Search

Una forma fundamental y efectiva de visualizar los patrones y propiedades dinámicas de una comunidad, es a través de las redes tróficas, las cuales son entendidas como el mapa de las interrelaciones entre la estructura de las comunidades con los procesos que ocurren dentro del ecosistema. En este estudio se describe una red trófica acuática, conformada por invertebrados acuáticos, detritus y perifiton, asociada con la planta Egeria densa. Se realizaron muestreos en periodos de transición y lluvias, en cuatro estaciones en la zona litoral del Lago de Tota. En cada sitio se recolectaron tres muestras de 300 g de material vegetal. Se midieron in situ los siguientes parámetros: conductividad eléctrica, pH, oxígeno disuelto y temperatura. Por medio de información bibliográfica y en algunos casos mediante observación, se asignaron los hábitos alimenticios. Finalmente, se desarrolló un modelo de trama trófica tipo estático. Se registraron 112866 individuos distribuidos en 26 taxones que fueron clasificados según sus hábitos alimenticios en: dos trofoespecies tope, 16 intermedias y dos basales. Esta red trófica presentó una conectancia media de 0,13 y una densidad de uniones de 2,95. En conjunto, estos resultados muestran a E. densa como generadora de detritus y sustrato de perifiton, consideradas en el modelo como trofoespecies basales que sustentan la comunidad. Además de la presencia de 10 trofoespecies consumidoras primarias que generan alta redundancia ecológica y a la vez garantizan el flujo de recursos hacia niveles tróficos superiores.

Increased global temperatures caused by climate change are causing species to shift their ranges and colonize new sites, creating novel assemblages that have historically not interacted. Species interactions play a central role in the response of ecosystems to climate change, but the role of trophic interactions in facilitating or preventing range expansions is largely unknown.The goal of our study was to understand how predators influence the ability of range‐shifting prey to successfully establish in newly available habitat following climate warming. We hypothesized that fish predation facilitates the establishment of colonizing zooplankton populations, because fish preferentially consume larger species that would otherwise competitively exclude smaller‐bodied colonists.We conducted a mesocosm experiment with zooplankton communities and their fish predators from lakes of the Sierra Nevada Mountains in California, USA. We tested the effect of fish predation on the establishment and persistence of a zooplankton community when introduced in the presence of higher‐ and lower‐elevation communities at two experimental temperatures in field mesocosms.We found that predators reduce the abundance of larger‐bodied residents from the alpine and facilitate the establishment of new lower‐elevation species. In addition, fish predation and warming independently reduced the average body size of zooplankton by up to 30%. This reduction in body size offset the direct effect of warming‐induced increases in population growth rates, leading to no net change in zooplankton biomass or trophic cascade strength.We found support for a shift to smaller species with climate change through two mechanisms: (a) the direct effects of warming on developmental rates and (b) size‐selective predation that altered the identity of species' that could colonize new higher elevation habitat. Our results suggest that predators can amplify the rate of range shifts by consuming larger‐bodied residents and facilitating the establishment of new species. However, the effects of climate warming were dampened by reducing the average body size of community members, leading to no net change in ecosystem function, despite higher growth rates. This work suggests that trophic interactions play a role in the reorganization of regional communities under climate warming. [ABSTRACT FROM AUTHOR]

Introduction: The benthic fauna of the littoral zone in lakes is important in transferring energy to other trophic levels, habitat coupling, and helping to keep habitat stability. The study of this type of interactions in lentic systems is priority, since functional aspects about biological communities are unknown. Objective: Describing the trophic relations of aquatic invertebrates of the littoral zone in a tropical high mountain lake by characterizing gut content and stable isotope analysis of δ13C and δ15N. Methods: Samples of benthic invertebrates were collected in the littoral zone of the Lago de Tota where Egeria densa was present using a handheld net method. Samples were processed in the laboratory, organisms were identified, counted and weighed. Gut contents and δ13C and δ15N stable isotopes analysis were performed as well. Results: Records of the trophic relations of aquatic invertebrates, which live in the littoral in high mountain lentic ecosystem in the Neotropics are shown. The analysis of gut contents distinguished seven food items, microphytes and MOPF were the most frequent, and through the stable isotopes analysis (δ15N) we identified four trophic levels, among resources (macrophytes and POM), and consumers (detritivores, herbivores, and predators). The two upper trophic levels concentrated greater diversity and biomass. Conclusion: Most of the organisms studied were linked to omnivorous habits, evidenced in a wide spectrum of food items in their diet. The δ15N values show an enrichment, which occurs due to the effects of the tendency towards eutrophication of the system or due to unknown values of protozoa and bacteria that plays a fundamental role in the diet of these organisms, besides the δ13C values reported in organisms consumes, allows us to suggest an affinity with native resources of the littoral zone. [ABSTRACT FROM AUTHOR]

The keystone roles of mega‐fauna in many terrestrial ecosystems have been lost to defaunation. Large predators and herbivores often play keystone roles in their native ranges, and some have established invasive populations in new biogeographic regions. However, few empirical examples are available to guide expectations about how mega‐fauna affect ecosystems in novel environmental and evolutionary contexts. We examined the impacts on aquatic ecosystems of an emerging population of hippopotamus (Hippopotamus amphibus) that has been growing in Colombia over the last 25 yr. Hippos in Africa fertilize lakes and rivers by grazing on land and excreting wastes in the water. Stable isotopes indicate that terrestrial sources contribute more carbon in Colombian lakes containing hippo populations, and daily dissolved oxygen cycles suggest that their presence stimulates ecosystem metabolism. Phytoplankton communities were more dominated by cyanobacteria in lakes with hippos, and bacteria, zooplankton, and benthic invertebrate communities were similar regardless of hippo presence. Our results suggest that hippos recapitulate their role as ecosystem engineers in Colombia, importing terrestrial organic matter and nutrients with detectable impacts on ecosystem metabolism and community structure in the early stages of invasion. Ongoing range expansion may pose a threat to water resources. [ABSTRACT FROM AUTHOR]