Symbiosis is a mutualistic relationship that takes place between two completely different organisms. In certain cases each of them depends completely on the other in order to survive. The greatest bonds are those who become life long partners that involve a close physical or biochemical connection. This is properly known as a ‘symbiotic’ relationship.
The bond between a human being and their service dog revolves completely around that physical contact. Service dogs are not just house pets; they are their partner’s eyes, ears, hands, legs, heart monitors, seizure detectors, and all around support systems.
From what I have researched on the term 'symbiosis,' it has been used to describe fish that live on sharks bellies, ants that help trees grow, and leeches. After spending time with people who have service animals, I noticed that the meaning this word also applies directly to humans and who have service dogs as well! This is only a theory I have developed, but I am curious to know why there isn't more research on it.