The entire sequence of communities that successively change in a given area are called:
- (a)Ecological succession
- (b)Sere
- (c)Climax community
- (d)Parallel evolution
Correct — B, Sere. A sere is the whole series of communities that replace one another at one site — from the pioneer community on a bare substrate, through the intermediate (seral) communities, up to the climax community. Note the exact wording of the stem: it asks for the name of the entire sequence of communities. That sequence is the sere; the process that drives it is ecological succession; the community sitting at the end of it is the climax.
- (a)Ecological succession — This is the tempting near-miss. Succession is the process — the orderly, directional change by which one community replaces another over time. The sere is the product of that process: the actual series of communities. Succession is the verb, the sere is the noun.
- (c)Climax community — The climax is only the last stage of a sere — the relatively stable, self-perpetuating community in equilibrium with the local climate and soil. It is one community, not the whole sequence the question asks about.
- (d)Parallel evolution — An evolutionary concept, not an ecological one: related lineages independently evolving similar features under similar selection pressures. It says nothing about communities replacing one another in a given area.
Ecological succession is the directional change in the species composition of a community at a place over time. The complete series of communities produced at that place is the sere; each community within it is a seral stage or seral community; the terminal, self-perpetuating stage is the climax community. Getting full marks on this family of questions is entirely a matter of keeping four words apart: succession (process), sere (whole series), seral stage (one link), climax (last link).
Seres are named after the habitat where succession begins — hydrosere in a pond or lake, xerosere in dry conditions, lithosere on bare rock, psammosere on sand, halosere in saline conditions. Succession is also classed by starting point: primary succession begins on a lifeless substrate with no soil (bare rock, new lava, fresh sand), and is slow because soil has to be built first; secondary succession restarts on land that already has soil after a disturbance such as fire, flood or the abandonment of a field, and is therefore much faster.
- Sere = the entire sequence of communities at a site, from the pioneer community to the climax
- Succession = the process of change; seral community = one stage within a sere; climax = the final, stable, self-perpetuating community
- Seres named by starting habitat: hydrosere (water), xerosere (dry), lithosere (bare rock), psammosere (sand), halosere (saline)
- Primary succession starts where there is no soil and is slow; secondary succession starts on existing soil after a disturbance and is faster
- Lichens are the typical pioneers on bare rock — they weather the rock and help form the first soil
- Bare substrate — rock, new lava or sand; no soil yet
- Pioneer community — lichens and mosses; they weather the rock and build the first soil
- Seral communities — herbs, then grasses, then shrubs, as soil deepens
- Climax community — stable and self-perpetuating; e.g. a mature forest
- All of stages 1 → 4 taken together = the SERE (the process moving along the chain = ecological succession)
The stem asks for the name of the whole chain, not for the process that moves along it and not for its last box — so the answer is 'sere'.
- Answering 'ecological succession' because the stem contains the word 'successively' — succession is the process, the sere is the sequence of communities
- Confusing 'sere' (the whole series) with 'seral community' (a single stage inside it)
- Treating the climax as fixed forever — it is stable only relative to the prevailing climate and can shift if the climate or disturbance regime changes
MPPSC asks the definition directly and hides the answer behind a near-synonym, as here. UPSC asks it applied — why grasses hold a site against trees, or what makes lichens capable of starting succession on bare rock — so learn the mechanism, not just the vocabulary.
Lichens, which are capable of initiating ecological succession even on a bare rock, are actually a symbiotic association of
- (a) algae and bacteria
- (b) algae and fungi
- (c) bacteria and fungi
- (d) fungi and mosses
Answer(b) algae and fungi
The first link of the same chain — the pioneer community that starts a lithosere, the sequence MPPSC is asking you to name.
In the grasslands, trees do not replace the grasses as a part of an ecological succession because of
- (a) insects and fungi
- (b) limited sunlight and paucity of nutrients
- (c) water limits and fire
- (d) None of the above
Answer(c) water limits and fire
Same concept from the other end — what stops a sere from advancing to its expected climax stage.
- practice — not a real PYQ
Succession that begins in a water body such as a pond or a lake is called:
- (a)Hydrosere
- (b)Xerosere
- (c)Lithosere
- (d)Psammosere
Answer(a) Hydrosere — seres are named after the habitat in which succession begins.
- practice — not a real PYQ
Secondary succession proceeds faster than primary succession mainly because:
- (a)the climate is always more favourable
- (b)soil is already present at the site
- (c)no pioneer species are involved
- (d)it does not end in a climax community
Answer(b) soil is already present at the site — primary succession must first build soil from bare substrate.