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 |

`cex.octave` |
Character expansion for octave labels. |

`cex.legend` |
Character expansion for legend. |

`cex.pt` |
Character expansion for symbols. |

`...` |
Additional arguments from |

### 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`

.

### Author(s)

Ken Aho

### References

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

### See Also

### Examples

```
data(BCI.count)
BCI.ttl<-apply(BCI.count,2,sum)
Preston.dist(BCI.ttl)
```

*asbio*version 1.9-7 Index]