Abstract
In the last century, Italian freshwater ecosystems have been invaded by several non-native fish species. In the subalpine Lake Mergozzo (northern Italy), several recently introduced non-native species dramatically expanded their populations. We used carbon and nitrogen stable isotopes to describe the isotopic niches and trophic positions of native and non-native fish species in Lake Mergozzo. We evaluated their trophic niches, trophic diversity, trophic redundancy and trophic evenness utilizing isotopic niche metrics, and estimated asymmetrical niche overlaps. The trophic traits of non-native fish species and Perca fluviatilis clearly define them as trophic generalists, in terms of among-individual variability of their isotopic niches. The historical increase in abundance of fish non-native species in this lake, their dominance by numbers and biomass within the assemblage, and their broad asymmetrical niche overlaps suggest that their higher degree of trophic generalism might have been one of the key factors that have promoted the invasion of the recipient community.
Highlights
In both terrestrial and aquatic ecosystems, the structural change determined by introduced alien species that become established in a recipient community can have severe ecological and economic impacts [1,2,3]
Such traits can facilitate the integration of NNS into the food web, increasing both their invasive potential [16], and their resistance to fluctuations in resource availability [22]
No commercial fisheries are active in the lake [56], which is included in the protected area ‘Lago di Mergozzo and Montorfano’, within the Natura 2000 European network for biodiversity protection, according to the “Habitat Directive” [58]
Summary
In both terrestrial and aquatic ecosystems, the structural change determined by introduced alien species that become established in a recipient community can have severe ecological and economic impacts [1,2,3]. Successful NNS invaders frequently have relatively wide trophic niches, or have trophic niches dissimilar than other species in the receiving community (‘vacant niche hypothesis’ [17]; but see [18]), being able to use trophic resources unexploited by the NS community [19,20,21]. Such traits can facilitate the integration of NNS into the food web, increasing both their invasive potential [16], and their resistance to fluctuations in resource availability [22]. NNSs’ trophic niches may overlap with those of NS and compete for the same limiting resources [23,24,25], with a range of possible outcome scenarios, depending on the synergistic effect of factors such as spatiotemporal variability, presence of predators, number of resources, and environmental conditions [13]
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