The human body has about 10 bacterial cells for every eukaryotic cell. bacteria coat our skin, gut, and mouth. also present are protists, archaeans, and viruses. collectively, these organisms are our microbiota. for most members of our microbiota, our body provides their environment (or space to live). they, in turn, have no effect on us. this is an example of: predation. mutualism. commensalism. an antagonistic relationship.

commensalism

Explanation:

Commensalism is a type of ecological interaction between two species in which one speices benefits while other is unaffected. Commensalism  also can be considered as a type of symbiosis-two species that live together. The interaction between human and its microbiota is beneficial for microbiota while it has no effects on humans.

Although, some bacteria (gut bacteria) can help in digestion. In this case, interaction with human is mutualism (both have benefits).

not necessarily. higher fitness requires the organism to be reproductive successful. for example, an organism at age 10 with 15 offspring is much more fit than an organism at age 15 with only 5 offspring.