Ecological Niche

In ecology, a niche refers to the specific set of environmental conditions, resources and interactions that allow a species to survive, grow and reproduce. It encompasses the ways in which organisms respond to factors such as food availability, climate, competitors, predators and pathogens, as well as the ways in which they themselves influence these factors. Niches differ widely between species, and the importance of particular environmental and biological variables can vary across geographical regions and ecological contexts. The study of ecological niches is central to ecological biogeography, which explores the distribution of species and communities across space and time, including how both species’ traits and environmental change influence these patterns.
Most species occupy what may be regarded as standard ecological niches characterised by behavioural adaptations and ecological functions comparable to closely related species. However, some species deviate from such expected patterns. A notable example is the flightless kiwi of New Zealand, which occupies a mammal-like niche, feeding on soil invertebrates and living a largely nocturnal, ground-dwelling existence. Island ecosystems often illustrate the presence of unfilled niches and distinctive ecological roles developed in isolation.
Three major concepts of ecological niche are widely recognised: the Grinnellian, Eltonian and Hutchinsonian niches. These frameworks, while related, emphasise different ecological dimensions and have shaped much of the contemporary understanding of species–environment relationships.

Grinnellian Niche

The Grinnellian niche concept defines the niche primarily through the habitat in which a species lives and the behavioural traits that enable it to survive and reproduce in that environment. It emphasises how a species responds to non-interactive, abiotic factors acting at broad geographical scales.
In this framework, a species’ niche comprises the physical environment and the behavioural patterns that complement it. A classic example is the California thrasher, a bird that lives in chaparral shrubland. Its behaviours—feeding and nesting within dense underbrush and escaping predators by moving between shrubs—are supported by its physical traits, such as short wings and camouflaging plumage. These characteristics together define its habitat-based niche.
Grinnellian niches are often examined through variables such as temperature, precipitation, solar radiation and terrain. Much research uses this perspective, especially in modelling species distributions and forecasting responses to climate change. This viewpoint also allows for the identification of ecological equivalents—species from different taxonomic groups occupying similar habitats and exhibiting comparable adaptations. Succulent plants in African and American deserts, such as euphorbias and cacti, are examples of ecological equivalents arising through convergent evolution. Similarly, the anole lizards of the Greater Antilles illustrate repeated evolution of similar ecomorphs on separate islands.

Eltonian Niche

The Eltonian niche concept focuses on the functional role of a species within its ecosystem, particularly its position in food webs and its relationships with predators, prey and competitors. It emphasises how species not only respond to environmental conditions but also alter them through their activities.
This perspective highlights the way organisms influence both biotic and abiotic factors. A classic example is the beaver, which relies on certain habitats for survival but also creates new environments by constructing dams that alter water flow and landscape structure. This engineering behaviour affects numerous other species in the ecosystem. More subtle Eltonian interactions include species that consume resources at different rates, thereby influencing the dynamics of resource availability and population growth.
Eltonian niches concentrate on biotic interactions at local scales, often requiring detailed field observations. Although challenging to measure over large areas, this framework is valuable in understanding how species respond to environmental change. Alterations in biotic relationships eventually modify abiotic conditions, making this approach effective for interpreting the broader impacts of environmental shifts on species.

Hutchinsonian Niche

The Hutchinsonian niche defines a niche as a multidimensional hypervolume, where each dimension represents an environmental condition or resource essential for a species’ population to persist. This approach formalises the niche concept using mathematical and statistical tools to describe how multiple ecological factors combine to create the conditions under which species coexist.
In this multidimensional space, resources such as light, nutrients, habitat structure and prey size are represented as axes, with the niche defined by the specific range of values a species can use. This framework distinguishes between:

• Fundamental niches, representing the full range of conditions a species could theoretically use.
• Realised niches, reflecting the narrower range actually occupied in the presence of competitors and predators.