One butterfly lives on every continent but Antarctica; another needs ants
A habitat is not just a place but a specific set of conditions one species needs. The small white butterfly thrives almost anywhere with mixed plants. The large blue butterfly is far fussier: it lives only on chalk grassland where wild thyme grows and where particular Myrmica ants are present to complete its life cycle.
Ecologists define habitat as the resources and conditions in an area that let a particular species survive and reproduce, a physical expression of its niche. That makes it species-specific; broader categories like forest or desert are properly called habitat types. The word has been in English since about 1755, from Latin habitare, to dwell, rooted in habere, to hold, and it overlaps with biotope, an area of uniform conditions tied to a community of organisms.
Habitats can be surprisingly small. The inside of a plant stem, a rotting log, a clump of moss or a single rock can serve. For a parasite, the habitat is its host's body, one organ such as the gut, or even a single cell. Requirements mix physical factors such as soil, moisture, temperature and light with biological ones like food supply and predators. Generalists tolerate a wide spread of conditions; specialists depend on a narrow set.
Change comes in many speeds. Volcanic eruptions, tsunamis and wildfires reshape habitat overnight, while advancing and retreating ice sheets work over millennia. Humans add deforestation, ploughed grasslands, dammed rivers, drained marshes and dredged seabeds. Introduced species can devastate native wildlife by preying on it, outcompeting it, or bringing diseases it has no defence against.
Counterintuitively, some disruption keeps habitats diverse. Left undisturbed, vegetation matures into a dominant cover that crowds newcomers out. In tropical forests, lightning strikes and fallen trees open gaps for pioneer species. Along coasts, storms rip away kelp and shifting sediment exposes fresh ground. Even sown wildflower meadows fade within a few years unless patches of bare soil give seedlings room. Whether a suitable place is actually occupied also depends partly on luck and on how well a species disperses and colonises.
Source: Habitat
