I was not referring to a case of mutualism. Mutualism implies a bidirectional benefit of the relationship. I believe the ants you refer to trade defense service

I was not referring to a case of mutualism. Mutualism implies a bidirectional benefit of the relationship. I believe the ants you refer to trade defense services for honeydew from smaller bugs, for example. Mutualism is still very interesting, but what I was referring to was a case of preserving another organism without a direct benefit. For example, wild dolphins protecting humans from sharks or similar.