It is also a story of how genetic diversity helps species survive. No new mutation occurred to help the moth adjust to changing circumstances. Rather, both light and dark moths existed before and after England industrialized, but the relative success of the different colors changed. Variety in the moth population helped it adjust to changing circumstances. Biodiversity in a ecosystem helps the whole system adjust to weather changes throughout the year and between years, and to climate changes over time.
Evolution works best when there is variety.
Reducing the area occupied by an ecosystem reduces the number of species there. Perhaps two-thirds of species live in the tropics, with over half of land species in the rain forest. Over the coming 100 years, a still greater cause of loss is expected to be the burning of fossil fuels, which pollutes, increases CO2 in the atmosphere, and produces global climate change. Especially critical is climate change, which will occur faster than many ecosystems, especially those dependent on trees, can migrate a midrange estimate is that many will have to move 300 km over the next century. Global climate change will be an important contributor to destroying boreal, lake, and stream biomes.