By César Luis Barrio Amorós
According to current data, Venezuela is the sixth most amphibian-diverse country in the world, with over 300 species known and many more to discover and report (Barrio, 1998; unpublished data). Of the known species, Rodríguez & Rojas Suárez (1995-1999), in the Red Book on Venezuelan Fauna, identify three endangered categories containing eleven species of amphibians. The dendrobatids Dendrobates leucomelas and Minyobates steyermarki are placed in the category of "Lower Risk; Least Concern" together with the salamanders Bolitoglossa borburata and B. orestes. In no case has there been thorough monitoring to determine the rarity of any of these animals except for very local instances as with Bolitoglossa borburata at Rancho Grande biological station, where it can no longer be found. Not enough is known about B. orestes to include it in any endangered category since it is a very difficult species to find (Barrio & Fuentes, 1999b). Dendrobates leucomelas is an attractive animal as a pet, hence the current concern about its extinction in Venezuela. Nevertheless, the selling price for this animal in international markets has decreased a lot since it is very easy to breed in captivity (Barrio & Fuentes, 1999a). Our own observations show that D. leucomelas is abundant in all places sampled (Barrio & Fuentes, 1998). Minyobates steyermarki should be considered under a threatened species category since its restricted habitat (the top of Cerro Yacapana, an isolated "tepui" in Amazonas Sate) makes it vulnerable to any natural or artificial catastrophe. As is now known, an illegal expedition extracted some 150 animals for a German breeding center. The main threat, however, comes from open air gold mining mostly by Brazilian "garimpeiros", which causes widespread deforestation, soil erosion, general depredation and mercury poisoning (Barrio & Fuentes, 1999a).
The species that appear under the two most endangered categories according to the Red Book all belong to the genus Atelopus. Atelopus carbonerensis is the most threatened under the "In Critical Danger" section; the remainder (A. cruciger, A. mucubajiensis, A. oxyrhynchus, A. pinangoi, A. sorianoi and A. tamaense) are all in the "Endangered" category despite the fact that none have been seen for the past 5 years and, though there are no precise details about A. tamaense, the rest have been searched for several times in the past few years without positive results (La Marca & Reinthaler, 1991; La Marca & Lotters, 1997). It is too soon to consider them extinct but alarm signals have gone up. There have been hopeful reports of recent observations of at least three species. These are still to be confirmed.
Vial & Saylor (1993) mention in their list of threatened or endangered amphibians several Venezuelan species (some shared by the Red Book). The first is a rare anuran, a characteristic element of the Guayana shield, Allophryne ruthveni. Nothing is known about the populations of this species in Venezuela other than some anecdotal data (Duellman, 1997) and new sightings (Barrio, 1998). Ceratophrys calcarata is a fossorial species that inhabits xerophytic zones which only shows up during the wet season for frantic reproductive activity. No population monitoring is underway to confirm that it is under threat.
Also on the list are three species of Oreophrynella, O. huberi, O. macconelli and O. quelchii. This genus of small bufonids has adapted to marginal conditions on the top of some tepuis (pre-cambrian mountains with a table-top and heights of between 1000 and 3000 m) on the Guianan shield and present a very limited distribution which might make them susceptible to any catastrophe. Nonetheless, so far no information is available on a decrease in the population of O. quelchii. O. huberi is known as an inhabitant of the plateau of "Cerro el Sol", a small tepui. O. macconelli deserves taxonomic study, but nothing is known about its identity and the state of its population.
Venezuelan dendrobatids mentioned in the list are Colostethus humilis, C. leopardalis, C. mandelorum, C. saltuensis, Mannophryne collaris, Nephelobates alboguttatus, N. duranti, N. haydeeae, N. mayorgai, N. meridensis, N. orostoma and N. serranus (updated nomenclature). Little is known about their population status though it is likely that some are undergoing population declines locally (some of these species inhabit minute areas isolated by human activity). C. humilis is not an uncommon species in the Andean foothills (W. Schargel, pers. com.). C. leopardalis, once abundant on the páramo de Mucubají, is currently extremely difficult to locate. Mannophryne collaris has undergone a drastic reduction in numbers in some areas, such as the city of Mérida and its surroundings in the Venezuelan Andes (La Marca, 1995), but it is still abundant in areas of the Barinas foothills (Barrio & Fuentes, 1999a). Three species of Andean Hyla are also mentioned: H. jahni, H. lascinia and H. platydactyla. Populations of all of them can be found in brooks of cloud forests without difficulty. Finally, three species of Eleutherodactylus also appear on the list: E. ginesi, E. lancinii and E. paramerus. Declines of E. ginesi have occurred in places where it was formerly abundant such as the páramo de Mucubají, even though it is still plentiful in areas rarely visited between 2800 and 4000 m. The latter two species have suffered alarming declines to the point where they are very hard to find. These species have perhaps suffered from overcollection and are now down to a minimum.
Apart from the species dealt with in the Red Book and in Vial & Saylor (1993), there are others which have never been included in any other "warning" list and which should be considered as such since there are indications that their populations have either dwindled noticeably or have not been reported at all in the past few years. A decline of Gastrotheca ovifera has been mentioned in the last few years at Parque Nacional Henri Pittier (Caribbean coastal mountain range). However, this must be a very localized case since the species was detected in very large numbers at Parque Nacional El Avila in March 1997. Phyllomedusa medinai was described in 1962 as endemic to the cloud forests of Parque Nacional Henri Pittier, and very much the object of collection until 1974, when the last gathered samples are registered. Since then, there has been no news on its population situation. It has apparently not been sighted again. Aromobates nocturnus is a dendrobatid with apparently unique peculiarities (Myers et al., 1991). This species is found only at 2200 m. elevation at its type locality in Trujillo State in an Andean cloud forest. It has recently been the object of an intense search by teams from the Universidad de Los Andes without any luck.
