Urea excreted by tropical frogs is explained by their body mass and the mass of insects consumed (original) (raw)
Related papers
Juvenile amphibians do not avoid potentially lethal levels of urea on soil substrate
Environmental Toxicology and Chemistry, 2001
We examined the effects of a forest fertilizer (urea) on newly metamorphosed terrestrial amphibians (Western toads, Bufo boreas; Cascades frogs, Rana cascadae; long-toed salamanders, Ambystoma macrodactylum; and roughskin newts, Taricha granulosa). We examined avoidance behavior of Western toads and Cascades frogs on both paper towel and soil substrates dosed with urea (control and 100 kg N/ha and an additional treatment of 50 kg N/ha for Western toads on soil substrate) and avoidance behavior of long-toed salamanders on soil substrate dosed with urea. We further examined the survival and feeding behavior of all four species exposed to urea on soil substrate (100 kg N/ha) for 5 d. Juvenile Western toads and Cascades frogs avoided paper towels dosed with urea but did not avoid urea-dosed soil substrate. However, Western toads and Cascades frogs both suffered significant mortality when exposed to urea on a soil substrate for 5 d. Furthermore, after adjusting for weight, we found that ureaexposed juvenile Western toads and Cascades frogs consumed significantly fewer prey items (crickets) compared with nonexposed control animals. Long-toed salamanders did not discriminate against soil substrate dosed with urea, and neither long-toed salamanders nor roughskin newts died or reduced prey consumption as a result of urea exposure. Juvenile amphibians may not be able to detect and avoid harmful levels of urea fertilizer on a natural substrate. Furthermore, anthropogenic stressors such as urea fertilizer can significantly reduce the survival and prey consumption of juvenile amphibians. These effects are important to consider in light of possible threats to the conservation status of many amphibian species.
Reduced body condition and enzymatic alterations in frogs inhabiting intensive crop production areas
Ecotoxicology and Environmental Safety, 2011
Parameters indicative of general condition and health were compared amongst adult frogs inhabiting uncultivated lands and fields subjected to agricultural practices typical of the humid pampas of Argentina. Whereas no significant differences existed in the parasite load and external malformations prevalence rate of adult frogs from either environments, a reduced condition factor was clearly demonstrated in frogs from agricultural lands. This conclusion was reached for four frog species of different life habits: the terrestrial fossorial Rhinella fernandezae, the terrestrial Leptodactylus latinasus, the semi-aquatic Leptodactylus ocellatus, and the arborescent Hypsiboas pulchellus. A distinct pattern of enzymatic modifications was furthermore observed in L. ocellatus and H. pulchellus from agricultural lands, including elevated hepatic activities of catalase and cholinesterase, and an inhibition of liver GST activity. Further studies should investigate the causes and consequences of the systematically low condition factor observed in frogs from agricultural fields of the humid pampas of Argentina.
Sensitivity to Urea Fertilization in Three Amphibian Species
Archives of Environmental Contamination and Toxicology, 2001
Forest fertilization with granular urea is a wellestablished management practice in many forested regions of the world. We hypothesize that chemical forest fertilizers may be affecting forest-dwelling wildlife. In the laboratory, we studied the effects of fertilization doses of granular urea on three species of forest-dwelling amphibians (Plethodon vehiculum, Rhyacotriton variegatus, and Taricha granulosa). In avoidance experiments, the three species avoided a substrate treated with a dose of 225 kg N/ha urea. In toxicity experiments, we exposed amphibians to urea at doses of 225 kg N/ha and 450 kg N/ha for 4 days. The observed effects increased with time and dose, and there were significant differences in sensitivity among the species. Both treatment levels had an acute effect on survival of P. vehiculum and R. variegatus. At 24 h, mortality at the highest dose was 67% for P. vehiculum, and 47% for R. variegatus. In contrast, there was no mortality for T. granulosa at these concentrations. We suggest that environmental levels of urea could be affecting behavior and survival of some amphibians species in fertilized forests.
Journal of Experimental Zoology Part A: Ecological Genetics and Physiology, 2008
It has long been suspected that urea accumulation plays a key role in the induction or maintenance of metabolic suppression during extended dormancy in animals from diverse taxa. However, little evidence supporting that hypothesis in living systems exists. We measured aerobic metabolism of isolated organs from the wood frog (Rana sylvatica) in the presence or absence of elevated urea at various temperatures using frogs acclimatized to different seasons. The depressive effect of urea on metabolism was not consistent across organs, seasons, or temperatures. None of the organs from summer frogs, which were tested at 201C, or from winter frogs tested at 41C were affected by urea treatment. However, liver, stomach, and heart from spring frogs tested at 41C had significantly lower metabolic rates when treated with urea as compared with control samples. Additionally, when organs from winter frogs were tested at 101C, metabolism was significantly decreased in urea-treated liver and stomach by 1515% and in urea-treated skeletal muscle by 1550%. Our results suggest that the presence of urea depresses the metabolism of living organs, and thereby reduces energy expenditure, but its effect varies with temperature and seasonal acclimatization. The impact of our findings may be wide ranging owing to the number of diverse organisms that accumulate urea during dormancy.
