A Distributional Study of the Amphibians of the Isthmus of Tehuantepec, México

by William Edward Duellman

Adults were found along streams and in marshes in savannas and rainforest. These frogs are wary and difficult to capture, even at night. Rana palmipes is another species that has a discontinuous distribution in the isthmus. The species does not occur on the Pacific lowlands of the isthmus, but does occur on the more humid Pacific slopes of Chiapas and Guatemala.

Tadpoles were found in a small sluggish tributary to the Río Sarabia.

Rana pipiens Schreber

Oaxaca: Agua Caliente; Cerro Quiengola; Escurano (14); Río Sarabia (2); Tapanatepec (5); Tehuantepec (24). Veracruz: Acayucan; Cuatotolapam (15); Jesús Carranza (2); 20 km. S of Jesús Carranza (11); 25 km. SE of Jesús Carranza; 20 km. ENE of Jesús Carranza (10); San Lorenzo (10).

As in most other places in México and northern Central America, this species occurs wherever there is permanent water. Males were heard calling from woodland ponds and from savanna ponds.

SUMMARY

Investigations of the amphibians and their environments in the Isthmus of Tehuantepec have been presented with the aim of gaining an understanding of the present biological and of the historical events responsible for the present patterns of distribution of amphibians in this region.

The Isthmus of Tehuantepec embraces three major environments—savanna, semi-arid scrub forest, and quasi-rainforest. The rainforest presents an environment noticeably different from the other two and has a different amphibian fauna.

Analysis of present patterns of distribution shows that certain species are restricted to the rainforests on the Gulf lowlands; others live only in the semi-arid scrub forests on the Pacific lowlands. A third group of species lives on both the Gulf and Pacific lowlands; most of these species occur only in the scrub forests or savannas on the Gulf lowlands, but some also inhabit the rainforest. In one way or another the isthmus presents a barrier to the distribution of 75 per cent of the species of amphibians living in the lowlands; it is a greater barrier still to the species inhabiting the highlands on either side.