Biases in the current knowledge of threat status in lizards, and bridging the 'assessment gap'

Reptiles represent the world's most diverse group of terrestrial vertebrates (~ 10,300 recognized species). Knowledge of their conservation status, however, lags behind that of birds, mammals and amphibians. Only ~ 40% of the world's reptile species have had their conservation status assessed by the IUCN, and detailed analysis of extinction risk has been limited to a subset of 1500 species. Using lizards (Sauria and Amphisbaenia), the most diverse group of reptiles, we investigated whether biases in distribution, ecology, life-history and taxonomy exist in the species that have been assessed to date by the IUCN. Our results highlight that only 36% of the ~ 6300 described lizard species have had their conservation status assessed. Whilst data deficiency is a key concern in lizards (16% of assessed species), the large number of non-assessed species (~ 4000 species) represents a larger and more pressing issue. Accentuating this 'assessment gap' is the fact that biases exist in the subset of lizard species that have been assessed by the IUCN. Australia and Asia, as well as tropical areas in general, were the least assessed regions. Assessed lizard species were more likely to have larger body and clutch sizes, broader distributional and elevational ranges, occur at more northerly latitudes, and have a viviparous mode of reproduction. Some evidence suggests that they also tend to be diurnal, surface active, and with developed limbs. The level of assessment also differed significantly among lizard families and higher taxa. We recommend the implementation of an integrated approach to bridge the 'assessment gap' in lizards, involving regional and taxon-specific working groups associated with the IUCN's Global Reptile Assessment, predictive modelling, enhanced knowledge of lizard distribution and biology, and improved taxonomic methods.