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Apply IUCN Red List Criterion B (size thresholds plus sub-criteria)

Source: R/utils.R
iucn_criterion_B.Rd

Combines the EOO (B1) and AOO (B2) size thresholds of Criterion B with the sub-criteria required for a threatened listing, following the IUCN Red List Categories and Criteria (v3.1) and the Guidelines for Using them (Section 6, Criterion B; Section 10, DD/NT/NE), and aligning the category selection with the ConR package (Dauby et al. 2017, cat_criterion_b()). Unlike iucn_category_B (size flags only), this returns a category that can actually be applied.

Usage

iucn_criterion_B(
  eoo_km2 = NA_real_,
  aoo_km2 = NA_real_,
  n_locations = NA_real_,
  severe_fragmentation = NA,
  decline = NA,
  extreme_fluctuation = NA,
  assume_decline = TRUE,
  decline_detail = NULL
)

Arguments

eoo_km2, aoo_km2

EOO and AOO in km^2 (NA if undefined).

n_locations

Estimated number of locations (NA if unknown). This is the value that caps the category through sub-criterion (a); see Details.

severe_fragmentation

Logical; TRUE if the taxon is severely fragmented (meets condition (a) at any level). NA (default) = not assessed.

decline

Logical; TRUE if there is a continuing decline (sub-criterion b), FALSE if a decline is known to be absent. NA (default) = not documented, resolved by assume_decline.

extreme_fluctuation

Logical; TRUE if there are extreme fluctuations (sub-criterion c). NA (default) = not documented (never assumed).

assume_decline

Logical; how an undocumented decline (decline = NA) is treated. TRUE (default) assumes a continuing decline is present, as ConR does and as the conversion data support; FALSE treats it as not met (a stricter, more conservative screening). Ignored when decline is TRUE/FALSE.

decline_detail

Optional character giving the element(s) of the continuing decline for the IUCN code notation (v16, Section 6), appended in parentheses after the b in code: "i" EOO, "ii" AOO, "iii" area/extent/quality of habitat, "iv" number of locations/subpopulations, "v" number of mature individuals (combine with commas, e.g. "ii,iii"). NULL (default) omits it, so the code reads e.g. "EN B1ab"; with "iii" it reads "EN B1ab(iii)".

Value

A list with category (one of "CR", "EN", "VU", "NT", "LC", or NA when neither EOO nor AOO is available), code (e.g. "VU B1ab"), qualifies_size (the highest size level met, or NA), the evaluated sub-criteria a, b, c, and decline_assumed (TRUE when sub-criterion (b) was assumed rather than documented).

Details

A taxon qualifies for a threatened category (CR, EN, VU) only if it meets the size threshold and at least two of these three sub-criteria:

  • (a) severely fragmented or number of locations \(\le\) 1 (CR), 5 (EN) or 10 (VU);

  • (b) continuing decline (in EOO, AOO, area/extent/quality of habitat, number of locations/subpopulations, or mature individuals);

  • (c) extreme fluctuations.

Relation to the number of locations. Sub-criterion (a) is derived from n_locations (and severe_fragmentation when supplied), and it caps the category exactly as ConR does: the returned category is the less threatened of the level implied by range size and the level implied by the number of locations. A range whose EOO/AOO alone would be CR or EN but that is spread over, say, eight locations is therefore returned as VU (\(\le 10\) locations), not EN - the number of locations, not size alone, sets the category. Equivalently, per level: CR needs a single location, EN \(\le 5\), VU \(\le 10\) (unless severely fragmented, which meets condition (a) at any level).

Continuing decline (b), assumed by default. Sub-criteria (b) and (c) cannot be read from occurrence points. Following ConR - and because mappingAS is built around habitat-conversion data, which is direct evidence of a continuing decline in the area, extent and quality of habitat (sub-criterion b(iii)) - a continuing decline is assumed to be present when it is not explicitly documented (decline = NA with assume_decline = TRUE, the default). This is what makes the screening track the IUCN thresholds instead of collapsing every undocumented taxon to NT: with the location condition (a) met and decline (b) assumed, a small-range, few-location taxon is returned at its CR/EN/VU size-and-location level. Set assume_decline = FALSE (or decline = FALSE) to require a documented decline instead, in which case a size-and-location match with no second sub-criterion falls to NT. Extreme fluctuation (c) is never assumed.

Following Section 10: a taxon that meets a size threshold but not two sub-criteria (for example a small range spread over too many locations, or with decline explicitly absent) is returned as NT (Near Threatened, it "nearly meets" the requirements); one clearly far from every threshold as LC. DD and NE are never assigned automatically - they require the assessor's judgement about data adequacy and are left to the user.

References

Dauby G. et al. (2017) ConR: An R package to assist large-scale multispecies preliminary conservation assessments using distribution data. Ecology and Evolution 7:11292-11303. doi:10.1002/ece3.3704

See also

iucn_category_B

Examples

# EN-sized range with few locations: decline assumed by default -> EN B1ab
iucn_criterion_B(eoo_km2 = 3000, aoo_km2 = 400, n_locations = 4)$code
#> [1] "EN B1ab+2ab"
# Same size but spread over 8 locations -> capped to VU by the location count
iucn_criterion_B(eoo_km2 = 3000, aoo_km2 = 400, n_locations = 8)$category
#> [1] "VU"
# Require a documented decline: with none, a size/location match falls to NT
iucn_criterion_B(eoo_km2 = 3000, aoo_km2 = 400, n_locations = 4,
                 assume_decline = FALSE)$category
#> [1] "NT"