Which term describes the close ecological relationship in which at least one of the species benefits?

• A. Population Distribution
• B. Symbiosis
• C. Density-Dependent Factors
• D. Resource Partitioning

Answer: (B)

Symbiosis is the term for a close ecological relationship where at least one participant benefits. This umbrella includes mutualism (both benefit), parasitism (one benefits at the other's expense), and commensalism (one benefits, the other is unaffected). That core idea fits the prompt because it specifically describes interactions between species that confer a benefit to at least one of them.

The other terms describe different concepts: population distribution is about how individuals are spread in space; density-dependent factors are environmental pressures whose impact changes with how crowded the population is; and resource partitioning explains how species use different resources to avoid competing with each other. None of these inherently captures the idea of one or both species gaining from a close interaction. For example, mutualistic fungi and algae in lichens illustrate symbiosis, while parasitism is seen in tapeworms in hosts, and commensal relationships can be seen with barnacles on whales.