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Biology · 2026 · 4 marks
CBSE 2026 · Region 1 · Set 2 · Q30
The diagram below shows the distribution of two barnacle species, Chthamalus and Balanus on a rocky sea shore. When Balanus is experimentally…
The diagram below shows the distribution of two barnacle species, Chthamalus and Balanus on a rocky sea shore. When Balanus is experimentally removed, Chthamalus expands its range in lower intertidal zone.
Identify and define the ecological phenomenon demonstrated by this observation.
State the principle that explains the elimination of one species.
(b)
Two different species can compete for the same resource. Give another example of it.
(c)
How do species avoid competition in nature ? Explain with an example.
Marking-scheme solution
(a)
-Competitive release.
-A species whose distribution is restricted to small geographical area due to the presence of competitively superior species expands its distributional range when competing superior species is removed.
OR
(a)
Gause’s competitive exclusion principle, states that two closely related species cannot co-exist indefinitely and the competitively inferior one will be eliminated eventually.
(b)
In shallow south American lakes visiting flamingos and resident fishes compete for common food Zooplankton / any other correct example
(c)
By “Resource partitioning”
They choose different times for feeding or different foraging patterns e.g. Five closely related species of warblers avoid competition and coexist due to behavioural differences in their foraging activities / any other correct example.
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