Threatened or Data Deficient: assessing the conservation status of poorly known species

Aim: To determine whether extinction risk assessments based on biological collections and using Criterion B of the IUCN Red List Criteria reflect in part an accurate measure of species rarity and thus extinction risk.

Main conclusions: Species described more recently have smaller ranges and occupancies, fewer specimens and greater perceived extinction risk status. Levels of geographic uniqueness of collections are higher in species described more recently. Awareness of a species range increased faster than random, particularly in the first half of the sampling process, suggesting that newly discovered or yet to be discovered species are rare and likely have a higher risk of extinction. For many species, biological collections represent the sum of our knowledge. While data may be limited, such species should be listed in an appropriate Red List Category in accordance with the IUCN Red List Guidelines rather than as Data Deficient.