Transition zone of varied natural vegetation occupying the boundary between two adjacent and differing plant communities is known as

Correct — B, ecotone. An ecotone is the transition belt where two adjacent communities meet and blend, so it carries species from both sides plus species that live nowhere else. Because the conditions change steeply across it, the number of species and often the population density are higher in the ecotone than in either community it separates — the edge effect, and the species restricted to that band are called edge species. Mangroves between land and sea, an estuary between a river and the ocean, and the grassland strip between forest and prairie are the standard examples. The definition in the stem is the definition of an ecotone almost word for word: a transition zone at the boundary between two adjacent and differing plant communities.

• (a)ecological succession — Succession is change over time, not a place on a map. It is the orderly replacement of one community by another at the same site, running from a pioneer community through seral stages to a stable end point.
• (c)ecological niche — A niche is the functional role an organism plays — what it eats, what eats it, when it is active, what conditions it tolerates — together with the space it occupies. It describes a species, not a boundary between communities. UPSC asked precisely this distinction in 2013.
• (d)climax — The climax is the terminal, self-perpetuating community that succession settles into once it is in equilibrium with the local climate and soil. It is the last stage of the process in option (a), not a transition zone.

Four terms from a single chapter are set against one another here, and each answers a different question. Ecotone answers where, succession answers how a community changes over time, climax answers what it changes into, and niche answers what a species does. Once each word is pinned to its own question the option list sorts itself. An ecotone can be sharp, like the line where a mangrove gives way to open water, or broad, like the several hundred kilometres over which the taiga thins into tundra.

The edge effect is the fact worth carrying out of this item, because that is what examiners build the harder version around: an ecotone typically holds more species than either neighbouring community, since organisms from both sides overlap there and some species specialise in the margin itself. That richness is also why ecotones are fragile — a small shift in the boundary squeezes species that have nowhere else to go, which is the argument made about mangrove belts under sea-level rise.

• An ecotone is the transition zone between two adjacent ecological communities, holding species from both plus its own edge species.
• The edge effect describes the greater species richness and often greater population density found in the ecotone.
• Mangroves, estuaries and the grassland belt between forest and prairie are standard ecotone examples.
• Ecological succession is the sequence of communities at one site over time, ending in the climax community.
• An ecological niche is a species' functional role together with the physical space it occupies, which is what separates it from a habitat.

• Reading ecotone as a synonym for ecosystem or habitat.
• Mixing up climax, the end state, with succession, the process that reaches it.
• Defining a niche as merely the place where a species lives, which is a habitat.

Asked as a definition-to-term match, with the three other terms from the same ecology chapter used as distractors — the standard shape for this topic.

• practice — not a real PYQ

  The greater richness of species found where two adjacent communities meet is known as

  • (a)the founder effect
  • (b)the edge effect
  • (c)competitive exclusion
  • (d)the bottleneck effect

  Answer(b) the edge effect — the ecotone holds species from both communities plus edge species of its own.

• practice — not a real PYQ

  The stable, self-perpetuating community that a site reaches at the end of ecological succession is called the

  • (a)pioneer community
  • (b)sere
  • (c)climax community
  • (d)ecotone

  Answer(c) climax community — it is in equilibrium with the prevailing climate and soil.