Abstract
We explore the trophic role that a diverse sympatric group of fishes in the genus Chirostoma play in a large, shallow lake in central Mexico, Lake Chapala. We use δ13C and δ15N stable isotope - based food web analyses to explore how they relate to other components of the Lake Chapala ecosystem. We find five Chirostoma species in top trophic levels of the Chapala food web compared to other fishes, relying on a combination of zooplankton, fish and benthic resources as energy sources. Food web metric analyses showed generally overlapping trophic niches for members of Chirostoma, especially in terms of δ13C. However, C. jordani had lower mean δ15N isotopic values than C. promelas. As a group, "pescados blancos" (C. sphyraena and C. promelas) also had higher δ15N signatures than "charales" (C. consocium, C. jordani and C. labarcae) reflecting greater piscivory, but these differences were not strong for all food web metrics used. Trophic overlap among species of Chirostoma in Lake Chapala raises questions about the forces that might have led to a morphologically diverse but functionally similar and monophyletic group of species.
Highlights
Food web studies provide valuable insight into how energy flows across an ecosystem and about the structure of predator-prey relationships (Paine, 1980; Polis & Winemiller, 1996)
We found no significant differences among all Chirostoma spp. or for individual Chirostoma species δ15N and δ13C values between samples taken from sites close to or far from the shoreline of Lake Chapala
Coefficients of variation of δ13C were similar for C. consocium, C. jordani and C. labarcae (2.42, 2.23, and 2.04, respectively)
Summary
Food web studies provide valuable insight into how energy flows across an ecosystem and about the structure of predator-prey relationships (Paine, 1980; Polis & Winemiller, 1996) They can provide key guidelines for ecosystem management, as they inform how species interact with other ecosystem components, and allow a synthesis of multiple ecological processes (Vander Zanden et al, 2003; Fry, 2006). Mexican lakes have been subject to numerous anthropogenic effects (e.g., pollution, habitat modifications, species introductions, overexploitation, among others) (Lyons et al, 2000; Hansen et al, 2006; López-Hernández et al, 2007; Trasande et al, 2010). Their fish fauna contains a relatively high number of imperiled species, and species that are of significant commercial and cultural importance (Lyons et al, 1998; MoncayoEstrada et al, 2012)
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