Exotic species introductions into South America: an underestimated threat?

Abstract

Prior studies on the latitudinal extent and ecological impact of exotic plant species suggest that areas of high diversity, such as the Neotropics, may be relatively 'resistant' to invasions. To explore the generality of this assertion and assess the impact of alien species on continental tropical faunas, I compiled data for threatened Neotropical animals from the red data books of Bolivia, Brazil, Minas Gerais (a Brazilian state), Peru, and Venezuela. A total of 378 species (including both vertebrates and invertebrates) were considered. For each taxon, I recorded whether it is threatened by habitat conversion, overexploitation, and/or exotic species. As suggested by other researchers, exotic species introductions appear to be relatively unimportant in South America, threatening only 6% of animal taxa. However, many South American animals are themselves either recent invaders or survivors of the Great American Biotic Interchange (GABI) which began during the Pliocene. Here, I hypothesize that the GABI may have acted as an 'extinction filter', leaving faunal groups of mostly South American origin relatively more threatened by the current wave of exotic invaders than those with prominent North American representation. The data support this prediction. For taxa whose current diversity patterns were not strongly influenced by the GABI, exotic species are indeed an important threat. For example, alien invaders threaten 29% of continental fishes and 30% of amphibians, figures comparable to those recorded in temperate areas. As more information on these less-studied taxa becomes available, the magnitude of the threat posed by exotic species introductions will probably reveal itself to be large. Of critical importance is to assess the impact of invasions on biological realms that have only been recently exposed to alien taxa, such as the aquatic faunas of the numerous drainages that occur along the eastern and western slopes of the South American Andes. The results of these investigations provide predictions for similar research focussed on other continental tropical regions of the world.