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Commensalism is a type of relationship between two living organisms in which one organism benefits from the other without harming it. A commensal species benefits from another species by obtaining locomotion, shelter, food, or support from the host species, which (for the most part) neither benefits nor is harmed. Commensalism ranges from brief interactions between species to life-long symbiosis.
The term was coined in 1876 by Belgian paleontologist and zoologist Pierre-Joseph van Beneden, along with the term mutualism. Beneden initially applied the word to describe the activity of carcass-eating animals that followed predators to eat their waste food. The word commensalism comes from the Latin word commensalis, which means "sharing a table." Commensalism is most often discussed in the fields of ecology and biology, although the term extends to other sciences. Commensalism is often confused with related words: Mutualism - Mutualism is a relationship in which two organisms benefit from each other. Amensalism - A relationship in which one organism is harmed while the other is not affected. Parasitism - A relationship in which one organism benefits and the other is harmed. There's often debate about whether a particular relationship is an example of commensalism or another type of interaction. For example, some scientists consider the relationship between people and gut bacteria to be an example of commensalism, while others believe it is mutualistic because humans may gain a benefit from the relationship.
Inquilinism - In inquilinism, one organism uses another for permanent housing. An example is a bird that lives in a tree hole. Sometimes epiphytic plants growing on trees are considered iniquilism, while others might consider this to be a parasitic relationship because the epiphyte might weaken the tree or take nutrients that would otherwise go to the host. Metabiosis - Metabiosis is a commensalistic relationship in which one organism forms a habitat for another. An example is a hermit crab, which uses a shell from a dead gastropod for protection. Another example would be maggots living on a dead organism. Phoresy - In phoresy, one animal attaches to another for transport. This type of commensalism is most often seen in arthropods, such as mites living on insects. Other examples include anemone attachment to hermit crab shells, pseudoscorpions living on mammals, and millipedes traveling on birds. Phoresy may be either obligate or facultative. Microbiota - Microbiota are commensal organisms that form communities within a host organism. An example is the bacterial flora found on human skin. Scientists disagree on whether microbiota is truly a type of commensalism. In the case of skin flora, for example, there is evidence the bacteria confer some protection on the host (which would be mutualism). Domestic dogs, cats, and other animals appear to have started out with commensal relationships with humans. In the case of the dog, DNA evidence indicates dogs associated themselves with people before humans switched from hunting-gathering to agriculture. It's believed the ancestors of dogs followed hunters to eat remains of carcasses. Over time, the relationship became mutualistic, where humans also benefited from the relationship, gaining defense from other predators and assistance tracking and killing prey. As the relationship changed, so did the characteristics of dogs. Symbiosis comes from two Greek words that mean "with" and "living." It describes an ecological relationship between two organisms from different species that is sometimes, but not always, beneficial to both parties. Keep reading to learn about the different types of symbiosis and how they provide balance in various ecosystems around the world. There are several kinds of symbiosis to consider when looking for symbiosis examples. Each type is often found in a habitat, but some are more common than others. The most common types of symbiosis include:
These symbiotic relationships are different based on which species benefits the most and whether they can live without each other. However, each one allows an ecosystem to reach a sustainable balance. When people use the word symbiosis, they’re usually talking about a mutualistic symbiotic relationship. Mutualism is a close, long-lasting relationship where both parties benefit. Organisms can use other organisms for cleaning, protection or gathering food. In some mutualistic relationships, the organisms can’t survive without each other. Some examples of mutualism in nature include:
Commensalism is a one-sided relationship where one of the organisms benefits greatly from the symbiosis. The other is not helped, but it is not harmed or damaged from the relationship either. In some of these commensalism relationships, the organism that is reaping the benefit will use the other for protection or transportation. Examples of commensalism in habitats include:
In parasitism, one organism benefits from the relationship at the expense of the other. The parasitic organism may live inside another organism's body (endoparasitism) or on its surface (ectoparasitism). The host species often weakens and sometimes dies, but in most cases, the parasite needs it to stay alive so it can keep feeding on it. Examples of parasitic symbiosis include:
Many species compete for the same resources in an ecosystem, which is called competition symbiosis. It may seem like this type of relationship is the opposite of symbiosis, but ecosystems depend on a balance of different species being present. If one species has an abundance of resources and another doesn’t, both species could suffer and possibly die out. Examples of competition symbiosis include:
Predation is the process by which one organism feeds on another, typically one animal eating another animal. Herbivory relationships involve an animal eating part or all of a plant. It may seem like predation is not an example of symbiosis because only one organism survives the encounter. However, without predation, other species would become too numerous and resources would become source. Predatory (or even herbivory) animals never kill every member of the prey species unless the symbiotic relationship is out of balance. For example:
Whether it’s a mutually beneficial relationship, a parasitic relationship or a competitive relationship, symbiosis is an important part of our natural world. Without symbiosis in nature, many ecosystems would suffer and cease to flourish. Check out these examples of food chains in different ecosystems to see more about predation relationships. You can also explore heterotroph examples in food chains to learn more about how different organisms sustain themselves.
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