Title: Amphibians and Reptiles of the Rainforests of Southern El Petén, Guatemala
Author: William Edward Duellman
Release date: December 24, 2011 [eBook #38398]
Language: English
Credits: Produced by Chris Curnow, Joseph Cooper and the Online
Distributed Proofreading Team at http://www.pgdp.net
| PAGE | ||
| Introduction | 207 | |
| Acknowledgments | 208 | |
| Description of Area | 208 | |
| Physiography | 209 | |
| Climate | 209 | |
| Vegetation | 209 | |
| Gazetteer | 210 | |
| The Herpetofauna of the Rainforest | 211 | |
| Composition of the Fauna | 212 | |
| Ecology of the Herpetofauna | 212 | |
| Relationships of the Fauna | 217 | |
| Accounts of Species | 218 | |
| Hypothetical List of Species | 246 | |
| Summary | 247 | |
| Literature Cited | 247 | |
Early in 1960 an unusual opportunity arose to carry on biological field work in the midst of virgin rainforest in southern El Petén, Guatemala. At that time the Ohio Oil Company of Guatemala had an air strip and camp at Chinajá, from which place the company was constructing a road northward through the forest. In mid-February, 1960, J. Knox Jones, Jr. and I flew into El Petén to collect and study mammals, reptiles, and amphibians. While enjoying the comforts of the fine field camp at Chinajá, we worked in the surrounding forest and availed ourselves of the opportunity to be on hand when the road crews were cutting the tall trees in the forest, thereby bringing to the ground many interesting specimens of the arboreal fauna. We stayed at Chinajá until late March, with the exception of a week spent at Toocog, another camp of the Ohio Oil Company located 15 kilometers southeast of La Libertad and on the edge of the savanna. Thus, at Toocog we were able to work both in the forest and on the savanna. In the summer of 1960, John Wellman accompanied me to El Petén for two weeks in June and July. Most of our time was spent at Chinajá, but a few days were spent at Toocog and other localities in south-central El Petén.
Many areas in Guatemala have been studied intensively by L. C. Stuart, who has published on the herpetofauna of the forested area of northeastern El Petén (1958), the savannas of central El Petén (1935), and the humid mountainous region to the south of El Petén in Alta Verapaz (1948 and 1950). The area studied by me and my companions is covered with rainforest and lies to the north of the highlands of Alta Verapaz and to the south of the savannas of central El Petén. A few specimens of amphibians and reptiles were obtained in this area in 1935 by C. L. Hubbs and Henry van der Schalie; this collection, reported on by Stuart (1937), contained only one species, Cochranella fleischmanni, not present in our collection of 77 species and 617 specimens.
I am grateful to L. C. Stuart of the University of Michigan, who made the initial arrangements for our work in El Petén, aided me in the identification of certain specimens, and helped in the preparation of this report. J. Knox Jones, Jr. and John Wellman were able field companions, who added greatly to the number of specimens in the collection. In Guatemala, Clark M. Shimeall and Harold Hoopman of the Ohio Oil Company of Guatemala made available to us the facilities of the company's camps at Chinajá and Toocog. Alberto Alcain and Luis Escaler welcomed us at Chinajá and gave us every possible assistance. Juan Monteras and Antonio Aldaña made our stay at Toocog enjoyable and profitable. During our visits to southern El Petén, Julio Bolón C. worked for us as a collector, and between March and June he collected and saved many valuable specimens; his knowledge of the forest and its inhabitants was a great asset to our work. Jorge A. Ibarra, Director of the Museo Nacional de Historia Natural in Guatemala assisted us in obtaining necessary permits and extended other kindnesses. To all of these people I am indebted for the essential parts that they played in the completion of this study.
Field work in the winter of 1960 was made possible by funds from the American Heart Association for the purposes of collecting mammalian hearts. My field work in the summer of 1960 was supported by a grant from the Graduate Research Fund of the University of Kansas.
