Biodiversity refers to the variation of life forms. It can be used to describe the variation of life in a single ecosystem, a geographical region, or an entire planet. Many biologists believe that biodiversity is an important part of sustainability, and that the more biodiverse a region is, the healthier it is. As a general rule, biodiversity is greater around the equator and less marked at the poles, due to the more harsh and demanding environment at the poles.
The term appears to have been coined in print in 1988 by E.O. Wilson, a famous biologist. Concerns about biological diversity were already well established; as early as 1975, the Nature Conservancy was publishing studies on diversity in various regions, and talking about the impact of diversity on the well being of the land and other life forms. Studies on various regions often include a discussion of biodiversity, which can be calculated in a number of ways, ranging from complex rubrics to basic counts of how many different species there are.
One of the greatest benefits of biodiversity is flexibility. A large number of unique species can flex with changing conditions, with numbers of various life forms increasing or decreasing to meet a changing environment. Biodiversity can also help to make natural populations stronger and healthier, by promoting the best individuals through competition and predation. Biodiverse crops tend to fare better than single crops, and biodiversity also contributes to the delicate balance of ecosystems, helping to regulate waste disposal, water quality, fertilization, and environmental factors.
On the smallest levels, biologists examine biodiversity in terms of single ecosystems, sometimes also called biomes. They may also compare biodiversity across ecosystems; for example, two watersheds with similar geographic and geologic conditions might have different levels of biodiversity. Some biologists also look at larger regions, or entire countries; questioning, for example, the impact of heavy commercial agriculture on the biodiversity of a nation.
As a planet, Earth itself is incredibly biodiverse. The planet hosts organisms which range in size from tiny viruses to huge whales, and life forms have been discovered everywhere from the seemingly hostile environments around hydrothermal vents to the lush tropical regions which mark the Earth's equator. Many biologists feel that steps should be taken to preserve this biodiversity because it benefits the health of Earth as a whole, and further study may be required to understand the exact interactions of all the life forms on Earth. Biodiversity is also simply aesthetically pleasing, as many visitors to the tropics and other incredibly biodiverse regions have noted.