Fabián Gastón Jara

Estado del conocimiento de humedales del norte patagónico (Argentina): aspectos relevantes e importancia para la conservación de la biodiversidad regional

Las areas de humedal ocupan casi el 5 % del territorio de la Patagonia argentina. En la zona extrandina y el desierto patagonico estos ecosistemas son esenciales para sostener numerosas especies de fauna y flora silvestre. Ademas, los humedales del norte patagonico permiten el desarrollo de comunidades acuaticas complejas y constituyen el habitat critico de grupos de organismos como los peces y los anfibios incluidos en listados de conservacion prioritaria. Estos ecosistemas tienen un funcionamiento complejo que depende estrechamente de las fluctuaciones de las variables meteorologicas y son por lo tanto muy sensibles a los efectos del cambio climatico. En la actualidad el uso de la tierra, la introduccion de especies y la interaccion de estos aspectos con el cambio climatico constituyen las variables de mayor impacto sobre estos ambientes patagonicos. En este trabajo se presenta informacion geografica, geomorfologica y climatica de un numero de humedales del norte de la Patagonia argentina. Por otra parte, se sintetiza informacion sobre la flora y la distribucion de peces y anfibios con el proposito de enfatizar la importancia de estos ambientes en el mantenimiento de la biodiversidad regional. Por ultimo, se senalan los procesos que actualmente afectan a estos sistemas poniendo en evidencia la necesidad de obtencion de conocimientos basicos para el diseno de planes de manejo y conservacion de sus comunidades biologicas

Toad Tadpole Responses to Predator Risk: Ontogenetic Change between Constitutive and Inducible Defenses

Abstract Rhinella spinulosa is a toad common in rivers, streams, and steppe wetlands where they face a variety of insect predators. Rhinella spinulosa tadpoles are known to be unpalatable to dragonfly naiads at some developmental stages. In this paper, we studied susceptibility of R. spinulosa tadpoles to predation by two species of predators, water bugs (Belostoma bifoveolatum, Belostomidae) with piercing-sucking mouth parts and dragonfly larvae (Rhionaeschna variegata, Aeshnidae) with chewing mouth parts. We conducted feeding trials to test the effectiveness of tadpole chemical defenses against water bugs. We also performed behavioral and choice experiments to study whether tadpole behavior influences their vulnerability to predators, and whether R. variegata has the capacity of discern between palatable (stages 38–45) and unpalatable tadpoles (stages 24–26). Rhinella spinulosa tadpoles, when fully palatable, responded by reducing their activity levels in the presence of dragonfly larvae but did not alter their behavior at unpalatable-early stages. Chemical defenses were not effective against the sucking predator (B. bifoveolatum) and no changes in tadpole activity were observed. Selectivity experiments revealed the ability of dragonfly larvae to distinguish between unpalatable and palatable tadpoles. Inducible (behavior) and constitutive (toxins) defenses observed in R. spinulosa tadpoles and the transition between them could result in an important survival mechanism in response to variable predator risk in the habitats in which they co-occur.

Thermal Tolerances in Tadpoles of Three Species of Patagonian Anurans

ABSTRACT. Anurans living along the Andes cordillera exploit several thermal environments that vary with altitude and latitude. Studies on moderate and high-elevation tropical species suggest co-adaptation between thermal ecology and thermal physiology. Our objective was to test whether this is the case for three Patagonian anuran species. We focused on larval stages and analyzed critical maximum and minimum temperatures granting survivorship. The species studied were Abodes gargola, Pleurodema bufoninum and Rhinella spinulosa papillosa. Alsodes gargola lives primarily in high-elevation lakes and montane streams, has long larval development and overwinters. In contrast, tadpoles of P. bufoninum and R. s. papillosa use marshes and lower elevation ponds, and develop in three months. Tadpoles of Abodes gargola tolerated experimental temperatures up to 32°C and those of the other two species lost the ability to move at temperatures near 38°C. Tadpoles of all species tolerated experimental exposure to 0°C for a limited period of time, but A. gargola had higher mortality rates when exposed to freezing than the other two species. These results are consistent with some traits of thermal ecology, exemplified by the higher thermal stability of the environments used by A. gargola. However, other factors such as physiological trade-offs may partially explain this pattern.

Predatory insects in lentic freshwater habitats from northwest Patagonia: richness and phenology

The main purpose of this work was to study the richness, phenology and abundance of predatory insects throughout the hydroperiod and how they relate to the environmental parameters in lentic bodies of water in northwest Patagonia. Nineteen fishless wetlands and three wetlands with fish were studied, which are located in the surroundings of the Nahuel Huapi National Park. Biotic and abiotic variables were measured during the hydroperiod of each wetland. The dip-netting sampling technique was used to determine the richness of predatory insects and to study the phenology of the dominant species in four wetlands. Species richness in temporary wetlands ranged from one to nine species per wetland and does not differ from that observed in the permanent environments with or without fish predators. Maximum insect richness was recorded in late spring and was associated with the maximum depth of the wetland and its structural complexity as well as with the duration of the hydroperiod.

Distribution of backswimmers in shallow ponds of Patagonia and their predatory role on a common tadpole–copepod assemblage

In this study, the distribution and occurrence of backswimmers in 21 fishless ponds was analysed in the Nahuel Huapi National Park (Patagonia, Argentina). We performed laboratory experiments to study the impact of different developmental stages of the endemic backswimmer Notonecta vereertbruggheni on typical co-occurring prey. We recorded three species of backswimmers N. vereertbruggheni, Notonecta virescens and Notonecta fazi. A seasonal study in Fantasma pond showed that adults of N. vereertbruggheni colonise and reproduce in the pond in spring and summer, co-occurring with other macroinvertebrates and endemic tadpoles. Predation experiments explored the impact of N. vereertbruggheni on two large co-occurring prey, the calanoid copepod Parabroteas sarsi and the tadpoles of Pleurodema thaul. The backswimmer consumed more copepods than tadpoles when prey was offered separately. Selectivity experiments demonstrated that the copepods were preferred over the tadpoles. Backswimmers may impact the typical assemblages of organisms found in fishless ponds of Patagonia during spring and summer.

Lack of functional link in the tadpole morphology induced by predators

Abstract Most studies of predator-induced plasticity have focused on documenting how prey species respond to predators by modifying phenotypic traits and how traits correlate with fitness. We have previously shown that Pleurodema thaul tadpoles exposed to the dragonfly Rhionaeschna variegata responded strongly by showing morphological changes, less activity, and better survival than non-exposed tadpoles. Here, we tested whether there is a functional link between morphological plasticity and increased survival in the presence of predators. Tadpoles that experienced predation risk were smaller, less developed, and much less active than tadpoles without this experience. Burst speed did not correlate significantly with morphological changes and predator-induced deeper tails did not act as a lure to divert predator strikes away from the head. Although we have previously found that tadpoles with predator-induced morphology survive better under a direct predator threat, our results on the functional link between morphology and fitness are not conclusive. Our results suggest that in P. thaul tadpoles (1) burst speed is not important to evade predators, (2) those exposed to predators reduce their activity, and (3) morphological changes do not divert predator attacks away from areas that compromise tadpole survivalEE. Our results show that morphological changes in P. thaul tadpoles do not explain burst speed or lure attraction, although there was a clear reduction of activity, which itself reduces predation. We propose that changes in tadpole activity could be further analyzed from another perspective, with morphological change as an indirect product of behavior mediated by physiological mechanisms.