A vast lowland region stretches northward for approximately 700 kilometers from the highlands of Guatemala to the Gulf of Mexico. The northern two-thirds of this low plain is bordered on three sides by seas and forms the Yucatán Peninsula. The lowlands at the base of the Yucatán Peninsula make up the Departamento El Petén of Guatemala. The area with which this report is concerned consists of the south-central part of El Petén.
Immediately south of Chinajá is a range of hills, the Serrania de Chinajá, having an almost due east-west axis and a crest of about 600 meters above sea level. South of the Serrania de Chinajá are succeedingly higher ridges building up to the Meseta de Cobán and Sierra de Pocolha and eventually to the main Guatemalan highlands. The northern face of the Serrania de Chinajá is a fault scarp dropping abruptly from about 650 meters at the crest to about 140 meters at the base. From the base of the Serrania de Chinajá northward to the Río de la Pasión at Sayaxché the terrain is gently rolling and has a total relief of about 50 meters. North of the Río de la Pasión is a low dome reaching an elevation of 170 meters at La Libertad; see Stuart (1935:12) for further discussion of the physiography of central El Petén. The rocks in southern El Petén are predominately Miocene marine limestones; there are occasional pockets of Pliocene deposits. There is little evidence of subterranean solution at Chinajá, but northward in central El Petén karsting is common. The upper few inches of soil is humus rich in organic matter; below this is clay.
The climate of El Petén is tropical with equable temperatures throughout the year. Temperatures at Chinajá varied between a night-time low of 65° F. and a daytime high of 91° F. during the time of our visits. In the Köppen system of classification the climate at Chinajá and Toocog is Af. Rain falls throughout the year, but there is a noticeable dry season. To anyone who has traveled from south to north in El Petén and the Yucatán Peninsula, it is obvious from the changes in vegetation that there is a decrease in rainfall from south to north. There is a noticeable difference between Chinajá and Toocog. Although rainfall data are not available for Chinajá and Toocog, there are records for nearby stations (Sapper, 1932). At Paso Caballos on the Río San Pedro about 40 kilometers northwest of Toocog the average annual rainfall amounts to 1620 mm.; the driest month is March (21 mm.), and the wettest months are June (269 mm.) and September (265 mm.). At Cubilquitz, Alta Verapaz, about 35 kilometers south-southwest of Chinajá and at an elevation of 300 meters, the average annual rainfall is 4006 mm.; the driest month is March (128 mm.), and the wettest months are July (488 mm.) and October (634 mm.).
During the 18 days in February and March, 1960, that we kept records on the weather at Chinajá moderate to heavy showers occurred on seven days. During our stay there in June and July rain fell every day, as it did in Toocog. However, during the week spent at Toocog in March no rain fell.
The vegetation of northern and central El Petén has been studied by Lundell (1937), who made only passing remarks concerning the plants of the southern part of El Petén. No floristic studies have been made there. The following remarks are necessarily brief and are intended only to give the reader a general picture of the forest. I have included names of a few of the commoner trees that I recognized.
Chinajá is located in a vast expanse of unbroken rainforest. In this forest there is a noticeable stratification of the vegetation. Three strata are apparent; in the uppermost layer the tops of the trees are from 40 to 50 meters above the ground. The spreading crowns of the trees and the interlacing vines form a nearly continuous canopy over the lower layers. Among the common trees in the upper stratum are Calophyllum brasiliense, Castilla elastica, Cedrela mexicana, Ceiba pentandra, Didalium guianense, Ficus sp., Sideroxylon lundelli, Swietenia macrophylla, and Vitex sp. (Pl. 1, fig. 1). The middle layer of trees have crowns about 25 meters above the ground; these trees in some places where the upper canopy is missing form the tallest trees in the forest. This is especially true on steep hillsides. Common trees in the middle layer include Achras zapote, Bombax ellipticum, Cecropia mexicana, Orbignya cohune, and Sabal sp. The lowermost layer reaches a height of about 10 meters; in many places in the forest this layer is absent. Common trees in the lower stratum include Crysophila argentea, Cymbopetalum penduliflorum, Casearia sp., and Hasseltia dioica.
