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Extent of occurrence (EOO) for IUCN criterion B

Source: R/rl_eoo.R
rl_eoo.Rd

Compute the extent of occurrence from occurrence records as the area of the minimum convex polygon (convex hull) that encloses all points, following the IUCN Red List guidelines (section 4.9). The convex hull is the method the guidelines recommend for assessing the spatial thresholds of criterion B1.

Usage

rl_eoo(x, coords = c("longitude", "latitude"), crs = 4326)

Arguments

x

Occurrence records: an sf POINT object (for example the output of rl_occurrences()), or a data frame holding longitude and latitude columns.

coords

Character vector of length two giving the longitude and latitude column names when x is a data frame. Default c("longitude", "latitude").

crs

Coordinate reference system of the input coordinates, passed to sf. Used only when x is a data frame or an sf object without a CRS. Default 4326 (WGS84).

Value

A one row sf object with the convex hull in its geometry column (an empty polygon when fewer than three unique locations are available), returned in the input coordinate system, and the columns:

metric

"EOO".

area_km2

the extent of occurrence in square kilometres, or NA when fewer than three unique locations are available.

n_records

the number of records used.

n_unique

the number of unique locations.

method

the estimation method, "convex hull".

category_b1

the most threatened criterion B1 band the area reaches ("CR", "EN" or "VU"), or NA when it reaches none (the area exceeds every band, or the metric is undefined). This is the spatial threshold only, not a full assessment, which also requires the criterion B subconditions.

Details

Geographic coordinates (longitude and latitude) are projected to a local Lambert azimuthal equal area system before the area is measured, so the result is returned in square kilometres regardless of the input coordinate system.

The extent of occurrence is undefined with fewer than three unique locations, since a polygon cannot be drawn; in that case area_km2 is NA and a warning is issued. The guidelines also state that when EOO is smaller than AOO it should be raised to equal AOO; that adjustment is left to the assessor and is not applied here.

sf is required and is asked for interactively when it is not installed.

References

IUCN Standards and Petitions Committee. 2024. Guidelines for Using the IUCN Red List Categories and Criteria. Version 16, section 4.9. https://www.iucnredlist.org/documents/RedListGuidelines.pdf

See also

rl_aoo()

Examples

if (FALSE) { # \dontrun{
occ <- data.frame(
  longitude = c(2.1, 2.6, 3.0, 2.4, 2.9),
  latitude = c(9.1, 9.5, 9.0, 9.8, 9.3)
)
rl_eoo(occ)
} # }