Red List criteria are ill-suited for the majority of terrestrial animal
biodiversity
Abstract
Among the most widely used information underpinning conservation is the
concept of Red-Listing species according to criteria developed by the
IUCN. The Red List designates species extinction risk based on
geographic range, population size, or declines in either. However, it
has frequently been questioned whether Red List criteria are appropriate
for terrestrial arthropods, which comprise the bulk of animal diversity.
Due to their small size, difficulty in identification, and inherent
rarity, many invertebrates are hard to study, making Red List criteria
hard to apply. We assess this criticism using empirical evidence from
one of the largest terrestrial arthropod surveys to date, documenting
the abundance and distribution of over 13,000 species in Sweden. Of
these taxa, 13% have been found at a single site, and 11% of species
are found only in a single weekly sample. Using these data we
demonstrate that estimates of trends based on low sample sizes are
associated with major uncertainty and a major risk of misclassification
under IUCN criteria. We argue that even the most ambitious monitoring
efforts are unlikely to produce enough observations to reliably estimate
population sizes and ranges for more than a fraction of species. Thus,
there is likely to be substantial uncertainty in classifying most
species according to current criteria. In response, we discuss the
adaptation of IUCN criteria to more accurately capture the conservation
needs of invertebrates, and to adequately assess the future of the
majority of global animal diversity.