Table 2 Parameter fits for each of the fitted statistical distributions.

The estimated slope values, β, of the gSAD are given in bold by fits of the Pareto and Truncated Pareto distributions. Note that the estimated slope values differ from −1.0 expected from the unified neutral theory of biodiversity. Instead, the observed fitted slope, β, is steeper than expected from neutral theory (with fitted exponents more negative than −1.0). The steeper exponents indicate that of all of the observed plant species on Earth, proportionally more of them are rare and that there are more rare species than expected by demographic and evolutionary neutral processes. Thus, the processes creating and maintaining rare species on Earth generate proportionally more rare species.

ModelPlot dataAll data
Zipf-Mandelbrot, b13.31186.7
Zipf-Mandelbrot, c1.41.2
Log series, c0.90.9
Pareto fitted exponent, β−1.4−1.3
Weibull scale18.140.6
Weibull shape0.40.5
Poisson lognormal, m4.07 × 10−81.7
Poisson lognormal, s2.92.6
Pareto with finite sample
exponential adjustment (28)
fitted Pareto exponent, β
−1.3−1.1
Pareto with finite sample
exponential adjustment:
Exponential parameter, Ω
0.10.1