In Search of Critically Endangered Species: The Current Situation of Two Tiny Salamander Species in the Neotropical Mountains of Mexico

Worldwide, one in every three species of amphibian is endangered, 39 species have gone extinct in the last 500 years and another 130 species are suspected to have gone extinct in recent decades. Of the amphibians, salamanders have the highest portion of their species in one of the risk categories, even higher than the frogs. To date there have been few studies that have used recent field data to examine the status of populations of endangered salamanders. In this study we evaluate the current situation of two tiny salamanders, Parvimolge townsendi and Thorius pennatulus, both of which are distributed at intermediate elevations in the mountains of the northern Neotropics and are considered to be critically endangered; the first has been proposed as possibly extinct. By carrying out exhaustive surveys in both historical and potentially suitable sites for these two species, we evaluated their abundance and the characteristics of their habitats, and we estimated their potential geographic distribution. We visited 22 sites, investing 672 person-hours of sampling effort in the surveys, and found 201 P. townsendi salamanders in 11 sites and only 13 T. pennatulus salamanders in 5 sites. Both species were preferentially found in cloud forest fragments that were well conserved or only moderately transformed, and some of the salamanders were found in shade coffee plantations. The potential distribution area of both species is markedly fragmented and we estimate that it has decreased by more than 48%. The results of this study highlight the importance of carrying out exhaustive, systematic field surveys to obtain accurate information about the current situation of critically endangered species, and help us better understand the crisis that amphibians are facing worldwide.

全球范围内，每三种两栖动物中便有一种处于濒危状态；过去500年间已有39个物种灭绝，近数十年间另有130个物种被推测已灭绝。在两栖动物中，蝾螈（salamander）处于各类濒危等级的物种占比最高，甚至高于蛙类。迄今为止，利用最新野外数据调查濒危蝾螈种群现状的研究仍寥寥无几。本研究针对两种小型蝾螈——汤氏微螈（Parvimolge townsendi）和笔形狭口螈（Thorius pennatulus）——展开现状评估，二者均分布于新热带区北部山地的中海拔区域，均被列为极危物种，其中前者曾被推测可能已灭绝。研究团队对这两个物种的历史分布区及潜在适宜生境开展了全面普查，评估了它们的种群数量与栖息地特征，并估算了其潜在地理分布范围。本次调查共走访22个样点，累计投入672人时的采样工作量，最终在11个样点中记录到201只汤氏微螈，仅在5个样点中记录到13只笔形狭口螈。两种蝾螈均偏好栖息于保存完好或仅受轻度干扰的云雾林片段中，部分个体还被发现于遮阴咖啡种植园内。二者的潜在分布区显著破碎化，研究估算其分布范围已缩减超48%。本研究结果凸显了开展全面系统的野外普查对于准确掌握极危物种现状的重要性，也有助于我们更深入地理解全球两栖动物所面临的生存危机。