An ecological niche describes an organism’s unique role within its ecosystem, covering all its interactions with the living and non-living elements of its environment. It is more than just a physical space; it defines how a species survives, what it eats, what eats it, and how it reproduces. The habitat is the organism’s “address”—the physical place where it lives, such as a forest or a river, while the niche is its “profession,” encompassing its specific job and the full range of its relationships within that habitat.
Fundamental and Realized Niches
The fundamental niche represents the entire range of conditions and resources an organism could theoretically use if there were no limiting factors like predators or competitors. This is the ideal scenario, outlining every possible environmental variable that a species is capable of thriving in. For example, a plant’s fundamental niche might include a wide variety of soil types and sunlight levels where it could grow unopposed.
In reality, organisms rarely occupy their full fundamental niche. They are instead confined to a realized niche, which is the actual set of conditions and resources a species uses after accounting for real-world pressures. The presence of competing species, predation, and disease forces organisms into a narrower role. A useful analogy is a talented musician who has the skill to play many instruments (their fundamental niche) but joins an orchestra where they specialize in playing the violin (their realized niche), as other musicians already play the other instruments.
Two species of barnacles may have fundamental niches that overlap on a rocky shoreline. However, competition may lead to one species occupying the upper, drier zone while the other is restricted to the lower, wetter zone. This results in two distinct realized niches. This dynamic interaction shapes the structure and biodiversity of an ecosystem.
The Dimensions of a Niche
An ecological niche is defined by a combination of non-living and living factors, each contributing to the organism’s specific role. These dimensions determine where and how a species can survive and reproduce.
Abiotic Factors
Abiotic factors are the non-living components that establish the physical boundaries of a niche. These include temperature range, sunlight, water requirements, and soil composition, including its pH and nutrient content. For example, the niche of a desert cactus is defined by high temperatures, intense sunlight, and scarce water.
Biotic Factors
Biotic factors are the living components related to an organism’s interactions with other species. This includes its food sources, such as the prey it hunts or the plants it consumes, and its predators. Competition with other species for limited resources like food, territory, or mates is another biotic factor. For example, a lion’s niche is defined by the availability of prey like zebras and competition with hyenas.
Species Strategies and Interactions
Species adopt different strategies to survive within the constraints of their ecological niches. These strategies influence how they interact with other organisms and respond to environmental changes.
Generalists, like raccoons or coyotes, have broad niches and can adapt to a wide variety of environmental conditions and food sources. Their flexibility allows them to live in diverse habitats, including urban areas. In contrast, specialists, such as the koala which feeds almost exclusively on eucalyptus leaves, have very narrow niches and rely on specific resources to survive.
The Competitive Exclusion Principle states that two species cannot occupy the exact same niche and compete for the exact same resources indefinitely. Eventually, the more efficient competitor will drive the other to local extinction. To avoid this outcome, many species evolve through a process called niche partitioning, where they adapt to use resources differently. This allows them to coexist by minimizing direct competition.
Ecological Niches in Action
The concepts of niche partitioning and adaptation are clearly visible in nature, with classic examples demonstrating how species coexist by carving out unique roles.
One of the most famous examples is Darwin’s finches in the Galápagos Islands. These closely related bird species descended from a common ancestor but evolved distinct beak shapes and sizes. This variation allows different species to specialize on different food sources, such as hard seeds, soft seeds, or insects, effectively partitioning their dietary niches. During dry seasons when food is scarce, this specialization becomes even more pronounced, as each species retreats to the resources its beak is best adapted for, reducing competition.
Another compelling example is the Anolis lizards of the Caribbean islands. Different Anolis species avoid direct competition by partitioning their habitat. Some species live high in the sunny canopy of trees, while others occupy the shaded tree trunks, and still others are found on twigs or on the ground. These lizards have also adapted physiologically to the different microclimates of their preferred perches, with species in warmer, sunnier spots having a higher tolerance for heat. This fine-scale partitioning of both space and thermal environment allows multiple species to thrive in the same forest.