Different publications ‘ theories sing the latitudinal diverseness gradient were examined and analysed to try to demo how theories explicating the latitudinal diverseness gradient have changed in the period 1980-2010.
In entire, six chief theories were identified from the literature and resources studied by seeking abstracts and articles for relevant cardinal words.
The chief decision drawn was that no individual theory can adequately explicate the latitudinal diverseness gradient. Species diverseness is finally controlled by a combination of factors and until there is conclusive cogent evidence or understanding on this topic biogeographers and life scientists will go on to speculate on the affair of the drive factors behind the latitudinal diverseness gradient.
Latitudinal Diversity Gradient, Geographical, Species, Species Richness, Taxa, Hypothesis,
Biotic, Historical Perturbation, Climate Stability, Climate Harshness, Mid-Domain, Evolutionary Rate, Evolution.
The latitudinal diverseness gradient is the term used to depict the lessening in species richness as one moves off from the equator. [ 1 ] Discovered by Alexander von Humboldt in 1799, it has remained one of the cardinal inquiries in Evolutionary Ecology. Understanding the latitudinal diverseness gradient is indispensable in our apprehension of the spread of invasive species, disease and more pertinently, the effects of planetary clime alteration ( Bradford et al 2006 ) Hillebrand ( 2004 ) identified that this topic has received great attending but the bulk of surveies have concentrated on merely one or a little figure of beings. An illustration of this being Krebs ( 1985 ) who examined serpent and ant species throughout America. In the past 30 old ages at that place have been many different theories that attempt to explicate the latitudinal diverseness gradient, from farther reading into each single theory it became evident that no single theory is wholly self supporting, instead a combination of each is possibly the best manner to seek and reply the inquiry of what is the drive factor behind the latitudinal diverseness gradient.
The species-energy theorem Centres on the hypothesis that it is the sum of available energy that governs the possible species profusion of the system. Fraser and Currie examined this hypothesis in their 1995 paper ‘The Species Richness-Energy Hypothesis in a System Where Historical Factors are Thought to Predominate: Coral Reefs. ‘ They found that the best environmental forecasters of diverseness were temperature and biomass and besides that there was small encouraging grounds for other hypotheses such as environmental stableness. Turner et Al ( 1987 ) found that the diverseness of butterflies, measured as the figure of species is extremely correlated with sunlight and temperature during May to September, with these two variables accounting for about 80 % of the discrepancy in diverseness.
Originally proposed by Colwell and Hurtt, ( 1994 ) this hypothesis works on the footing that it is geographical restraints that contribute to species profusion. Colwell et Al ( 2004 ) province that if species ‘ scopes are shuffled indiscriminately within a delimited geographical sphere free of environmental gradients, ranges overlap progressively toward the Centre of the sphere, making a mid sphere extremum of species profusion. There is still debate over whether or non the Mid Domain Effect is responsible for the latitudinal diverseness gradient as empirical support for it is frequently weak. Zapata et Al ( 2005 )
Effective Evolutionary Time
Effective evolutionary clip hypothesizes that it is evolutionary clip and the factors associated with it, such as environmental energy, mutant, coevalss and choice that are responsible for the diverseness gradient. Rhode ( 1992 )
Climate Harshness and Climate Stability
The Climate Harshness theory speculates that fewer species are found at high latitudes due to their inability to get by with the force per unit areas that the environment topographic points upon them.
Climate Stability proposes that the ground for the diverseness gradient is due to species specialising into narrower and narrower niches due to stable clime conditions, ensuing in increased speciation and hence ensuing in temperate countries at high latitude holding a low diverseness as they experience more mutable conditions events throughout the twelvemonth. Climate stableness is even observed in marine environments with strong latitudinal gradients being observed. Kaustuv et Al ( 1999 ) every bit good as in tellurian environments. Lima-Ribeiro et Al ( 2009 ) .
Cardillo et Al ( 2005 ) argue that the increased diverseness observed at lower latitudes is due to high evolutionary rates ensuing in increased speciation. Mettelbach et Al ( 2007 ) found that there was grounds for higher rates of variegation in the Torrid Zones, with surveies of latitudinal fluctuation proposing greater speciation at lower latitudes. The consequences from these surveies show that there is so a nexus between low latitudes and evolutionary rate ensuing in increased speciation.
