A habitat is that geographical unit that effectively supports the survival and reproduction of a given species or of indivuals of a given species; the composite of other organisms as well as abiotic factors therein describe the geographical unit. Other organisms include the plants, animals, fungi, bacteria, viruses and protozoans that also live in a given habitat. Abiotic factors include soil types, water availability, temperature, sunlight, air quality and geometric aspects of landforms that facilitate resting, foraging, nesting, mating, metabolic functions and other activities.
Usage of the term
The term habitat is one of the most mis-used and poorly defined in the field of ecology; this stems from the fact that some authors have emphasized the Cartesian geometrical nature of the term, while others have stressed the organism associations inherent in the definition; in fact, geography, associated species and abiotic factors, are all inextricably linked to the concept of a natural habitat. Furthermore, there are several concomitant concepts that are intertwined:
- Habitat selection is the process or behavior that an individiual organism uses to select or choose a habitat in which to live.
- Habitat availability is the accessibility of potential area for an organism to find suitable locations for thriving and propagating
- Habitat destruction is the loss or degradation of the natural living area for individuals or populations of organisms
- Habitat fragmentation is an alteration of habitat resulting in a spatial separation of habitat areas from a previous state of greater continuity
- Habitat destruction is the removal or degradation of habitat, such that it no longer supports the range of species previously present
Niche is an allied term in ecology, connoting a habitat descriptor that refers to limits of viability associated with a more narrow set of parameters than "habitat"; for example the ecological thermal niche for a species might be defined by the upper and lower thermal limits, in which the species is viable; niche can also denote a position within a food web occupied by a given species. Range is frequently used as the geographic extent of occurrence of an organism, without regard to fragmentation, or unlivable spaces within the total range extent; thus the term range is a purely a geometric or spatial concept.
The chief abiotic factors can be grouped into the categories of meteorology; soils; air pollution, geometric or topographic features; water availability and water quality. In terms of meteorological factors, the primary variables are associated with temperature, precipitation, wind velocity, solar insolation and humidity. It should be noted that statistical variation and seasonal variation of these basic parameters can be important elements of the habitat description as well as the temporal correlation of these variables; for example, for certain amphibian species, it is not only the average annual rainfall which is important to reproductive success, but especially the timing of rainfall that occurs during breeding seasons or the rainfall that occurs within the temperature optima for breeding. In addition the thawing timing of ponds can also be significant.
Edaphic or soils factors include variables such as soil granularity, soil chemistry and nutrient content, as well as nutrient availability. These factors are made more complex in that there may be interactions of the appropriate concentrations of minerals or nutrients with the timing of precipitation; furthermore, the vertical profile of soil chemistry can also be significant.
Air pollution factors can be significant for both flora and fauna. In the case of fauna, the presence of such gases as carbon monoxide and sulfur dioxide can lead to degradation of circulatory or pulmonary function, and for high and prolonged concentrations, even death. In the case of vascular plants, air pollutants can enter into stomatal openings; upon such penetration, many air pollutants can impair metabolic function, particularly photosynthesis. Air pollutants can also damage leaf, stem and flowering organs. For lichens the interferences with metabolism can be even more sensitive, since most chemical uptake is via air; for example, in the case of certain lichens, there is little tolerance to excess concentrations of air pollutants . The sensitivity of a lichen to air pollution is directly related to the energy needs of the mycobiont, so that the stronger the dependency of the mycobiont on the photobiont, the more sensitive that lichen species is to air pollutants.
- ^ John A.Bissonette and Ilse Storch. 2003. Landscape ecology and resource management: linking theory with practice. 463 pages
- ^ Linnea S.Hall, Paul R. Krausman and Michael L. Morrison. 1997.The habitat concept and a plea for standard terminology. Wildlife Soc. Bull. 25(1):173-182
- ^ C. Michael Hogan. 2008. Rough-skinned Newt (Taricha granulosa), Globaltwitcher, ed. N. Stromberg
- ^ I.H.Beltman, L.J.de Kok, P.J.K.Kuiper and P.R.van Hasselt. 1980. Fatty acid composition and chlorophyll content of epiphytic lichens and a possible relation to their sensitivity to air pollution. Oikos 35 (3): 321–26.