Structure and dynamic of food webs in Andean North Patagonian freshwater systems: organic matter, light and nutrient relationships

Abstract

North Andean Patagonian aquatic systems include a number of deep and shallow oligotrophic lakes with a profuse hydrographic net. In this contribution we present a review of the researches carried out during the last decade in the food webs of North Patagonian water bodies. Food webs in these systems were studied based on field surveys, combining with field and laboratory experiments. Deep and shallow lakes were analyzed in relation to light, organic matter, and nutrient constraints as limiting interacting factors. In addition, we have also extended our knowledge on the structure and dynamics of stream food webs by analyzing different aspects of biotic interactions occurring both through the autotrophic and heterotrophic pathways. Since Andean lakes were defined as high-light low-nutrient environments, and in this scenario high C: P ratios would be expected, food webs of these lakes may be characterized by low food quality for herbivores. We analyzed how this low food quality affects the distribution of zooplankters, and the response at the cellular level. In shallow lakes, macrophytes contributed substantially to the dissolved organic matter content. Also the littoral zone offers higher food availability and refuge against predation. Finally, we analyzed the impact of the introduction of exotic salmonids on food webs of shallow lakes and headwater streams. (Keywords: bacterioplankton, phytoplankton, zooplankton, fish, insects, lakes and rivers) RESUMEN. Estructura y dinamica de tramas troficas en sistemas acuaticos andino-norpatagonicos: relaciones con la materia organica, la luz y los nutrientes: Los sistemas acuaticos de Patagonia incluyen lagos oligotroficos tanto profundos como someros con una importante red hidrografica. En este trabajo se presenta una revision de la informacion surgida a partir de los trabajos de investigacion en redes troficas de sistemas acuaticos de Patagonia realizados durante la ultima decada. Los estudios se basaron sobre muestreos de campo, experimentos en campo y laboratorio. Los lagos profundos y someros fueron estudiados en relacion a la luz, materia organica y las restricciones en la disponibilidad de nutrientes como factores limitantes. Por otra parte, tambien hemos incluido en nuestros estudios a las redes troficas de arroyos andinos, y analizamos las interacciones troficas tanto en las vias autotroficas como las heterotroficas. Los sistemas andinos han sido definidos como sistemas de elevada relacion luz:nutrientes, y bajo estas condiciones se generan altas relaciones C:P que resultan en redes troficas caracterizadas por una baja calidad de recursos para los herbivoros. Nosotros analizamos entonces como esta baja calidad de alimento