Final answer:
The interaction where one species benefits and the other is negatively affected is called parasitism, a symbiotic relationship in which the parasite benefits at the host's expense. The confusion may arise from commensalism, where one species benefits without any harm or benefit to the other species.
Step-by-step explanation:
The interaction described in the question where one species benefits without killing the other species, and the other is negatively affected, is best characterized as parasitism. This is a type of symbiotic relationship between two species wherein the parasite benefits at the expense of the host, which is harmed in the process.
An example of parasitism is a tick feeding on the blood of a mammal. The tick gains nourishment, while the mammal may suffer blood loss and potential disease transmission. However, it should be noted that the question's wording about the other species being 'negatively affected' indicates harm, which corresponds to parasitism, not commensalism, where the other species is not affected.
In a commensal relationship, one species benefits while the other neither benefits nor is harmed. An example of commensalism is a bird nesting in a tree; the bird benefits from the shelter while the tree is unaffected.