Do age-related changes in feeding habits of brown trout alter structural properties of food webs?
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The aim of this study was to quantify changes in food webs based on ontogenetic dietary shifts of a top fish predator (here brown trout Salmo trutta L.). Here, the food web of a river in Central Spain (River Tormes) was studied to test the hypothesis that food web structural properties may change according to age-related changes in feeding habits of brown trout. Thus, the food web was established separately for age-0, age-1 and age-2 brown trout using a forward procedure (individual, modular and river networks); next the complete trophic networks were established. Overall, the networks were characterized by generalist predators with numerous prey types; specialized feeding was limited to a low number of taxa. Food web structural properties (number of links, connectance and linkage density) had the highest values in the age-1 scenario. The highest trophic level (i.e. the highest number of energy steps) was also found in the age-1 scenario, but the lowest in the age-0 scenario. Vulnerability and generalization tend to be higher in age-1 and age-0 scenarios, respectively. The present study exemplifies that age-specific brown trout predation on invertebrate predators emerged as the key factor to understand the changes in food web structural properties among age scenarios. I conclude that ontogenetic dietary shifts of brown trout promote changes in food web structural properties. This conclusion underscores the importance of considering different life history stages of species (i.e. to cover their ontogenetic dietary shifts) in food web construction.
KeywordsAge-related traits Apex predator Food web Ontogeny Structural network properties
I am very grateful to Ricardo Sánchez Grande and Fernando Sánchez Grande for their field assistance. The author thank the facilities given by the Station of Hydrobiology of the USC “Encoro do Con”, with special mention to Dr. Fernando Cobo who lent all the necessary equipment to carry out the field work. I also appreciate constructive comments from two anonymous referees, which considerably improved the quality of the manuscript. The Servicio Territorial de Medio Ambiente de Ávila (Junta de Castilla y León) granted permission for sampling. Flow data was gathered by the Duero Basin Water Authority. J. Sánchez-Hernández was supported by a postdoctoral grant from the Galician Plan for Research, Innovation, and Growth 2011–2015 (PlanI2C, Xunta de Galicia).
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