Venezuela possesses a very high rate of endemism, particularly as regards mountain ranges (Andes, Coastal Range and Tepuis or highlands of the Guianan Shield). Many of these endemic species show very limited population distributions and are in danger either because of human activity (Andes) and/or they are susceptible to natural disasters (drought, floods, and bacterial, viral or fungus infections) or to over-collection. The following is a list of animals that ought to be taken into consideration when listing species likely to become extinct in the near future, though this is not the result of monitoring or specific studies: Atelopus chrysocorallus, Metaphryniscus sosae, Oreophrynella nigra, O. vasquezi, Centrolene gorzulai, Cochranella castroviejoi, C. duidaeana, C. riveroi, C. vozmedianoi, Hyalinobatrachium auyantepuianum, Mannophryne lamarcai, M. riveroi; all species of Stefania (S. evansi, S. ginesi, S. goini, S. marahuaquensis, S. oculosa, S. percristata, S. riae, S. riveroi, S. satelles, S. scalae, S. schuberti and S. tamacuarina); Hyla amicorum, H. aromatica, H. inparquesi, H. loveridgei, H. yaracuyana, Tepuihyla aecii, T. edelcae, T. galani, T. luteolabris, T. rimarum, Leptodactylus magistris, Dischidodactylus colonnelloi, D. duidensis, Eleutherodactylus anotis, E. avius, E. boconoensis, E. cantinans, E. cavernibardus, E. colostichos, E. memorans, E. pruinatus, E. reticulatus, E. riveroi, E. stenodiscus, E. turumiquirensis, E. yaviensis, Otophryne steyermarki, Bolitoglossa spongai and Microcaecilia rabei.
Two species of exotic amphibian have been introduced into Venezuela. The first, a few decades ago, is Eleutherodactylus johnstonei, which is to be found mostly in parks and gardens all over Venezuelan towns. Its presence has not been reported outside its artificial habitats so it is not a danger to autochthonous species. There has been a sighting recently (so far at a lagoon at a private property in the area of La Carbonera, some 30 km due northwest of the city of Mérida) of Rana catesbeiana, one of the species that has caused the most impact on local populations in all other countries where it has been introduced (such as Colombia and several European countries). Its impact on local amphibian populations is so far unknown but it is plausible to think that it can quickly extinguish Hyla meridensis from the lagoon and continue expanding to neighboring areas. This warrants prompt action before the presence of this species becomes an unsolvable problem.
What is known about the decline of amphibians in Venezuela is really very little and is usually based on conjectures or still-to-be-proved hypotheses (which should rely on proper methodology such as systematic long-term monitoring). I recommend the immediate monitoring of species highly susceptible to extinction such as Atelopus spp., Aromobates nocturnus and Phyllomedusa medinai.
Contact: César Luis Barrio Amorós, Executive Director, Fundación AndígenA, Apartado Postal 210, 5101-A Merida, Venezuela. cesarlba@yahoo.com
References
Barrio, C.L. (1998). Sistemática y Biogeografía de los anfibios (Amphibia) de Venezuela. Acta Biol. Venezuelica 18(2): 1-93.
Barrio, C.L. & Fuentes, O. (1998). Distribución de Dendrobates leucomelas (Anura: Dendrobatidae) en Venezuela. Acta Biol. Venezuelica 18(3): 35-41.
Barrio, C.L. & Fuentes, O. (1999a). Sinopsis de la familia Dendrobatidae (Amphibia: Anura) de Venezuela. Acta Biol. Venezuelica 19(3): 1-10.
Barrio, C.L., & Fuentes, O. (1999b). Una nueva especie de salamandra (Caudata: Plethodontidae: Bolitoglossa) de los andes venezolanos, con comentarios sobre el género en Venezuela. Acta Biol. Venezuelica 19(4): 9-19.
La Marca, E. (1995). Crisis de Biodiversidad en Anfibios de Venezuela: Estudio de casos. P.47 En: Alonso, M.(ed.) Cuad.-Quim. Ecol. 4 "La Biodiversidad Neotropical y la Amenaza de las extinciones" Fac. Cienc. ULA, Mérida,Venezuela.
La Marca, E. (1997). Lista actualizada de los anfibios de Venezuela. Pp: 103-120. En: La Marca (ed.). Vertebrados Actuales y Fósiles de Venezuela. Museo de Ciencia y Tecnología de Mérida, Venezuela.
La Marca, E. and Reinthaler, H.P. (1991). Population changes in Atelopus species of the Cordillera de Mérida, Venezuela. Herp. Review 22(4): 125-128.
La Marca, E. and Lötters, S. (1997). Monitoring of declines in Venezuelan Atelopus (Amphibia: Anura: Bufonidae). Herpetologia Bonnensis: 207-213.
Myers, C.W., Paolillo, A and Daly, J.W. (1991). Discovery of a defensively malodorous and nocturnal frog in the family Dendrobatidae: phylogenetic significance of a new genus and species from the Venezuelan Andes. Amer. Mus. Novitates 3002: 1-33.
Rodríguez, J.P. y Rojas-Suárez, F. (1995-1999). El Libro Rojo de la fauna Venezolana. PROVITA, Fundación Polar, Wildlife Cons. Soc., PROFAUNA-MARNR, UICN.
Vial, J.L., and Saylor, L. (1993). The status of amphibian populations: A compilation and analysis. DAPTF Working Document #1.