Mecanismos de coexistencia en poblaciones de palemónidos dulciacuícolas (Crustacea: decapoda: caridea)

Las comunidades bióticas que conforman un ecosistema están formadas por poblaciones de especies que interactúan entre sí determinando relaciones bidireccionales. Estas correspondencias se ajustan de tal manera que las especies pueden coexistir en el ambiente y sus poblaciones permanecer en el tiempo. En el valle aluvial del río Paraná, en su tramo medio, viven simpátricamete poblaciones de dos especies de camarones, Palaemonetes argentinus (Nobili 1901) y Macrobrachium borellii (Nobili 1896) (Crustacea Decapoda Caridea Palaemonidae), completamente dulciacuícolas. No hay diferencias aparentes de hábitats y es de suponer que estos camarones coexisten a través de algunos mecanismos que les permiten diferenciar alguna dimensión de sus nichos realizados. La pregunta de por qué y cómo coexisten P. argentinus y M. borellii se respondió a través de diversos aspectos demostrando la multidimensionalidad del nicho realizado de estas especies. Es de interés la acotación de que, para responder a algunos interrogantes, primero se debieron solucionar algunas cuestiones metodológicas o de análisis para alcanzar posteriormente un alto grado de exactitud y confianza en los resultados obtenidos. Se estudiaron en tres ambientes lénticos diferentes y distantes entre sí con conexión a ríos de distintas categorías del sistema del valle aluvial del río Paraná medio. Estos ambientes fueron caracterizados a lo largo del estudio para determinar su variabilidad a lo largo del año y cómo influencian los factores abióticos y bióticos sobre ambas especies y sus interrelaciones.Facultad de Ciencias Naturales y Muse

Ontogenetic predation capacity of Macrobrachium borellii (Caridea: Palaemonidae) on prey from littoral-benthic communities

Macrobrachium borellii is an abundant prawn of the Paraná River floodplain. Newly hatched juveniles have the general characteristics of adults, and they are proposed to have the same feeding habits. Its natural diet is composed mainly of animals' items rather than vegetals, of which dipteran larvae and oligochaetes are positively selected. However, the oscillations of the hydric cycle imply an adequacy of its selection according to prey availability in all seasons and moments of the ontogenetic development. This work verifies the predation behavior and the ontogenetic predation capacity of M. borellii feeding on three preys (cladoceran, dipteran larvae and oligochaetes) of different bioforms and mobility that represent its natural diet. The prawns were placed individually in containers where was offered one prey type in increasing amounts every 48 hours until any prawn ate the total amount offered. The predation behavior was recorded, and the amount consumed was verified after 24 hours. Both sizes of M. borellii were capable of preying on all food items used in this study. The search and catch was always made with the second queliped, suggesting a non-visual prey perception, and the handling was different for each prey. Cladoceran was the most consumed, followed by dipteran larvae and oligochaetes. The results show that, in both sizes, M. borellii has a trophic plasticity due to its capacity to prey on a variety of bioforms with differing mobility. This capacity could favor the ability of prawns to select the most profitable prey according to the changes in abiotic and ecological factors

Ontogenetic predation capacity of Macrobrachium borellii (Caridea: Palaemonidae) on prey from littoral-benthic communities

Macrobrachium borellii is an abundant prawn of the Paraná River floodplain. Newly hatched juveniles have the general characteristics of adults, and they are proposed to have the same feeding habits. Its natural diet is composed mainly of animals' items rather than vegetals, of which dipteran larvae and oligochaetes are positively selected. However, the oscillations of the hydric cycle imply an adequacy of its selection according to prey availability in all seasons and moments of the ontogenetic development. This work verifies the predation behavior and the ontogenetic predation capacity of M. borellii feeding on three preys (cladoceran, dipteran larvae and oligochaetes) of different bioforms and mobility that represent its natural diet. The prawns were placed individually in containers where was offered one prey type in increasing amounts every 48 hours until any prawn ate the total amount offered. The predation behavior was recorded, and the amount consumed was verified after 24 hours. Both sizes of M. borellii were capable of preying on all food items used in this study. The search and catch was always made with the second queliped, suggesting a non-visual prey perception, and the handling was different for each prey. Cladoceran was the most consumed, followed by dipteran larvae and oligochaetes. The results show that, in both sizes, M. borellii has a trophic plasticity due to its capacity to prey on a variety of bioforms with differing mobility. This capacity could favor the ability of prawns to select the most profitable prey according to the changes in abiotic and ecological factors

Trophic ecology of the freshwater prawn, Pseudopalaemon bouvieri (Decapoda: Palaemonidae) in Northeastern Argentina, with remarks on population structure.

