Equatorial forests are unique for their high plant and animal diversities. Diversity results from speciation and is historically related to patterns of biogeography that result in part from plate tectonics. Causal factors that generate high tropical diversity are warm and wet climate, equitable seasonality, large area, high plant productivity and complex biotic interactions leading to ecological specialization. Within the tropics, wet forests exhibit the highest animal diversity, likely due to greater plant productivity and less harsh seasonality. Some species of long-distance migrant birds have evolved in the tropics and are integral components of tropical forests during their winter residencies. Fragmentation of forests has accelerated globally and threatens numerous animal species with potential extinction. Conservation efforts must recognize factors such as importance of large area, need for animal-assisted pollination and seed dispersal, minimal hunting pressure and habitat connectivity.