Biogeography and The Great American Interchange Approximately 3 million years ago, the plates of the earth had nearly completed their shift to their present geographic spaces. At this time, the land bridge that connects North America and Central America through Panama closed, allowing for various species of plants, animals, and fungi to migrate from North America into South America and vise-a-versa. This major migration is termed the “Great American Interchange.” The plants and animals involved in the Interchange are well documented. But no one had previously studied how fungi responded to the connection of the continents. The study of the current distribution of organisms, and the history of how these distribution patters came to be is called biogeography. By developing baseline data on the species composition and distribution in Costa Rica, this information can then be compared to information of what macrofungi are known from North America and South America. This information can then be used to describe how the flora, fauna, and mycota within Central American tropical forests formed. Our data from Costa Rican tropical oak forests suggest that the ectomycorrhizal fungi that we have been collecting have migrated with their oak tree hosts as they migrated into Costa Rica from the north. We can assume this because the species that we have collected either show a range from Eastern North America through Costa Rica, or are a new species that have their closest relative found in Eastern North America. Many of the decomposer species appear to be either of South American or North American origin. continue >>