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. 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.[2]
For other uses, see Habitat (disambiguation).
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, with habitat generalist species able to thrive in a wide array of environmental conditions while habitat specialist species requiring 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.[3]
Habitat types are environmental categorizations of different environments based on the characteristics of a given geographical area, particularly vegetation and climate.[2] Thus habitat types do not refer to a single species but to multiple species living in the same area. For example, terrestrial habitat types include forest, steppe, grassland, semi-arid or desert. 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.
Habitat types may change over time. Causes of change may include a violent event (such as the eruption of a volcano, an earthquake, a tsunami, a wildfire or a change in oceanic currents); or change may occur more gradually over millennia with alterations in the climate, as ice sheets and glaciers advance and retreat, and as different weather patterns bring changes of precipitation and solar radiation. 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. The introduction of alien species can have a devastating effect on native wildlife – through increased predation, through competition for resources or through the introduction of pests and diseases to which the indigenous species have no immunity.
Definition and etymology[edit]
The word "habitat" has been in use since about 1755 and derives from the Latin habitāre, to inhabit, from habēre, to have or to hold. Habitat can be defined as the natural environment of an organism, the type of place in which it is natural for it to live and grow.[4][5] It is similar in meaning to a biotope; an area of uniform environmental conditions associated with a particular community of plants and animals.[6]
Environmental factors[edit]
The chief environmental factors affecting the distribution of living organisms are temperature, humidity, climate, soil and light intensity, and the presence or absence of all the requirements that the organism needs to sustain it. Generally speaking, animal communities are reliant on specific types of plant communities.[7]
Some plants and animals have habitat requirements which are met in a wide range of locations. The small white butterfly Pieris rapae for example is found on all the continents of the world apart from Antarctica. Its larvae feed on a wide range of Brassicas and various other plant species, and it thrives in any open location with diverse plant associations.[8] The large blue butterfly Phengaris arion is much more specific in its requirements; it is found only in chalk grassland areas, its larvae feed on Thymus species, and because of complex life cycle requirements it inhabits only areas in which Myrmica ants live.[9]
Disturbance is important in the creation of biodiverse habitat types. In the absence of disturbance, a climax vegetation cover develops that prevents the establishment of other species. 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.[10] Lightning strikes and toppled trees in tropical forests allow species richness to be maintained as pioneering species move in to fill the gaps created.[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. Another cause of disturbance is when an area may be overwhelmed by an invasive introduced species which is not kept under control by natural enemies in its new habitat.[12]
