What type of ecological interaction exists between the snake and the mouse

Updated March 09, 2018

By Angela Ryczkowski

Ecological relationships describe the interactions between and among organisms within their environment. These interactions may have positive, negative or neutral effects on either species' ability to survive and reproduce, or "fitness." By classifying these effects, ecologists have derived five major types of species interactions: predation, competition, mutualism, commensalism and amensalism.

Predation includes any interaction between two species in which one species benefits by obtaining resources from and to the detriment of the other. While it's most often associated with the classic predator-prey interaction, in which one species kills and consumes another, not all predation interactions result in the death of one organism. In the case of herbivory, a herbivore often consumes only part of the plant. While this action may result in injury to the plant, it may also result in seed dispersal. Many ecologists include parasitic interactions in discussions of predation. In such relationships, the parasite causes harm to the host over time, possibly even death. As an example, parasitic tapeworms attach themselves to the intestinal lining of dogs, humans and other mammals, consuming partially digested food and depriving the host of nutrients, thus lowering the host's fitness.

Competition exists when multiple organisms vie for the same, limiting resource. Because the use of a limited resource by one species decreases availability to the other, competition lowers the fitness of both. Competition can be interspecific, between different species, or intraspecific, between individuals of the same species. In the 1930s, Russian ecologist Georgy Gause proposed that two species competing for the same limiting resource cannot coexist in the same place at the same time. As a consequence, one species may be driven to extinction, or evolution reduces the competition.

Mutualism describes an interaction that benefits both species. A well-known example exists in the mutualistic relationship between alga and fungus that form lichens. The photsynthesizing alga supplies the fungus with nutrients, and gains protection in return. The relationship also allows lichen to colonize habitats inhospitable to either organism alone. In rare case, mutualistic partners cheat. Some bees and birds receive food rewards without providing pollination services in exchange. These "nectar robbers" chew a hole at the base of the flower and miss contact with the reproductive structures.

An interaction where one species benefits and the other remains unaffected is known as commensalism. As an example, cattle egrets and brown-headed cowbirds forage in close association with cattle and horses, feeding on insects flushed by the movement of the livestock. The birds benefit from this relationship, but the livestock generally do not. Often it's difficult to tease apart commensalism and mutualism. For example, if the egret or cowbird feeds on ticks or other pests off of the animal's back, the relationship is more aptly described as mutualistic.

Amensalism describes an interaction in which the presence of one species has a negative effect on another, but the first species is unaffected. For example, a herd of elephants walking across a landscape may crush fragile plants. Amensalistic interactions commonly result when one species produces a chemical compound that is harmful to another species. The chemical juglone produced in the roots of black walnut inhibit the growth of other trees and shrubs, but has no effect on the walnut tree.

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By David H. Nguyen, Ph.D.

Organisms occupy what are called niches. A niche includes the physical space in which they live, how they use the resources that are in that space, and how they interact with other organisms in that space. The interaction among organisms within or between overlapping niches can be characterized into five types of relationships: competition, predation, commensalism, mutualism and parasitism. The last three subtypes are classically defined as relationships exhibiting symbiosis, but predation and competition can also be considered as forms of symbiosis. Symbiosis refers to a close relationship in which one or both organisms obtain a benefit.

Predation is when one organism eats another organism to obtain nutrients. The organism that is eaten is called the prey. Examples of predation are owls that eat mice, and lions that eat gazelles. Competition is when individuals or populations compete for the same resource, and can occur within or between species. When organisms compete for a resource (such as food or building materials) it is called consumptive or exploitative competition. When they compete for territory, it is called interference competition. When they compete for new territory by arriving there first, it is called preemptive competition. An example is lions and hyenas that compete for prey.

Commensalism is a relationship in which one organism benefits while the other is neither helped nor harmed. Examples are barnacles that grow on whales and other marine animals. The whale gains no benefit from the barnacle, but the barnacles gain mobility, which helps them evade predators, and are exposed to more diverse feeding opportunities. There are four basic types of commensal relationships. Chemical commensalism occurs when one bacteria produces a chemical that sustains another bacteria. Inquilinism is when one organism lives in the nest, burrow, or dwelling place of another species. Metabiosis is commensalism in which one species is dependent on the other for survival. Phoresy is when one organism temporarily attaches to another organism for the purposes of transportation.

Parasitism is a relationship in which one organism benefits and the other organism is harmed, but not always killed. The organism that benefits is called the parasite, and the one that is harmed is the host. Parasitism is different from parasitoidism, which is when the host is always killed, such as when one organism lays its egg inside another organism that is later eaten by the hatchlings. Parasites can be ectoparasites -- such as ticks, fleas, and leeches -- that live on the surface of the host. Parasites can also be endoparasites -- such as intestinal worms – that live inside the host. Endoparasites can be further categorized into intercellular parasites, that live in the space between cells, or intracellular parasites, which live inside of cells. There is also something called hyperparasitism, which is when a parasite is infected by another parasite, such as a microorganism living in a flea, which lives on a dog. Lastly, a relationship called social parasitism is exemplified by an ant species that does not have worker ants, living among another ant species that do, by using the host species’ workers.

Mutualism is a relationship in which both species benefit. Mutualistic interaction patterns occur in three forms. Obligate mutualism is when one species cannot survive apart from the other. Diffusive mutualism is when one organism can live with more than one partner. Facultative mutualism is when one species can survive on its own under certain conditions. On top of these, mutualistic relationships have three general purposes. Trophic mutualism is exemplified in lichens, which consist of fungi and either algae or cyanobacteria. The fungi's partners provide sugar from photosynthesis and the fungi provide nutrients from digesting rock. Defensive mutualism is when one organism provides protection from predators while the other provides food or shelter: an example is ants and aphids. Dispersive mutualism is when one species receives food in return for transporting the pollen of the other organism, which occurs between bees and flowers.

Students watch videos and discuss ecological relationships with a focus on observing symbiosis. Then they classify the ecological relationships they observe as mutualism, commensalism, and parasitism.

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