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Geographic range limit
A geographic range limit is the geographic boundary beyond which a species does not occur, the limit or limits of the range of a species. "Core populations" are populations of individuals occurring within the center of the range, and "peripheral" or "edge populations" are groups of individuals near the boundary of the range.
The inability of a species to expand its range beyond these limits is because of some factor or factors that constrain the species from adapting to overcome the factors that are imposing limits on its distribution. In some cases, geographical range limits are entirely predictable, such as the physical barrier of an ocean for a terrestrial species.〔 In other cases, reasons why species do not pass these boundaries are unknown, however the main determinants of the distribution of a species across its range are ecological and evolutionary processes.
For many species of invertebrate animals, the exact geographic range limits have never been precisely ascertained, because not enough scientific field work has been carried in many parts of the world to map distribution more precisely, therefore finding a range extension for species, especially marine species, is not an uncommon occurrence.
==Abiotic factors==
Gradients in climactic factors create physiological barriers to dispersal.〔 All species have limits of tolerance to abiotic factors, which can lower their survival and reproductive success and limit range expansion beyond the edge. Changes in temperature may cause a species to change its geographical distribution. With increasing temperatures resulting from global warming, species have been seen to expand their range northward due to increased survival and reproduction as a result of warming. Precipitation can also be a key determinant in limiting the geographic range edges of species. This is often seen in organisms with high water demands, whose survival and reproduction would decrease beyond the edge due to dry conditions, limiting expansion. Moisture of soil or air is also seen to limit range expansion. In terms of soil moisture, limited range expansion for species that forage on soil organisms or for species that reside in soil and rely on it for nutrients are seen. If moisture requirements are not met beyond the species range, they will not be able to expand due to resulting reductions in fitness. There are many other abiotic factors that can determine a species range, including dissolved oxygen, canopy cover, conductivity, alkalinity and pH.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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