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An Extension of Presence/Absence Coefficients to Abundance Data: A New Look at Absence
Júlia Tamás, János Podani and Péter Csontos
Journal of Vegetation Science
Vol. 12, No. 3 (Jun., 2001), pp. 401-410
Published by: Wiley
Stable URL: http://www.jstor.org/stable/3236854
Page Count: 10
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Alternative community analyses, based on quantitative and presence/absence data, are comparable logically if the data type is the only factor responsible for differences among results. For presence/absence indices that consider mutual absences, no quantitative alternatives are known. To facilitate such comparisons, a new family of similarity coefficients is proposed for abundance data. Formally, this extension is achieved by generalizing the four cells of the usual 2 x 2 contingency table to the quantitative case. This implies an expanded meaning of absence: for a given species at a given site it is understood as the difference between the actual value and the maximum detected in the entire study. The correspondence between 10 presence/absence coefficients and their quantitative counterparts is evaluated by graphical comparisons based on artificial data. The behaviour of the new functions is also examined using field data representing post-fire regeneration processes in grasslands and a chronosequence pertaining to forest regeneration after clear-cut. The examples suggest that the new coefficients are most informative for data sets with low beta-diversity and temporal background changes.
Journal of Vegetation Science © 2001 Wiley