Tropical rainforests vary because of differences in latitude, altitude, soils, or water supply. Because of their immense diversity, they provide many different niches in which organisms can live. A niche consists an organism’s total role and interactions with its ecosystem and environment. Generally speaking, niches will be related to vertical position in the forest, i.e., above the canopy, in the top canopy, in the understory, in the lower part of the forest, or on the ground. Of course, there are horizontal niches as well, and there are many other niches in rivers and lakes, in flooded, cloud, and montane forests. The important point here is not to categorize all possible niches and habitats within forests, but to recognize their immense number and diversity. This is an opportunity for an explosion of species, and so rainforests are generally the most species-rich ecosystems on earth, rivaled only by coral reefs. The forest has many microclimates – places with a variety of temperatures, shady and sunny areas, moister and drier areas, and so on. The trees provide habitats for climbers, epiphytes, vines, insects, birds and arboreal animals. The forest growth cycle provides yet more habitats – differing sizes of gaps in the forest, variations in the forest canopy cover, differing fruiting cycles, and on and on. Another important feature of rainforests is that, since large trees of any one species are not usually close neighbors, any organisms whose habitat includes that tree species must of necessity have a large range. In contrast, trees in the understory are much closer together, and form a continuous layer of foliage which provides habitat for many arboreal animals (and plants). The much greater diversity of animals in rainforests in comparison with temperate forests consists mainly of arboreal animals – particularly insects.
Because of these almost innumerable variations the forest is a mosaic of varied groupings of species, both plant and animal. Most of these species never move from one level of the forest to another, each layer having its own particular characteristics. Many rainforest species are specialists; that is, they can live in only one of the myriads of niches or habitats available in a forest. Often, the organism is so specialized that it lives only in a single area or in patches of unusual habitat.