Habitat

In ecology, habitat refers to the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species.

Fresh-water 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 sea bed, deep water and submarine vents.

Other changes come as a direct result of human activities, such as deforestation, the plowing of ancient grasslands, the diversion and damming of rivers, the draining of marshland and the dredging of the seabed.

Wildflower meadows are sometimes created by conservationists but most of the flowering plants used are either annuals or biennials and disappear after a few years in the absence of patches of bare ground on which their seedlings can grow.

[11] Similarly, coastal habitat types can become dominated by kelp until the seabed is disturbed by a storm and the algae swept away, or shifting sediment exposes new areas for colonisation.

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.

[15] 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.

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.

[18] Further variations include rock pools, sand banks, mudflats, brackish lagoons, sandy and pebbly beaches, and seagrass beds, all supporting their own flora and fauna.

Rats and mice have followed man around the globe, pigeons, peregrines, sparrows, swallows and house martins use the buildings for nesting, bats use roof space for roosting, foxes visit the garbage bins and squirrels, coyotes, raccoons and skunks roam the streets.

Every habitat includes large numbers of microhabitat types with subtly different exposure to light, humidity, temperature, air movement, and other factors.

[25] 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.

There are bacteria, for example, living in Lake Whillans, half a mile below the ice of Antarctica; in the absence of sunlight, they must rely on organic material from elsewhere, perhaps decaying matter from glacier melt water or minerals from the underlying rock.

Boreholes drilled 300 m (1,000 ft) into the rocky seabed have found microbial communities apparently based on the products of reactions between water and the constituents of rocks.

[34] The lower limit for photosynthesis is 100 to 200 m (330 to 660 ft) and below that depth the prevailing conditions include total darkness, high pressure, little oxygen (in some places), scarce food resources and extreme cold.

Their growth rates and metabolisms tend to be slow, their eyes may be very large to detect what little illumination there is, or they may be blind and rely on other sensory inputs.

A number of deep sea creatures are bioluminescent; this serves a variety of functions including predation, protection and social recognition.

[35] In general, the bodies of animals living at great depths are adapted to high pressure environments by having pressure-resistant biomolecules and small organic molecules present in their cells known as piezolytes, which give the proteins the flexibility they need.

[37] The basis for this teeming life is chemosynthesis, a process by which microbes convert such substances as hydrogen sulfide or ammonia into organic molecules.

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.

[39] Besides providing locomotion opportunities for winged animals and a conduit for the dispersal of pollen grains, spores and seeds, the atmosphere can be considered to be a habitat-type in its own right.

The airborne microbial community may be as diverse as that found in soil or other terrestrial environments, however, these organisms are not evenly distributed, their densities varying spatially with altitude and environmental conditions.

[40] There are other examples of extreme habitat types where specially adapted lifeforms exist; tar pits teeming with microbial life;[41] naturally occurring crude oil pools inhabited by the larvae of the petroleum fly;[42] hot springs where the temperature may be as high as 71 °C (160 °F) and cyanobacteria create microbial mats;[43] 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;[44] salt pans that harbour salt-tolerant bacteria, archaea and also fungi such as the black yeast Hortaea werneckii and basidiomycete Wallemia ichthyophaga;[45][46] ice sheets in Antarctica which support fungi Thelebolus spp.,[45] glacial ice with a variety of bacteria and fungi;[47] and snowfields on which algae grow.

The birds that nest in their crevices, the epiphytes that hang from their branches and the invertebrates in the leaf litter are all adversely affected and biodiversity is reduced.

Without the corridors, seeds cannot disperse and animals, especially small ones, cannot travel through the hostile territory, putting populations at greater risk of local extinction.

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.

A dominant colonization can occur from retardant chemicals exuded, nutrient monopolization, or from lack of natural controls, such as herbivores or climate, that keep them in balance with their native habitat types.

[68] 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.