The ground cover is sparce; apparently only a few small herbs and ferns live on the heavily shaded forest floor. Important herpetological habitats include the leaf litter, rotting stumps, and rotting tree trunks on the forest floor and the buttresses of many of the gigantic trees, especially Ceiba pentandra (Pl. 2). Epiphytes, especially various kinds of bromeliads, are common. Most frequently these are in the trees in the upper and middle strata.
At Toocog there is sharp break between savanna and forest (Pl. 7, fig. 2). The forest is noticeably drier and more open than at Chinajá (Pl. 9). The crowns of the trees are lower, and there is no nearly continuous canopy between 40 and 50 meters above the ground. Although Swietenia macrophylla and other large trees occur, they are less common than at Chinajá. Especially common at Toocog are Achras zapote, Brosimum alicastrum, and various species of Ficus.
The localities from which specimens were obtained are cited below and shown on the accompanying map (Fig. 1).
Chinajá.—Lat. 16° 02´, long. 90° 13´, elev. 140 m. Camp of the Ohio Oil Company of Guatemala and formerly a small settlement. On some maps Chinajá is located just to the north of the Alta Verapaz—El Petén boundary; recent surveys place the location just to the south of the imaginary line through the rainforest. Field work was conducted in the immediate vicinity of the camp, on the lower slopes of the Serrania de Chinajá, and at several sites to the northwest and north-northwest of Chinajá, where the forest was being cleared. The entire area supports rainforest.
La Libertad.—Lat. 16° 47´, long. 90° 07´, elev., 170 m. A town on the savannas in central El Petén; although we collected there in the rainy season, the specimens obtained on the savannas are not included in this report.
Paso Subín.—Lat. 16° 38´, long. 90° 12´, elev. 90 m. A small settlement on the Río Subín, a tributary of the Río de la Pasión. Specimens were obtained in rainforest in the immediate vicinity of the settlement.
Río de la Pasión.—A large river flowing northward through southern El Petén and thence westward into the Río Usumacinta. Specimens were obtained along the river between the Río Subín and Sayaxché.
Río San Román.—A river flowing northward in south-central El Petén to the Río Salinas (Usumacinta). We collected along the river at a place about 16 kilometers north-northwest of Chinajá, approximately at Lat. 16° 10´, long. 90° 17´, elev. 110 m. In the dry season the river was clear; it is surrounded by rainforest.
Sayaxché.—Lat. 16° 31´, long. 90° 09´, elev. 80 m. A town on the southern bank of the Río de la Pasión. Specimens were obtained in the rainforest and in cleared areas in the immediate vicinity of the town.
Toocog (formerly Sojío).—Lat. 16° 41´, long. 90° 02´, elev. 140 m. A camp of the Ohio Oil Company of Guatemala located at the rainforest-savanna edge, 15 kilometers southeast of La Libertad. Although we collected on the savannas as well as in the forest, especially to the east of the camp, only species obtained in the forest are considered in this report.
In presenting an account of the herpetofauna of southern El Petén three items need to be considered: (1) The composition of the fauna; (2) the ecology of the fauna; (3) the relationships of the fauna. Each of these topics is discussed briefly below. Logically a discussion of the origin of the fauna should follow, but this is being withheld for inclusion in a report on the herpetofauna of the entire El Petén by L. C. Stuart and the author; at that time the above topics will be expanded to cover the herpetofauna of the whole region.
Table 1.—Composition of the Herpetofauna in Southern El Petén, Guatemala.
Group |
Families | Genera | Species |
| Gymnophiona | (1)[A] | (1) | (1) |
| Caudata | 1 | 1 | 2 |
| Salientia | 6 | 10 (1) | 19 (1) |
| Crocodilia | 1 | 1 | 1 |
| Testudines | 4 | 7 | 8 |
| Sauria | 6 | 13 (1) | 19 (1) |
| Serpentes | 4 | 21 (7) | 29 (10) |
Total |
22 (1) | 53 (10) | 78 (13) |
[A] Numbers in parenthesis indicate the number of additional taxa that probably occur.
