Stable isotopes reveal mild trophic modifications in a native–invasive competitive relationship
Temporal or evolutionary changes in the effects of invasive competitors on native species have not been studied in great depth. In this study, we explored possible modifications in the trophic shifts of native and invasive tadpoles in a set of ephemeral ponds with different amounts of time elapsed since the invasion, i.e., with different degrees of naiveté of the native species to its invasive competitor. Using stable isotopes analysis, we found that the native (Epidalea calamita) and invasive (Discoglossus pictus) species always segregated in their trophic position within ponds. Furthermore, the isotopic signature of the tadpoles was affected by the composition and diversity of the surrounding vegetal and animal communities. The amount of time elapsed since the invasion did not influence the magnitude of the trophic differences between the species, but it did affect the nature of this segregation. Segregation at the trophic level occurred most frequently during the first stages of invasion, with the invasive species occupying higher trophic levels. However, segregation was progressively attained through the consumption of different items within the same trophic level when the amount of time since invasion increased. Thus, our results point that the native species no longer uses a lower trophic level after several generations of coexistence. In contrast, changes in the trophic niche width of either species during the invasion process were largely undetected.
KeywordsAmphibians Discoglossus pictus Epidalea calamita Rapid evolution Syntopy Tadpoles
We would like to thank Felipe Campos, Berta Capellà and Àlex Garcia-Cisneros for help in the fieldwork, and two anonymous reviewers for useful comments on the manuscript. Permissions to capture were granted by the Departament d’Agricultura, Ramaderia, Pesca, Alimentació i Medi Natural de la Generalitat de Catalunya. EPB did part of the fieldwork necessary for the study during the financial support of a FPU grant (AP2010-5563, Ministerio de Educación, Cultura y Deporte, Spain). The study strictly adhered to the Guidelines for the Care and Use of Laboratory Animals of the University of Barcelona and was approved by the institution. Procedures followed the regulations that cover animal housing and experimentation in Catalonia (Spain) contained in the Generalitat de Catalunya’s Decret 214/1997 of 30th July and Llei 5/1995 of 21st June, which apply the European Directive 86/609/CEE to Spanish law in Catalonia.
- Benjamini Y, Hochberg Y (1995) Controlling the false discovery rate: a practical and powerful approach to multiple testing. J R Stat Soc B 57:289–300Google Scholar
- Burnham KP, Anderson DR (2003) Model selection and multimodel inference: a practical information-theoretic approach. Springer, New YorkGoogle Scholar
- Calcagno V (2013) Glmulti: model selection and multimodel inference made easy. R package version 1.0.7. https://CRAN.R-project.org/package=glmulti. Accessed Jan 2017
- Campeny R (2001) Ecologia de les larves d’amfibis anurs al Montseny. PhD thesis, University of BarcelonaGoogle Scholar
- Codron D, Hull J, Brink JS, Codron J, Ward D, Clauss M (2011) Effect of competition on niche dynamics of syntopic grazing ungulates: contrasting the predictions of habitat selection models using stable isotope analysis. Evol Ecol Res 13(3):217–235Google Scholar
- Cox GW (2004) Alien species and evolution. Island Press, WashingtonGoogle Scholar
- Geniez P, Cheylan M (2012) Les amphibiens et les reptiles du Languedoc-Roussillon et régions limitrophes: atlas biogéographique. Biotope, Mèze; Muséum national d'Histoire naturelle, ParisGoogle Scholar
- Gosner KL (1960) A simplified table for staging anuran embryos and larvae with notes on identification. Herpetologica 16(3):183–190Google Scholar
- Llorente GA, Montori A, Pujol-Buxó E (2015) El sapillo pintojo mediterráneo (Discoglossus pictus) en la península ibérica. Bol Asoc Herpetol Esp 26(2):12–17Google Scholar
- Martins F, Oom MDM, Rebelo R, Rosa GM (2013) Differential effects of dietary protein on early life-history and morphological traits in natterjack toad (Epidalea calamita) tadpoles reared in captivity. Zoobiology 32(4):457–462Google Scholar
- R Core Team (2015) R: a language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. https://www.R-project.org/
- Wintrebert P (1908) Présence à Banyuls-sur-Mer (Pyrénées-Orientales) du Discoglossus pictus Otth. Bull Soc Zool Fr 33:54Google Scholar