Brent Cornell

    
An ecological niche describes the functional position and role of an organism within its environment

• It consists of all physical and biological conditions which determine the organism’s survival and reproductive prospects

An ecological niche will be comprised of various components, including:

• The habitat in which an organism lives
• The activity patterns of the organism (e.g. periods of time during which it is active)
• The resources it obtains from the environment (e.g. food sources, territorial boundaries, etc.)
• The interactions that occur with other species in the community (e.g. predator prey relationships, competition, etc.)

    
If two distinct species share an identical niche, there will be interspecific competition for available space and resources

• This competition between the two species will result in the fitness of one being lowered by the presence of the other
  
• Inevitably, the less well-adapted species will struggle to survive and reproduce – it will eventually be eliminated from the niche

Interspecific competition within a shared niche will typically prompt one of two responses:

• Competitive exclusion – One species uses the resources more efficiently, driving the other species to local extinction
• Resource partitioning – Both species alter their use of the habitat to divide resources between them (i.e. niche separation)

Niche Differentiation

    
Some species may not be able to occupy their entire niche due to the presence or absence of other species

• Hence a species may occupy a smaller subset of their niche than is theoretically possible (fundamental vs realised niche)

Fundamental Niche

A fundamental niche is the entire set of conditions under which an organism can survive and reproduce (where it could live)

• It is the theoretical habitat and may not be fully occupied due to the presence of competing species
• In a rocky shore environment, the Chthalamus barnacle can potentially occupy the entire rocky shore (if in isolation)

Realised Niche

A realised niche is the set of conditions used by an organism after including interactions with other species (where it does live)

• It is the actual habitat that is completely occupied by an organism in the presence of competing species
• In a rocky shore environment, the Chthalamus barnacle only occupies regions where the Semibalanus barnacle is absent

Fundamental vs Realised Niche – Rocky Shore Data