In general, the diversity of plants and animals increases dramatically from the polar regions to the tropics. But we do not yet know why rainforests are so exceptionally rich in biodiversity. Is it due to inter- species struggle for specialization? Or is it a matter of the gradual accumulation of species under relatively stable tropical forest conditions over millions of years? Other theories hold that species evolve more rapidly in warm climates; that variations in micro-climate and periods where pockets of rainforest have been isolated in a drier or colder climate have fostered diversity; or that the geological changes that elevated lowlands to mountains (like the Andes) have stimulated the huge variety of plants and animals. The many theories are not mutually exclusive. Probably, all these factors have been involved in shaping the rich diversity of the world’s rainforests as we know them today.
From collection: State of the Rainforest