In ecology, a niche is a term with a variety of meanings related to the behavior of a species
living under specific environmental conditions.
The ecological niche describes how an organism or population responds to the distribution
of resources and competitors and how it in turn alters those same factors.
"The type and number of variables comprising the dimensions of an environmental niche vary
from one species to another...[and]...the relative importance of particular environmental
variables for a species may vary according to the geographic and biotic contexts".
The notion of ecological niche is central to ecological biogeography, which focuses
on spatial patterns of ecological communities.
"Species distributions and their dynamics over time result from properties of the species,
environmental variation..., and interactions between the two — in particular the abilities
of some species, especially our own, to modify their environments and alter the range dynamics
of many other species."
Alteration of an ecological niche by its inhabitants is the topic of niche construction.
The majority of species exist in a standard ecological niche, but there are exceptions.
A premier example of a non-standard niche filling species is the flightless, ground-dwelling
kiwi bird of New Zealand, which feeds on worms and other ground creatures, and lives its
life in a mammal niche.
Island biogeography can help explain island species and associated unfilled niches.
Grinnellian niche The ecological meaning of niche comes from
the meaning of niche as a recess in a wall for a statue, which itself is probably derived
from the Middle French word nicher, meaning to nest.
The term was coined by the naturalist Joseph Grinnell in 1917, in his paper "The niche
relationships of the California Thrasher".
The Grinnellian niche concept embodies the idea that the niche of a species is determined
by the habitat in which it lives and its accompanying behavioral adaptations.
In other words, the niche is the sum of the habitat requirements and behaviors that allow
a species to persist and produce offspring.
For example, the behavior of the California Thrasher is consistent with the chaparral
habitat it lives in—it breeds and feeds in the underbrush and escapes from its predators
by shuffling from underbrush to underbrush.
Its 'niche' is defined by the felicitous complementing of the thrasher's behavior and physical traits
with this habitat.
This perspective of niche allows for the existence of both ecological equivalents and empty niches.
An ecological equivalent to an organism is an organism from a different taxonomic group
exhibiting similar adaptations in a similar habitat, an example being the different succulents
found in American and African deserts, cactus and euphorbia.
As another example, the Anolis lizards of the Greater Antilles are a rare example of
convergent evolution, adaptive radiation, and the existence of ecological equivalents:
the Anolis lizards evolved in similar microhabitats independently of each other and resulted in
the same ecomorphs across all four islands.
Eltonian niche In 1927 Charles Sutherland Elton, a British
ecologist, defined a niche as follows: "The 'niche' of an animal means its place in the
biotic environment, its relations to food and enemies."
Elton classified niches according to foraging activities: "For instance there is the niche
that is filled by birds of prey which eat small animals such as shrews and mice.
In an oak wood this niche is filled by tawny owls, while in the open grassland it is occupied
by kestrels.
The existence of this carnivore niche is dependent on the further fact that mice form a definite
herbivore niche in many different associations, although the actual species of mice may be
quite different."
Hutchinsonian niche
The Hutchinsonian niche is an n-dimensional hypervolume, where the dimensions are environmental
conditions and resources, that define the requirements of an individual or a species
to practice "its" way of life, more particularly, for its population to persist.
The "hypervolume" defines the multi-dimensional space of resources available to organisms,
and "all species other than those under consideration are regarded as part of the coordinate system."
The niche concept was popularized by the zoologist G. Evelyn Hutchinson in 1957.
Hutchinson wanted to know why there are so many types of organisms in any one habitat.
His work inspired many others to develop models to explain how many and how similar coexisting
species could be within a given community, and led to the concepts of 'niche breadth',
'niche partitioning', and 'niche overlap'.
Statistics were introduced into the Hutchinson niche by Robert MacArthur and Richard Levins
using the 'resource-utilization' niche employing histograms to describe the 'frequency of occurrence'
as a function of a Hutchinson coordinate.
So, for instance, a Gaussian might describe the frequency with which a species ate prey
of a certain size, giving a more detailed niche description than simply specifying some
median or average prey size.
One advantage in using statistics is illustrated in the figure, where it is clear that for
the narrower distributions there is no competition for prey between the extreme left and extreme
right species, while for the broader distribution, niche overlap indicates competition exists
between all species.
For such a bell-shaped distribution, the position, width and form of the niche correspond to
the mean, standard deviation and the actual distribution itself.
An organism free of interference from other species could use the full range of conditions
and resources in which it could survive and reproduce which is called its fundamental
niche.
However, as a result of pressure from, and interactions with, other organisms species
are usually forced to occupy a niche that is narrower than this, and to which they are
mostly highly adapted.
This is termed the realized niche.
Hutchinson used the idea of competition for resources as the primary mechanism driving
ecology, but overemphasis upon this focus has proved to be a handicap for the niche
concept.
In particular, overemphasis upon a species' dependence upon resources has led to too little
emphasis upon the effects of organisms on their environment, for instance, colonization
and invasions.
The term adaptive zone was coined by the paleontologist George Gaylord Simpson to explain how a population
could jump from one niche to another that suited it, jump to an 'adaptive zone', made
available by virtue of some modification, or possibly a change in the food chain, that
made the adaptive zone available to it without a discontinuity in its way of life because
the group was 'pre-adapted' to the new ecological opportunity.
Hutchinson's "niche" is subtly different from the "niche" as defined by Grinnell.
A niche is a very specific segment of ecospace occupied by a single species.
On the presumption that no two species are identical in all respects and the competitive
exclusion principle, some resource or adaptive dimension will provide a niche specific to
each species.
Species can however share a 'mode of life' or 'autecological strategy' which are broader
definitions of ecospace.
For example, Australian grasslands species, though different from those of the Great Plains
grasslands, exhibit similar modes of life.
Once a niche is left vacant, other organisms can fill that position.
For example, the niche that was left vacant by the extinction of the tarpan has been filled
by other animals.
Also, when plants and animals are introduced into a new environment, they have the potential
to occupy or invade the niche or niches of native organisms, often outcompeting the indigenous
species.
Introduction of non-indigenous species to non-native habitats by humans often results
in biological pollution by the exotic or invasive species.
The mathematical representation of a species' fundamental niche in ecological space, and
its subsequent projection back into geographic space, is the domain of niche modelling.
Parameters The different dimensions, or plot axes, of
a niche represent different biotic and abiotic variables.
These factors may include descriptions of the organism's life history, habitat, trophic
position, and geographic range.
According to the competitive exclusion principle, no two species can occupy the same niche in
the same environment for a long time.
The parameters of a realized niche are described by the realized niche width of that species.
See also
Fitness landscape Niche construction
Niche differentiation Overpopulation in wild animals
Phylogenetic niche conservatism Resource
Unified neutral theory of biodiversity, a theory that attempts to explain how a high
number of species co exist in a community by ignoring the presence of the ecological
niche.
References
External links Concept of ecological niche
Environmental Niche – Extinction of the Dinosaurs
Ontology of the niche Niche restriction and segregation
Vacant niche Latitude-niche width hypothesis