Vicariance (from Latin vicarius, derived from vicis; change, alternation, stead) is a process by which the geographical range of an individual taxon, or a whole biota, is split into discontinuous parts by the formation of a physical or biotic barrier to gene flow or dispersal.
Vicariance of whole biotas occurs following large-scale geophysical events such as the uplift of a mountain chain, or the separation of continents. A well-documented example of vicariance in the marine realm was the formation of the Isthmus of Panama about 3 million years ago, which resulted in the evolution of related (geminate) species pairs on the Atlantic and Pacific sides. Another well known example of vicariance in continental ecosystems was the separation of South America from Africa about 100 million years ago, which isolated many taxa on either side of the newly forming South Atlantic.
Historically vicariance has been contrasted with biological dispersal as a means of explaining the patterns of distribution among related species. For example, the occurrence of some plant genera in both Africa and Australia may be explained in one of two different ways:
- The genus may have a Gondwanan origin; that is, it may have arisen before Africa and Australia separated into distinct continents. What was once a contiguous range was broken into a widely disjunct distribution by continental drift; this is an example of vicariance.
- The genus may be much younger, having arisen on one continent, and subsequently established populations on the other by long-distance seed dispersal.
Once a species has been split by vicariance into multiple populations with little to no genetic exchange, the populations begin to drift independently. Thus vicariance is a necessary precursor to allopatric speciation.
In biogeography, vicariance can be contrasted with geodispersal, which is the erosion of barriers to gene flow and biological dispersal. The relative importance of these different factors has long been a subject of debate.
- James S. Albert; Roberto E. Reis (8 March 2011). Historical Biogeography of Neotropical Freshwater Fishes. University of California Press. p. 308. Retrieved 28 June 2011.
- Gutiérrez, Eliécer E.; Boria, Robert A.; Anderson, Robert P. (2014). "Can biotic interactions cause allopatry? Niche models, competition, and distributions of South American mouse opossums". Ecography 37. doi:10.1111/ecog.00620.
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- Albert, J. S. and W.G.R Crampton (2010). "The Geography and Ecology of Diversification in Neotropical Freshwaters". Nature Education Knowledge 3 (10): 13.
- de Queiroz, Alan, The Monkey's Voyage: How Improbable Journeys Shaped the History of Life contrasts vicariance and several alternatives.
- Mao, K., Milne, R. I., Zhang, L., Peng, Y., Liu, J., Thomas, P., Mill, R. R. and S. S. Renner (May 2012). "Distribution of living Cupressaceae reflects the breakup of Pangea". Proceedings of the National Academy of Sciences 109 (20): 7793–7798. doi:10.1073/pnas.1114319109.