Abstract
Invasive alien predators pose a threat to native fauna and the studies of their feeding habits are crucial to understanding their impact on prey populations. Diet of the American mink Neovison vison, an invasive species in Europe, is relatively well studied based on scat analysis, however, the use of other methods of diet analysis enables a better overview of this issue. We analyzed the isotopic composition of carbon and nitrogen in the livers, which reflects the diet from about 30–40 days (scat analysis provides information on the diet over 1–2 days only) of the American mink from four national parks in Poland and in the muscles of three types of mink prey (root voles, common frogs, and roach) in order to estimate their contribution to the mink diet. Mink in Biebrza and Narew National Parks fed mainly on frogs and fish, in Drawa National Park on voles and fish, and in Warta Mouth National Park almost exclusively on fish—as shown by Bayesian mixing models calculated for three selected groups of prey. There was no isotopic evidence for differences between the diets of male and female mink. In all groups of prey, we found surprisingly high differences between individuals of the same species from different study sites in the isotopic composition of both δ13C (up to 3‰) and δ15N (up to 6‰). Based on a detailed literature review, we predict that the main reasons for these variations are differences in abiotic environment, food availability, and trophic position. We also indicate a lack of data on trophic discrimination in fish and amphibians, which makes it hard to assess the influence of differences in trophic position on isotopic variations. We suggest caution to authors who plan to study geographical variations in diet of animals using stable isotope analysis without acknowledging that taxonomically and ecologically similar prey can differ in isotopic composition between studied areas.
Highlights
Information about the diets of predators is essential for evaluating their impact on prey populations, for analyzing the influence of prey abundance on predator dynamics, or for understanding inter- and intra-specific competitive interactions betweenCommunicated by: Karol Zub Electronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.Mamm Res (2019) 64:343–351Another method for studying predator diet composition is the analysis of stable isotopes in predator tissue, followed by comparison to the isotope composition in prey (Newsome et al 2009; Adams et al 2010; Ben-David and Flaherty 2012)
All the samples used for isotopic analysis of wild animals were collected in four national parks and their surroundings: Warta Mouth NP (WMNP) (52° 36′ N 14° 46′ E), Drawa NP (DNP) (53° 07′ N 15° 59′ E), Biebrza NP (BNP) (53° 28′ N 22° 38′ E), and Narew NP (NNP) (53° 04′ N 22° 50′ E)
Both δ13C and δ15N values were very similar in BNP and NNP, and in DNP and WMNP, with significant differences in δ15N between these two pairs
Summary
This technique can provide results difficult to obtain with other methods, despite its limitations, which are mainly a result of the large number of factors that influence isotopic fractionation (change in isotopic composition between diet and tissue of the consumer) at different trophic levels (Laiolo et al 2015), the uncertainty in tissue turnover rates (time at which nutrients derived from diet are incorporated in a tissue and their isotopic composition reach equilibrium) (Vander Zanden et al 2015) and the uncertainty included in statistical modeling of isotope data (Caut et al 2008) This is the case for population and individual level studies at different geographic scales (Urton and Hobson 2005; Adams et al 2010; Resano-Mayor et al 2014). The stable isotope method is widely used in diet analysis (Boecklen et al 2011), where the isotopic composition of an animal tissue reflects the isotopic composition of its food with an enrichment factor (DeNiro and Epstein 1978)
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