Since the 1980 ‘s there have been suggestions of new theories and re scrutinies of others, for illustration Zapata et Al ( 2005 ) rhenium examine the mid sphere consequence and turn to its unfavorable judgments. Each of the single theories discussed earlier proposes its ain account for the latitudinal diverseness gradient. Some hypotheses are round and some are founded on deficient grounds, Rhode ( 1992 ) . In the past 30 old ages theories purporting to explicate the latitudinal diverseness gradient have changed from back uping one point of view as the exclusive cause of the latitudinal diverseness gradient to being more inclusive of other hypotheses, the Evolutionary clip theory is the most inclusive of other theories as it recognises that no individual factor can be the cause of such a complex system.
Mentions and Literature Cited
1. On-line Biology Book, L, Latitudinal diverseness gradient
hypertext transfer protocol: //mac122.icu.ac.jp/biobk/BioBookglossL.html
Accessed on 17-08-2010
Hawkynss, B.A, Diniz-Filho, J.A.F, Jaramillo, C.A. , Soeller, S.A. , 2006. Post-Eocene clime alteration, niche conservativism, and the latitudinal diverseness gradient of New World birds. Journal of Biogeography.
Cardillo, M. Orme, C. D. L. , Owens, I.P.F. 2005. Testing for Latitudinal Bias in Diversification Ratess: An Example Using New World Birds. Ecology.
Colwell, R.K. Hurtt, G.C 1994. Nonbiological Gradients in Species Richness and a Specious Rapoport Effect. The American Naturalist, Vol. 144, No. 4 October 1994
Colwell, R, K. Rahbeck, C. Gotelli, N, J. 2004 The Mid-Domain Effect and Species Richness Patters: What have we learned so far? Vol. 163. No.3 March 2004
Fraser, R.H, Currie, D.J. 1995. The Species Richness-Energy Hypothesis in a System Where Historical Factors are Thought to Predominate: Coral Reefs. The American Naturalist Vol.148, No. 1 July 1996
Hillebrand, H. 2004. On the Generality of the Latitudinal Diversity Gradient. The American Naturalist, Vol 163, No. 2. 2004.
Kaustuv, R. , Jablonski, D. , Valentine, J. W. 1999. Dissecting Latitudinal Diversity Gradients: functional groups and clades of marine pelecypods. The Royal Society
Krebs, C.J.1985. Ecology. The Experimental Analysis of Distribution and Abundance. Third edition. Harper & A ; Row, New York.
Lima-Ribeiro, M. , Diniz-Filho, J. A. F. , Barberi, M. 2010. Climate Stability and the Current Patterns of Terrestrial Vertebrate Species Richness on the Brazilian Cerrado. Quaternary International, Volume 222, Issue 1-2. August 2010
Mittelbach, G. G. , Schemske, D. W. , Cornell, H. V. , Allen, A. P. , Brown, J. M. , Bush, M. B. , Harrison, S. P. , Hurlbert, A. H. , Knowlton, N. , Lessios, H. A. , McCain, C. M. , McCune, A. R. , McDade, L. A. , McPeek, M. A. , Near, T. J. , Price, T. D. , Ricklefs, R. E. , Roy, K. , Sax, D. F. , Schluter, D. , Sobel, J. M. and Turelli, M. 2007. Development and the latitudinal diverseness gradient: speciation, extinction and biogeography. Ecology Letterss
Rhode, K. 1992. Latitudinal Gradients in Species Diversity: The hunt for the primary cause. Oikos. Vol. 65, No. 3. December 1992
Turner, J.R.G. Gatehouse, C.M and Corey, C.A. 1987. Does Solar Energy Control Organic Diversity? Butterflies, Moths and the British Climate. Oikos, Vol. 48. No.2
Zapata, F.A. , Gaston, K. J. , Chown, S. L. 2005 The Mid-Domain Effect Revisited. The American Naturalist, Vol. 166, No. 5 November 2005.