Abstract

Simple SummaryInvasive species are widely recognized to negatively affect native species through both direct and indirect interactions. When diet overlap between the native and invasive species increases, their competitive interaction is expected to increase too. This in turn may lead to displacement of one of the species. However, the specific mechanisms of the diet displacement are still unclear. In this study, we analysed the diet and diet overlap between the critically endangered European mink and the invasive American mink during the invasion process of the latter species by means of stable isotope analyses. We found a significant diet overlap between the native and invasive mink when they co-occur, an important individual variation of diet, and no significant change of diet of the native species in response to the arrival of the invasive mink. These results suggest significant competitive pressure imposed on the native European mink by the invasive American mink. As such, urgent implementation of control measures of invasive species is needed to ensure the viability and conservation of endangered European mink populations.The pressure elicited by invasive species on native species significantly increases with the increase of the overlap of their ecological niches. Still, the specific mechanisms of the trophic displacement of native species during the invasion process are unclear. The effects of the invasive American mink (Neovison vison) on the critically endangered European mink (Mustela lutreola) was assessed by analyses of diet and niche overlap during the invasion process. To do this, the isotopic composition (δ13C and δ15N) of both species of mink and their four main types of prey was analysed. Significant trophic overlap between the native European mink and invasive American mink was found when they coexisted in sympatry. Furthermore, both mink species were characterised by significant individual variation in diet and no obvious change in diet of the native species in response to the arrival of the introduced species was observed. High niche overlap registered between both species in sympatry with no displacement in diet of the native mink in response to the arrival of the invasive mink is expected to have important consequences for the viability and conservation of the native mink populations, as it suggests high competitive pressure.

Highlights

  • The negative effect of many invasive non-native species (INNS) on native species through direct and indirect interactions is widely recognised [1,2,3]

  • The pressure employed by INNS on native species is especially significant when they exercise a competitive or predator–prey interaction

  • We addressed the following research questions: (1) Did the diet composition of the native species change during the invasion, i.e., did their diets differ between allopatric and sympatric populations in terms of the trophic position and proportion of the prey types consumed? (2) What is the level of trophic niche overlap between the native and invasive species when they coexist in sympatry?

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Summary

Introduction

The negative effect of many invasive non-native species (INNS) on native species through direct and indirect interactions is widely recognised [1,2,3]. When high levels of trophic niche overlap are observed (frequently as a result of limitation of food resources available to the native species by the INNS), competitive exclusion of one of the species may occur [6]. This may cause the native species to feed on suboptimal prey [1], eventually affecting fitness of its individuals and its populations and their survival [7,8]

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