Cropland ecosystem functioning may be affected by human perturbations transmitted from adjacent ecosystems, such as freshwater systems. However, our limited knowledge of the ecological interactions within cropland–freshwater networks hinders projecting the consequences of anthropogenic pressures. We reviewed the information from freshwater and cropland communities in the Mediterranean zone of Chile and constructed an ecological metanetwork for characterizing the structure and projecting responses of this system facing environmental pressures. We performed a semi-qualitative analysis to identify the nodes that strongly influence other network components and (or) could significantly affect the transmission of effects within the system. Our analyses show that omnivore fish, amphibians, annual pollinated crops, and deciduous orchards are the most important groups. Although we expected that amphibious predators were the most important groups in transmitting perturbations between ecosystems, we also found groups of plants and pollinators performing this function. We stress that the fate of crop systems facing environmental disturbances should be assessed in a broader context rather than as an isolated system.

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.

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.

In this work the available information from scientific and technical studies is compiled and analyzed, to determine the taxonomic composition and trophic structure of river communities belonging to five hydrological basins of Chile, located within an arid-Mediterranean environmental gradient. The basins were: Loa, Huasco, Limari, Cachapoal y Mataquito. The four most important taxonomic groups were considered: fish, benthic macroinvertebrates, macrofites and benthic diatoms. The taxonomic and trophic structures of 10 communities from the studied basins were determined. The analyses indicated that: (a) each basin shows a characteristic taxonomic structure; (b) no patterns were found of increase or decrease in diversity along the arid-Mediterranean gradient, only finding a pattern along the upstream-downstream gradient within a system; (c) benthic macroinvertebrates shows a taxonomic particular and differentiable composition for the zones arid, semiarid and Mediterranean; (d) the taxonomic composition of each group was found to be significantly nested between rivers, and (e) five types of food webs were identified for the total of studied community systems, represented by functional groups and their feeding relationships. Future research should be oriented towards increasing the taxonomic resolution of the food webs and incorporate other relevant functional features.

En este trabajo se recopila y analiza la informacion disponible contenida en estudios cientificos y tecnicos a fin de determinar la composicion taxonomica y la estructura trofica de comunidades de rios pertenecientes a cinco cuencas hidrograficas de Chile, ubicadas en un gradiente ambiental arido-mediterraneo. Las cuencas fueron: Loa, Huasco, Limari, Cachapoal y Mataquito. Se consideraron los cuatro grupos taxonomicos mas importantes: peces, macroinvertebrados bentonicos, macrofitas y diatomeas bentonicas. Se logro determinar la estructura taxonomica y trofica para 10 comunidades pertenecientes a las cuencas estudiadas. Los analisis indicaron que: (a) cada cuenca muestra una estructura taxonomica caracteristica; (b) no se aprecian patrones de aumento o disminucion de diversidad en el sentido del gradiente arido-mediterraneo, existiendo solo un patron en el gradiente aguas abajo-aguas arriba dentro de un sistema; (c) el grupo de los macroinvertebrados bentonicos muestra una composicion taxonomica particular y diferenciable para las zonas arida, semiarida y mediterranea; (d) la composicion taxonomica de cada grupo resulto significativamente anidada entre rios y (e) se identificaron cinco tipos de mallas troficas para el total de sistemas comunitarios estudiados, representadas por grupos funcionales y sus relaciones alimentarias. Investigaciones futuras deben orientarse a aumentar la resolucion taxonomica de la representacion de las mallas troficas e incorporar otros aspectos funcionales relevantes.

En las comunidades ecologicas, las perturbaciones producidas por los contaminantes ejercen efectos inmediatos en los individuos sensibles, pero estos efectos podrian ser transmitidos entre los organismos interactuantes y extenderse sobre la comunidad a traves de multiples vias. Esto hace dificil la evaluacion y prediccion de las consecuencias ecologicas de la contaminacion. La propagacion de los efectos de una perturbacion entre los organismos puede ser horizontal, entre organismos que coexisten espacial y temporalmente, y vertical, entre organismos que pertenecen a generaciones diferentes. Este ultimo proceso ha sido escasamente entendido, en particular en organismos planctonicos enfrentados a contaminacion por metales. En este estudio evaluamos la transferencia vertical de los efectos producidos por un estres subletal de cobre sobre la tasa de latidos cardiacos, el crecimiento corporal y la fertilidad de Daphnia pulex. Para evaluar esto, se realizo 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 exposicion de las madres al cobre ejercio 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 inversion de recursos en los procesos de reparacion/ desintoxicacion en la generacion parental, asignando menos recursos a la calidad de su descendencia. Nuestros resultados sugieren que la reactividad de los organismos al estres depende de la historia parental.