Risks to Colombian Amphibian Fauna from Cultivation of Coca
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Journal of Toxicology and Environmental Health, Part A, 72: 974–985, 2009 ISSN: 1528-7394 print / 1087-2620 online DOI: 10.1080/15287390902929733 RisksUTEH to Colombian Amphibian Fauna from Cultivation of Coca ( Erythroxylum coca ): A Geographical Analysis J. D.Risks to Colombian Lynch Amphibian Fauna from Coca Cultivation and S. B. Arroyo Laboratorio de Anfibios, Instituto de Ciencias Naturales, Universidad Nacional de Colombi, Bogotá, Colombia species of frogs at risk. These include Ameerega bilingua, Den- The Colombian amphibian fauna is among the richest known dropsophus bifurcus, Pristimantis colomai, P. degener, P. diade- in the world, with about 20 species of salamanders (order Cau- matus, P. quaquaversus, P. variabilis, and Trachycephalus data), 35 of the limbless caecilians (order Gymnophiona), and jordani. Other species may also be at risk but exact numbers are more than 700 species of frogs and toads (order Anura) recorded unknown since few investigations were undertaken in these from localities within the country. The potential effects of expo- areas during the past 30 yr. The main ranges for these species sure to glyphosate on amphibians arising from production of were assumed to be in Ecuador. illegal crops (coca) were examined. The analysis was based on (1) behavior and ecology of species and (2) proximities of actual museum records to localities in which illegal crops are being grown and the subset of those that have been sprayed with gly- Currently the herbicide glyphosate (Glyphos) is used to phosate. Based on data on the location of amphibians collected in Colombia, records were obtained for 193 species (28% of the control coca ( Erythroxylum coca ) production through an aerial national diversity) of frogs and toads found in localities within spray eradication program (Solomon et al., 2007). Several 10 km of areas where coca is grown. Further analyses with ARC concerns have been raised regarding the spray control program, MAP software allowed for measurement of the direct distance ranging from peripheral crop damage to adverse environmental separating collection locations for frogs, known coca fields, and effects. As larval stages of amphibians are sensitive to formu- areas where aerial spraying was being conducted. Records in or near coca fields included data for 11 of 13 families of frogs and lated glyphosate (Bernal et al., 2009a), these organisms may be toads known to be present in Colombia. Only Ceratophryidae particularly at risk. In addition, the pesticides used by growers in and Pipidae were not reported from these locations and appear the production of coca also present a risk to larval amphibians, Downloaded At: 20:08 2 October 2009 not to be at risk. For eight species ( Dendrobates truncatus , Crau- should they be found in or close to the edge of coca fields gastor raniformis , Pristimantis gaigeae, Smilisca phaeota, Ela- (Brain & Solomon, 2009). chistocleis ovale, Hypsiboas crepitans, Trachycephalus venulosus , and Pseudis paradoxa ) selected to represent several habitat pref- All amphibians have permeable skins and hence are espe- erences and life-cycle strategies, large areas of their distribu- cially susceptible to application of extraneous chemicals, such tions lie outside coca production regions and their populations as pesticides, to their environment (Stebbins & Cohen, 1995). as a whole are at low risk. For a limited number of species that Pathways of exposure in terrestrial amphibians include direct barely enter Colombian territory, the consequences of coca contact of spray droplets on the exposed skin or through contact production may be more serious and may have placed several with sprayed surfaces, such as the animals moving over leaves that have been sprayed. In addition, contamination of water ©General Secretariat of the Organization of American States, through direct overspray or spray drift may result in exposure 2009. This paper was prepared as part of a Study entitled “Production to aquatic larval stages. of Illicit Drugs, the Environment and Human Health,” financed with contributions from the Governments of Colombia and the United The behavior of most amphibians reduces the risk of direct States of America. The conclusions and opinions expressed herein exposure to spray. With few exceptions, Colombian amphibians are those of the authors and not necessarily those of the Organization are nocturnal organisms, emerging when the air temperatures of American States and its General Secretariat, which as of the date have fallen and the relative humidity of the air exceeds the dew of this copyright, have not formulated any opinion with respect point. Aside from Dendrobatids, a frog family composed of to them. The authors