In Situ Conservation
The goal of conservation is to maintain biodiversity in nature, to preserve and continue the health of the ecosystem at every level. In situ, or on-site, conservation does this, targeting either populations of specific species, or whole ecosystems.
Keeping species in their natural homes is the best strategy for their long-term survival, as it allows for the continuation of natural process and interactions with other species. These are hard to replicate in an unnatural setting.
In general, in situ conservation is achieved by establishing protected areas. The International Union for Conservation of Nature (IUCN) defines these as: "a clearly defined geographical space, recognised, dedicated and managed, through legal or other effective means, to achieve the long term conservation of nature with associated ecosystem services and cultural values."
Protected areas prohibit or restrict access to humans or our activities. Some argue that this is the only way to preserve ecosystems and species, ie the best thing we can do for them is to keep away from them.