For more than eighty years, ecologists have recognised that the size of an area of wild habitat correlates strongly with the number of plant and animal species to be found in that area. In 1921, a Swedish plant ecologist named Olof Arrhenius published a paper straightforwardly titled "Species and Area", which is considered a classical work in ecology and has been embraced by most ecologists in the world. Based on investigation of species diversity within certain delimited plots, Arrhenius (1921) concluded that the number of species increases continuously less as the area increases. This phenomenon is known as the species/area relationship (SAR). This is reflected in the quantitative formula S = cAz, in which S represents the number of species and A the size of the area. The constant c is an empirically determined multiplier that varies among taxa and areas (USA Commission on Life Sciences 1995), and which may be ignored when comparing the percentages of S and A, as done in this analysis. The exponent z varies according to the topographic diversity, the isolation of the area and the mobility of the taxon. It is usually higher* for islands (around 0.3) than for the mainland (commonly assumed less that 0.2). Dobson (1996) suggests 0.15. 

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