Biodiversity is the variety of different living organisms in an area. Human activity can reduce it or protect it. Most negative effects come from land use, hunting and pollution.
Land use: when forest, grassland or wetland is cleared for farming, building or roads, the habitats of many species are lost. Habitat destruction means the number of species in the area falls. Farmers who remove hedgerows to make bigger fields also remove food and shelter for wildlife. Hunting too many individuals of a species can lead to its extinction, because the population becomes too small to recover.
Pollution also harms biodiversity. Burning fuels releases sulfur dioxide, which dissolves in rain to form acid rain. Acid rain lowers the pH of soil and lakes, so seeds fail to germinate and fish die. Lichens are sensitive to sulfur dioxide, so few lichens growing on trees suggests the air is polluted. Species that show pollution levels like this are useful indicators.
Positive interactions protect species and habitats. Nature reserves and protected areas keep habitats safe. A captive breeding programme breeds endangered animals in zoos, and some are later released into the wild. Replanting hedgerows and woodland gives wildlife new habitats and so helps biodiversity to increase.