A total of 78 species of amphibians and reptiles has been found in the rainforests in southern El Petén; a break down into families and genera is given in table 1. Another 13 species probably occur in southern El Petén (see Hypothetical List of Species). The fauna primarily is composed of typical humid lowland forest inhabitants, such as:
| Hyla ebraccata | Eumeces sumichrasti |
| Hyla loquax | Ameiva festiva edwardsi |
| Phyllomedusa callidryas taylori | Imantodes cenchoa leucomelas |
| Smilisca phaeota cyanosticta | Leptophis ahaetulla praestans |
| Anolis biporcatus | Xenodon rabdocephalus mexicanus |
| Anolis capito | Bothrops nasutus |
| Anolis humilis uniformis | Bothrops schlegeli schlegeli |
Nevertheless, the region also provides at least a limited amount of habitat suitable for some species that are more frequently found in open forest of a drier nature; such species include:
| Hyla microcephala martini | Anolis sericeus sericeus |
| Hyla staufferi | Eumeces schwartzei |
| Hypopachus cuneus nigroreticulatus | Oxybelis aeneus aeneus |
Because of the absence of sufficiently open habitat or owing to the presence of competitors, some conspicuous members of sub-humid forests are not present in southern El Petén. Conspicuous absentees are the following:
| Rhinophrynus dorsalis | Ameiva undulata |
| Phrynohyas spilomma | Cnemidophorus angusticeps |
| Triprion petasatus | Conophis lineatus |
| Anolis tropidonotus | Masticophis mentovarius mentovarius |
| Ctenosaura similis |
Our two visits to Chinajá and Toocog afforded the opportunity to gather data on the ecology of the rainforests of southern El Petén and to study the relationships between the environment and members of the herpetofauna. Tropical rainforests present the optimum conditions for life, and it is in this environment that life reaches its greatest diversity. Here, too, biological inter-relationships are most complex. This complexity is illustrated by the presence of many species of some genera, all of which are found together in the same geographic region. In the rainforests of southern El Petén there are six species of Anolis, five of Hyla, four of Bothrops, and three of Coniophanes. Obviously, the diversity of ecological niches in the rainforest is sufficient to support a variety of related species. Of the examples mentioned above, fairly adequate ecological data were obtained for most of the species of Anolis, which will be used to show the ecological diversity and vertical stratification of sympatric species in the rainforests.
Of the six species of Anolis, all except A. sericeus are typically found in humid forests. Anolis sericeus sericeus is poorly represented in the collections from southern El Petén, where it may be in competition with Anolis limifrons rodriguezi that resembles Anolis s. sericeus in size, coloration, and habits. Therefore, Anolis sericeus sericeus is excluded from the following discussion. The common terrestrial species is Anolis humilis uniformis; sometimes this small species perches or suns on the bases of small trees or buttresses of some large trees. When disturbed it takes to the ground and seeks cover in the leaf litter or beneath logs or palm fronds. Anolis lemurinus bourgeaei is about twice the size of Anolis humilis uniformis and is usually observed on buttresses of large trees or on the lower two meters of tree trunks. Individuals were seen foraging on the ground along with Anolis humilis uniformis. At no time were Anolis lemurinus bourgeaei observed to ascend the trunks of large trees; they always took refuge near the bases of trees. Anolis limifrons rodriguezi is found on the stems and branches of bushes. It is a small species that sometimes is observed on the ground but was never seen ascending large trees. Anolis capito is about the same size as Anolis lemurinus bourgeaei and lives on the trunks of large trees. In the tops of the trees lives a large green species, Anolis biporcatus.
Similar segregation habitatwise can be demonstrated for other members of the herpetofauna. The avoidance of interspecific competition in feeding is well illustrated by three species of snakes that probably are the primary ophidian predators on frogs. Drymobius margaritiferus margaritiferus is diurnal and terrestrial; it feeds on frogs at the edges of breeding ponds by day. Also during the day Leptophis mexicanus mexicanus feeds on frogs in bushes and trees. At night the activities of both of these species is replaced by those of Leptodeira septentrionalis polysticta, which not only feeds on the frogs in the trees and bushes, but descends to the ground and even enters the water in search of food.
