Ecological niches

The idea of the niche probably had its first roots in ecology in 1910. At that time, Roswell Johnson wrote that different species utilize different niches in the environment. He theorized that individuals of a particular species are only in certain places because of food supply and environmental factors that limit their distribution in an area. Later, in 1924, Joseph Grinnell developed his concept of niche that centered on an organism’s distribution having limits set on it by climatic and physical barriers. At the same time, Charles Elton was defining his own idea of niche. His description of niche involved the way an organism makes its living—in particular, how it gathers food.

Trophic Levels

For many years, ecologists focused on Elton’s definition and referred to niche in terms of an organism’s place in the food pyramid. The food pyramid is a simplified scheme in which organisms interact with one another while obtaining food. It represents the niche’s biomass, organisms, and energy distribution. The food pyramid is described as a triangle, often with four horizontal divisions, each with a different trophic level.

The base of the food pyramid is the first trophic level and contains the primary producers: photosynthetic plants, which make their own food using photosynthesis or chemosynthesis. The primary consumers are at the second trophic level, including herbivores like deer and rabbits, which feed directly on the primary producers. Secondary and tertiary consumers are found at the third trophic level. This level contains carnivores and omnivores, such as mountain lions and bears. The members of the uppermost trophic level are the scavengers and decomposers, including hyenas, buzzards, fungi, and bacteria. The organisms in this trophic level break down all the nutrients (such as carbon and nitrogen) in the bodies of plants and animals and return them to the soil to be absorbed and used by plants.

It should be noted that no ecosystem actually has a simple and well-defined food pyramid. Many organisms interact with more organisms than those at the adjacent trophic levels. For example, a coyote could be considered to belong to the third trophic level with the carnivores, but the coyote also occasionally feeds on fruits and other primary producers. All living things are dependent on the first trophic level because it alone has the capability to convert solar energy to energy found in, for example, glucose and starch. The food pyramid takes the geometric form of a triangle to show the flow of energy through a system.

Photosynthetic plants lose 10 percent of the energy they absorb from the sun as they convert solar energy into glucose and starch. In turn, the herbivores can convert and use only 90 percent of the energy they obtain by eating plants. Hence, less energy is found at each higher trophic level. Because of this reduction in energy, fewer organisms can be supported by each higher trophic level. Consequently, the sections of the pyramid get smaller at each higher trophic level, representing the decreasing levels of energy and number of members.

Interrelationships Among Organisms

Through the years, two concepts of niche have evolved in ecology. The first is the place niche, the physical space in which an organism lives. The second is the ecological niche, and it encompasses the particular location occupied by an organism and its functional role in the community.

The functional role of a species is not limited to its placement along a food pyramid; it also includes the interactions of a species with other organisms while obtaining food. For example, the methods used to tolerate the physical factors of its environment, such as climate, water, nutrients, soils, parasites, and the like, are all part of its functional role. In other words, the ecological niche of an organism is its natural history: all the interactions and interrelationships of the species with other organisms and the environment.

The study of the interrelationships among organisms has been the focus of ecological studies since the 1960s. Before this time, researchers had focused on the food pyramid and its effect on population changes of merely a single species. One example is the classic population study of the lynx and the snowshoe hare of Canada, which originally focused on the interactions of the species in the food pyramid. The study found that the lynx had a ten-year population cycle closely following the population cycle of its prey, the snowshoe hare. The lynx population appeared to rise, causing a decline in the snowshoe hare population. In subsequent investigations, however, studies diverted the focus from the food pyramid to other elements of the niche of the two species. For example, the reproductive nature of the hare provided a contradiction to the simple predator-prey explanation. The hare has a faster rate of reproduction than the lynx. It seemed impossible that the significantly lower lynx population could effectively place sufficient predator pressure on the hare to cause its drastic decline in numbers. Therefore, the research concluded that the hare and lynx population dynamics were regulated by more than simply a predator-prey relationship.

Later studies of the lynx and hare suggested that the peaks and dives in the two populations may also be a factor of parasites of the hare that are carried by the lynx. A rise in the lynx population increases the carriers of parasites of the hare. Therefore, it is thought that, although the hare has a much greater reproduction rate than the lynx, the population of hares will still decline because of the combination of predation by the lynx and the increased frequency of parasites of the hare. This study involved looking at more than one dimension of the ecological niche of a species and broke away from concentrating on only the interactions between organisms in the food pyramid.