Freshwater decapod crustaceans are important components of food webs in these environments, but little is known about the diet of species that live in tropical waters. We studied the feeding ecology of the prawn Pseudopalaemon bouvieri and its population structure in two different areas with six lagoons, with a different composition and abundance of aquatic macrophytes. At each site of macrophytes banks, 18 prawns sample was collected with a hand net (1mm mesh size) from 1m². In the laboratory, prawns cephalothorax length was measured, sex determined, and a total of 208 stomachs were examined for food items. Our results showed that the population abundance varied between 10 ind/m2 and 1 411 ind/m2. The cephalothorax length ranged between 6mm and 21mm, and the male:female ratio varied between 0.3 and 1.0, with a higher proportion of ovigerous females (21%) in area one than area two. P. bouvieri is omnivorous, and its diet was principally based on algae, plant remains, Protozoa, Rotifera, Oligochaeta, Crustacea, Insecta, detritus and other items. The analysis of the stomach content did not reveal any significant difference in the diet between juveniles and adults, and males and females of both areas consumed a similar diet (Kruskal-Wallis test p=0.8273). We concluded that the dietary items consumed by prawns and the niche breadth were similar between the two areas, although the proportion of items consumed varied between lagoons of both areas. The density of P. bouvieri was different between areas, but the size of cephalothorax (CL) was similarLos crustáceos decápodos de agua dulce son un componente importante de la cadena trófica, pero poco se sabe sobre la dieta de las especies que viven en aguas tropicales. Nosotros estudiamos la ecología alimentaria del camarón Pseudopalaemon bouvieri y la estructura de su población en dos áreas diferentes con seis lagunas, con una diferente composición y abundancia de macrófitas acuáticas. En cada sitio poblado con macrófitas, se tomaron 18 muestras con una red manual (1mm de tamaño de malla) de 1m². En laboratorio, se midió la longitud de cefalotórax de los camarones y se determinó el sexo. Asimismo, fueron examinados un total de 208 estómagos para determinar su alimentación. Nuestros resultados mostraron que la abundancia de la población varió entre 10 ind/m2 y 1 411 ind/ m2. La longitud de cefalotórax osciló entre 6 y 21mm, y la razón macho:hembra varió entre 0.3 y 1.0, con una mayor proporción de hembras ovígeras (21%) en el área 1 que en el área 2. P. bouvieri es omnívoro y su alimentación se basa principalmente en algas, restos de plantas, protozoos, rotíferos, Oligochaeta, crustáceos, Insecta, detrito y otros ítems. El análisis del contenido estomacal no reveló ninguna diferencia significativa en la dieta entre juveniles y adultos, y los machos y hembras de ambas áreas consumieron una dieta similar (Kruskal-Wallis, p=0.8273). Nosotros concluimos que los ítems alimentarios consumidos por los camarones y la amplitud de nicho fueron similares entre las dos áreas, aunque la proporción de ítems consumidos varió entre lagunas de ambas áreas. La densidad de P. bouvieri fue diferente entre áreas, pero el tamaño del cefalotórax (CL) fue similar

Trophic ecology of the freshwater prawn, Pseudopalaemon bouvieri (Decapoda: Palaemonidae) in Northeastern Argentina: with remarks on population structure

Freshwater decapod crustaceans are important components of food webs in these environments, but little is known about the diet of species that live in tropical waters. We studied the feeding ecology of the prawn Pseudopalaemon bouvieri and its population structure in two different areas with six lagoons, with a different composition and abundance of aquatic macrophytes. At each site of macrophytes banks, 18 prawns sample was collected with a hand net (1mm mesh size) from 1m². In the laboratory, prawns cephalothorax length was measured, sex determined, and a total of 208 stomachs were examined for food items. Our results showed that the population abundance varied between 10 ind/m² and 1 411 ind/m². The cephalothorax length ranged between 6mm and 21mm, and the male:female ratio varied between 0.3 and 1.0, with a higher proportion of ovigerous females (21%) in area one than area two. P. bouvieri is omnivorous, and its diet was principally based on algae, plant remains, Protozoa, Rotifera, Oligochaeta, Crustacea, Insecta, detritus and other items. The analysis of the stomach content did not reveal any significant difference in the diet between juveniles and adults, and males and females of both areas consumed a similar diet (Kruskal-Wallis test p=0.8273). We concluded that the dietary items consumed by prawns and the niche breadth were similar between the two areas, although the proportion of items consumed varied between lagoons of both areas. The density of P. bouvieri was different between areas, but the size of cephalothorax (CL) was similar