Read How Species Compete or Coexist
Competition arises when species depend on a limiting shared resource; outcomes range from exclusion to coexistence.
Competition is the central idea in this question pattern. Identify the condition in the stem before applying the method below.
When exclusion occurs
Gause’s principle predicts that species competing for the same limiting resource cannot coexist indefinitely under constant conditions. The inferior competitor is excluded. Balanus excluding Chthamalus from part of a shore is a classic example.
How coexistence persists
Natural communities can reduce overlap through resource partitioning—using resources at different times, places or in different ways. This helps explain why laboratory exclusion can be more obvious than in nature.
Read allelopathy from the response
Allelopathy is a chemical effect of one plant on another. Compare species and plant parts on the graph: Lantana leaf extract affects maize, finger millet and tef differently, so never generalise from one crop. The tested maize and finger millet responses support cultivation after Lantana removal; the tef result does not show a positive benefit.
Read allelopathy species by species
Allelopathic chemicals need not affect every species or organ equally. Compare each crop's root and shoot response with its water control: Lantana extract has differential effects, while maize and finger millet retain responses consistent with cultivation after removal. Do not infer a uniform benefit for tef. Choose A and C.
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- ✓Competition is intensified by limited shared resources.
- ✓Gause: same niche competitors cannot coexist indefinitely.
- ✓Resource partitioning reduces direct overlap.
- ✓Allelopathic effects can differ by species, concentration and plant part.
- ✓Interpret each plotted response against its control before recommending a crop.
- ✓Allelopathic effects must be interpreted separately for each species and measured response.
Resource partitioning is not elimination; it is a way of reducing competition.
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