Niche Overlap

The goal of understanding how species interact with one another can also be better accomplished by defining the degree of niche overlap, the degree of the sharing of resources between two species. When two species use one or more of the same elements of an ecological niche, they exhibit interspecific competition. It was once believed that interspecific competition would always lead to survival of only the better competitor of the two species. That was the original concept of the principle of the competition exclusion law of ecology: No two species can utilize the same ecological niche. It was conjectured that the weaker competitor would either migrate, begin using another resource not used by the stronger competitor, or become extinct. It is now believed that the end result of two species sharing elements of ecological niches may not always be exclusion.

Ecologists theorize that similar species do, in fact, coexist despite the sharing of elements of their ecological niches because of character displacement, which leads to a decrease in niche overlap. Character displacement involves a change in the morphological, behavioral, or physiological state of a species without geographical isolation. Character displacement occurs as a result of natural selection arising from competition between one or more ecologically similar species. Examples might be changes in mouth sizes so that they begin to feed on different sizes of the same food type, thereby decreasing competition.

Similarly, resource partitioning involves similar animals avoiding extinction by using resources in different ways so they may coexist. This type of resource use increases productivity and overall health of the ecological niche because it diversifies the resources used and the species diversity.

Species Specialization

The more specialized a species, the more rigid it will be in terms of its ecological niche. A species that is general in terms of its ecological niche needs will be better able to find and use an alternative for the common element of the niche. Since a highly specialized species cannot substitute whatever is being used, it cannot compete as well as the other species. Therefore, a specialized species is more likely to become extinct.

For example, a panda is a very specialized feeder, eating mainly bamboo. If a pest is introduced into the environment that destroys bamboo, the panda will probably starve, being unable to switch to another food source. On the other hand, the coyote is a generalized feeder. It has a broad variety of food types that make up its diet. If humans initiate a pest-control program, killing the population of rabbits, the coyote will not fall victim to starvation because it can switch to feeding predominantly on rodents, insects, fruits, and domesticated animals (including cats, dogs, and chickens). Hence, species with specialized ecological niche demands (specialists) are in greater danger of extinction than those with generalized needs (generalists). Although this fundamental difference in survival can be seen between specialists and generalists, it must be noted again that exclusion is not an inevitable result of competition. Many cases of ecologically similar species coexist.

When individuals of the same species compete for the same elements of the ecological niche, it is referred to as intraspecific competition. Intraspecific competition has the opposite effect of interspecific competition: niche generalizations. In increasing populations, the first inhabitants will have access to optimal resources. The opportunity for optimal resources decreases as the population increases; hence, intraspecific competition increases. Deviant individuals using marginal resources may slowly begin to use less optimal resources that are in less demand. That can lead to an increase in the diversity of ecological niches used by the species as a whole. In other words, the species may become more generalized and exploit wider varieties of niche elements.

Representing a situation on the opposite end of the spectrum from that of two organisms competing for the same dimension of an ecological niche is the vacant niche theory. This ecological principle states that when an organism is removed from its ecological niche, space, or any other dimension of the niche, another organism of the same or similar species will reinvade.

Field Research

Theoretical studies of ecological niches are abstract, since humans are limited to three-dimensional diagrams, and there are more than three dimensions to an ecological niche. This multidimensionality is referred to as the n-dimensional niche. This abstract n-dimensional niche can be studied mathematically and statistically, but ecology is mainly a field science. Therefore, the focus of techniques is on those used for field research of the ecological niche.

Research that attempts to describe all the elements of the n-dimensional ecological niche would require extensive observations. Yet, ecological niches are difficult to measure not only because of the plethora of data that would have to be collected but also because of the element of change in nature. The internal and external environment of an organism is always dynamic. Nothing in life is static, even if equilibrium has been established.

These constant fluctuations create daily and seasonal changes in space and ecological niches. Therefore, because of the constant fluctuations, any merely descriptive field observations would not be reliable depictions of an organism’s ecological niche. Ecologists must also resort to quantitative data of measurable features of an organism’s ecological niche. For example, the temperature, pH, light intensity, algae makeup, predators, and activity level of the organism are measurable features of an ecological niche in a pond community. The difficulty is in the collection of each of the necessary measurements making up an ecological niche. The ecologist would have to limit the data to a manageable number of specific dimensions of the niche based on conjecture and basic intuition. Such limitations often lead to incomplete and disconnected measurements that can, at best, only partially describe a few of the dimensions of the ecological niche.

