Ecosystems of South America northeast Brazil that cause a dry rain shadow in the interior northeast region; the Guyana Highlands that block the trade winds and cause a dry winter effect in their leeward slopes; and the Sierras de Cordoba and Patagonian Plateau in Argentina, which affect air temperature and can collect moisture from humid air masses crossing Patagonia (Figure 2) There are also dry inter-Andean valleys localized along its range Biogeography 109 reported for Colombia, 468 in Brazil, 374 in Ecuador, 298 in Peru, and 293 in Venezuela, including species of snakes, turtles, and iguanas –which other than in South America only occur in the Fiji and Tonga Islands of the Pacific Brazil is also considered as the country with highest diversity of freshwater fish species in the world with 43000 species reported, Colombia the second (41500), Venezuela the fourth (41200), and Peru the seventh (4850) The diversity of invertebrates is also outstanding; for example, there are more than 350 endemic species of butterflies reported for Peru, 300 for Colombia, 200 for Brazil, and 200 for Bolivia Early History and Associations Biogeographers include central and northern South America in the Neotropical Kingdom, which also contains the Antilles and most of tropical Central America Until approximately the Early Cretaceous, South America, Africa, Australia, and Antarctica were joined together composing the supercontinent Gondwanaland, thus allowing for a continuous interchange of their ancient biotas Africa and South America share many plant families like Annonaceae, Myristicaceae, Cecropiaceae, Sterculiaceae, and Bombacaceae Some plant genera are very diverse in one continent and barely represented on the other, for instance, Mayaca (about eight species in America and one in Africa), Duvernoya (B35 species in Africa and three in America), and Hyptis (B400 species in America and two in Africa) The southern cone of South America is included within the Holantartic Kingdom, which includes the temperate mesic-adapted floras of southern South America, New Zealand, and southwestern Australia The genera of trees Araucaria, Podocarpus, and Nothofagus are typical although not exclusive to the southern cone Fossil records have also shown strong ancient faunal associations between South America, Africa, Antarctica, and Australia For instance, some of the existing species of fishes of South America, as well as their parasites, show affinities with African groups There are also close phylogenetic relations among groups of South American, African, and New Zealand invertebrates including, among others, arachnids and mollusks After the separation of South America from the rest of Gondwanaland in the Early Cretaceous, the biota of the continent was isolated for millions of years Because of their isolation, South American flora and fauna are extraordinarily rich in endemic groups and species It is estimated that about 7% of the total world’s superior plants are endemic species from Brazil, 6.8% from Colombia, 3.2% from Venezuela, 2.1% from Peru, and 2% from Ecuador Brazil is the country with more mammal species reported in the world (4520 of which more than 130 are endemic), Colombia the fourth (4455), and Peru the ninth (4345 of which 46 are endemic) Endemic faunal families include the armadillos Dasypodidae, the anteaters Myrmecophagidae, and the monkeys Cebidae Particularly important are the marsupials that in South America are represented by two genera, two families, and 87 species There are no fewer than 3000 bird species with two orders and 30 endemic families The humming birds, which are endemic of the New World, have more than 250 species in South America and populate ecosystems from the Amazonian lowlands to the high Andean Mountains The diversity of endemic reptiles is exceptional; there are 520 endemic species Late Tertiary Although it is likely that some exchange occurred between North and South America during the Eocene and Miocene, the land bridge of the Panama Isthmus connected permanently South, Central, and North America about 3.5 million years ago The completion of the Panamanian land bridge in the Early Pliocene was perhaps one of the most influential biogeographical events that has occurred in the continent and it dramatically changed the ancient biota of South America The significant exchange of South and North American biotas is called by biogeographers as "the great American Interchange" Among the many invaders that entered South America through the isthmus are rattlesnakes, rodents, tapirs, deer, peccaries, felids (including jaguars and pumas), canids, and humans About 40% of the mammal fauna of South America are species that arrived since the Pliocene Among the South American forms that migrated to North America are the ground sloth, which disappeared about 10,000 years ago, and opossums and armadillos, which are still expanding their range The dynamic interchange of plant and animal forms between South and North America continues at present Quaternary During the past million years, climatic fluctuations of dry glacial and wet interglacial periods affected the geographic ranges of both temperate and tropical areas Palynological sequences indicate that at least during the Pleistocene, major climatic changes affected speciation and biogeographic patterns in South America The modern geographical distributions of many endemic taxa resulted from Quaternary speciation and redistribution of species overlaid with previously existing range patterns The explicit mechanisms that generated current biogeographical patterns are not fully understood, in part due to their inherently historical nature that is difficult to reconstruct (Bush, 1994, 2003) Paleoecological studies initially assumed that the richness and complexity of plant communities were a consequence of continuous favorable growing conditions persisting over long time periods Many areas have been identified as centers of endemism and proposed as tropical forest refugia occurring during the period spanning 18,000 to 13,000 years ago (Haffer, 1969) According to this hypothesis, during the last four glaciating cycles of the Pleistocene, tropical forest contracted during dry glacial periods causing most of the Amazon Basin, as well as other forested areas, to be occupied by savanna vegetation Continuous but isolated islands of forest