Habitat

In ecology, a habitat is the specific set of resources and living factors in a location that allow a particular species to survive and reproduce. It is a concept tied directly to a single species, unlike broader terms like "environment" or "vegetation assemblages," which are better described as "habitat types." Physical elements of a habitat include soil, moisture, temperature range, and light intensity. Biotic elements include the availability of food and the presence or absence of predators. Every species has its own habitat requirements; generalist species can thrive in many different conditions, while specialists need a very narrow set of factors. A species' habitat is not necessarily a large geographical area—it could be the inside of a stem, a rotten log, a rock, or a clump of moss. For a parasite, its habitat is the body of its host, a part of that body (like the digestive tract), or even a single cell within the host.

Habitat types, by contrast, are broad environmental categories based on the characteristics of a geographical area, especially vegetation and climate. They refer to multiple species living in the same area, not just one. Terrestrial habitat types include forests, steppe, grassland, semi-arid areas, and deserts. Freshwater habitat types include marshes, streams, rivers, lakes, and ponds. Marine habitat types include salt marshes, the coast, the intertidal zone, estuaries, reefs, bays, the open sea, the seabed, deep water, and submarine vents.

Habitat types can change over time. Some changes are violent and sudden, such as a volcanic eruption, earthquake, tsunami, wildfire, or shift in ocean currents. Others occur gradually over millennia due to climate shifts, the advance and retreat of ice sheets and glaciers, or changes in precipitation and solar radiation. Human activities also cause change—through deforestation, plowing ancient grasslands, diverting and damming rivers, draining marshland, and dredging the seabed. The introduction of alien species can devastate native wildlife by increasing predation, competing for resources, or bringing pests and diseases to which indigenous species have no immunity.

The word "habitat" has been in use since around 1755, coming from the Latin *habitāre* (to inhabit), from *habēre* (to have or hold). It can be defined as the natural environment of an organism—the kind of place where it naturally lives and grows. It is similar in meaning to "biotope," an area of uniform environmental conditions associated with a particular community of plants and animals.

The main environmental factors affecting the distribution of living organisms are temperature, humidity, climate, soil, light intensity, and the presence or absence of all requirements the organism needs to sustain itself. Generally, animal communities depend on specific types of plant communities. Some plants and animals have broad habitat requirements; for example, the small white butterfly (*Pieris rapae*) is found on every continent except Antarctica. Its larvae feed on many Brassicas and other plants, and it thrives in any open location with diverse plant communities. In contrast, the large blue butterfly (*Phengaris arion*) is much more specific—it is found only in chalk grassland, its larvae feed on *Thymus* species, and due to its complex life cycle, it lives only where *Myrmica* ants are present.

Disturbance plays a key role in creating biodiverse habitat types. Without disturbance, a climax vegetation cover develops that prevents other species from establishing. Wildflower meadows created by conservationists often rely on annuals or biennials, which disappear after a few years without patches of bare ground for seedlings. In tropical forests, lightning strikes and toppled trees maintain species richness by allowing pioneering species to fill gaps. Similarly, coastal habitat types can become dominated by kelp until a storm disturbs the seabed and sweeps the algae away, or shifting sediment exposes new areas for colonization. Another cause of disturbance is when an invasive introduced species overwhelms an area, unchecked by natural enemies in its new habitat.

Terrestrial habitat types include forests, grasslands, wetlands, and deserts. Within these broad biomes are more specific habitat types with varying climates, temperature regimes, soils, altitudes, and vegetation. Many of these habitats grade into one another, each with its own typical communities of plants and animals. A particular habitat type may suit a species well, but its presence or absence at any location depends partly on chance, its dispersal abilities, and its efficiency as a colonizer.

Arid habitats are those with little available water. The most extreme arid habitats are deserts. Desert animals have various adaptations to survive dry conditions. Some frogs live in deserts, creating moist underground habitats and hibernating during adverse conditions. Couch's spadefoot toad (*Scaphiopus couchii*) emerges from its burrow when a downpour occurs and lays its eggs in the transient pools that form; the tadpoles develop quickly before the water evaporates.