Ecological niche refers to the role or way of life of an organism in its biological community. The niche is a combination of where the organism lives (its habitat) and how it lives there (the physical and behavioural characteristics of the organism that enable it to survive and reproduce in the conditions of its habitat).
The ecological niche of an organism includes where it lives, its feeding habits, activity patterns (nocturnal/diurnal), how it responds to environmental stress (heat, humidity, drought, being eaten by other organisms, etc.) and anything else relevant to its way of life. It is the sum total o f the organism’s use of biotic and abiotic resources in its environment.
Each species in a habitat has a unique niche. Where the niches of different species overlap, competition between them occurs. The greater the overlap, the greater the competition. If the niches become too similar, then the species cannot co-exist in the same habitat; one species will out-compete and eliminate the other – this is known as the competitive exclusion principal . If species are to coexist in the same habitat, their niches cannot be exactly the same.
Example
– Two species of caterpillar are found living in flax bushes in
New Zealand. They have the same habitat (the leaves of Harakeke) but are able to coexist only because they feed on different parts of the leaf.
One caterpillar has biting/chewing mouthparts and eats ‘notches’ from

the edge of the leaf. The other caterpillar has rasping/scraping mouthp arts and scrapes holes or ‘windows’ from the middle of the leaf.
Fundamental versus Realised niche
The actual niche that an organism occupies (also called realised niche ) may be different from its potential niche. The potential niche
(also called fundamental niche ) is that which a population can occupy in ideal conditions i.e. where there is no competition with other species.
The realised niche is smaller than the fundamental niche because competition with other species or predation prevents the population from using all the resources it could otherwise be utilizing.
Example - If you look at two species of barnacle growing on the rocky shores, one called Balanus balanoides
(we will call it ‘big barnacle’) and the other called Chthamalus stellatus (we will call this ‘small barnacle’), you will find that the small barnacles live at the top of the rocks and the bigger barnacles live lower down. The big barnacles can’t stand the too long a period of dryness when the tide goes out. However, small barnacles can tolerate more dryness. If you remove all the big barnacles from lower down the small barnacles quickly occupy the

empty space and are “very happy there”. It’s just that they are unable to stand the competition from big barnacles. So, the fundamental niche for the small barnacle is the whole rocky shore, but its realised niche is the upper layers of the rocky shore.