Niche

The niche is an important ecological notion that considers the role that an organism or species plays in its community. Important aspects of the niche are environmental tolerance, use of resources, activities, and interactions with other organisms. Niche is an integrating concept because it considers organisms within the context of their biological tolerance of environmental extremes but is significantly modified by the influence of their interactions with other organisms, particularly through competition .

It must be understood that the niche is an abstract concept. Although niches cannot be seen or felt, ecologists can nevertheless understand their dimensions on the basis of environmental tolerances and opportunities as is discussed below.

The multidimensional niche

Species have limited abilities to tolerate extremes of environmental conditions. In other words, for all environmental factors there are upper and lower bounds of intensity that organisms can endure. For example, a particular species of plant or animal might be able to survive over an extended period of time within a zone of temperature bounded by certain high and low extremes. Extended exposures to hotter or colder temperatures cannot be tolerated, and the species will not occur in such environments. The boundaries of temperature tolerance can be represented as a component of the niche of the species in a single dimension-that of environmental temperature.

There are similar boundaries of tolerance for other environmental factors including climatic, chemical, and habitat variables, each of which can be similarly represented as a component of the larger niche in a single dimension. Conceptually, the niche of the species can be viewed as a multidimensional composite in which all of the boundaries of tolerance of diverse environmental influences are assembled into a single, multivariate factor. This is known as the fundamental niche, or the multidimensional zone (also known as a hypervolume) of environmental tolerance, in which an individual can potentially survive or in which a species can maintain viable populations.

However, in natural ecosystems species are rarely faced with habitat opportunities that are only defined by the boundaries of their tolerance of diverse environmental factors. The actual utilization of the fundamental niche is also significantly influenced by ecological interactions of various sorts. For example, other species may have similar tolerances of environmental factors. These species will seek to utilize some portion of the environmental opportunities that are available, resulting in the ecological interaction known as competition. Competition exerts a very important influence on the ability of species to optimally exploit their fundamental niche and on the structure of ecological communities. If species have very similar fundamental niches, then competition between them will be intense. In extreme cases this can cause one species to be eliminated from the community through a process known as competitive exclusion. More often, however, species are displaced by competition to particular zones within their fundamental niche.

Exploitation of the fundamental niche is also constrained by other ecological interactions such as predation, parasitism, and disease . All of these can restrict the opportunities for species to exploit their fundamental niche in an optimized fashion. Ecologists define the realized niche as the multidimensional hypervolume of environmental factors that species actually manage to exploit in nature in view of the powerful influences of competition, predation, parasitism, and disease.

Species must be present in the habitat in order to realize the benefits of some part of the range of their fundamental niche. If a location containing potentially suitable habitat cannot be colonized by a species, then it cannot utilize that part of its fundamental niche.

Realized niches are variable over time because they can respond to changes in the nature of ecological interactions. The introduction of a new, more capable competitor can eliminate an original species from its ecological community through competitive exclusion. A similar effect can be caused by introduced predators, parasites , and diseases. In contrast, the elimination of an important competitor, predator , parasite, or disease can release a species from a previously controlling influence, allowing it to expand the dimensions of its realized niche.

In general, the realized niche of species does not represent the environment conditions to which they are optimally adapted. The combined influences of diverse ecological interactions commonly relegate species to sub-optimal portions of their fundamental niche.

Ecological communities can be viewed as populations of various species that co-occur in space and time. Each species in the community maintains its populations by utilizing the opportunities available in its realized niche within the larger habitat. The number of species that can be maintained in the community and their relative abundance are determined by the diversity of niche opportunities, their stability over time, and the intensity of ecological interactions. The influences of these factors are optimized in old-growth tropical rain forests which maintain a greater diversity of species than any other terrestrial ecosystem . Among oceanic ecosystems, species diversity is greatest in coral reefs.

What is the niche of humans?

Humans also have fundamental and realized niches. Like other species, the fundamental niche of humans is bounded by their biological tolerance of extremes of environmental conditions.

However, unlike other species humans have developed an extraordinary ability to utilize technology to mitigate extremes of environmental conditions, allowing survival in otherwise inhospitable places. In this sense, humans have utilized technological innovations to greatly expand the boundaries of their realized niche. Humans can now sustain themselves in Antarctica , on mountain tops, in the driest deserts, in phenomenal densities in cities, and even in spacecraft.

