Practice question

Antibiotic secretion by a fungus that suppresses nearby bacteria is a standard example of amensalism, specifically antibiosis, when the fungus is treated as unaffected and the bacteria are harmed. The fungal metabolite inhibits bacterial cell-wall synthesis, protein synthesis, membrane function, or another essential process, depending on the compound. Penicillin, for instance, blocks transpeptidation during peptidoglycan assembly, causing susceptible growing cells to lyse. Ecological sign notation represents this simplified outcome as (0, −): no measurable effect on the producer and a negative effect on the recipient. This differs from parasitism, where the beneficiary obtains resources through an intimate association with a host, and from mutualism or commensalism, which do not impose this negative effect. In nature, the producer may indirectly benefit through reduced competition, making some cases better interpreted as interference competition rather than strict amensalism. The textbook classification assumes no demonstrated benefit to the fungus. Recognizing that assumption is important because interaction categories describe net fitness effects under specified conditions, not immutable properties of the species.