims about the same condition, so the false statement must be one of them — and abundant resources support more species, not fewer.
- Reading a 'which is NOT true' stem as 'which is true' — UPPSC sets at least one negative-stem ecology item almost every year.
- Treating habitat and niche as synonyms; the niche includes the functional role, not just the physical space.
- Confusing dominant species (most abundant, greatest biomass) with keystone species (disproportionately large effect relative to abundance) — a keystone species is often rare.
UPPSC tests ecology through 'which statement is NOT true' options built around niche, diversity and succession, and often plants two directly contradictory options so the answer is decidable without recall. UPSC prefers a definitional single-line item ('which term describes both the physical space and the functional role?') or a statements-based item on protected-area categories.
Which one of the following terms describes not only the physical space occupied by an organism, but also its functional role in the community of organisms?
- (a) Ecotone
- (b) Ecological niche
- (c) Habitat
- (d) Home range
Answer(b) Ecological niche
The definitional half of the same concept — UPSC asks what an ecological niche is (space plus functional role), which is the exact idea UPPSC then tests through four statements about niche breadth and species number.
Which of the following statement is NOT true ?
- (a) Species diversity increases from equator towards poles.
- (b) Tropics harbour more species than temperate areas.
- (c) Greatest biodiversity occurs in Amazonean rain forest.
- (d) Species diversity decreases from temperate areas towards poles.
Answer(a) Species diversity increases from equator towards poles.
The same negative-stem drill on the same idea — resource-rich, productive, stable environments carry more species. There the trap is the direction of the latitudinal gradient; here it is the direction of the resources–species relationship.
- practice — not a real PYQ
The principle that two species competing for exactly the same limiting resource cannot coexist indefinitely in the same habitat is known as :
- (a)Allen's rule
- (b)Gause's competitive exclusion principle
- (c)Liebig's law of the minimum
- (d)Hutchinson's hypervolume rule
Answer(b) Gause's competitive exclusion principle — demonstrated by G. F. Gause with Paramecium cultures. Liebig's law concerns the single most limiting nutrient, and Allen's rule concerns body-appendage size and climate.
- practice — not a real PYQ
The part of a species' fundamental niche that it actually occupies in the presence of competitors is called its :
- (a)Habitat
- (b)Home range
- (c)Realised niche
- (d)Ecotone
Answer(c) Realised niche — the fundamental niche is what the species could occupy without competition; competition compresses it into the smaller realised niche. An ecotone is a transition zone between two communities.