Humans have also expanded the dimensions of their realized niche by managing the intensity of their interactions with other species. Humans control their own competitors, predators, parasites, and diseases, thereby reducing the constraints that these biological stressors exert on the realized, human niche. Humans also manage the ecological constraints of their mutualistic plants and animals such as agricultural cows, pigs , chickens, and plant crops .

The phenomenal expansion of their realized niche has allowed a great increase in the abundance of humans. For most of their evolutionary history, humans engaged in a hunting and gathering lifestyle, and their global population was probably a few million individuals. The first significant expansions of the realized human niche involved the domestication of fire and the development of primitive tools and agricultural methods, all of which allowed populations to increase. During the past several centuries of extraordinary technological development, populations of humans have grown especially quickly, and in 1995 almost six billion people were alive on Earth . This growth has been accomplished through expansion of the realized niche of industrial humans.

However, it must be understood that the remarkable technological expansions of the realized niche of humans require large and continual subsidies of energy , food, and other resources. These are needed in order to maintain the colonization of difficult environments and to continue the control of constraining ecological influences. If access to these resources is somehow diminished, then the ability of humans to colonize and manage their environment is diminished as well, or it collapses.

See also Biodiversity; Symbiosis.

Resources

books

Begon, M., Harper, J.L., and Townsend, C.R. Ecology. Individuals, Populations and Communities. 2nd ed. London: Blackwell Sci. Pub., 1990.

Ricklefs, R.E. Ecology. New York: W.H. Freeman and Co., 1990.

Bill Freedman

KEY TERMS

Community

—In ecology, a community is an assemblage of populations of different species that occur together in the same place and at the same time.

Competition

—An interaction between organisms of the same or different species associated with their need for a shared resource that is present in a supply that is smaller than the potential, biological demand.

Niche

—The role that an individual or species plays in its community, including its activities, resource demands, and interactions with other organisms.

Niche

In geophysical and ecological terms, a niche designates the relationship between a species and its area of inhabitation. The term is specifically used to describe a species' unique position both in terms of physical area, and as a set of characteristics that relate the species' biological and ecological functions to its geophysical environment.

Although not the subject of this article, the term niche is also used to describe a type of glacier (e.g., niche glacier) that forms inside an irregular recess on or within a mountainside.

Four distinct stages of niche theory development in biological ecology can be identified: (1) Joseph Grinnell's original formulation of niche (in 1917 and 1928) as a geophysical spatial unit; (2) Charles Elton's formulation (in 1927) of niche as a functional unit; (3) Gause's (1934) competitive exclusion principle; and (4) E. Evelyn Hutchinson's concept of multidimensional niche in the 1950s.

Although Darwin understood the idea of niche and a few other biologists used the term earlier, Grinnell is credited with its formal development. To Grinnell, niche was a spatial unit that stood for the "concept of the ultimate distributional unit, within which each species is held by its structural and instinctive limitations." His conception of niche was "preinteractive"—that is, it referred to the entire area within which an organism could survive in the absence of other organisms. This is in contrast to the "post-interactive" niche, the actual place occupied by the organism in an environment after it has interacted with other organisms.

At about the same time, Charles Elton was developing the niche concept along somewhat different lines. Elton conceived of niche as a functional unit to describe the organism's "place in the biotic environment, relations to food and enemies." Although Elton presented niche as an organism's ecological position in a larger framework like a community or ecosystem, he then restricted its use to the food habits of an organism. Accordingly, Elton's niche is considered to be postinteractive.

Gause is credited with being the first investigator to perceive the connection between natural selection, competition, and niche and to see the interacting aspects of these concepts. Gause stated that "it is admitted that, as a result of competition, two similar species scarcely ever occupy similar niches, but displace each other in such a manner that each takes possession of certain peculiar kinds of food and modes of life in which it has an advantage over its competitor. Gause experimentally tested the general conclusions drawn from the Lotka-Volterra competitive equations, confirming and amplifying them. These conclusions are summarized in the "competitive exclusion principle," which states that two species cannot coexist at the same locality if they have identical ecological requirements. Gause based the principle on an Eltonian definition of niche.

The Eltonian niche dominated ecological theory during the period 1930–1950 and began to be referred to as an organism's "occupation" or "profession." Hutchinson responded to this rather limited idea of niche by incorporating selected features from both Grinnell's and Elton's niche definitions and redefining niche as an "n-dimensional hypervolume," an abstract multidimensional space defining the environmental limits within which an organism is able to survive and reproduce. Hutchinson's "fundamental niche" is preinteractive, composed of "close to innumerable" dimensions, each corresponding to some requisite for a species. By setting the number of defining dimensions at "close to innumerable," Hutchinson attempted to illustrate the complexity of the systems within which organisms exist and interact. He depicted it by plotting each identifiably important environmental variable along an axis to show the points below which and above which the given organism could not survive.

