The asymmetry in the Great American Biotic Interchange in mammals is consistent with differential susceptibility to mammalian predation

Aim One of the most widely cited natural experiments in biogeography is the Great American Biotic Interchange (GABI). Here, we re‐assess the famous asymmetry in the exchange for mammals, with North American clades being much more successful in South America than vice versa. We investigate if this directionality could reflect higher susceptibility to predation in South American mammals rather than low competitive ability, as is usually believed. Location North and South America. Methods Prior to the GABI, South America lacked effective mammalian predators. Since its fauna did not co‐evolve with such predators, colonization of North America may only have been possible for species whose natural history makes them less susceptible to mammalian predation. To investigate this we used phylogenetic regressions to investigate species traits associated with the ability of clades originally from South America to colonize North America, and vice versa, during the GABI. Analyses were conducted both with and without species that went extinct in the late Quaternary. Results When extinct species were included, traits associated with lower predation risk (large body size, arboreality) were associated with greater success in colonizing North America for South American clades. This pattern was not visible in analyses based on the current fauna, since most of the mammals that invaded North America went extinct at the end of the Pleistocene, probably due to human predation. The pattern for northern colonizers of South America was similar whether or not extinct species were included and was not linked to predation risk. Conclusions Our findings are consistent with the asymmetric GABI in mammals being explained by predation and not with expectations from competition. The GABI therefore illustrates that trophic interactions can be a powerful driver of long‐term dynamics of biotic interchange, as seen in many human‐driven invasions of formerly isolated regions.