Global Assessment of Reptile Distributions
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Hiding in plain sight: rare lizards are more common than we think

23/11/2017

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In a recently published paper in Diversity and Distributions we try to illuminate aspects regarding the biology, and conservation of all narrow ranged lizard species, across the globe.
We defined lizard species with the smallest ranges as those only known from a single locality, with a maximum range extent no larger than 10 km. Surprisingly, more than 900 species, or roughly 1 in seven of all known lizard species, have such small ranges. Furthermore, about 750 of these species have never been seen again after their initial discovery, and more than 200 lizard species are only known to science from a single individual.
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Enyailoides altotambo from Ecuador ( Photo: Omar Torres Carvajal)
When exploring different attributes of small ranged species we found that most of them inhabit relatively inaccessible places in tropical climates worldwide. Furthermore, they are mostly small bodied species; many of them are active at night; and live in rocky habitats. Among the different lizard groups geckos and skinks dominate with many rare species.
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Riama yumborum from Ecuador (Photo: Omar Torres Carvajal)
Many of these species (such as those inhabiting small islands or caves) may truly have small ranges. However others may actually have larger ranges, and we are simply ignorant of the true extent of their distribution. This is especially true those found in remote, inaccessible places with no obvious barriers to their dispersal. Thus their small ranges are potentially only an artifact of our poor knowledge. Distinguishing between these two possibilities is both illuminating from an ecological and evolutionary perspective and extremely important from a conservation point of view.
 This work could help better focus conservation efforts by pointing at the species, and places, that are in the greatest need of protection. Many of the species, especially those which have not been observed for decades, may well be already extinct. However, to-date only six of the species studied have been officially recognized as such. In order to examine the true extent of such extinctions, and try to prevent future ones, the study provides invaluable information for directing future research and conservation efforts.
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Lizard species known only from their type localities. Circles: species not observed after 1967. Crosses: species observed after 1967.
Authors: Shai Meiri and Uri Roll
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Large and lonely - lately extinct reptiles were mostly on islands, and usually big

17/8/2016

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When exploring the extinction of Late Quaternary reptiles it seems that body-size was an important predictor of extinction rate. Larger reptiles were more likely to go extinct - published now in Global Ecology and Biogeograpy.
As extinction rates in our world increase at an alarming rate, proper conservation actions require detailed knowledge of the factors influencing extinction. These could be both anthropogenic pressured placed on natural environments, as well as particular species traits which make them especially vulnerable to these pressures. Over the last 50,000 years in which humans have spread across the Earth, there have been waves of mass extinctions of birds and mammals wherever humans colonized. These extinctions were particularly pronounced for large-bodied animals.
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Meiolania Platyceps
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Varanus priscus from the Melbourne Museum
We set out to examine if a similar pattern could be found for reptiles. In other words, we wanted to know if extinction also favored larger-bodied reptiles. We compiled data on body sizes of all currently known extant species of reptiles, just over 10,000 different species, as well as on 82 species of reptiles known to have gone extinct during the Late Quaternary, following human colonization of their original distribution ranges. By comparing the two groups, extant and extinct, we found that at least for lizards and turtles, extinct species were remarkably large.
Prime examples include the largest lizard to have ever lived, the Megalania monitor Varanus priscus, or the various species of giant tortoises on islands in the Indian and Pacific Oceans. By far the clearest pattern, however, is that extinctions mostly occurred on islands. Almost 90% of all extinct reptile species were endemic to islands!
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Hoplodactylus delcourti
The causes for these extinctions are numerous, and include over-harvesting by humans, introduction of invasive carnivores and rats, habitat change by human colonization, and possibly indirect cascade effects caused by the extinction of other, co-existing species. Our study helps us better understand the mechanisms of extinction in reptiles, and therefore might prove useful for pinpointing species which might be vulnerable to anthropogenic pressures in the future, and thus in need of conservation planning.
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localities of extinct late Quaternary reptiles
Author: Alex Slavenko
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    Mainly maintained by Shai Meiri and Uri Roll

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