William Edward Duellman

“ Among the anurans in the isthmus the four species of Eleutherodactylus, the two species of Syrrhophus, and the one species of Microbatrachylus are either known, or presumed, to lay eggs on the ground; these develop directly into small frogs. All of the other anurans deposit their eggs in water or attach them to objects over water (Phyllomedusa) ; these hatch into tadpoles, which later metamorphose into frogs. Hylella sumichrasti is known to breed only in streams. All of the other species breed in ponds, but at times some species deposit their eggs in streams ”

“ In comparing the ecological differences in the amphibian assemblages in the three major habitats, the most obvious difference is the great percentage of arboreal species in the rainforest as compared with savanna and scrub forest. Only four arboreal species are found in the scrub forest, none in the savannas, but eleven in the rainforest. Likewise, there is an absence of ground-dwelling forms in the arid habitats; in the latter the only terrestrial [Pg 41] species are those that are found near water. A possible exception is Syrrhophus pipilans. ”

“ In life the adults vary greatly in color pattern. The dorsal ground color is yellowish tan to olive brown with olive brown or dark brown spots, some of which in certain individuals are connected to form longitudinal dark stripes. On the posterior surface of the thighs are small white flecks. The belly is white, and the vocal sac is a rich yellow. Twenty males have an average snout-vent length of 26.3 mm.; they have no horny nuptial pads. No noticeable differences in either color or body proportions were found between the populations on either side of the isthmus. ”

“ Although there is not an abundance of data concerning the seasonal activity of the fauna, what is available shows some interesting correlations with the environments. During the dry season in the scrub forest there is essentially no amphibian activity; an occasional Rana pipiens may be seen along a river, or a Bufo marinus may be seen at night. In the rainforest the terrestrial-breeding amphibians are active during the dry season. Eleutherodactylus rugulosus is found at night or by day along streams. ”

“ The average snout-vent length of ten adult males is 41.8 mm. There is considerable variation in the extent of the yellowish brown glandular areas on the belly. Some have none, whereas others have a broad area on the chest, a band along the flanks, and a thin band across the lower abdomen. Individuals collected in the dry season vary in the same fashion as do those collected in the rainy season, at which time they were breeding. The glands are equally well-developed in adults of both sexes, and were present in some juveniles with snout-vent lengths of less than 20 mm. ”

“ Throughout the month of July, 1956, Phyllomedusa was breeding in ponds in or adjacent to the rainforest in northern Oaxaca and in southern Veracruz. Only at Alvarado was it found breeding in a grassy pond. Males and females alike were found on bushes and trees in and around the ponds. The call is a single "wank." Amplexing males continue to call, but the call is softer and less nasal in quality. The eggs are encased in pale green gelatin and attached to leaves on branches overhanging the water. ”

“ Environments are vertically stratified in the rainforests. There is the deep alluvial soil, the ground litter of leaves and decaying logs, the low bushes and small trees, and finally the tall trees of the forest. Each of these provides certain types of shelter for amphibians. The moist soil and litter on the forest floor is an important microhabitat for fossorial and strictly terrestrial species. The dense foliage of the trees, tree holes, and bromeliads growing on the trees provide shelter for arboreal species. ”

“ A large number of species are found on the forest floor; characteristic inhabitants of the leaf litter are: Bufo valliceps, Eleutherodactylus rhodopis, Microbatrachylus pygmaeus, and Syrrhophus leprus. Other terrestrial amphibians usually are not scattered throughout the rainforest, as are those named immediately above, but instead inhabit areas of forest adjacent to ponds or streams; these species include: Bufo marinus, Eleutherodactylus natator, Eleutherodactylus rugulosus, Leptodactylus labialis, Leptodactylus melanonotus, Rana palmipes and Rana pipiens. ”

“ On the Gulf Coastal Plain (Minatitlán station) the average annual [Pg 29] rainfall is 3085 mm. In this region the driest months are February through May, during which time 236 mm. of rain falls. At Salina Cruz the wettest month is June; at Minatitlán it is September. There is little variation in temperature throughout the isthmus; the average annual temperature at Salina Cruz is 26.6° C.; that at Minatitlán is 26.2° C. During the winter when masses of air from the arctic move southward into the Great Plains of the United States, cool winds blow across the isthmus. ”

“ The snout-vent length is 42.0 mm. in a male and averages 59.5 mm. in three adult females. The tarsal fold is low and extends about half the length of the tarsus; the first and second fingers are subequal in length; the tibiotarsal articulation extends beyond the tip of the snout. The patches of vomerine teeth lie between the posterior margins of the choanae. The throat and belly are immaculate, and the soles of the feet are dark. In the isthmus this species can be distinguished from Eleutherodactylus rugulosus by less rugose skin on the dorsum and absence of dark ventral mottling. ”

“ From the above analysis of ecological distribution we may see that the rainforest provides a variety of habitats for amphibians and that these habitats are suitable for amphibian life throughout the year. ”

“ Oaxaca: El Barrio (3) ; Matías Romero; Tehuantepec (2) . Veracruz: Cosamaloapan; Cuatotolapam (2) .
The two specimens from Cuatotolapam were collected by Ruthven in an area of mixed savanna and forest. The three specimens (USNM 30535-7) listed above from El Barrio were collected by Sumichrast; possibly they came from another locality. The city of Tehuantepec is divided into seven districts called "barrios." The two specimens listed from Tehuantepec (MCZ 1604) merely bear the data "Tehuantepec, Mexico." They may have come from the town, the district, or from anywhere in the isthmus. ”

“ There is a dark brown bar in the loreal region and a dark brown bar extending posteriorly from the eye to a point above the insertion of the forelimb. The iris is a copper color. The toes are completely webbed; the fingers, one-third webbed. There is a small axillary web that is evident when the forelimbs are at right angles to the body. ”

“ With the advent of the first heavy summer rains the stream beds fill with water, marshes expand, and many depressions become ponds (Pl. 5, fig. 2) . At this time the amount of free water in the scrub forests and savannas greatly increases, much more so than that in the rainforests. ”

“ Five specimens from San Lorenzo, Veracruz (USNM 123516-20) , were identified as Bufo cristatus by Smith (1947:408) . Firschein (1950:83) redefined the cristatus group of Bufo and assigned these specimens to valliceps.
Eleutherodactylus alfredi Boulenger
Oaxaca: Tolosita (2) . Veracruz: 35 km. SE of Jesús Carranza (6) .
These specimens were collected in rainforest. Shreve (1957:247) pointed out the close resemblance between E. alfredi and E. conspicuus from Piedras Negras, Guatemala, and treated them as subspecies. ”

“ In parts of savannas where clumps of trees surround depressions containing water throughout the year, individuals of the species named above, together with Hyla loquax and Phyllomedusa callidryas taylori, may not only breed, but remain throughout the year. ”