Population interactions are ecological relationships between individuals of different species living in the same habitat. These interactions influence the survival, growth, reproduction, and distribution of organisms. Depending on whether the interacting species benefit, are harmed, or remain unaffected, population interactions are classified into mutualism, competition, predation, parasitism, commensalism, and amensalism.
Competition (−/− Interaction)
Definition
Competition is an interaction in which both species are harmed (-/-) because they compete for the same resource.
Resources may include:
- Food
- Water
- Space
- Light
- Nutrients
Darwin’s View
- Darwin considered competition (struggle for existence) as a major driving force of organic evolution.
- According to him, only the fittest survive (“Survival of the Fittest”).
Important Facts
1. Competition is not limited to closely related species.
Wrong belief: Only closely related species compete.
Correct: Even unrelated species can compete.
Example:
- Flamingoes and fishes compete for zooplankton in South American lakes.
2. Resources need not always be limited.
Competition can occur even when food is abundant.
This is called:
Interference Competition
- One species directly interferes with another.
- The presence of one species reduces the feeding efficiency of the other.
Even if:
- Food is abundant
- Space is abundant
competition may still occur.
Best Definition of Competition
Competition is a process in which
The fitness (intrinsic rate of increase, r) of one species decreases in the presence of another species.
Fitness
Means the ability to survive and reproduce.
r (Intrinsic Rate of Increase)
Represents how fast a population can grow.
Competition lowers the value of r.
Competitive Exclusion
Laboratory experiments show that
When resources are limited,
➡️ The competitively stronger species eliminates the weaker species.
Example 1: Galápagos Tortoise
- Abingdon tortoise lived on Galápagos Islands.
- Goats were introduced.
- Goats were better browsers.
- Tortoise became extinct.
Reason:
- Strong competition for vegetation.
Competitive Release
Definition
When a competitively superior species is removed,
the weaker species expands its geographical distribution.
This phenomenon is called
Competitive Release
Example 2: Connell’s Barnacle Experiment
Two barnacle species:
- Balanus
- Chthamalus (correct spelling; NCERT may print Chathamalus)
Results:
- Balanus is larger and competitively superior.
- It occupies the intertidal zone.
- Chthamalus is pushed into higher zones.
When Balanus is removed,
→ Chthamalus spreads into the intertidal region.
This demonstrates competitive release.
Herbivores vs Carnivores
Competition affects:
- Herbivores → More
- Plants → More
- Carnivores → Less
Gause’s Competitive Exclusion Principle
Statement
Two closely related species competing for the same limiting resources cannot coexist indefinitely. The competitively inferior species will eventually be eliminated.
Condition
This principle is mainly true when:
✅ Resources are limiting.
If resources are abundant, coexistence may still be possible.
Modern View
Recent studies suggest that
Competition does not always end in extinction.
Species may evolve ways to coexist.
Resource Partitioning
Definition
When competing species use the same resource in different ways, competition decreases.
They may differ in:
- Feeding time
- Feeding place
- Feeding method
This allows coexistence.
Example: MacArthur’s Warblers
- Five closely related warbler species lived on the same tree.
- They survived together because:
- Each searched for insects in different parts of the tree.
- Their feeding behaviour differed.
This is called resource partitioning.
NEET Important Examples
| Example | Concept |
|---|---|
| Flamingoes vs Fishes | Competition between unrelated species |
| Abingdon Tortoise vs Goats | Competitive exclusion in nature |
| Balanus vs Chthamalus | Competitive release |
| Five Warbler Species | Resource partitioning |
One-Line Revision
- Competition = (-/-) interaction
- Darwin → Survival of the fittest
- Competition can occur between related or unrelated species
- Resources need not be limiting
- Interference competition → Competition despite abundant resources
- Fitness decreases → r decreases
- Gause’s Principle → Two species competing for the same limiting resource cannot coexist indefinitely
- Competitive release → Removal of superior competitor expands weaker species’ range
- Resource partitioning → Different feeding habits reduce competition
- MacArthur → Five warbler species coexist by resource partitioning
- Connell → Balanus excludes Chthamalus
- Goats caused extinction of the Abingdon tortoise
NEET Memory Trick
“FGBCW”
- F → Flamingoes vs Fishes (unrelated competition)
- G → Gause’s Competitive Exclusion Principle
- B → Balanus excludes Chthamalus
- C → Competitive Release
- W → Warblers → Resource Partitioning
Sarvan sir- Chemistry For All 