Nabors, Lisa Karina. (2005) Amphibians and human- altered habitats: A case study in the Llanos of Venezuela.
Human alteration of the landscape is one of the major threats to the preservation of biodiversity, in particular the conversion of land to crop cultivation. Land conversion often changes the type and quantity of water bodies available in a landscape and, consequently, its associated fauna may be affected. This study assessed the value of rice fields for the amphibian community in the Llanos of Venezuela by comparing these artificial wetlands to natural wetlands that have been grazed by cattle (hereafter “Llano wetlands”). I documented the patterns of adult and larval distribution and abundance in both natural wetlands and in rice paddies. I surveyed the larval anurans, their associated aquatic predator community, and abiotic factors that might explain the observed patterns of larval anuran abundance in the two types of wetlands. Amphibian species diversity was lower in the rice fields that in the Llanos wetlands, as were tadpole abundances. Predator abundances were not significantly different between the rice- cultivated areas and the natural wetlands. Across all water bodies, there was an association between the distribution of larval anuran species and the aquatic community. Overall, the rice fields with their large areas had lower density of tadpoles and locally common species were predominant. To assess rice fields as potential breeding habitat for amphibians, I conducted a field experiment in which I evaluated the effects of land use (rice, llanos), density (low, high), and predation on growth, survival, and development of Pleurodema brachyops (family Leptodactylidae) tadpoles in enclosure. Tadpoles development was slower in the high-density treatment in the rice fields that the same treatment in the llanos wetlands. Tadpole survival and growth was hindered in some of the rice field enclosure. In summary, the rice fields do not mimic llanos wetlands. A few individual species may be able to use this habitat successfully, but these artificial wetlands do not support the full potential range of amphibian species found in the llanos wetlands from which the rice fields were converted.