Telfers change index is designed to assess the relative change in range size of species between two time periods (Telfer et al 2002). This function can take multiple time periods and will complete all pairwise comparisons.

telfer(taxa, site, time_period, minSite = 5, useIterations = TRUE,
  iterations = 10)

Arguments

taxa

A character vector of taxon names

site

A character vector of site names

time_period

A numeric vector of user defined time periods, or a date vector

minSite

The minimum number of sites occupied in the first time period in order for a trend to be calculated for a taxon.

useIterations

A logical variable indicating whether iterations should be used. Iterations are used to account for increased variation in the logit proportions close to zero and one (see Telfer et al 2002). Default is TRUE

iterations

If useIterations is TRUE, then this parameter indicates the number of iterations to be used. In Telfer et al 2002 the number of iterations used were 7 and 8 for the two datasets for which it was applied. The defualt here is 10.

References

Telfer, M.G., Preston, C.D., & Rothery, P. (2002) A general method for measuring relative change in range size from biological atlas data. Biological Conservation, 107, 99-109.

Examples

# Create fake data SS <- 5000 # number of observations taxa <- sample(letters, SS, replace = TRUE) site <- sample(paste('A', 1:20, sep = ''), SS, replace = TRUE) time_period <- sample(1:3, SS, replace = TRUE) TelferResult <- telfer(taxa, site, time_period)
#> Warning: 3493 out of 5000 observations will be removed as duplicates
head(TelferResult)
#> taxa Nsite_1.x Nsite_2.x Telfer_1_2 Nsite_1.y Nsite_3.x Telfer_1_3 Nsite_2.y #> 1 a 20 19 -0.5140155 20 19 -0.4521761 19 #> 2 b 20 19 -0.5140155 20 19 -0.4521761 19 #> 3 c 19 20 0.6886459 19 19 -0.7970458 20 #> 4 d 19 20 0.6886459 19 20 1.1535228 20 #> 5 e 19 18 -1.6642860 19 19 -0.7970458 18 #> 6 f 18 18 -1.9636241 18 19 -1.0475778 18 #> Nsite_3.y Telfer_2_3 #> 1 19 -0.5159189 #> 2 19 -0.5159189 #> 3 19 -0.8173482 #> 4 20 1.0717983 #> 5 19 -0.3782280 #> 6 19 -0.3782280