Which term is used to describe a lineage that evolves separately and occupies a unique adaptive zone?

The term that accurately describes a lineage that evolves separately and occupies a unique adaptive zone is "evolutionary significant unit." This term is used in conservation biology to refer to a population or group of populations that has significant evolutionary potential. An evolutionary significant unit is important for preserving genetic diversity and adaptive potential, which can be critical for species' survival, especially in changing environments.

An evolutionary significant unit consists of organisms that are genetically distinct from other lineages and that contribute to the evolutionary legacy of a biodiversity hotspot. This distinction emphasizes the importance of recognizing specific populations that may be adapting to unique ecological niches, thereby occupying adaptive zones that are different from other populations.

In contrast, the other terms listed in the question correlate with different biological concepts that do not capture the essence of a lineage evolving separately in its unique adaptive zone. Ecospecies often refers to a group of species or a species that occupy similar ecological roles; adaptive radiation describes a process by which organisms diversify rapidly into a wide variety of forms to adapt to different environments; and lineage broadly refers to a sequence of species, organisms, or cells from a common ancestor. Therefore, "evolutionary significant unit" is the most fitting term for the description provided.