Ontogenic changes in the feeding habits of the fishes Agonostomus monticola (Mugilidae) and Brycon behreae (Characidae), Térraba River, Costa Rica

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Abstract

Las dietas de los peces varían con respecto a la calidad, la cantidad y el tamaño del alimento. Esta variación puede deberse a factores como la estacionalidad y la fase del desarrollo del individuo. Estudiamos los cambios ontogénicos en los hábitos alimentarios de dos peces dulceacuícolas, Agonostomus monticola y Brycon behreae, de la Cuenca del Río Térraba, Pacífico sur de Costa Rica. Ambas poblaciones son omnívoras, pero con cambios ontogénicos en la cantidad y calidad de los ítemes consumidos. Conforme crecía, A. monticola modificó su dieta de insectívora hacia un mayor consumo de materia vegetal, asociado con un aumento en la longitud relativa del intestino. Aunque mantuvo su dependencia de alimentos vegetales, B. behreae diversificó su dieta de dos formas. Primero, pasó de partes suaves de plantas a semillas, hojas y frutos. Luego, los ítemes cambiaron de insectos hacia una dieta más carnívora (peces y camarones). Estos hallazgos para ambas especies enfatizan la importancia de proteger la vegetación riparia de estos ecosistemas tropicales.

Translated abstract

Fish diets can vary in food quality, quantity and size. The variation can be caused by several factors, including season and the ontogenic phase of the individual (McCormick 1998). We studied the ontogenic changes in feeding habits of two freshwater fishes, Agonostomus monticola and Brycon behreae, from the Térraba River basin, South Pacific of Costa Rica. Both populations were omnivorous, but displayed ontogenic shifts in terms of quantity and quality of the food items consumed. As it grew, A. monticola modified its diet from insectivorous towards a higher consumption of vegetables, which was accompanied by an increase in relative length of the intestine. While remaining dependent on vegetation as staple food, B. behreae diversified its diet in two ways. Initially, from soft plant parts to seeds, leaves, and fruits. Secondly, prey items changed from insects into a more carnivore diet (fish and shrimp). These findings for both species stress the importance of protecting riparian vegetation in these tropical ecosystems. Rev. Biol. Trop. 57 (Suppl. 1): 285-290. Epub 2009 November 30.

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On the Measurement of Niche Breadth and Overlap

Robert K. Colwell, Douglas Futuyma (1971)

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The developmental basis for allometry in insects.

Claudio D. Stern, Douglas Emlen (1999)

Within all species of animals, the size of each organ bears a specific relationship to overall body size. These patterns of organ size relative to total body size are called static allometry and have enchanted biologists for centuries, yet the mechanisms generating these patterns have attracted little experimental study. We review recent and older work on holometabolous insect development that sheds light on these mechanisms. In insects, static allometry can be divided into at least two processes: (1) the autonomous specification of organ identity, perhaps including the approximate size of the organ, and (2) the determination of the final size of organs based on total body size. We present three models to explain the second process: (1) all organs autonomously absorb nutrients and grow at organ-specific rates, (2) a centralized system measures a close correlate of total body size and distributes this information to all organs, and (3) autonomous organ growth is combined with feedback between growing organs to modulate final sizes. We provide evidence supporting models 2 and 3 and also suggest that hormones are the messengers of size information. Advances in our understanding of the mechanisms of allometry will come through the integrated study of whole tissues using techniques from development, genetics, endocrinology and population biology.