No abstract

Population demography in Rhinella arenarum (Anura: Bufonidae) and Physalaemus biligonigerus (Anura: Leiuperidae) in agroecosystems in the province of Córdoba, Argentina. The advancing agricultural frontier has led to an important loss of natural habitats, with significant consequences for biodiversity. The demography for two species of anurans, Physalaemus biligonigerus and Rhinella arenarum, both associated with agricultural systems in the central region of the Córdoba Province, were analyzed and compared in this study. Four sites were sampled: three agroecosystems with different alteration degrees (C1, C2 and SM1) and a fourth site not cultivated (SM2). The sampling was conducted during two reproductive periods, from September 2008 to April 2009 and September 2009 to April 2010. Individuals were captured using live pitfall traps for the metamorphic, juveniles and adults; and visual encounter survey, for the capture of eggs and larvae. With the abundance data, the survival for each age class was estimated using the KNM method (Kiritani Nakasuki Manly). With survival rates and fertility population, Leslie matrices were elaborated to obtain a quantitative projection of the population size. Altered environments showed lower eggs and larvae survival. Population projections were favorable in the site SM2 and were less favorable and a tendency to extinction, in sites dominated by crops. This study showed that the agroecosystems of this region are possibly inhospitable environments for reproduction and survival of the species studied. The aquatic stages in the life cycle of both species would be the more affected, since water bodies deterioration is present or may occur in those areas. We can recognize species-specific effects of agricultural ecosystems; P. biligonigerus was the most affected species, possibly because of their life histories and habitat requirements. We suggested that environmental degradation caused by the cropland in the central region of Argentina would impact on the demographics of the anuran populations in the area.

Trophic ecology in tadpoles of Rhinella arenarum (Anura: Bufonidae) in agroecosystems and their possible implications for conservation. The progress of the agriculture border has led an important loss of natural habitats, with significant consequences for biodiversity. In this sense, the studies in anuran amphibian tadpoles inhabiting these environments are relevant, because the larval stage is a phase of population regulation. The aim of this study was to analyze the body condition and diet in Rhinella arenarum, tadpoles, an anuran species widely distributed in South America and that inhabit agroecosystems. Three sites were sampled, two agroecosystems with different alteration degrees (C1 and C2) and an uncultured (SM) third place. The captured tadpoles were anesthetized, fixed and preserved in formaldehyde (10%). Subsequently, body measurements were made and the complete intestine was removed and analyzed for food items under a binocular microscope. The diet in R. arenarum tadpoles has a dominance of algae Bacillariophyceae, followed by Cyanophyceae. In particular, the class Bacillariophyceae, due to the presence of the genus Navicula, Nitzschia, Gomphonema and Hantzschia, was important in the diet of the anurans in those agroecosystems. Class Cyanophyceae, mainly represented by genus Oscillatoria and Euglenophyceae represented by Euglena and Strombomonas, were predominant in the diet of the anurans in SM. Some differences in the total items consumed by tadpole were observed between the studied sites. Tadpoles that inhabit the modified sites (C1 and C2) recorded a significantly smaller amount of food. Moreover, the tadpoles that inhabit these sites showed a lower body condition. The presence of certain algae associated with eutrophic environments, could indicate some pollution in agroecosystems (C1 and C2). Food resources would be lesser in places with strong agricultural activity, possibly with a greater degree of eutrophication. A smaller food amount could have consequences at population level for the short and long time terms, because of its impact on individual growth. Larval diet is suggested as a potential bioindicator of environmental health for these areas.