title: Trophic Strategies of a Non-Native and a Native Amphibian Species in Shared Ponds.
abstract: One of the critical factors for understanding the establishment, success and potential impact on native species of an introduced species is a thorough knowledge of how these species manage trophic resources. Two main trophic strategies for resource acquisition have been described: competition and opportunism. In the present study our objective was to identify the main trophic strategies of the non-native amphibian Discoglossus pictus and its potential trophic impact on the native amphibian Bufo calamita. We determine whether D. pictus exploits similar trophic resources to those exploited by the native B. calamita (competition hypothesis) or alternative resources (opportunistic hypothesis). To this end, we analyzed the stable isotope values of nitrogen and carbon in larvae of both species, in natural ponds and in controlled laboratory conditions. The similarity of the δ15N and δ13C values in the two species coupled with isotopic signal variation according to pond conditions and niche partitioning when they co-occurred indicated dietary competition. Additionally, the non-native species was located at higher levels of trophic niches than the native species and B. calamita suffered an increase in its standard ellipse area when it shared ponds with D. pictus. These results suggest niche displacement of B. calamita to non-preferred resources and greater competitive capacity of D. pictus in field conditions. Moreover, D. pictus showed a broader niche than the native species in all conditions, indicating increased capacity to exploit the diversity of resources; this may indirectly favor its invasiveness. Despite the limitations of this study (derived from potential variability in pond isotopic signals), the results support previous experimental studies. All the studies indicate that D. pictus competes with B. calamita for trophic resources with potential negative effects on the fitness of the latter.
authors.affiliation: Departament de Biologia Animal (Vertebrats), Facultat de Biologia, Universitat de Barcelona, Avinguda Diagonal, 643, 08028, Barcelona, Spain; CICGE-Centro de Investigação em Ciências Geo-Espaciais, Observatório Astronómico Prof. Manuel de Barros, Alameda do Monte da Virgem, 4430-146, Vila Nova de Gaia, Portugal; Departamento de Herpetología, Aranzadi Zientzia Elkartea-Sociedad de Ciencias Aranzadi, Zorroagagaina, 11, 20014, Donostia-San Sebastián, Spain.
authors.forename: Olatz
authors.initials: O
authors.lastname: San Sebastián
authors.affiliation: Department of Conservation Biology, Estación Biológica de Doñana (EBD-CSIC), Avda. Américo Vespucio s/n, Sevilla, 41092, Spain.
authors.forename: Joan
authors.initials: J
authors.lastname: Navarro
authors.affiliation: Departament de Biologia Animal (Vertebrats), Facultat de Biologia, Universitat de Barcelona, Avinguda Diagonal, 643, 08028, Barcelona, Spain.
authors.forename: Gustavo A
authors.initials: GA
authors.lastname: Llorente
authors.affiliation: Department of Ecology and Genetics, Uppsala Universitet, Norbyvägen 18 D, 752 36, Uppsala, Sweden.
authors.forename: Álex
authors.initials: Á
authors.lastname: Richter-Boix
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D001001:Anura / Q000254:growth & development / Q000502:physiology*; D002025:Bufonidae / Q000254:growth & development / Q000502:physiology; D002247:Carbon Isotopes / Q000032:analysis; D003163:Competitive Behavior; D004032:Diet; D017753:Ecosystem; D005247:Feeding Behavior; D058865:Introduced Species; D007814:Larva; D008954:Models, Biological; D009587:Nitrogen Isotopes / Q000032:analysis; D009752:Nutritional Status; D061005:Ponds; D013030:Spain; D013045:Species Specificity
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes