What is the Great American Biotic Interchange? (GABI)
Event in which land and freshwater fauna interchanged between South and North Americans through centeral America. The Isthmus of Panama rose up from the sea floor and formed a filter-bridge between the two continents.Migration peaked dramatically.
What's special about GABI?
Major milestone for dating
Theory of invasion and interchange
Biogeographic patterns (is there a maximum biodiversity for a region?)
Understanding what is happening now (re-uniting Pangea)
North America: Pre-connected
Evolution in isolation led to formation of many species that have gone extinct.
S. America isolated from all other continents; little interchange
Formation of Atlantic Ocean, S. America began isolation.
Late Cretaceous, mammals may have island hopped to reach the continent from either N. America, Australia, and Antarctica.
Oceans- evidence of splitting of marine taxa before terrestrial interchange.
Rapid, relatively balanced interchange
Establishment of quasi equilibrium
Vastly different fates
Fate of invaders to North America
Invasion of some S. American forms such as porcupines, oppossums, and armadillos and now extinct glyptodonts and bear-sized giant ground sloths.
Fate of the invaded S. America Fauna
Overall, the diversity of the S. American increased because because of the invasion and establishment of lineages from North America. Several S. America endemic species went extinct.
Fate of invaders to S. America
Fate of the invaded N. American Fauna
Remained virtually unchanged.
Why Northern forms have 3 advantages.
They were better migrators- Northern lineages were able to immigrate to S. America and colonize new areas, whereas S. American lineages colonized northward across the Isthmus of Panama, but extend no farther than the tropical forest of Southern MexicoThey were better survivors and speciators- N. American lineages not only survived, but also diversified there. While N. American lineages were diversifying, S. American lineages dwindled away because speciation didn’t keep up with extinction.
They were better competitors-N. American forms increased in generic and species diversity at the expense of S. American lineages. Furthermore, they radiated to usurp their ecological roles.