Q.10 An interaction where one species is harmed and the other is unaffected is called
1. commensalism
2. facilitation
3. parasitism
4. amensalism
Species Interaction: One Harmed, Other Unaffected is Amensalism
Ecological interactions between species shape communities through benefits, harms, or neutrality. The correct answer is 4. amensalism, a (-/0) relationship where one organism inhibits another without gaining benefit.
This contrasts with mutualism (+/+), commensalism (+/0), and parasitism (+/-), highlighting amensalism’s one-sided harm.
Amensalism Defined and Examples
Amensalism occurs when one species releases a substance or behaves in a way that harms another, while remaining unaffected itself. No direct benefit accrues to the inhibitor—harm is incidental.
Classic examples include black walnut trees secreting juglone, which poisons nearby plants, or penicillin-producing fungi killing susceptible bacteria without consuming them. The inhibitor continues unaffected.
Explanation of All Interaction Options
Each option represents a distinct +/- outcome in biotic interactions.
| Option | Interaction | Effect on Species 1 / Species 2 | Example | Matches Query? |
|---|---|---|---|---|
| 1 | Commensalism | + / 0 | Barnacles on whales (barnacles get transport) | No—one benefits |
| 2 | Facilitation | + / + or + / 0 | Nurse plants shelter seedlings | No—both benefit or one benefits |
| 3 | Parasitism | + / – | Tapeworms in host gut | No—parasite benefits |
| 4 | Amensalism | 0 / – | Walnut juglone killing grasses | Yes—one harmed, other unaffected |
Ecological Significance
Amensalism structures communities by creating “inhibition zones,” influencing plant succession or microbial competition. Unlike predation or parasitism, it lacks trophic transfer—pure allelopathy or resource exclusion.
Recognizing these prevents misclassifying incidental harms as parasitism, crucial for conservation and agriculture.
Correct Answer: 4. amensalism
