A One-Way Relationship in Which One Species Benefits at the Expense

Question

A one-way relationship in which one species benefits at the expense of another is ____.  
A) commensalism
B) competitive exclusion
C) parasitism
D) obligate mutualism
E) a neutral relationship

Accepted Answer

This is the definition of parasitism, where one species benefits (the parasite) and the other is harmed (the host). Commensalism (A) is a one-way relationship where one species benefits and the other is neither helped nor harmed. Competitive exclusion (B) refers to the idea that two species competing for the same resources cannot coexist indefinitely. Obligate mutualism (D) is a type of mutualism where the two species have a dependent relationship on each other. A neutral relationship (E) is one where the two species have no effect on each other.