Could you explain what is neutralism with an example?

 Neutralism describes the relationship between two species which interact but do not affect each other. It describes interactions where the fitness of one species has absolutely no effect whatsoever on that of the other. True neutralism is extremely unlikely or even impossible to prove. When dealing with the complex networks of interactions presented by ecosystems, one cannot assert positively that there is absolutely no competition between or benefit to either species. Since true neutralism is rare or nonexistent, its usage is often extended to situations where interactions are merely insignificant or negligible.

Many weeds seem to co-exist with each other in a near-neutral type of relationship. A square meter of a vacant lot covered in weeds, often contains a surprising number of species.