En este trabajo se recopila y analiza la información disponible contenida en estudios científi cos y técnicos a fi n de determinar la composición taxonómica y la estructura trófi ca de comunidades de ríos pertenecientes a cinco cuencas hidrográfi cas de Chile, ubicadas en un gradiente ambiental árido-mediterráneo. Las cuencas fueron: Loa, Huasco, Limarí, Cachapoal y Mataquito. Se consideraron los cuatro grupos taxonómicos más importantes: peces, macroinvertebrados bentónicos, macrófi tas y diatomeas bentónicas. Se logró determinar la estructura taxonómica y trófi ca para 10 comunidades pertenecientes a las cuencas estudiadas. Los análisis indicaron que: (a) cada cuenca muestra una estructura taxonómica característica; (b) no se aprecian patrones de aumento o disminución de diversidad en el sentido del gradiente árido-mediterráneo, existiendo solo un patrón en el gradiente aguas abajo-aguas arriba dentro de un sistema; (c) el grupo de los macroinvertebrados bentónicos muestra una composición taxonómica particular y diferenciable para las zonas árida, semiárida y mediterránea; (d) la composición taxonómica de cada grupo resultó signifi cativamente anidada entre ríos y (e) se identifi caron cinco tipos de mallas trófi cas para el total de sistemas comunitarios estudiados, representadas por grupos funcionales y sus relaciones alimentarias. Investigaciones futuras deben orientarse a aumentar la resolución taxonómica de la representación de las mallas trófi cas e incorporar otros aspectos funcionales relevantes.
In ecological communities, pollution driven perturbations exert immediate effects on sensitive individuals, but these effects may be transmitted among interacting organisms and spread over the community through several paths. This makes the assessment and prediction of ecological consequences of pollution difficult. The propagation of perturbation effects among organisms can be horizontal among organisms that coexist in space and time, and vertical among organism that belong to different generations. The latter process is poorly understood, in particular in planktonic organisms facing metal pollution. In this study we evaluate the vertical transfer of effects driven by sublethal copper stress on the heartbeat rate, somatic growth and fertility of Daphnia pulex. In order to evaluate this, we performed a factorial experiment in which parental and filial generations were exposed to both copperenriched and control media. We found that parental exposure to copper exerted a significant effect on the heartbeat rate, somatic growth and fertility of offspring, revealing a transgenerational effect in D. pulex. This response may be explained by a higher resource investment on repair/detoxification processes in the parental generation, allocating fewer resources to offspring quality. Our results suggest that responsiveness of organisms to stress is dependent on parental history.Key words: ecotoxicology, heartbeat rate, maternal effects, transgenerational effects, zooplankton. RESUMENEn las comunidades ecológicas, las perturbaciones producidas por los contaminantes ejercen efectos inmediatos en los individuos sensibles, pero estos efectos podrían ser transmitidos entre los organismos interactuantes y extenderse sobre la comunidad a través de múltiples vías. Esto hace difícil la evaluación y predicción de las consecuencias ecológicas de la contaminación. La propagación de los efectos de una perturbación entre los organismos puede ser horizontal, entre organismos que coexisten espacial y temporalmente, y vertical, entre organismos que pertenecen a generaciones diferentes. Este último proceso ha sido escasamente entendido, en particular en organismos planctónicos enfrentados a contaminación por metales. En este estudio evaluamos la transferencia vertical de los efectos producidos por un estrés subletal de cobre sobre la tasa de latidos cardiacos, el crecimiento corporal y la fertilidad de Daphnia pulex. Para evaluar esto, se realizó un experimento factorial en el cual las generaciones parental y filial fueron expuestas tanto a medios enriquecidos con cobre como a medios control. Encontramos que la exposición de las madres al cobre ejerció un efecto significativo en la tasa de latidos cardiacos, el crecimiento corporal y la fertilidad de la descendencia, revelando un efecto transgeneracional en D. pulex. Esta respuesta puede explicarse por una mayor inversión de recursos en los procesos de reparación/ desintoxicación en la generación parental, asignando menos recursos a la calidad de su descendencia. Nuestros resultados ...
In nature the effect that pollutants exert on exposed organisms could depend on the state and dynamics of natural environmental factors as well as on the internal state of the exposed organisms. In this study we evaluated how level and variability of food, as well as the age of exposure can modify the effects of the pesticide deltamethrin on the freshwater crustacean Daphnia magna. The effects of the pesticide were measured on life history and nutritional traits (lipid storage) of the test organisms, which were exposed at different juvenile ages under constant (high and low) food as well as food shortage treatments. Our results show that deltamethrin exerts significant effects on all evaluated traits of Daphnia, and several responses are shaped by deltamethrin interacting with food and age of exposure. Two novel results are remarkable. First, at constant food treatments the effects of the pesticide were stronger on younger individuals, whereas in food shortage treatments the effects were stronger on older individuals. Second, we observed that deltamethrin exerted stronger effects on certain traits (survival, body growth and median consumption time of lipids) in Daphnia exposed to food shortage, as compared to constant low food treatments. Our results highlight the importance of the dynamics of resources in freshwater systems for shaping the vulnerability of herbivores to pollutants released to the ecosystem and improve our understanding of how the organismal responses to environmental stress are determined by the ecological condition of the organisms at the instant of being exposed to perturbations.
Interaction strength among species plays a crucial role in shaping the functioning of ecological communities, but it is often assumed to be insensitive to inter-individual variation in underlying parameters such as attack rates or handling time. Ecological factors including stressors exert age/size-dependent effects on such behavioral parameters, promoting shifts in the distribution of parameter values over ages. Here we analyze the effects of the pesticide methamidophos on the Daphnia-microalga interaction strength. We first analyze age-dependent effects of the pesticide on the Daphnia functional response, and then decompose the population-level effects of the stressor into contributions of shifts in elevation (i.e., vertical effect) versus shifts in nonlinearity (i.e., nonlinear effect) of the response of interaction strength over consumer age. Our results show that (1) Rogers and Holling type II functional response models best fitted the empirical functional responses of Daphnia of different ages, (2) attack rate and handling time were affected by the pesticide, (3) these effects were age-specific, shifting the average attack rate and both the mean and coefficient of variation of handling time of different age classes, (4) population level interaction strength was affected by pesticide exposure by variation in both elevation and nonlinearity of its response over consumer age. We show that both vertical and nonlinear effects were important in magnitude but opposite in sign. The consequences of factors that exert age/size dependent effects can only be evaluated through properly considering inter-individual variation.Fondo Nacional de Desarrollo Cientifico y Tecnologico (Ministry of Education, Chile) FONDECYT 1150348 CONICYT Doctoral fellowship (CONICYT-PCHA/Doctorado Nacional) 2015-211521 CONICY
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