Also biological diversity. Designates different levels of living diversity: first, the number of species in an area, the biodiversity; secondly, the diversity of ecosystems or habitats in an area and thirdly, the diversity within species, i.e. the differences in genetic information between individuals and populations. A high level of species richness can result, for example, from heterogeneous habitats or a wide range of resources, and the species richness of the animal world is often dependent on the species richness of the plant world. Globally, an increase in species richness can be observed from the north and south poles to the equator. The tropical rain forests are considered to be important biodiversity hotspots.