Paleoecological changes associated with Phanerozoic mass extinctions and radiations can be categorized into four nonhierarchical, nonadditive levels. First-level changes include colonization of a new ecosystem. Structural changes within an established ecosystem represent the second level, changes within an already established ecological structure are the third-level, and taxonomic changes within a community represent the fourth-level. Applying these levels to the Ordovician radiation, end-Ordovician extinction and Silurian recovery, as well as the end-Permian extinction and Triassic recovery demonstrate that paleoecological changes associated with these major events can be evaluated and compared in a more rigorous manner than previously done. Results of this analysis demonstrate that use of these levels indicates that the relative magnitude of an event as measured by taxonomic criteria may be decoupled from its paleoecological significance.