High mountain lakes are extremely valuable ecosystems currently facing several anthropogenic threats, both at the global and local scale. Fish introduction shows a negative impact on these naturally fishless ecosystems, with huge effects on aquatic communities, but also affecting both semi-aquatic and terrestrial species which rely on aquatic food subsidies. Although the effects on some of these components are already well-studied, much less is known about the effects on semi-aquatic vertebrate Neomys fodiens Pennant (1771). This study aims to test the hypothesis that alien fish introduced in mountain lakes could have a negative impact on Neomys fodiens, because both predators rely on the same shared food resource, that is aquatic macroinvertebrates. Baited tubes were employed to monitor the presence/absence of Neomys fodiens in lakes with introduced fish and in pristine lakes without fish in the Gran Paradiso National Park and Mont Avic Natural Park (Western Italian Alps). The presence of Neomys fodiens is verified when it leaves its faecal pellets in the tubes. The collected faecal samples underwent a macroscopic and microscopic analysis, and a subsample underwent confirmatory genetic analysis, which provided 12 informative sequences supporting the correct identification of the species as Neomys fodiens. Generalized Linear Mixed Models (GLMM) with a Bayesian Markov Chain Monte Carlo (MCMC) approach were used to test the hypothesis, given the presence data of Neomys fodiens in relation to other variables, such as fish presence, sampling season and other environmental variables. Results show that: i) fish negatively affect the probability of detecting Neomys fodiens, confirming the study hypothesis, ii) that the largest impact is observed in lakes with only Salmonids, and iii) that both Salmonids and Cyprinids have the largest negative effects when they do not live together. Altogether, results suggest that the impact is mediated by a complex combination of competition and predation between fish and water shrews. Moreover, the probability of detecting Neomys fodiens increases along the sampling season, suggesting that Neomys may use lakes placed at very high altitudes opportunistically (during its summer nomadic movements) or incidentally (when young individuals disperse across the hydrographic system).
I laghi di alta quota sono ecosistemi di notevole valore, che attualmente sono sottoposti a diverse minacce antropogeniche, sia a scala globale che locale. L’introduzione di pesci porta ad impatti negativi su questi ecosistemi naturalmente privi di pesci, comportando enormi effetti sulle comunità acquatiche, ma anche condizionando le specie semi-acquatiche e terrestri che dipendono dalle risorse acquatiche per il sostentamento. Nonostante gli effetti su alcune di queste componenti siano già ben conosciuti, ancora poco è noto a proposito degli effetti di queste introduzioni sul vertebrato semi-acquatico Neomys fodiens Pennant (1771). Questo studio si propone di testare l’ipotesi che l’introduzione di pesci alieni nei laghi di alta montagna possa produrre effetti negativi su Neomys fodiens, in quanto entrambi i predatori si cibano della stessa risorsa trofica condivisa, ovverosia invetebrati acquatici. Per monitorare l’assenza/presenza di Neomys fodiens, sono state utilizzate delle trappole con esca (baited tubes) innescate presso laghi con o privi di pesci introdotti presso le aree del Parco Nazionale del Gran Paradiso e del Parco Naturale del Mont Avic (Alpi Italiane Occidentali). La presenza di Neomys fodiens è verificata quando esso lascia escrementi all’interno della trappola. Gli escrementi collezionati sono stati sottoposti ad analisi macroscopica e microscopica, e un sottocampione anche ad analisi genetiche di conferma, fornendo 12 sequenze informative che hanno convalidato la corretta identificazione della specie quale Neomys fodiens. Per testare l’ipotesi sono stati utilizzati dei Modelli Misti Lineari Generalizzati (GLMM) con un approccio Bayesian Markov Chain Monte Carlo (MCMC), dove i dati di presenza di Neomys fodiens sono stati posti in relazione con altre variabili, quali la presenza di pesci, la stagione di campionamento e altre variabili ambientali. I risultati mostrano che: i) i pesci condizionano negativamente la possibilità di rilevare Neomys fodiens, confermando perciò l’ipotesi di studio, ii) il maggiore impatto è osservabile in laghi contenenti solamente Salmonidi, iii) entrambi i Salmonidi e Ciprinidi provocano il più alto impatto negativo quando non convivono. Complessivamente, i risultati suggeriscono che l’impatto si mediato da una complessa combinazione di competizione e predazione tra i pesci e i toporagni acquatici. Inoltre, la probabilità di osservare Neomys fodiens aumenta con l’avanzare della stagione di campionamento, suggerendo che Neomys possa utilizzare i laghi posti ad alta quota opportunisticamente (durante i suoi spostamenti nomadici estivi) o casualmente (quando i giovani individui si disperdono seguendo il sistema idrografico).
Impatto della presenza di pesci introdotti sulle popolazioni di toporagno acquatico Neomys fodiens Pennant (1771) dei laghi alpini d’alta quota
BELLO, LUCIA
2022/2023
Abstract
High mountain lakes are extremely valuable ecosystems currently facing several anthropogenic threats, both at the global and local scale. Fish introduction shows a negative impact on these naturally fishless ecosystems, with huge effects on aquatic communities, but also affecting both semi-aquatic and terrestrial species which rely on aquatic food subsidies. Although the effects on some of these components are already well-studied, much less is known about the effects on semi-aquatic vertebrate Neomys fodiens Pennant (1771). This study aims to test the hypothesis that alien fish introduced in mountain lakes could have a negative impact on Neomys fodiens, because both predators rely on the same shared food resource, that is aquatic macroinvertebrates. Baited tubes were employed to monitor the presence/absence of Neomys fodiens in lakes with introduced fish and in pristine lakes without fish in the Gran Paradiso National Park and Mont Avic Natural Park (Western Italian Alps). The presence of Neomys fodiens is verified when it leaves its faecal pellets in the tubes. The collected faecal samples underwent a macroscopic and microscopic analysis, and a subsample underwent confirmatory genetic analysis, which provided 12 informative sequences supporting the correct identification of the species as Neomys fodiens. Generalized Linear Mixed Models (GLMM) with a Bayesian Markov Chain Monte Carlo (MCMC) approach were used to test the hypothesis, given the presence data of Neomys fodiens in relation to other variables, such as fish presence, sampling season and other environmental variables. Results show that: i) fish negatively affect the probability of detecting Neomys fodiens, confirming the study hypothesis, ii) that the largest impact is observed in lakes with only Salmonids, and iii) that both Salmonids and Cyprinids have the largest negative effects when they do not live together. Altogether, results suggest that the impact is mediated by a complex combination of competition and predation between fish and water shrews. Moreover, the probability of detecting Neomys fodiens increases along the sampling season, suggesting that Neomys may use lakes placed at very high altitudes opportunistically (during its summer nomadic movements) or incidentally (when young individuals disperse across the hydrographic system).È consentito all'utente scaricare e condividere i documenti disponibili a testo pieno in UNITESI UNIPV nel rispetto della licenza Creative Commons del tipo CC BY NC ND.
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https://hdl.handle.net/20.500.14239/16427