Ecological Niche and Competitive Exclusion

Ecological Niche

• Definition: The role an organism has in its ecosystem, including the conditions required for its survival.
  • Comprises:
  • Food sources
  • Feeding activities
  • Special habitat
  • Reproduction mechanisms
  • Relationships with other organisms

Types of Niche

• Fundamental Niche:
  • The potential role an organism could fulfill without competition from other species.
• Realised Niche:
  • The actual ecological niche a species occupies after accounting for competition and interactions with other organisms.
• Specialised Niche:
  • Adaptation of a species to a narrower range of conditions, resources, and interactions.

Niche Differentiation

• Definition: A process where competing species utilize the environment differently, allowing coexistence.

  • Examples include:
  • Consuming different food sources
  • Utilizing different areas of habitat
  • Being active at different times (diurnal vs nocturnal)

• Key Point: No two organisms can occupy the same niche simultaneously.

  • Actions considered: What an organism does, where it does it, and when it does it.

• Realised Niche: Where we find a species.

• Fundamental Niche: Where a species could be found, often reduced by competition.

Competitive Exclusion

• Definition: The principle stating that two species competing for the same resources cannot coexist if one has even a slight advantage.
  • Proposed by Gregory Gause through experiments with two paramecium species (designated A and B).
  • Findings:
  • A initially dominated B but later, under resource competition, B drove A to extinction.
  • Altering environmental parameters allowed A to survive.
  • Conclusion: Competitive exclusion law is only valid if ecological factors are constant.

Resource Partitioning

• Definition: The divided use of resources allowing coexistence among multiple species in an ecosystem.
  • Comparison with competitive exclusion:
  • Competitive exclusion leads to local extinction of one species, while resource partitioning enables coexistence through niche differentiation (e.g., feeding at different times).

Evolutionary Outcomes

• In competition scenarios where two species share identical resource requirements:
  • The species with even a slight advantage will thrive, while the other will die off due to lack of resources.
  • Competitive exclusion informs our understanding of species diversity, reducing the number of species that can coexist.

Case Study: Cane Toads in Australia

• Introduced in 1935 to control pests but led to unintended consequences:
  • Killed native predators of pests through predation and poisoning.
  • Competed for resources with native species, resulting in competitive exclusion and dramatically reduced populations of native insects, frogs, reptiles, and others.

Adaptation Strategies in Coexistence

• When species share the same niche:
  • They may adapt by slightly altering their niche, such as:
  • Hunting at different times or places.
  • Utilizing slightly different food sources.

Considerations for Introducing New Species

• When introducing a new species:
  • Analyze competition for resources.
  • Assess potential for killing or overexploiting organisms similar in niche due to resource competition.

Experiment for Understanding Competition

1. Choose two species of microorganisms sharing a niche.
2. Place species A into a resource container and do the same for species B, keeping resource quantities constant.
3. Place both species in a single container with equal amounts and types of resources.
4. Observe the competition over time.