Computes geographical restrictedness from a site-species matrix.
Geographical restrictedness is an index related to the extent of a species
in a given dataset, it is close to 1 when the species is present in only a
single site of the dataset (restricted) and close to 0 when the species is
present at all sites. It estimates the geographical extent of a species in a
Details section to have details on the formula used for
the computation. The sites-species matrix should have sites
in rows and species in columns, similar to vegan package
a site-species matrix, with species in rows and sites in columns, containing presence-absence, relative abundances or abundances values
a logical (default = FALSE), indicating if restrictedness should be computed relative to restrictedness from a species occupying a single site
Geographical Restrictedness aims to measure the regional extent of a species in funrar it is computed the simplest way possible: a ratio of the number of sites where a species is present over the total number of sites in the dataset. We take this ratio off 1 to have a index between 0 and 1 that represents how restricted a species is:
R_i = 1 - (N_i/N_tot),
where R_i is the geographical restrictedness value, N_i the total
number of sites where species i occur and N_tot the total number
of sites in the dataset.
relative = TRUE, restrictedness is computed relatively to the
restrictedness of a species present in a single site:
R_i = R_i / R_one
R_i = (1 - K_i/K_tot)(1 - 1/K_tot)
R_i = (K_tot - K_i)(K_tot - 1)
Other approaches can be used to measure the geographical extent (convex hulls, occupancy models, etc.) but for the sake of simplicity only the counting method is implemented in funrar.
A stacked data.frame containing species' names and their
restrictedness value in the Ri column, similar to what
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