Species migration events are common features of the fossil record, but the impacts of immigration events vary. In this paper, the pattern and impact of two types of immigration events are compared: ephemeral invasion and biotic immigration events (BIMEs). Specifically, this study focuses on biotic patterns preserved in Edenian, Maysvillian, and Richmondian (Late Ordovician, Katian) age strata in the Cincinnati, USA region. New Edenian occurrences of rhynchonelliformean brachiopod taxa belonging to the classic “Richmondian Fauna” are documented, and the ecological and evolutionary impacts of these short-lived pre-Richmondian invasions and the sustained Richmondian Invasion are compared. The Richmondian Invasion produced substantial ecological changes and evolutionary impacts within the Cincinnatian paleocommunity; however, the ephemeral invasions that occurred in the Kope Formation did not produce a marked or lasting impact on ecological relationships within Cincinnatian paleocommunities. In each instance, an Edenian novel immigration or biotic event was limited in temporal duration and did not exceed the time to deposit a single sedimentary package. Although such ephemeral invasions do not result in community-scale changes, they nevertheless provide important information about basin connectivity, provide insight into abiotic environmental conditions, and can be useful stratigraphic indicators.