Estimating the feeding range of a mobile consumer in a river–flood plain system using δ13C gradients and parasites
2011
Bertrand, Micheline | Cabana, Gilbert | Marcogliese, David J. | Magnan, Pierre
1. The feeding range of an individual is central to food web dynamics as it determines the spatial scale of predator–prey interactions. However, despite recognition of its importance as a driving force in population dynamics, establishing feeding range is seldom done as detailed information on trophic interactions is difficult to obtain. 2. Biological markers are useful to answer this challenge as long as spatial heterogeneity in signal is present within the area investigated. A spatially complex ecosystem, Lake St. Pierre (LSP), a fluvial lake of the St Lawrence River (Québec, Canada), offered a unique opportunity to determine the feeding range of a secondary consumer, yellow perch (Perca flavescens) using isotopic ratios of carbon (δ13C). However, because food chains based on phytoplankton have generally more negative δ13C than those depending on periphyton, it was essential to determine the contribution of zooplankton in fish diet to correctly interpret spatial patterns of δ13C. We used parasites in perch to examine whether their δ13C was reflecting local δ13C baseline conditions rather than a feeding specialization on zooplankton. 3. δ13C of primary consumers was highly variable and exhibited a striking gradient along the shore–channel axis, suggesting that δ13C should reflect an individual consumer’s spatial position in LSP. 4. This strong isotopic gradient allowed us to estimate the spatial scale of the resources used by individual perch following an approach presented by Rasmussen, Trudeau & Morinville (Journal of Animal Ecology, 78, 2009, 674). By comparing the δ13C variability in perch to that of primary consumers, we estimated that the adults feeding range was around 2 km along the shore–channel axis. 5. The combined use of isotopic ratios and parasites allowed us to determine that the adult population uses a wide range of habitats between the flood plain and the main channel. However, individually, each perch depended on a limited foodshed.
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