Biodiversity (a contraction of the phrase biological diversity) means the variety of life on earth, or within one particular ecosystem, in terms of the number of distinct biological species present. Tropical rainforests, for example, support a huge variety of species, so are highly biodiverse, while polar regions are far less so. Scientists worry that deforestation, such as that associated with planting crops for biofuels, animal feed and human consumption is reducing biodiversity. See also monoculture.