Symbiosis is the close and often long lasting relationship that exists between two biologically different species.
The definition of symbiosis is controversial among scientists. Some believe symbiosis should only refer to persistent mutualisms, while others believe it should apply to any types of persistent biological interactions. Examples of this would include Parasitic, Commensalistic and Mutualistic interactions.
Some symbiotic relationships are obligate, meaning that both organisms entirely depend on each other for survival. For example, some lichens cannot live without other lichens being present. Others are facultative, meaning that they can rely on other organisms, but they do not have to interact with the other organism in order to survive.
Mutualism is any relationship between individuals of different species where both individuals derive a benefit. In general, only lifelong interactions involving close physical and biochemical contact can properly be considered symbiotic. Mutualistic relationships may be either obligate for both species, obligate for one but facultative for the other, or facultative for both.
An example is the Clownfish which feeds on small invertebrates that potentially cause harm to Sea Anemones. The territorial Clownfish also chase away other fish that feed on anemones. The fecal matter from the Clownfish provides nutrients for the sea anemone to feed on. The Clownfish also receives a benefit in that it is protected from predators by the Anemone's stinging cells. The Clownfish has developed a protective mucus that is found around its body that protects it from the tentacles of the Anemones.
Commensalism describes a relationship between two living organisms where one benefits and the other is not significantly harmed or helped. For example, Cattle Egrets forage in fields among cattle or other livestock for food. As cattle and other livestock graze, they cause movements that stir up various insects that the Cattle Egrets then feed on. The Egrets benefit from this but the livestock are typically unaffected by this relationship.
There are three specific types of Commensalist relationships : Metabiosis- When an organism uses something another organism has created as a home. Phoresy- Involves one organism using another for transportation Inquilinism- When one organism uses another organism as a home.
Metabiosis- Hermit Crabs using snail shells to protect their bodies. Phoresy- This category mainly includes insects that travel on other organisms. Inquilinism- Orchids that grow on trees, or birds using holes in cactus and trees as nests.
A parasitic relationship is one in which one member of the association benefits while the other is harmed. An example is the cowbird, which do not build nests of their own but rather deposit their eggs in nests of other species. The host bird raises the young as their own. The cowbird’s parasitism does not necessarily harm its host’s brood. However, some may remove one or more host eggs to avoid detection, and furthermore the young cowbird may heave the host’s eggs and nestlings out of the nest.
Parasitic Relationships: Endoparasites- Organisms that live within the host's body in order to survive. For example, Tape Worms. Ectoparasites- Organisms that live on the surface of the host organism’s body. For example, Mites.
Parasites may be... Necrotrophic- The parasite kills their host as they use them. For example, Strangler Fig. Biotrophic- The parasite relies on their host's surviving. For example, Leeches.