Q.Explain why the realised niche of a species is usually narrower than its fundamental niche.

Charles Elton, in his pioneering work on animal ecology, first described the concept of the ecological (functional/trophic) niche of a species.

A niche describes the complete functional role and position of a species within its ecosystem -- not merely where it lives (its habitat) but how it lives: what it feeds on, how it obtains and uses resources, its interactions with other organisms, and its role in energy flow. Among early ecologists, Charles Elton is credited with formally introducing and developing this concept (often referred to as the 'Eltonian niche', emphasising an organism's trophic/functional position, such as its place in the food chain), in his influential 1927 book on animal ecology. This distinguishes the niche concept from a habitat, which is simply the physical/geographical area where an organism lives. Among the alternatives listed, John Ray and Jordon were naturalists/taxonomists associated with classification and the concept of species, and Charles Darwin is renowned for the theory of evolution by natural selection, not specifically for coining the niche concept.

Habitat is where an organism lives; niche is what it does there.

Habitat refers to the specific physical location or environment in which a particular species/organism naturally occurs and lives — for example, a pond, forest floor, or intertidal rocky shore. Niche, on the other hand, describes the organism's complete functional role within that habitat/ecosystem — the range of physical, chemical and biological conditions it requires, the food it eats, the predators/competitors it interacts with, and the role it plays in energy flow and nutrient cycling. A simple analogy: the habitat is an organism's 'address', while the niche is its 'profession' or role in the community.

Niche = the unique functional role ('profession') a species plays in its ecosystem.

Definition. The ecological niche is the specific functional role and space occupied by a species in its community — including the conditions it tolerates, the resources it uses, how it feeds, when it is active, where it lives, and its interactions with other organisms.

Key idea. Habitat is the physical address of an organism, whereas niche is its occupation/profession. According to the competitive-exclusion principle, no two species can occupy exactly the same niche in the same habitat indefinitely; the sharing of resources allows several species to coexist.

Habitat is the specific place where an organism lives and carries out its life functions.

Every organism occupies a habitat -- the particular type of locality, with its characteristic physical and biological conditions (such as a pond, a forest floor, or the bark of a tree), where it is normally found and where it performs its essential life activities such as feeding, growth and reproduction. Ecologists often summarise this by saying the habitat is an organism's "address." This is a distinct concept from niche, which is the organism's functional role within that habitat -- described as its "occupation" -- encompassing what it eats, what eats it, how it interacts with other species, and how it uses the available resources; two species can share the same habitat but occupy different niches, or vice versa. A landscape is a much larger geographic mosaic made up of many interacting ecosystems and habitats, and a biome is larger still, a broad regional or global ecological unit (such as tropical rainforest or grassland) defined by climate and characteristic vegetation, encompassing many landscapes, ecosystems and habitats within it.