The Neotropical Realm includes most of Central and South America with the exception of the Caribbean Islands, the drier areas to the west of the Andes in north-western South America along with the central and southern Andes, and the subtropical, temperate, and subarctic zones of the south-east, all of which are dealt with separately in this book. It is here divided into two zoogeographic regions (the Mesoamerican and Amazonian). This area is mostly tropical, extending slightly into the subtropical zone in the south-east. It has more rainforests, mainly in the Amazon basin, than any other continent, as well as drier forests and savannas. Among the mountain chains of the world the Andes are second only to the Himalayas in height. They form a western border for the whole of South America and a formidable barrier separating the Pacific Ocean and its shores from the interior of the continent. The Andean highlands are almost a world unto themselves. Great valleys, plains, slopes, and cordilleras divide this enormous chain, transversely as well as from north to south. The range of microclimates as well as of vegetation is very wide, not only because of the extreme variations in altitude from the ocean shore to the highest peaks, but also because of the range in latitudes from the Caribbean shore in the north to southern Peru and Bolivia in the south.