Saturday, January 5, 2013

A Global Assessment of Reptiles

The first global overview of reptile extinction risk has been published in the journal Biological Conservation (Böhm et al. 2013). 220 species assessed on the IUCN Red List and another 1280 species with revised or new assessments provided by a global network of herpetologists formed the basis for the study. Thus, the sample included about 16% of known reptile species. The processes forming the major threats to the species and the proportion of species threatened by each predominant threat were mapped. Three of the species were found to lack sufficient distributional data and were not included in the mapping process, leaving 1497 species represented in the maps.

The study found 59% of reptile species in the assessment as species of Least Concern, 5% as Near Threatened, 15% as threatened (Vulnerable, Endangered or Critically Endangered) and 21% as Data Deficient. Based on this, the authors estimated the true percentage of threatened reptiles in the world to be about 19-20%. Another 7% of species are estimated as Near Threatened. These are the species most likely to become threatened in the future if measures are not taken to eliminate the negative human activities which currently impact their populations. None of the species in the sample were classified as Extinct or Extinct in the Wild, although three lizard species in the Critically Endangered category were flagged as possibly extinct (Anolis roosevelti [see below] Ameiva vittata and Stenocercus haenschi) and their status may be changed pending the results of future field surveys

223 reptilian species were classed as threatened, about half of these (47%) were assigned to the Vulnerable category; another 41% and 12% were assessed as Endangered and Critically Endangered respectively. Threat estimates for terrestrial species mirrored that recorded for all reptiles (19% threatened) because the vast majority of reptiles inhabit terrestrial environments. However 30% of reptiles associated with marine and freshwater environments are estimated to be threatened. Reptile species diversity is greatest in tropical latitudes, Central America, portions of South America, tropical West Africa, south Africa, Sri Lanka, southern India, and Southeast Asia eastward to the Philippines have the highest proportions of threatened species. Species classified as Data Deficient were in Inodomalaysia (33%), the Neotropics (20%), and the Afrotropics (18%).

Of the 24 known species of crocodilians, four species were assessed, and three of the four are threatened. Of the 323 known species of turtle, 46 were assessed and 51% of these were threatened. Snakes and lizards (including amphisbaenids) appear to be in better shape with 28% and 12% of those assessed considered threatened.

For comparison to other higher vertebrate groups, 25% of freshwater fishes, 42% of amphibians, 13% of birds, and 25% of mammals are considered threatened. Thus, the 20% of threatened reptiles would appear to be a moderate number.

But, reptiles are under studied, there is a large number of undescribed species (more than 153 new species were described in 2012 alone, an increase of almost 2%) and this study notes that 21% are classified as Data Deficient.

The composite above shows the Culebra Island Giant anole, Anolis roosevelti. One species of reptiles than may be extinct in the wild. The male holotype was described in 1931 by Chapman Grant. It had a body length of 160 millimeters  It was observed again in 1932  and there have been unconfirmed sightings since 1973 . Some speculate it may still exist, others are less optimistic. Its preferred  habitat was gumbo-limbo and ficus trees and it fed on the fruits of the trees. Human activities destroyed most of its habitat. Photo and artist credit:  A. Photo by Chapman Grant, B. Photo by Leo Shapiro. C. Artists reconstruction by Genny Wilson.

Böhm, M. et al. 2013. The conservation status of the world's reptiles. Biological Conservation 157, 372-385.

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