From the examples discussed above, the importance of the three dimensional aspect of the rainforest is apparent. The presence of a large and diverse habitat above the ground is of great significance in the rainforest, for of the non-aquatic components of the herpetofauna in the rainforests of southern El Petén, 42 per cent of the species spend at least part of their lives in the bushes and trees. Another important part of the forest is the subterranean level—the rich mulch, underground tunnels, and rotting subterranean vegetation. Of the 78 species of amphibians and reptiles in southern El Petén, seven are primarily fossorial, and half-a-dozen others are secondarily fossorial. Probably the fossorial members of the fauna are the least well represented in the collection, for such widespread species as Dermophis mexicanus mexicanus, Rhadinaea decorata decorata and Tantilla schistosa schistosa were expected, but not found.
In the following discussion of the ecological distribution of amphibians and reptiles in the rainforest I have depended chiefly on my observations made in southern El Petén, but have taken into consideration observations made on the same species in other regions, together with reports from other workers. The reader should keep in mind that the evidence varies from species to species. Of some species I have observed only one animal in the field; of others, I have seen scores and sometimes hundreds of individuals. For species on which I have few observations or rather inconclusive evidence, the circumstance of inadequate data is mentioned.
In analyzing the ecological distribution within the forest, it is convenient to recognize five subdivisions (habitats); each is treated below as a unit.
1. Aquatic.—This habitat includes permanent streams and rivers (Pl. 10, fig. 1), some of which are clear and others muddy. In the rainy season temporary ponds form in depressions on the forest floor (Pl. 10, fig. 2); these are important as breeding sites for many species of amphibians. Aquatic members of the herpetofauna are here considered to be those species that either spend the greatest part of their lives in the water or usually retreat to water for shelter. Seven species of turtles and one crocodilian are aquatic. Of these, Dermatemys mawi, Staurotypus triporcatus, and Pseudemys scripta ornata inhabit clear water, whereas Chelydra rossignoni, Claudius angustatus, Kinosternon acutum, and K. leucostomum inhabit muddy water. Crocodylus moreleti apparently inhabits both clear and muddy water, for in the dry season it lives along the clear rivers, but in the rainy season inhabits flooded areas in the forest as well.
2. Aquatic Margin.—Extensive marshes were lacking in the part of southern El Petén that I visited; consequently, the aquatic margin habitat is there limited to the edges of rivers and borders of temporary ponds. Bufo marinus, Rana palmipes, and Rana pipiens are characteristic inhabitants of the aquatic margin, although in the rainy reason Bufo marinus often is found away from water. Observations indicate that Tretanorhinus nigroluteus lateralis inhabits the margins of ponds and streams and actually spends considerable time in the water. Although Iguana iguana rhinolopha is arboreal, it lives in trees along rivers, into which it plunges upon being disturbed. Species included in this category are those that customarily spend most of their lives at the edge of permanent water. Frogs and toads that migrate to the water for breeding and the snakes that prey on the frogs at that time are not assigned to the aquatic-margin habitat.
3. Fossorial.—Characteristic inhabitants of the mulch on the forest floor are Bolitoglossa moreleti mulleri, Lepidophyma flavimaculatum flavimaculatum, Scincella cherriei cherriei, Ninia sebae sebae, Pliocercus euryzonus aequalis, and Micrurus affinis apiatus. Other species of snakes that spend most of their lives above ground often forage in the mulch layer; among these are Coniophanes bipunctatus biserialis, Coniophanes fissidens fissidens, Coniophanes imperialis clavatus, Lampropeltis doliata polyzona, and Stenorrhina degenhardti. Among the amphibians, at least Hypopachus cuneus nigroreticulatus, Eleutherodactylus rostralis, and Syrrhophus leprus are known to seek shelter in the mulch.