Ecologists realize that complete observations and measurements of all the dimensions of an organism’s ecological niche are unattainable. The focus in understanding how a species interacts with its community centers on determining the degree of niche overlap between any two species—in other words, the level of competition for niche space and resources. Studies of this niche overlap are typically limited to dimensions that can be quantitatively measured. Yet, there is still the problem of deciding which of the dimensions are involved in the competition between the two species. Again, the ecologist must usually rely on inherent knowledge about the two species in question. Often, researchers investigating niche competition measure no more than four ecological niche dimensions to determine the niche overlap in an attempt to understand how two individuals competing for the same space, resources, or other ecological niche features can coexist.

Field methods for observations and quantitative measurements of elements of ecological niches, niche overlap, and niche competition are probably endless. To name a few, describing an organism’s niche may involve fecal samples to determine its diet, fecal samples of possible predators to identify its primary predator, animal and plant species checklists of its space niche along with soil components, climatic trends, and the like. Niche competition and overlap often can be studied first in the laboratory under controlled situations. One method might involve recording the population dynamics of the species as different elements in the ecological niche are manipulated to determine which is the better competitor and what resource is most responsible for limiting the population size.

Niche and Community

The shift in meaning and study from merely space and trophic level placement in the food pyramid to ecological niche of n dimensions has been beneficial for the field of ecology. This focus on community ecology is obviously much more productive for the goal of ecology, the understanding of how all living organisms interact with one another, and with the nonliving elements in the environment.

Perhaps more important is the attempt to describe niches in terms of community ecology, which can be essential for some of humankind’s confrontations with nature. For example, it becomes more and more apparent that synthetic chemicals are often too costly and too hazardous to continue using for control of crop pests and carriers of diseases. The goal is to control pests effectively with biological controls. Biological controls can involve the introduction of natural predators of the undesirable pest or the introduction of a virus or bacteria that eliminates the pest and is harmless to humans and wildlife.

The success of biological control is directly proportional to the knowledge of the pest’s n-dimensional ecological niche and the other organisms with which it comes in contact. A classic example of the havoc that can result from manipulations of nature without adequate ecological information is when Hawaii attempted to use biological controls to eradicate a population of snakes, which humans had accidentally introduced. The biological control used was the snake’s natural predator, the mongoose. One very important dimension of the ecological niche of both species was ignored. One species was active only at night, while the other was active only during the day. This particular venture with biological control was not a success.

Another relevant function of community-oriented studies of ecological niches involves endangered species. In addition to having aesthetic and potential medicinal values, an endangered organism may be a keystone species, a species on which the entire community depends. A keystone species is so integral to keeping a community healthy and functioning that if the species is obliterated, the community no longer operates properly and is not productive. Examples include bees, wasps, bats, and other pollinators, as well as predatory fish and beavers. Without pollinators, plants would not be able to produce, which negatively impacts every being in the ecological niche. Predatory fish maintain the populations of Earth's water sources, and beavers build structures that have a significant impact on the streams in North America.

Habitat destruction has become the most common cause of drastic population declines of endangered species. To enhance the habitat of the endangered species, it is undeniably beneficial to know what attracts a species to its particular preferred habitat. This knowledge involves the details of many of the dimensions of its ecological niche integral to its population distribution. Another common cause of endangering the survival of a species is when an introduced organism or exotic species competes for the same resources and displaces the native species. Solving such competition between native and introduced species would first involve determining niche overlap.

It is often stated that an ounce of prevention is worth a pound of cure. Thus, researching and understanding all the dimensions of ecological niches are integral components of preventing environmental manipulations by humankind that might lead to species extinction. Many science authorities agree that future research in ecology and related fields should focus on solving three main problems: species endangerment, soil erosion, and solid waste management. However, as climate change continues to alter ecological niches, the focus of ecological management may shift. The loss of biodiversity, particularly in tropical ecological niches, will increase with changing temperatures and adverse weather patterns.

This focus on research in ecology often means that studies of pristine communities, those undisturbed, will be the most helpful for future restoration projects. Although quantitative and qualitative descriptions of pristine areas seem to be unscientific at the time they are made, because there is no control or experimental group, they are often the most helpful for later investigations. For example, after a species has shown a drastic decline in its population, the information from the observations of the once-pristine area may help to uncover what niche dimension was altered, causing the significant population decrease.

Principal Terms

Community: All the populations of plant and animal species living and interacting in a given habitat or area at a given time

Environment: All the external conditions that affect an organism or other specified system during its lifetime

Food Pyramid: Diagram representing organisms of a particular type that can be supported at each trophic level from a given input of solar energy in food chains and food webs

Habitat: Place or type of place where an organism or community of organisms naturally thrives

Organism: Any form of life

Trophic Level: A level in a food chain or food web at which all organisms consume the same general types of food

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