n., plural: realized niches
Definition: part of a fundamental niche that an organism occupies as a result of limiting factors in its habitat
Table of Contents
What is a niche? A niche can be defined as the means by which a species or an individual interacts with its environment. In other words, a niche identifies the way in which a species lives in its environment and what its role is in the community. There are several behavioral dimensions of a niche, such as methods of finding food, locomotion, and survival. The temperature limits of an environment also define the niche of an organism. Whether above or below a certain temperature, the species will either be unable to survive as some of the biological activities may be interrupted, worse, may come to a halt. In ecology, a niche is defined as the response of a biological population to the limiting factors, e.g. the presence of competitors and the distribution of resources. Another example is when the species population increases in number when there are fewer predators, pathogens, and parasites. Thus, in such a niche, the species will thrive. On the other hand, an increased number of predators or risk for diseases caused by parasites and pathogens will result in the decrease of the population of that species. Consequently, the species would have to adapt, for example, by acquiring adaptations that boost immunity against diseases. Or, they would need to move to a more favorable environment to sustain their species existence. The favorable environment will, then, be the niche of that species.
Different definitions of niche have been defined by scientists, such as Grinnellian niche (1917), Eltonian niche (1927), and Hutchinsonian niche (1957). The Grinnellian niche is determined by the habitat in which the species lives and its behavioral adaptations. The Eltonian niche is determined by the relation of a species with food and its enemies in the biotic environment. The Hutchinsonian niche is a broader term and attempts to explain why so many species coexist in a similar environment. He also defined the term “hyper-volume”, which means the multidimensional space of resources such as nutrients, water, light, etc. As hyper-volume is multidimensional with no constraints on the dimensions, so Hutchinson described it as an n-dimensional hyper-volume. The dimensions of this volume are environmental conditions and resources in which species can co-exist and thrive (Chase & Leibold, 2003).
In the next sections, we will define realized niche with respect to the fundamental niche.
Realized Niche Definition
A realized niche can be defined as the environmental position that a species occupies and lives in. Realized niche is also called “post-competitive”. Realized niche is the result of the presence of limiting factors (such as food, light, water, the presence of other species, etc.) forcing the species or organisms to move to certain environments where they may thrive. A realized niche is therefore defined as the space in the environment where a species is most highly adapted to play its role and reproduce (Malanson, Westman, & Yan, 1992).
The concept of realized niche can be better understood when comparing it in the context of the fundamental niche. Both realized and fundamental niches represent the environmental position of a species in the ecosystem. However, the fundamental niche defines all the environmental conditions in which a species can live and reproduce. This includes both biotic (e.g. presence of food, such as grass, or other animals in the case of carnivores) and abiotic (e.g. temperature, humidity, sunlight, etc.) conditions.
The fundamental niche is an ideal condition for a species to thrive without any competition. However, we know that in one habitat there could be multiple species co-existing. And so there would be a competition for food, mate, and other limited resources that affect the population size of the different species co-existing in the same environment. This competition may then result in a realized niche.
Realized niche is usually smaller than a fundamental niche. Moreover, the realized niche of the same species living at different locations can also be different because of the number of competitors and predators present in that particular environment.
Fundamental vs. Realized Niche
The fundamental niche represents all the environmental conditions in which a species can easily survive and reproduce to continue its generation. Realized niche, on the other hand, is where the species actually live. On earth, the species have to live in an environment where other species or competitors are also present. Apart from competitors, there are other factors such as climate, terrain, and resources that define the position of a species in its environment.
If multiple species occupy the exact same niche within their habitat, the competitive exclusion principle could apply. According to this principle, one species will outcompete the others. There will be two options for the outcompeted species, i.e. to die out or adapt.
The flexibility in the utilization of resources can allow different species to coexist together and avoid competition. In other words, the species have to modify their realized niches to achieve this kind of coexistence (Stachowicz, 2012). Figure 2 depicts the difference between a fundamental niche and a realized niche where the possibility of the existence of a species outside the fundamental niche is zero.
