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Area of occupancy (AOO) for IUCN criterion B

Source: R/rl_aoo.R
rl_aoo.Rd

Compute the area of occupancy from occurrence records by counting the number of occupied grid cells and multiplying by the cell area, following equation 4.1 of the IUCN Red List guidelines (section 4.10). The guidelines require a reference scale of 2 by 2 km cells (an area of 4 square kilometres), which is the default here.

Usage

rl_aoo(x, coords = c("longitude", "latitude"), crs = 4326, cell_size = 2000)

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).

cell_size

Grid cell side length in metres. Default 2000 (the IUCN reference scale of 2 by 2 km). Change it only with good reason, since the criterion B2 thresholds assume this scale.

Value

A one row sf object whose geometry column holds the occupied grid cells as a MULTIPOLYGON, returned in the input coordinate system, and the columns:

metric

"AOO".

area_km2

the area of occupancy in square kilometres.

n_records

the number of records used.

n_occupied_cells

the number of occupied grid cells.

cell_size_km

the cell side length in kilometres.

category_b2

the most threatened criterion B2 band the area reaches ("CR", "EN" or "VU"), or NA when it reaches none. 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 grid is applied, so cell sizes are measured in metres regardless of the input coordinate system.

The count uses a single grid whose origin is fixed at the projected origin. The guidelines note that shifting the grid can change the count and that the smallest estimate should then be used; that refinement is left to the assessor.

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 4.10. https://www.iucnredlist.org/documents/RedListGuidelines.pdf

See also

rl_eoo()

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_aoo(occ)
} # }