This species' historical range includes several sites in Departamento Nariño, southern Colombia, through to Provincia Imbabura, in northern Ecuador, ranging between 2,800–3,900 m asl (Coloma et al. 2010). Its historical extent of occurrence (EOO) is estimated to be about 3,127 km2 (Coloma et al. 2010) although its current range is probably smaller at 2,331 km2 based on calculations of survey results (in Coloma et al. 2010).
Habitat and Ecology
It has only been found in tropical montane habitats above the treeline, primarily in damp, grazed páramo and subpáramo, with bunched grass and a few cushion plants (Coloma et al. 2010). Individuals appear to crawl around vegetation or hide under rocks during the day (Coloma et al. 2010). Very little is known of the breeding biology, although it is expected to breed in flowing water by larval development, as with other congeners. Adult females have previously been found to contain eggs and males have been observed in amplexus with females (Coloma et al. 2010).
It was considered to be relatively abundant in some sites in the 1970s: in 1975 a field survey recorded 90 individuals at Páramo El Ángel (with a survey effort of 0.50 individuals/person/minute), in Ecuador, and in 1986 densities of 10 individuals/m2 were recorded at the same site (Coloma et al. 2010). In Ecuador the last living individuals were seen in 1993, despite many subsequent survey attempts in several different localities across its range (Coloma et al. 2010). Several dead or unhealthy individuals were seen prior to its disappearance in this country; some of these individuals tested positive for chytrid fungus (Merino-Viteri (2001) in Coloma et al. 2010). In Colombia, although this species was previously abundant in several sites, no individuals have been found since November 1982 (Cepeda-Quilindo and Rueda-Almonacid 2005). Given the lack of recent records in spite of intensive surveys, it is possible that the species could be extinct.
This species has tested positive for chytrid fungus (see Coloma et al. 2010 and references therein). In addition, climate change has also been identified as a potential threat, although the mechanisms by which these factors could have contributed to this species' decline are still not understood.
It is not known to occur in any protected areas. Further surveys are urgently required to determine whether this species is still extant in Colombia and Ecuador.
Red List Status
Critically Endangered (CR)
Listed as Critically Endangered given that it has experienced a precipitous population decline in the 1980s-1990s and no live individuals have been reported since 1993, despite intensive and ongoing searches in suitable habitat in historical localities, suggesting that if this species is still extant the pool of remaining mature individuals is likely no greater than 50.
IUCN SSC Amphibian Specialist Group, 2013. Atelopus pastuso. The IUCN Red List of Threatened Species 2013: e.T18435537A18622516. http://dx.doi.org/10.2305/IUCN.UK.2013-1.RLTS.T18435537A18622516.en