Hutchinson's "realized niche" usually corresponds to a smaller hypervolume because competition and other interactions serve to restrict organisms from some parts of their fundamental or potential niche. Although most current works in niche theory use some variation of Hutchinson's multidimensional niche, both the Eltonian and the Hutchinson niches are still found in contemporary ecology and are still useful. Any application of niche, however, is only an approximation of reality, because niche dimensions are too numerous to be counted.

See also Archeological mapping; Physical geography; Topography and topographic maps

Niche

Resources

The niche is an important ecological concept that considers the role that an organism or species plays in its community through the organism’s occupation of a physical space and the use of resources in that space. Other important aspects of the niche are environmental tolerance, the organism’s activities, and interactions (competitive and more harmonious) with other organisms.

Species have limited abilities to tolerate environmental extremes. For example, a particular species of plant or animal might be able to survive over an extended period of time within a zone of temperature bounded by certain high and low extremes. Extended exposures to hotter or colder temperatures cannot be tolerated, and the species will not occur in such environments. This temperature range becomes part of the niche of the particular organism.

Other environmental and geographic factors are important in determining an organism’s niche. As well, other species may have similar tolerances of environmental factors. These species will seek to utilize some portion of the environmental opportunities that are available, resulting in the ecological interaction known as competition.

Competition exerts a very important influence on the ability of species to optimally exploit their niche and so is important in determining the variety of life in a community. If species have very similar fundamental niches, then competition between them will be intense. In extreme cases this can cause one species to be eliminated from the community; this is known as competitive exclusion. More often, species are displaced by competition to particular zones within their niche. The niche may thus not be ideal for an organism, but rather is the best that can be achieved under the circumstances.

Ecological communities can be viewed as populations of various species that live together at the same time and in the same geographic area. Each species in the community maintains its population by utilizing the opportunities available in its niche within the larger habitat. The number of species that can be maintained in the community and their relative abundances are determined by various factors: the number of niches (i.e., trees, streams, grasslands, soil); their stability over time; and the intensity competition for food and space. The influences of these factors are optimized in old-growth tropical rain forests, which maintain a greater diversity of species than any other terrestrial ecosystem. Among oceanic ecosystems, species diversity is greatest in coral reefs.

Like other species, the fundamental niche of humans is bounded by their biological tolerance of extremes of environmental conditions. However, unlike other species, humans have utilized technology to lessen these extremes, allowing survival in otherwise inhospitable places. Humans can now sustain themselves in Antarctica, on mountaintops, in the driest deserts, in phenomenal densities in cities, and even in spacecraft. However, the burgeoning human population and the production of noxious compounds is imposing stresses that, without alteration, threaten human life on Earth.

Resources

BOOKS

Allaby, Michael and Richard Garratt. Temperate Forests (Biomes of the Earth). New York: Chelsea House Publications, 2006.

Callahan, Gerald N. Infection: The Uninvited Universe. New York: St. Martin’s Press, 2006.

Cote, Isabelle and John D. Reynolds. Coral Reef Conservation. Cambridge: Cambridge University Press, 2006.

Bill Freedman

Niche

The term niche is used in ecology with a variety of distinct meanings. It may refer to a spatial unit or to a function unit. One definition focuses on niche as a role claimed exclusively by a species through competition . The word is also used to refer to "utilization distribution" or the frequency with which populations use resources. Still, niche is well enough established in ecology that Stephen Jay Gould can label it as "the fundamental concept" in the discipline, "an expression of the location and function of a species in a habitat." Niche is used to address such questions as what determines the species diversity of a biological community , how similar organisms coexist in an area, how species divide up the resources of an environment , and how species within a community affect each other over time.

Niche has not been applied very satisfactorily in the ecological study of humans. Anthropologists have used it perhaps most successfully in the study of how small pre-industrial tribal groups adapt to local conditions. Sociologists have not been very successful with niche, subdividing the human species by occupations or roles, creating false analogies that do not come very close to the way niche is used in biology. More recently, sociologists have extended niche to help explain organizational behavior, though again distorting it as an ecological concept.