The Journal of experimental biology, 1982
Sharp-nosed African reed frogs, Hyperolius nasutus Gunther, are small (0.4 g) hyperoliids which have minimal rates of evaporative water loss (4.5 mg g-1 h-1; 0.3 mg cm-2 h-1) that are only 1/10 to 1/20 that of a typical frog, Hylaregilla, of comparable size (171 mg g-1 h-1, 4.8 mg cm-2 h-1). The surface-area-specific resistance to water flux of H. nasutus dorsal skin (96-257 sec cm-1) is similar to that of other 'waterproof' frogs (300-400), of cocooned frogs (40-500), and of desert reptiles (200-1400). However, H. nasutus can greatly increase the rate of evaporative water loss during radiative heat stress by mucous gland discharge, and by exposing the ventral skin. Urea is the principal nitrogenous waste product of H. nasutus and uric acid comprises less than 1% of the total nitrogen excretion for both H. nasutus and H. regilla. Other 'waterproof' frogs, in contrast, are uricotelic. Lethal dehydration requires less than two weeks in H. nasutus, despite its low surfa...
Herpetology Notes, 2024
The change of natural environments into agricultural areas is generally accompanied by the control of invertebrate populations, which can alter prey availability for amphibians. The way frogs deal with such changes will determine their survival or extinction from these agricultural landscapes. We compared changes in the diet of the semiaquatic frog Pseudis minuta between populations from natural and agricultural environments in the Pampa biome, southern Brazil. We evaluated 34 individuals from agricultural environments and 42 from natural environments, located 1 km from each other, and we also analysed prey availability. In agricultural environments, the diet was composed mostly of beetles, one of the less frequently consumed prey groups in natural environments. This suggests that individuals of P. minuta are forced into a narrower trophic niche in agricultural areas, with the availability of food types likely a consequence of the anthropic changes.
Journal of Tropical Ecology
Determining the ubiquity of top-down control effects of predators on their prey and ecosystem processes is important for understanding community and ecosystem-level consequences that may result from predator loss. We conducted experiments at two spatial scales to investigate the effects of terrestrial frogs (Eleutherodactylus coqui) on aerial and litter invertebrates, plant growth and herbivory, and litter decomposition. At both scales, frogs reduced aerial invertebrates and leaf herbivory, but had no effect on litter invertebrates. At the smaller scale, frogs increased foliage production rates, measured as the number of new leaves and new leaf area produced, by 80% and decomposition rates by 20%. The influence of E. coqui on increasing primary productivity and decomposition rates at the smaller scale appeared to be a result of elimination and excretion rather than of controlling prey. While the results provide evidence for frogs controlling herbivorous prey at both scales, species effects on ecosystem processes were only detectable at the smaller scale. The results highlight the difficulties in conducting experiments at large spatial scales. The findings from this study imply that the loss of amphibians and other species of higher trophic levels may affect nutrient cycling rates in tropical forests.
Journal of Natural History, 2007
The diet of males of five syntopic hylid species from the Araucaria plateau of Rio Grande do Sul was studied by stomach flushing. Because the duration of their breeding seasons was rather different, the levels of food intake at the respective breeding sites were analysed. We found a positive correlation between the length of the male calling period and the ingestion of prey. The longer the species‐specific reproductive activity of the males, the more individuals fed during that time. The results are discussed under congruence aspects of feeding and mating microhabitats in these tree frogs. In addition, differences in niche breadth may influence the temporal and spatial partitioning between the species studied and result in quantitative as well as qualitative patterns of prey consumption, thereby ensuring a maximum of fitness gain.
Top-down effects of a terrestrial frog on forest nutrient dynamics
Oecologia, 2002
Many studies have found top-down effects of predators on prey, but few studies have linked top-down effects of vertebrate predators to nutrient cycling rates in terrestrial systems. In this study, large and significant effects of a terrestrial frog, Eleutherodactylus coqui (coquí), were recorded on nutrient concentrations and fluxes in a subtropical wet forest. In a manipulative experiment, coquís at natural densities were contained in or excluded from 1 m3 enclosures for 4 months. Chemistry of leaf wash (throughfall), foliage, and decomposed leaf litter in the enclosures were measured as indicators of coquí effects on nutrient cycling. Coquí exclusion decreased elemental concentrations in leaf washes by 83% for dissolved organic C, 71% for NH4+, 33% for NO3–, 60% for dissolved organic N, and between 60 and 100% for Ca, Fe, Mg, Mn, P, K, and Zn. Coquí exclusion had no effect on foliar chemistry of plants transplanted into the enclosures. However, coquí exclusion decreased nutrient availability in decomposing mixed leaf litter by 12% and 14% for K and P, respectively, and increased C:N ratios by 13%. Changes in nutrient concentrations that occurred with coquí exclusion appear to be due to concentrations of nutrients in coquí waste products and population turnover. The results supported our hypothesis that coquís have an observable effect on nutrient dynamics in this forest. We suggest that the primary mechanism through which they have this effect is through the conversion of insects into nutrient forms that are more readily available for microbes and plants. The potential for higher trophic level species to affect nutrient cycling through this mechanism should not be overlooked.