Preston.dist {asbio} R Documentation

## Preston diversity analysis

### Description

A diversity and richness analysis method based on the Preston (1948) log-normal distribution.

### Usage


Preston.dist(counts, start = 0.2, cex.octave = 1, cex.legend = 1, cex.pt = 1, ...)


### Arguments

 counts Vector of counts for species in a community dataset. start Starting value for non-linear least squares estimation of a in n = n_0 \times e^{-aR^2}. cex.octave Character expansion for octave labels. cex.legend Character expansion for legend. cex.pt Character expansion for symbols. ... Additional arguments from plot.

### Details

Preston (1948) proposed that after a log_2 transformation species abundances, grouped in bins representing a doubling of abundance (octaves), would be normally distributed. Thus, after this transformation most species in a sample would have intermediate abundance, and there would be relatively few rare or ubiquitous species. The Preston model is based on the Gaussian function: n = n_0 \times e^{-aR^2}, where, n_0 is the number of species contained in the modal octave, n is the number of species contained in an octave R octaves from the modal octave, and a is an unknown parameter. The parameter a is estimated using the function nls, using a starting value, 0.2, recommended by Preston. The area under Preston curve provides an extrapolated estimate of richness and thus an indication of the adequacy of a sampling effort. Preston called a line placed at the 0th octave the veil line. He argued that species with abundances below the veil line have not been detected due to inadequate sampling.

### Value

Graph of the Preston log-normal distribution for a dataset given by "counts", and a summary of the analysis including the fitted Gaussian equation, the estimated number of species, and an estimate for the percentage of sampling that was completed i.e. [length(counts)/Est.no.of.spp]*100.

Ken Aho

### References

Preston, F.W. (1948) The commonness and rarity of species. Ecology 29, 254-283.

dnorm, nls