Which relationship describes a situation where both species benefit but are not essential for each other's survival?

The relationship described as one where both species benefit but are not essential for each other's survival is protocooperation. In protocooperation, the interaction between the two species is beneficial and may enhance their survival or reproduction, but one species is not reliant on the other for its existence. This differentiates protocooperation from mutualism, where the relationship tends to involve a more obligatory connection where one or both species may struggle to survive without the other.

In contrast, parasitism is a relationship that benefits one organism at the expense of another, and competition involves two species vying for the same resources, which typically results in stress or detriment to one or both parties rather than mutual benefit. Hence, protocooperation is characterized specifically by its non-essential, yet beneficial nature for the species involved.