Humans have explored most of the world and have populated much of it. As the human species has had a strong effect on the land compared to other organisms, governments have set aside parcels of land as nature reserves. In these areas the natural wildlife and plant species can grow with little interference from humans. Typically, people can enter a nature reserve for leisure purposes, but cannot make significant changes to the ecosystem, or develop any of the land.
There is no single definition for the rules of a nature reserve. Instead, the regulations as to what constitutes a nature reserve depends on the country. Some international regulations, such as the United Nations Education, Science and Culture Organization (UNESCO) World Heritage site regulations, do have the same rules across countries that have signed up to abide by the rules of that organization. Typically, though, the term "nature reserve" is a general one, that can be used to refer to any area of land that is protected due to its natural inhabitants.
Most often, a governmental agency designates a certain area of land as a nature reserve due to the exceptional native organisms that live there. These special organisms may be a particularly good example of an uncommon native species, or a particularly rich collection of species living together. Sometimes the reserve is home to an endangered species, or is a part of the country with a unique form of ecology, such as a wetland.
All types of organisms may be part of a nature reserve. Large animals may be the reason the nature reserve exists, but the choice of that area as a reserve could also be down to a creature as small as a snail or an insect. Plants also make a difference when a government chooses a site to protect from people, especially if they are rare and only native to that country. Even a place that is relatively barren of organisms, but has a particular geology may be made a nature reserve.
As the reserve is supposed to be an area that retains its natural beauty and interest, along with its diversity of species, a management structure has to be in place to regulate the reserve. Typically this is a government organization, who enforce the laws of the area and punish people who break those laws. Examples of potential rules include a ban on vehicles, prohibition of open air fires and a restriction on the places where people can walk. Fees may apply to entrants into a reserve, and the government may also approve certain businesses inside the park, such as refreshment kiosks and businesses that predated the creation of the reserve like stores.