Ecological Niche Concept

                                         Ecological niche is a term used to denote the position of a species within an ecosystem. The term includes all of the interactions between a species and the biotic and abiotic environments. It is the functional role/position of an organism within an ecological community. The term ecological niche was coined by the naturalist Joseph Grinnell in 1917.

                                        Ecological niche is the total way of life of a species or functional role (its profession) in an ecosystem. It involves all the physical, chemical and biological conditions. Niche focuses on the environmental factors that influence growth, survival and reproduction of a species.

                                       At present an ecological niche is characterized in relation to 3 principal axes that combine most of the relevant variables of the environment: a habitat axis (climatic and physico-chemical variables), a trophic axis (feeding relationships) and a temporal axis (mode of use of food resources and of land cover as a function of time).

Definition of niche concept

Charles Elton (1927) defined niche as the status of an organism in its community to indicate what is doing and not merely what it looks like.

Hutchinson (1944-58) defined niche as the sum of all the environmental factors acting on the organism.

Odum (1971) defined the niche of a species as its role in the ecosystem. He referred the habitat as address of the species and niche as the profession of a species.

Difference between habitat and niche

Habitat is the living place of an organism. In other words habitat is a suitable environment or habitable place for a species.

But niche is the role of a species in a community and also its relationship with its environment. Niche is the ecological function of a species.

Objective of niche concept

The niche concept was formulated to determine the role of organisms in a community (Hutchinson, 1957).

Types of niches

Fundamental niche – a species’ niche is usually less extensive, when competitors and predators present. Its niche in the absence of these organisms is known as its fundamental niche.

Realized niche – It is the portion of the fundamental niche that a species actually occupies.

Functional niche – refers to a species position in food webs and trophic chains.

Spatial niche – the niche occupied by a species is favourable to it because it furnishes a suitable substratum and microclimate to it.

Trophic niche – two species living in the same habitat, may have different food habits. For example elephant, rabbit and deer are three types of herbivores living in a forest habitat. But each of them occupies different trophic niches. Elephant feeds on large trees; deer feeds on shrubs and rabbit feeds on herbs and grasses.
Ecological niche - the position of a species in a community.
Food niche - the food choice of a species in a trophic level.
Time niche -animals tend to be active at different times of the day e.g.,diurnal/nocturnal.
Place niche -different species foraging in different ways and in different places.

Joseph Grinnell’s concept (1917) of niche as habitat

Grinnell referred niche as an organism’s physical environment. It is the ultimate distributional unit. No two species in the same general territory can occupy the same ecological niche for long time. Grinnell’s niche is now referred as spatial niche.

Eltonian’s concept (1927) of niche as functional unit

Charles Elton defined the niche as the ecological role the organism plays in the community. He considered niche as its occupation. It refers to how an organism transforms energy, behaves, responds to and modifies its physical and biotic environment.

Hutchinson’s concept (1957) of niche as multidimensional hypervolume space

Hutchinson suggested that niche could be modelled as an imaginary space with many dimensions. Each dimension or axis represents the range of an environmental condition or resource that is required by the species i.e. abiotic or environmental factors axis, food resource axis and function of time axis.

Niche overlap – the degree to which two species share niche space. This is assumed to be proportional to the degree of competition. In the absence of competition, niches do not overlap. But under intense competition, there is greater overlap.

Niche breadth – it is a product of niche overlap. The narrower the niche, the more specialized the species.

Niche separation – It is the distance between the mean resource use curves for two species. It may be close or far.

Significance of ecological niches

1.    By occupying different spatial or trophic niches, animals escape from competition.

2.    The niche occupied by a species is favourable to it because it contributes a suitable substratum and microclimate.

3.    The segregation of each species into different niches permits the full exploitation of the available resources.

4.    The segregation into niches avoids confusion of activities between organisms in the community. It gives more orderly and efficient life patterns for each species.

5.    Overlapping niches leads to competition between two species and in the competition one species will be replaced by another – competitive exclusion principle.