Some attempts were made to build on the vernacular sense of niche as in "he found his niche," a measure of how individual human beings attain multidimensional "fit" with their surroundings. But this usage was again criticized as too much of a distortion of the original meaning of niche in biology. The word and related concepts remain common, however, and are widely understood in vernacular usage to describe how individual human beings make their way in the world.

The niche concept has not been much employed by environmental scientists, though it might be helpful in attempts to understand the relationships between humans and their environments, for instance. Efforts to formulate niche or a synonym of some sort for use in the study of such relationships will probably continue. The best use of niche might be in its utility as an indicator of the richness and diversity of habitat , serving in this way as an indicator of the general health of the environment.

[Gerald L. Young Ph.D. ]

RESOURCES

BOOKS

Schoener, T. W. "The Ecological Niche." In Ecological Concepts, edited by J. M. Cherrett. Oxford, England: Blackwell Scientific Publications, 1989.

PERIODICALS

Broussard, C. A., and G. L. Young. "A Reorientation of Niche Theory in Human Ecology: Toward a Better Explanation of the Complex Linkages between Individual and Society." Sociological Perspectives 29 (April 1986): 259–283.

Colinvaux, P. A. "Towards a Theory of History: Fitness, Niche, and Clutch of Homo Sapiens." Coevolution Quarterly 41 (Spring 1984): 94–107.

Mark, J., G. M. Chapman, and T. Gibson. "Bioeconomics and the Theory of Niches." Futures 17 (December 1985): 632–51.

Niche

The term niche refers to the particular job, or function, that a living thing plays in the particular place it lives. Also called an ecological niche, this concept refers to the precise way in which an organism fits into its environment. A niche includes all the factors that are important to the organism's existence. No two species can occupy the same niche.

In order to study a niche, life scientists must understand all of the factors that are important to a living thing's existence. These factors include: an organism's: diet; energy, light, and moisture requirements, ideal temperature; ideal habitat; and ideal reproduction conditions. Therefore, the word function is key to understanding the idea of an ecological niche.

The idea of niche as a function has also been described as the job a living thing has—and as with any job—it can be very specialized or very general. Some organisms have very broad niches, meaning that they are fairly flexible in terms of the type of things they eat and temperature they tolerate. In other words, their overall living needs can be met in a less specialized environment. The opossum and the raccoon are examples of animals with very broad niches since they eat a wide variety of plants and animals and adjust well to different climates. However, many species play a narrow or specialized role and therefore have a narrow niche. Two examples are the giant panda of central China and the koala of Australia. The panda lives in the bamboo forests and eats only one type of bamboo, while the koala can only live where certain species of eucalyptus trees grow and survives by eating the leaves. Other factors influence a niche, and in the case of the koala, its existence becomes more fragile since it must live in a warm climate and it does not produce its young in great numbers. Not surprisingly, animals with the broader niche survive fairly easily and thrive in certain areas, while those animals with the more specialized niche, like the koala and the giant panda, are more likely to become endangered species as their habitats are destroyed.

Some life scientists say that a niche can be understood primarily in terms of competition, while others say it has more to do with one species being best fitted for a certain role. As early as the 1930s, life scientists developed the principle called competitive exclusion. One of the pioneers arguing for the primary importance of competition was the Russian microbiologist Georgil F. Gauze (1910– ), who conducted tests on different species of protozoa (one-celled organisms). Gauze successfully raised different species of protozoa, each in its own environment. He then put them together and discovered that one died out completely while the other thrived. In another test, he found that although the two species survived, neither did so in great numbers, and each occupied a different territory (or a separate part of the test tube). From this work came Gauze's nowaccepted principle that although two species may occupy the same habitat, they never share the same niche. A common example of such a phenomenon is that of the woodpecker and nuthatch. Both are birds that eat grubs (insects) that they find under tree bark. However, despite the fact that they are both after the same meal, neither occupies the niche of the other since woodpeckers start at the bottom of a tree and work their way up, while nuthatches begin at the top and work down.

Beyond an organism's feeding habits, there are scores of other factors that go into describing an organism's niche. For example, the simple earthworm plays a key role in its habitat as a consumer of dead organic matter and as food for other animals (such as birds). It is a host for certain parasites, and its burrowing has a beneficial plowing effect on the soil, loosening it up and allowing air to circulate. As the example of the earthworm shows, understanding an organism's niche also allows scientists to better understand both the organism and the environment it lives in.