4. Terrestrial.—One turtle, Geoemyda areolata, is primarily terrestrial. Among the lizards, conspicuous terrestrial species are Anolis humilis uniformis and Ameiva festiva edwardsi; Anolis lemurinus bourgeaei and Basiliscus vittatus spend part of their lives on the ground, but also live on trees and in bushes. Eumeces schwartzei and E. sumichrasti apparently are terrestrial. The only terrestrial lizard that is nocturnal is Coleonyx elegans elegans, which by day hides in the leaf litter or below ground. Nocturnal amphibians that are terrestrial include Bufo marinus, Bufo valliceps valliceps, Eleutherodactylus rugulosus rugulosus, Syrrhophus leprus, and Hypopachus cuneus nigroreticulatus. A large number of active diurnal snakes are terrestrial; these include Boa constrictor imperator, Clelia clelia clelia, Dryadophis melanolomus laevis, Drymarchon corais melanurus, Drymobius margaritiferus margaritiferus, Pseustes poecilonotus poecilonotus, and Spilotes pullatus mexicanus. Nocturnal terrestrial snakes include three kinds of Bothrops (B. atrox asper, B. nasutus, and B. nummifer nummifer), all of which seem to be equally active by day.
5. Arboreal.—In this habitat the third dimension (height) of the rainforest probably is the most complex insofar as the inter-relationships of species and ecological niches are concerned. I have attempted to categorize species as to microhabitats within the arboreal habitat; in so doing, I recognize four subdivisions—bushes, tree trunks, tree tops, and epiphytes.
Bush inhabitants include several species of lizards and snakes, all of which have rather elongate, slender bodies, and long tails. Common bush-inhabitants in southern El Petén are Anolis limifrons rodriguezi, Basiliscus vittatus, Laemanctus deborrei, Leptophis mexicanus mexicanus, and Oxybelis aeneus aeneus. All of these are diurnal, and all but Laemanctus have been observed sleeping on bushes at night.
Tree-trunk inhabitants include five species of lizards. Thecadactylus rapicaudus lives on the trunks of large trees; Sphaerodactylus lineolatus lives beneath the bark on dead trees and on corozo palms. Anolis lemurinus bourgeaei lives on the bases and buttresses of large trees, from which it often descends to the ground. Corythophanes cristatus and Anolis capito were found only on tree trunks and large vines.
The least information is available for the species living in the tree tops. The following species were obtained from tops of trees when they were felled, or have been observed living in the tree tops: Anolis biporcatus, Iguana iguana rhinolopha, Celestus rozellae, Leptodeira septentrionalis polysticta, Leptophis ahaetulla praestans, Sibon dimidiata dimidiata, and Sibon nebulata nebulata.
Epiphytes, especially the bromeliads, provide refuge for a variety of tree frogs and small snakes. Of the tree frogs, Hyla picta, Hyla staufferi, Phyllomedusa callidryas taylori, Similisca baudini, and Similisca phaeota cyanosticta have been found in bromeliads; other species probably occur there. Among the snakes, Imantodes cenchoa leucomelas, Leptodeira frenata malleisi, Leptodeira septentrionalis polysticta, Sibon dimidiata dimidiata, and Sibon nebulata nebulata are frequent inhabitants of bromeliads; all of these snakes are nocturnal.
Most of the 78 species of amphibians and reptiles definitely known from the rainforest in southern El Petén have extensive ranges in the Atlantic lowlands of southern México and Central America; many extend into South America. Sixty-two (80%) of the species belong to this group having extensive ranges in Middle America. Three species (Syrrhophus leprus, Leptodeira frenata, and Kinosternon acutum) are at the southern limits of their distributions in southern El Petén and northern Alta Verapaz, whereas Eleutherodactylus rostralis and Thecadactylus rapicaudus are at the northern and western limits of their distributions in El Petén. Nine (11%) species have the center of their distributions in El Petén and the Yucatán Peninsula; representatives of this group include Claudius angustatus, Dermatemys mawi, Laemanctus deborrei, and Eumeces schwartzei.
In determining a measure of faunal resemblance, I have departed from the formulae discussed by Simpson (1960) and have analyzed the degree of resemblance by the following formula used to calculate an index of faunal relationships: