The Ecological Niche

An organism’s niche = the biotic and abiotic factors that the  organism needs in its habitat.

• We often focus on an organism’s role in its food chain (e.g. producer, predator, parasite, etc.) and might include more details like the specific food (e.g. leaf-eater, insectivore, grassland grazer  etc.).
• The abiotic factors that comprise an organism’s niche can be shown on a graph.
• Members of the same population (i.e. same species)  always have the same niche.
• So, the niche of a population is genetically-determined, not learned.
• Successful organisms are always well-adapted to their niche, so a niche can also be thought of as all thebiotic and abiotic factors to which members of a population are adapted.
• Identifying the different niches in an ecosystem helps us to understand the interactions between populations.

The niche concept is summarised in the competitive  exclusion principle:  Two species cannot coexist in the same habitat if they have the same niche.

Species with narrow niches are called specialists.

• Many different specialists can coexist in the same habitat because they are not
  competing, so this can lead to high diversity.
• Specialists rely on a constant supply of their food, so are generally found in abundant, stable habitats such as  the tropics.

Species with broad niches are called generalists.

• Generalists in the same habitat will compete, so  there can only be a few, so this can lead to low diversity.
• Generalists can cope with a changing food supply (such as seasonal changes) since they can switch from one food to another or even one habitat to another (for example by migrating).

The competitive exclusion principle may apply whenever a new species is introduced to an ecosystem.