Extinct, obscure or imaginary: The lizard species with the smallest ranges

Abstract

Aim Small geographic ranges make species especially prone to extinction from anthropogenic disturbances or natural stochastic events. We assemble and analyse a comprehensive dataset of all the world's lizard species and identify the species with the smallest ranges—those known only from their type localities. We compare them to wide‐ranging species to infer whether specific geographic regions or biological traits predispose species to have small ranges. Location Global. Methods We extensively surveyed museum collections, the primary literature and our own field records to identify all the species of lizards with a maximum linear geographic extent of <10 km. We compared their biogeography, key biological traits and threat status to those of all other lizards. Results One in seven lizards (927 of the 6,568 currently recognized species) are known only from their type localities. These include 213 species known only from a single specimen. Compared to more wide‐ranging taxa, they mostly inhabit relatively inaccessible regions at lower, mostly tropical, latitudes. Surprisingly, we found that burrowing lifestyle is a relatively unimportant driver of small range size. Geckos are especially prone to having tiny ranges, and skinks dominate lists of such species not seen for over 50 years, as well as of species known only from their holotype. Two‐thirds of these species have no IUCN assessments, and at least 20 are extinct. Main conclusions Fourteen per cent of lizard diversity is restricted to a single location, often in inaccessible regions. These species are elusive, usually poorly known and little studied. Many face severe extinction risk, but current knowledge is inadequate to properly assess this for all of them. We recommend that such species become the focus of taxonomic, ecological and survey efforts.

Traits of lizards of the world: Variation around a successful evolutionary design

“…Whether the species maximum linear distribution extent is higher than 10 km (“wide ranging”), or not. Species with smaller ranges are divided into those known only from the description paper (“description”), or only from the holotype (“specimen”), or whether they were observed after they were first described (“locality”; Meiri et al, ). Latitude and longitude centroids (from Roll et al, and newer data; in decimal degrees, rounded to 2 decimal points). Insular endemic ‐ whether species reside only on landmasses smaller than Australia ‐ or not. SVL: Three values: The maximum known snout‐vent length (SVL, all in mm) of the species, the mean female SVL (midpoints between the minimum and maximum values where means are not reported), and midpoint of hatchling or neonate SVL. Leg development – whether the species has four functioning legs (“four‐legged”), reduced pair or two pairs of legs (“leg reduced”, usually meaning either that the species has fewer than 20 fingers or very short limbs relative to the expectation given its body length. I acknowledge the latter is sometimes arbitrary), only forelimbs or hind‐limbs, or no limbs at all. Mass equations – the best equation I have for converting the species (log10) SVL (in mm) into (log 10) mass (in grams; Feldman et al, ; Meiri, ).…”

“…Ovoviviparous species are considered viviparous because the mother carries the young until full term is reached carries the young in her abdomen until parturition. Clutch size: Minima, maxima and means (highest and lowest reported means) of clutch or litter sizes. Breeding age: The youngest and oldest reported ages (in months) of first breeding (of females if data are given separately for males and females). Body temperature: The highest and lowest reported mean body temperatures of active lizards recorded in the field (in °C). Family – according to the taxonomy of the reptile database (or slightly more conservative). Phylogeny: Whether there are published accounts of the phylogeny of the species (and hence, likely, GenBank records), and the genes used to infer it. IUCN red‐list assessment and population trends, as of January 2018. Data were converted to the Reptile Database taxonomy when needed (3,021 species are missing assessments [“NE”]; and an additional 453 species are listed as data deficient; population trend is not assessed for 3,097 species, and is unknown for 1620 more). Extant/Extinct: Whether the species is known or strongly suspected to be extinct (43 species; Slavenko et al, ), or whether (to the best of our knowledge, but see Meiri et al, ) it is still extant. Two species are considered extinct in the wild (EW: Lepidodactylus listeri and Cryptoblepharus egeriae ).…”

“…Over the last 12 years I have been assembling a dataset of lizard traits (e.g., Meiri, 2008Meiri, , 2010Meiri, , 2016Meiri et al, 2012;Meiri et al, 2018). Using the continuously evolving Reptile Database (Uetz, 2018, February 2018 as the taxonomic backbone, I have strived to map important and commonly studied traits of all lizard species.…”

“…Whether the species maximum linear distribution extent is higher than 10 km ("wide ranging"), or not. Species with smaller ranges are divided into those known only from the description paper ("description"), or only from the holotype ("specimen"), or whether they were observed after they were first described ("locality"; Meiri et al, 2018). Roll et al, 2017 and newer data; in decimal degrees, rounded to 2 decimal points).…”

The global biogeography of lizard functional groups

“…Lizards are a phylogenetically ancient and diverse group, demonstrating wide variation in morphological, physiological, behavioural and ecological characteristics (e.g., Pianka & Vitt, ; Losos, ; Mesquita, Faria, Colli, Vitt, & Pianka, ). Most importantly, lizards are of great conservation concern because of their small ranges (Meiri et al, ; Meiri & Chapple, ) and their sensitivity to habitat alterations, climatic changes, direct prosecution and introduced species (e.g., Ribeiro, Metzger, Martensen, Ponzoni, & Hirota, ; Sinervo, , Pincheira‐Donoso, Tregenza, Witt, & Hodgson, ; Slavenko, Tallowin, Itescu, Raia, & Meiri, ).…”