Competition (-/-) and Gause's Competitive Exclusion Principle
Biology · Organisms and Populations · NEET
Competition is a (-/-) interaction: both species lose because their fitness (measured by 'r', the intrinsic rate of increase) drops when the other is present. Gause's Competitive Exclusion Principle says two closely related species competing for the SAME limiting resources cannot co-exist forever, and the weaker competitor is eliminated. Memory hook: "Same resource, one loses the fight" - and remember the word is SAME (not different) resources, which is exactly where NEET sets its trap.
Both competitors lose fitness (-/-). When the shared resource is limiting, the superior species rises while the inferior species is excluded - Gause's Competitive Exclusion Principle.
Your doubts, answered
Does competition happen only between closely related species?
No. NCERT says this is a common belief but is not entirely true. Even totally unrelated species can compete for the same resource. The classic NCERT example: in some shallow South American lakes, visiting flamingoes (a bird) and resident fishes compete for their common food, the zooplankton. So do not answer 'only closely related species' in an exam.
Do resources have to be limited for competition to occur?
Not always. In interference competition, one species reduces the feeding efficiency of another just by its interfering or inhibitory presence, even when food and space are abundant. That is why NCERT defines competition by its RESULT: the fitness (r) of one species is significantly lower in the presence of another species.
What does Gause's Competitive Exclusion Principle actually state?
It states that two closely related species competing for the SAME resources cannot co-exist indefinitely, and the competitively inferior one will be eliminated eventually. NCERT adds an important condition: this may be true if resources are limiting, but not otherwise. The word 'same' is critical - 'different resources' is a wrong version NTA plants in traps.
What is competitive release?
It is evidence of competition in nature. A species whose distribution is restricted to a small area because a competitively superior species is present will dramatically expand its range when that competitor is experimentally removed. This 'release' proves competition was limiting the species all along.
How is competition different from predation and parasitism in signs?
Competition is (-/-): both species are harmed. Predation and parasitism are (+/-): only one benefits (predator or parasite) while the other (prey or host) is harmed. A common NEET question gives 'both species negatively impacted' and asks which interaction - that is competition, NOT predation.
Who proposed the Competitive Exclusion Principle?
G. F. Gause. Darwin spoke of the struggle for existence and survival of the fittest and believed interspecific competition drives evolution, but the exclusion PRINCIPLE itself is credited to Gause, based on his laboratory experiments. Verhulst and Pearl are linked to logistic growth, and MacArthur to the warbler resource-partitioning study - do not mix these names up.
⚠️ The NEET trap ✗ Gause's principle says species competing for DIFFERENT resources cannot co-exist. ✓ Gause's principle says species competing for the SAME (limiting) resources cannot co-exist indefinitely; the inferior competitor is eliminated. 🧠 NEET 2024 flipped 'same' to 'different' to make Statement I false. Also note the second common trap: HERBIVORES and plants are more adversely affected by competition than carnivores (NOT the other way round).
Real NEET questions
NEET 2016 (Phase 1)
Gause's principle of competitive exclusion states that:
A · More abundant species will exclude the less abundant species through competition
B · Competition for the same resources excludes species having different food preferences
C · No two species can occupy the same niche indefinitely for the same limiting resources ✓
D · Larger organisms exclude smaller ones through competition
Solution: Gause's Competitive Exclusion Principle states that two closely related species competing for the same limiting resources cannot co-exist indefinitely; the competitively inferior one is eliminated. This is equivalent to saying no two species can occupy the same niche indefinitely for the same limiting resources. Abundance and body size are not the deciding factors.
NEET 2016 (Phase 2)
The principle of competitive exclusion was stated by:
A · C. Darwin
B · G. F. Gause ✓
C · MacArthur
D · Verhulst and Pearl
Solution: The Competitive Exclusion Principle was stated by G. F. Gause, based on his laboratory experiments. Darwin discussed the struggle for existence; MacArthur studied warbler resource partitioning; Verhulst and Pearl gave the logistic growth equation. Keep these four names separated.
NEET 2024
Statement I: Gause's competitive exclusion principle states that two closely related species competing for different resources cannot exist indefinitely. Statement II: According to Gause's principle, during competition, the inferior will be eliminated. This may be true if resources are limiting. Choose the correct answer:
A · Both Statement I and Statement II are false.
B · Statement I is true but Statement II is false.
C · Statement I is false but Statement II is true. ✓
D · Both Statement I and Statement II are true.
Solution: Statement I is FALSE because Gause's principle concerns species competing for the SAME resources, not 'different' resources. Statement II is TRUE - the inferior competitor is eliminated, and NCERT adds this holds if resources are limiting. So Statement I false, Statement II true.
Solved Organisms and Populations NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Competition is (-/-): both interacting species are harmed because each lowers the other's fitness. (+/-) is used for predation and parasitism.
What is the difference between interference and exploitation competition?
In exploitation (resource) competition, species compete by using up a limited shared resource. In interference competition, one species directly reduces the feeding efficiency of another by its inhibitory presence, even when resources are abundant.
Give the NCERT example of Connell's barnacle experiment.
On rocky sea coasts of Scotland, the larger, competitively superior barnacle Balanus dominates the intertidal zone and excludes the smaller barnacle Chthamalus from it. This is direct field evidence of interspecific competition.
How do competing species co-exist instead of one being excluded?
Through resource partitioning. MacArthur showed five warbler species on the same tree co-existed by feeding on different parts and using different foraging behaviours, avoiding direct competition.
Are carnivores or herbivores more affected by competition?
In general herbivores and plants appear to be more adversely affected by competition than carnivores. NEET frequently reverses this to make a statement false.
