The word habitat is often used by humans to designate a particular kind of local environment--a hardwood forest, a marsh, or a coral reef. In biology, it is used to designate that distinct environment inhabited by a particular species. Habitat is species specific. Writers often append the word 'natural' to habitat, meaning the habitat of an indigenous species, that place to which a species has long been adapted, that place with the conditions suitable for its survival. But habitat can also refer to places with conditions commensurate to the needs of an exotic, migrant species. Finding favorable habitat conditions, especially with an advantageous competitive situation, invaders can become established and even prosper. Habitat requirements of the world's organisms vary widely, and can be very different even for similar species. Changes in habitat can quickly alter the conditions for survival of a species.

Human impacts on the habitat of other species range widely. General examples of such impact include numerous alterations of weather and increasing influence on climate, widespread deforestation and desertification, lowering the water table below the level where plant roots can reach moisture, and the sedimentation, salinization, acidification, and even desiccation of water bodies and streams. Seemingly subtle and small-scale changes, such as in the shade pattern for example, can mean drastically altered conditions for some species.

Degradation, fragmentation, or complete destruction of habitat specifically required for survival by a particular species is one of the major ways in which human activities threaten the existence of other organisms. This is particularly true for species that are very specialized. One example is the giant panda, which feeds only on certain species of bamboo, species that are being decimated by human developments. Destruction of the conditions essential for the survival of the bamboo eliminates the habitat necessary for the survival of the panda. Biologists who study the giant panda do not expect it to survive in the wild, only in zoos. Another example is the radical alteration of the habitat for anadromous fish resulting from the construction of dams on river systems.