gratefully acknowledge the contributions of Policia nearly exclusively diurnal species, the nocturnal activity cycles Antinarcótica de Colombia , which provided mapping data on the of amphibians render them least likely to experience direct appli- location of coca production and aerial eradication spraying. cation of the sprays. Exceptions are some species that “sleep” in Address correspondence to J. D. Lynch, Laboratorio de Anfibios, exposed positions—the Rana platanera, known to Colombians Instituto de Ciencias Naturales, Universidad Nacional de Colombi, visiting the lowlands adjacent to the eastern cordillera, is a Bogotá, Colombia. E-mail: [email protected] 974 RISKS TO COLOMBIAN AMPHIBIAN FAUNA FROM COCA CULTIVATION 975 species (actually, a pair of species) with many casual observa- installations. In military installations more removed from natural tions of frogs “sleeping” on leaves in full sunlight—as well as forests (for example, those immediately adjacent to Leticia), juveniles of many species and tadpoles of some species. Since only 12 species of frogs and toads were found. In the parks of the eradication spraying is only conducted in daylight and early in city (and in undeveloped lots), only 6 species of frogs were the day (Solomon et al., 2007), the most likely pathway of detected. exposure is via contact with sprayed surfaces. Glyphosate and These data provide a necessary background against which the polyethoxylated talowamine (POEA) surfactant with which one can assess the effect of coca production (as an illegal crop) it is formulated are strongly adsorbed to soils and organic mat- on the Colombian amphibian fauna. Cultivations of coca dis- ter (Tsui & Chu, 2004; Wang et al., 2005), reducing likelihood play alterations that are even more severe than chagras of the of exposure from these sources; however, contact with wet indigenous communities in the area of Leticia (Lynch, 2005). leaves may allow exposure. Other more toxic pesticides, such Using this as a basis for comparison, cultivation of coca is as are used by coca growers (Brain & Solomon, 2009), may likely to reduce the resident frog fauna by approximately 90% not be strongly absorbed and may be more bioavailable by (see earlier discussion), prior to consideration of any effects of this route. glyphosate spraying upon the amphibian fauna. Habitat alterations sometimes favor some amphibians. Based on a study of Pristimantis * (Lynch, 1998) in the Cordillera COCA PRODUCTION Occidental (an area that was originally covered with evergreen In Colombia, coca plants grow in areas that were once wet montane forests) and on the fauna in the immediate environs of lowland tropical forest. The plant is a shrub and grows to Leticia (Lynch, 2005), an area that originally was wet lowland between 1.5 and 2 m. In most cases the coca plants are grown forests, there are some species in each fauna that appear to in clear-cut areas, but this illicit crop may be found in the have benefitted from human intervention (or habitat modifica- middle of other crops such as banana plantations with the tion). These species become common locally in areas that have objective of avoiding detection. The most obvious character- experienced complete or partial removal of the natural vegeta- istic of coca cultivation is the degradation of ecosystem. The tion, but that are rarely encountered during intensive searches farmers deforest from the canopy to the leaf litter in order to within natural (forested) habitats. These species (including prepare the land for a coca plantation (see Anonymous, 2006, Pristimantis brevifrons, P. erythropleura, P. palmeri, and p. 49), leaving the habitat completely destroyed by physical Craugastor raniformis ) perhaps become more abundant activities. because they have been relieved of the effect of competition Coca production results in the alteration of the natural habitat with other species (most species in each community react (Brain & Solomon, 2009), which may exert significant adverse adversely, in terms of numbers or visibility, to habitat alter- effects on frogs. Illustrations in the book Colombia/Monitoreo ation). However, additional clues are available from other spe- de Cultivos de Coca (Anonymous, 2006, pp. 21, 23, 25, 27, 29, cies, such as Trachycephalus venulosus, a canopy-dwelling 31, 33–35) graphically show the degree of environmental alter- Downloaded At: 20:08 2 October 2009 frog in lowland forests in Colombia. Although the adults live ations and/or destruction that accompanies coca plantations. within the confines of the forest, the species appears to need Alteration in the habitat may exert significant adverse effects “open” habitats in which to breed. Presumably, in times before on frogs, and these are illustrated in a study conducted in the human intervention (or habitat modification)