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Biol Invasions (2010) 12:30613069 DOI 10.1007/s10530-010-9697-8
ORIGINAL PAPER
Food web overlap among native axolotl (Ambystoma mexicanum) and two exotic shes: carp (Cyprinus carpio) and tilapia (Oreochromis niloticus) in Xochimilco, Mexico City
Luis Zambrano Elsa Valiente
M. Jake Vander Zanden
Received: 25 May 2009 / Accepted: 11 January 2010 / Published online: 7 February 2010 Springer Science+Business Media B.V. 2010
Abstract Two exotic shes, common carp (Cyprinus carpio) and tilapia (Oreochromis niloticus), were introduced more than 20 years ago into Xochimilco for aquaculture, and now dominate the system in terms of biomass and numbers. Over this same period, wild populations of the microendemic axolotl salamander (Ambystoma mexicanum) have been dramatically reduced, and it currently persists in isolated areas of this aquatic system, which is situated at the edge of Mexico City. In this study, we examine potential trophic interactions and niche overlap among two exotic shes: carp and tilapia, and the native axolotl. Axolotl had more diverse diets and a higher trophic position compared to the exotics. Stable isotope analysis revealed substantial trophic niche overlap among axolotl and the exotics. The two exotics occupied a larger niche area than the axolotl, suggesting higher levels of omnivory and diet specialization. Current exotic sh removal efforts
will further our understanding of interactions between the axolotl and exotic species, and are expected to benet axolotl recovery efforts.
Keywords Isotopes Gut contents
Urban lake Salamander Food web niche
Introduction
Food web studies are useful for understanding changes in freshwater ecosystems caused by exotic species. Networks of predatorprey interactions play a central role in inuencing population dynamics and community structure in diverse ecosystems (Paine 1966; Lynch 1979; Pringle and Hamazaki 1998; Hargrave et al. 2006; Vander Zanden et al. 2006a). Once established, exotic species can have major impacts on aquatic biodiversity (Li et al. 1999), as well as the ecosystem services humans derive from aquatic ecosystems. The introduction of exotic species is increasingly common in freshwater systems (Minns and Cooley 1999), though few studies have used a food web approach to help inform and guide efforts to manage and restore invaded aquatic ecosystems (Vander Zanden et al. 2003).
Information obtained from food web studies can be particularly useful in highly perturbed aquatic systems such as Xochimilco, the last remnant of a...