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On species-area relationships. 2, Slope and factor values of power function and exponential model

Ulrich W.

Polish Journal of Ecology

2000

Vol. 48, nr 1

21-35

Using model assemblages generated by a FORTRAN program the parameter values of the slope of the power function and the factor of the exponential model of species-area relationships have been studied. It appeared that the slope value is not a constant independent of area and sampling method but depends strongly on grain, sampling method and model fit. The fraction of singletons in the sample proofed to be of major importance. A plot of slope against assemblage structure (estimated by the standard deviation of log2 (densities) was bell shaped with the highest slope values at intermediate SD values. A comparison of this plot with SD values from theoretical relative abundance distributions showed that log-normal distributed assemblages should have slope values that are higher than previously reported in the literature. Although it was impossible to predict the slope from the relative abundance distribution, the opposite was possible. At any given slope value there are two linked relative abundance distributions. The factor of the exponential model was more independent of sampling methods but linearily connected with sampling efficacy. A high non-linear correlation between factor and Shannon diversity was detected and a general function of this relationship developed and tested. The factor of the exponential species-area relationship may serve as an estimate of regional diversity.