Do age-related changes in feeding habits of brown trout alter structural properties of food webs?

Abstract

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.