The main difference between the fundamental niche and the realized niche is that the realized niche is the actual environment where the species live whereas the fundamental niche is any type of environmental conditions in which a species can live. A fundamental niche is also referred to as a pre-competitive niche and is defined by a set of conditions and sources on which the species can survive, grow and reproduce. There is no competition for resources and predators; thus, the species can take advantage of both the biotic and abiotic requirements for sustained existence in the ecosystem.
An example of a fundamental niche is that of the red-winged blackbird. The bird species dominates the marches during the early spring. That area becomes a fundamental niche for the red-winged blackbirds. But later on, the tri-colored blackbirds arrive in the marshes during summer. They are more aggressive, and as a result, they occupy the best territory.
There is a multitude of environmental factors that affect every population existing on earth. A realized niche is a post-competitive niche and is considered as a sub-branch of fundamental niche. Realized niche is formed when the species within a fundamental niche has to deal with the pressure of co-existing with the other species in the environment. The species is forced to live in a smaller niche. An example of how a realized niche is formed is the coexistence of wolves and coyotes living across North America. Because both species inhabit the same area, coyotes would then compete for food and territory. The realized niche for coyotes was small due to the more aggressive nature of wolves. When European settlers came to the continent, hunting reduced the population of wolves. This favored the coyotes, and thus, their realized niche expanded.
The similarity between the fundamental and the realized niche is that both are two types of positions in the ecosystem occupied by similar species. Here is a comparison chart to further identify realized niche from a fundamental niche.
Realized Niche Examples
Scientists have studied the realized niches of different species to examine the distribution of these species in particular environments. One simple example of a realized niche is the rat’s intestine that limits the number of species that can live. In the mouse intestine, acanthocephalans (a group of worms) and tapeworms can exist as potential competitors. Both of these groups of parasitic worms obtain their nutrients from blood in the intestinal walls. The availability of carbohydrates in the gut depends on the location; more carbohydrates are available in the anterior than in the posterior portion. When there is a mixed infection, where both acanthocephalans and tapeworms are present, the niche of both groups is narrowed. The realized niche of the former species is narrowed towards the anterior portion while that of the latter species is narrowed towards the posterior portion of the gut.
Another example of the realized niche on bluegills fish based on Werener’s findings (Montana State University, n.d.). He created two distinct habitats by modifying a pond by dividing it with a net and introduced a predator (largemouth bass) into one half only. Three sizes of bluegills (i.e. small, medium, and large) were studied to change their interaction with food in the presence and without the presence of a predator. Three types of food were introduced, i.e. plankton, vegetation, and benthos. The absence of predators resulted in a fundamental niche and all sizes of fish consumed benthos as their food. On large bluegills, the presence of a predator did not affect them because they were not vulnerable to predation. The diet did not change. The medium bluegills were a little vulnerable and they started taking plankton. Small bluegills were most vulnerable and they chose vegetation as their food so that they could hide there as well. The realized niche for smaller bluegills narrowed down, to the lowest energy food.
Realized Niche Width
Realized niche width is the term used for representing the actual space occupied by an organism in the environment it lives. It can also be defined by the resources the species can consume as a result of the limiting pressure caused by the presence of other species. The specialist species have narrow realized niche width while the generalist species have broad niche width. The study of realized niche width can provide information about overlapping species niches.
- Chase, J. M., & Leibold, M. A. (2003). Ecological niches: linking classical and contemporary approaches. University of Chicago Press.
- Expii. (2020). Niche (Ecology) — Definition & Examples. Retrieved March 30, 2021, from https://www.expii.com/t/niche-ecology-definition-examples-10995
- Malanson, G. P., Westman, W. E., & Yan, Y.-L. (1992). Realized versus fundamental niche functions in a model of chaparral response to climatic change. Ecological Modelling, 64(4), 261–277.
- Stachowicz, J. (2012). Niche expansion by positive interactions: realizing the fundamentals. A comment on Rodriguez-Cabal et al. Ideas in Ecology and Evolution, 5.
- Montana State University. (n.d.). BIOL 303 1 Ecological Niches Ecological Niche: “the total of the adaptations of an organismic unit” Niches identify the “role of an organism in its community”, or “the way a species makes its living.” https://www.montana.edu/screel/teaching/bioe-370/documents/Biol%20303%20niches.pdf
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