The role of alien fish (the centrarchid Micropterus salmoides) in lake food webs highlighted by stable isotope analysis

Abstract

Non‐native freshwater fish species can have adverse ecological impacts on native populations. However, the mechanisms determining the success or otherwise of their invasion and their role in invaded communities remain largely unknown. This is particularly true for the Mediterranean region, where endemic species characterised by restricted natural ranges may be at high risk of extinction. The largemouth bass (Micropterus salmoides) is native to North America but is invasive in the Italian Peninsula. The aim of this study was to explore the trophic position of M. salmoides, its diet and niche overlap with native fish species in the littoral areas of a Mediterranean lake. Our study was supported by analysis of stable C and N isotopes in the tissues of fish and their potential food sources, twenty years after the introduction of the largemouth bass to Lake Bracciano (Italy). Samples were collected in locations varying in terms of physical structure and resource availability at lower trophic levels in the food web, which was greater in the southern (hereafter: South) than in the northern (hereafter: North) area of the lake. These differences made it possible to explore the mechanisms linking environmental conditions and the role of alien predators in the invaded food web. The abundance of M. salmoides was higher, and the diversity of native fish species was lower, in North than South. In North, M. salmoides had a piscivorous diet and occupied a higher trophic position in the food web than in South, where invertebrates constituted an important part of its diet. As a consequence, trophic niche interference with other fish species at intermediate trophic levels was higher in South. In contrast, in North, M. salmoides showed stronger trophic interference with the percid Perca fluviatilis, a native top predator in the food web, but weaker interference with remaining fish species. Our results help to understand the role of alien species in the food webs of Lake Bracciano, which primarily depends on the habitat and the availability of prey across trophic levels. Physical and ecological variations in the habitat were associated with differences in predatory interactions among native and alien fish species. This suggests that a reduction in productivity and biodiversity at lower trophic levels in lake food webs may favour the success of opportunistic invasive fish species, given the ability of the invaders to maintain some of their characteristics silent, and to fully express their genotype under favourable environmental conditions.

Antarctic food web architecture under varying dynamics of sea ice cover

“…Consideration of the mean and variance of the single ITUs’ isotopic signatures, defined by a common restricted δ-space, together with the multiple steps adopted for the selection of resources to be used in isotopic mixing models, allowed us to overcome the limits of Bayesian mixing when applied to complex communities 38,40 . Following our approach, it was thus possible to describe in unprecedented detail the food web structure of these biodiverse communities as well as the diet of single species, such as the omnivorous key species S .…”

Changing Isotopic Food Webs of Two Economically Important Fish in Mediterranean Coastal Lakes with Different Trophic Status

“…3.5.3, SIMMr package) [52] considering a Trophic Enrichment factor (TEF) of 3.4 ± 1.0% for δ 15 N and 1.0 ± 0.5% for δ 13 C [18,37,49,[53][54][55][56] and uninformative priors. These TEF values (expressed as mean ± standard deviation) are considered a robust and widely applicable assumption in the presence of multiple trophic pathways and different types of food sources [37,56]. For all SIMMr models, we ran three Markov Chain Monte Carlo chains of 300,000 iterations each with a burn-in of 200,000 and a thinning rate of 100 iterations.…”

“…The set of potential ITU food sources was considered on the entire δ 13 C axis and within a given range on the δ 15 N axis, i.e., within ±3.4% (the TEF) of the value of the consumer [31]. The Bray-Curtis similarity index (BC), based on the contribution of each resource to the diet of the two fish, was also calculated in order to quantify the diet similarity among lakes [36,56]. BC is expressed as proportional similarity ranging from 0, when no common food sources are found for the compared groups, to 1, when the compared groups have the same food sources in the same proportions [36,56].…”

Using stable isotopes to analyse extinction risks and reintroduction opportunities of native species in invaded ecosystems

“…Nevertheless, a moderate predation by M. salmoides on eels was found to be likely, in concordance with the feeding behaviour of M. salmoides 73 . Additionally, it is likely that M. salmoides might function as a competitor for eels 74 , as indicated by its wide feeding behaviour and wide trophic niche 75 . Accordingly, other possibilities that have led to the extinction of A. anguilla must be considered, as such, overfishing 69 and the closure of the reproductive migration through dams 76 , 77 .…”