Habitat

thumb|This [[coral reef in the Phoenix Islands Protected Area provides habitat for numerous marine species.]]

thumb|Few creatures make the [[ice shelf|ice shelves of Antarctica their habitat, but water beneath the ice can provide habitat for multiple species. Animals such as penguins have adapted to live in very cold conditions.]]

thumb| [[Ibex in an alpine habitat]]

In ecology, habitat refers to the array of resources, biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species' habitat can be seen as the physical manifestation of its ecological niche. Thus "habitat" is a species-specific term, fundamentally different from concepts such as environment or vegetation assemblages, for which the term "habitat-type" is more appropriate.

The physical factors may include (for example): soil, moisture, range of temperature, and light intensity. Biotic factors include the availability of food and the presence or absence of predators. Every species has particular habitat requirements, habitat generalist species are able to thrive in a wide array of environmental conditions while habitat specialist species require a very limited set of factors to survive. The habitat of a species is not necessarily found in a geographical area, it can be the interior of a stem, a rotten log, a rock or a clump of moss; a parasitic organism has as its habitat the body of its host, part of the host's body (such as the digestive tract), or a single cell within the host's body.

Habitat types are environmental categorizations of different environments based on the characteristics of a given geographical area, particularly vegetation and climate.

Types

Terrestrial

thumb|Rich rainforest habitat in [[Dominica]]

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

List of arid habitat types

Desert
Fog desert
Polar desert
Steppe
Savanna

Wetland and riparian

Other organisms cope with the drying up of their aqueous habitat in other ways. Vernal pools are ephemeral ponds that form in the rainy season and dry up afterwards. They have their specially-adapted characteristic flora, mainly consisting of annuals, the seeds of which survive the drought, but also some uniquely adapted perennials. Animals adapted to these extreme habitat types also exist; fairy shrimps can lay "winter eggs" which are resistant to desiccation, sometimes being blown about with the dust, ending up in new depressions in the ground. These can survive in a dormant state for as long as fifteen years. Some killifish behave in a similar way; their eggs hatch and the juvenile fish grow with great rapidity when the conditions are right, but the whole population of fish may end up as eggs in diapause in the dried up mud that was once a pond.

Examples of wetland and riparian habitat types

Bog
Marsh
Fen
Flooded grasslands and savannas
Floodplain
Shrub swamp
Swamp
Vernal pool
Wet meadow

Forest

Examples of forest habitat types

Boreal forest
Cloud forest
Peat swamp forest
Temperate coniferous forest
Temperate deciduous forest
Temperate rain forest
Thorn forest
Tropical dry forest
Tropical moist forest
Tropical rain forest
Woodland

Freshwater

thumb|Wetland habitat types in Borneo

Freshwater habitat types include rivers, streams, lakes, ponds, marshes and bogs. Although some organisms are found across most of these habitat types, the majority have more specific requirements. The water velocity, its temperature and oxygen saturation are important factors, but in river systems, there are fast and slow sections, pools, bayous and backwaters which provide a range of habitat types. Similarly, aquatic plants can be floating, semi-submerged, submerged or grow in permanently or temporarily saturated soils besides bodies of water. Marginal plants provide important habitat for both invertebrates and vertebrates, and submerged plants provide oxygenation of the water, absorb nutrients and play a part in the reduction of pollution.

There are numerous different microhabitat types in a wood; coniferous forest, broad-leafed forest, open woodland, scattered trees, woodland verges, clearings, and glades; tree trunk, branch, twig, bud, leaf, flower, and fruit; rough bark, smooth bark, damaged bark, rotten wood, hollow, groove, and hole; canopy, shrub layer, plant layer, leaf litter, and soil; buttress root, stump, fallen log, stem base, grass tussock, fungus, fern, and moss. Other bacteria can be found in abundance in the Mariana Trench, the deepest place in the ocean and on Earth; marine snow drifts down from the surface layers of the sea and accumulates in this undersea valley, providing nourishment for an extensive community of bacteria.

Other microbes live in environments lacking in oxygen, and are dependent on chemical reactions other than photosynthesis. Boreholes drilled into the rocky seabed have found microbial communities apparently based on the products of reactions between water and the constituents of rocks. These communities have not been studied much, but may be an important part of the global carbon cycle. Rock in mines two miles deep also harbour microbes; these live on minute traces of hydrogen produced in slow oxidizing reactions inside the rock. These metabolic reactions allow life to exist in places with no oxygen or light, an environment that had previously been thought to be devoid of life.

thumb|right|Dense mass of white crabs at a hydrothermal vent, with stalked barnacles on right

Hydrothermal vents were first discovered in the ocean depths in 1977. These bacteria and Archaea are the primary producers in these ecosystems and support a diverse array of life. About 350 species of organism, dominated by molluscs, polychaete worms and crustaceans, had been discovered around hydrothermal vents by the end of the twentieth century, most of them being new to science and endemic to these habitat types. hot springs where the temperature may be as high as and cyanobacteria create microbial mats; cold seeps where the methane and hydrogen sulfide issue from the ocean floor and support microbes and higher animals such as mussels which form symbiotic associations with these anaerobic organisms; salt pans that harbour salt-tolerant bacteria, archaea and also fungi such as the black yeast Hortaea werneckii and basidiomycete Wallemia ichthyophaga;

Habitat change

thumb|right|Twenty-five years after the devastating eruption at [[Mount St. Helens, United States, pioneer species have moved in.]]

Whether from natural processes or the activities of man, landscapes and their associated habitat types change over time. There are the slow geomorphological changes associated with the geologic processes that cause tectonic uplift and subsidence, and the more rapid changes associated with earthquakes, landslides, storms, flooding, wildfires, coastal erosion, deforestation and changes in land use. Even where legislation protects the environment, a lack of enforcement often prevents effective protection. However, the protection of habitat types needs to take into account the needs of the local residents for food, fuel and other resources. Faced with hunger and destitution, a farmer is likely to plough up a level patch of ground despite it being the last suitable habitat for an endangered species such as the San Quintin kangaroo rat, and even kill the animal as a pest. The non-native freshwater zebra mussel, Dreissena polymorpha, that colonizes areas of the Great Lakes and the Mississippi River watershed, is a zoological monotypic habitat example; the predators or parasites that control it in its home-range in Russia are absent.