Choose the correct statements regarding population interactions between two species.

A. In both parasitism and commensalism, only one species benefits and the other species is harmed.
B. Both species benefit in mutualism.
C. Both species benefit in commensalism.
D. In parasitism, only one species benefits and the other species is harmed.
E. In amensalism, one species is harmed and the other is unaffected.

Choose the correct answer from the options given below :

The question asks which of the listed statements about interspecific population interactions are correct.

Definitions of the interactions:

• Mutualism: Both species obtain a benefit from the relationship.

• Parasitism: One species (the parasite) benefits, while the other (the host) is harmed.

• Commensalism: One species benefits and the other is neither helped nor harmed (unaffected).

• Amensalism: One species is harmed while the other is unaffected.

Evaluation of each statement:

• Statement A: “In both parasitism and commensalism, only one species benefits and the other species is harmed.”
In parasitism this is true, but in commensalism the second species is unaffected, not harmed. Therefore statement A is false.

• Statement B: “Both species benefit in mutualism.”
By definition, mutualism involves reciprocal benefits, so statement B is true.

• Statement C: “Both species benefit in commensalism.”
Commensalism provides a benefit to only one species; the other is unchanged. Hence statement C is false.

• Statement D: “In parasitism, only one species benefits and the other species is harmed.”
This matches the definition of parasitism, making statement D true.

• Statement E: “In amensalism, one species is harmed and the other is unaffected.”
This is precisely the definition of amensalism, so statement E is true.

Collecting the true statements gives B, D, and E. The option that lists exactly these statements is “B, D and E only”.