The degradation of dead organic matter is one of the processes underlying the functioning of ecosystems. The bodies of dead animals constitute a source of matter and energy that supports the community of detritivores and decomposers. These organisms, in addition to playing a fundamental role in maintaining ecological functions, are references used in the forensic field. In the terrestrial environment, the succession of organisms that leads to the complete degradation of a dead animal has been extensively studied while for the aquatic environments, to date, information is very scarce and, in Italy, it is limited to fish carcasses. The degradation of a dead animal in any environment involves 5 stages defined by the morphological characteristics of the carcass, which becomes an ecosystem characterized by an abundant and differentiated fauna (that changes over time also due to the effect of colonizers) and the trophic role they play. This project focuses on the study of the fauna that develops on pig carcasses placed in a freshwater environment and of the trophic roles that characterize it. The use of Sus scrofa domesticus as an animal model represents an innovative element compared to previous publications concerning decompositions in Italian aquatic environments. The choice is motivated by the physiological and anatomical similarity of this animal with the human species, which could therefore allow a possible application of the obtained results in the forensic field. The degradation of 12 pig carcasses was studied during 4 experimental sessions distributed in the years 2018 and 2019. The carcasses were positioned in 3 sampling points along the perimeter of a small pond in the Modena Apennines located at an altitude of 865 m a.s.l.. Before the immersion of the carcasses, the community of the pond was studied with pre-operational samples for both years. The experimental sessions (spring-summer and late summer) were partially overlapped from a temporal point of view. The sampling of the fauna and the recording of the chemical-physical-environmental parameters were carried out at regular intervals of time, different according to the stage of degradation. The sampled fauna was morphologically determined in the laboratory at the species level. The averages of the various chemical-physical parameters (conductivity, pH, dissolved oxygen and water and air temperatures) calculated over the stages were evaluated according to the progress of the degradation (quantifiable with the stage number). The only parameter that has a good correlation coefficient is the temperature. A quantitative relationship between degradation rate and average water temperature was determined upon linear regression; it is observed that as the temperature increases, degradation occurs faster. A rich and diverse fauna, mostly represented by arthropods, was sampled from the carcasses. Considering the trophic roles in relation to the number of taxa and individuals sampled, it is generally appreciated that the presence of detritivores (collectors and fragmenters) is influenced by the stage. These in fact vary in number of individuals and taxa on the basis of trophic availability, which is in turn influenced by the stage of degradation and by competition with terrestrial fauna, when present. No relationship was observed between the Shannon, Margalef and Pielou indices and the temperature. This might be due to the sampling effort, i.e. the number of field visits made during the session, different for each stage, replica, session and year.

La degradazione della sostanza organica morta è uno dei processi che sta alla base del funzionamento degli ecosistemi. I corpi degli animali morti costituisco una fonte di materia ed energia che sostiene la comunità dei detritivori e dei decompositori. Questi organismi, oltre a svolgere un ruolo fondamentale per il mantenimento delle funzioni ecologiche, costituiscono riferimenti utilizzati in campo forense. In ambiente terrestre la successione degli organismi che porta alla completa degradazione di un animale morto è stata ampliamente studiata mentre per gli ambienti acquatici le informazioni, ad oggi, sono molto scarse e, In Italia, sono limitate a carcasse di pesci. La degradazione di un animale morto in un qualunque ambiente prevede 5 stadi definiti dalle caratteristiche morfologiche della carcassa che diviene un ecosistema caratterizzato da una abbondante e differenziata fauna che si modifica nel tempo anche per effetto dei colonizzatori e del ruolo trofico che svolgono. Il presente progetto è incentrato sullo studio della fauna che si sviluppa su carcasse di maiale poste in ambiente dulciacquicolo e dei ruoli trofici che la caratterizzano. L’utilizzo di Sus scrofa domesticus come modello animale rappresenta un elemento innovativo rispetto a precedenti pubblicazioni riguardanti decomposizioni in ambiente acquatico italiano. La scelta è motivata dalla somiglianza fisiologica ed anatomica di questo animale con la specie umana che quindi potrebbe permettere una possibile applicazione dei risultati ottenuti in campo forense. È stata studiata la degradazione di 12 carcasse di maiale durante 4 sessioni sperimentali distribuite negli anni 2018 e 2019. Le carcasse sono state posizionate in 3 punti di campionamento lungo il perimetro di un piccolo stagno dell’appennino modenese sito ad un’altitudine di 865 m s.l.m.. Prima dell’immersione delle carcasse si è studiata la comunità dello stagno con dei campionamenti pre-operazionali per entrambi gli anni. Le sessioni sperimentali (primaverile-estiva e tardo estiva) erano parzialmente sovrapposte dal punto di vista temporale. I campionamenti della fauna e la registrazione dei parametri chimico-fisici-ambientali sono stati effettuati ad intervalli regolari di tempo, differenti a seconda dello stadio di degradazione. La fauna campionata è stata determinata morfologicamente in laboratorio a livello di specie. Le medie dei diversi parametri chimico-fisici (conducibilità, pH, ossigeno disciolto e temperature di acqua e aria) calcolate sugli stadi sono state valutate in funzione del progredire della degradazione (quantificabile con il numero dello stadio). L’unico parametro che presenta un buon coefficiente di correlazione è la temperatura. All’aumentare della temperatura la degradazione avviene più velocemente; una relazione quantitativa fra detta velocità e temperatura è stata determinata mediante regressione lineare. Una ricca e diversificata fauna rappresentata per la maggior parte da artropodi è stata campionata dalle carcasse. Considerando i ruoli trofici in relazione con il numero di taxa e di individui campionati si apprezza in generale che la presenza dei detritivori (i collettori e i frammentatori) è influenzata dallo stadio. Questi infatti variano in numero di individui e taxa sulla base della disponibilità trofica che è influenzata a sua volta dallo stadio di degradazione e dalla competizione con la fauna terrestre, quando presente. Ponendo gli indici di Shannon, Margalef e Pielou in relazione con la temperatura non si è osservata alcuna relazione. Ciò potrebbe essere causato dallo sforzo di campionamento, cioè il numero di visite in campo effettuate durante la sessione, diverso per ogni stadio, replica, sessione ed anno.

Successione di Specie nella Decomposizione di Carcasse di Mammiferi in un Ecosistema Dulciacquicolo dell'Italia del Nord / Andrea Benassi , 2021 Sep 20. 33. ciclo, Anno Accademico 2019/2020.

Successione di Specie nella Decomposizione di Carcasse di Mammiferi in un Ecosistema Dulciacquicolo dell'Italia del Nord

BENASSI, Andrea
2021

Abstract

The degradation of dead organic matter is one of the processes underlying the functioning of ecosystems. The bodies of dead animals constitute a source of matter and energy that supports the community of detritivores and decomposers. These organisms, in addition to playing a fundamental role in maintaining ecological functions, are references used in the forensic field. In the terrestrial environment, the succession of organisms that leads to the complete degradation of a dead animal has been extensively studied while for the aquatic environments, to date, information is very scarce and, in Italy, it is limited to fish carcasses. The degradation of a dead animal in any environment involves 5 stages defined by the morphological characteristics of the carcass, which becomes an ecosystem characterized by an abundant and differentiated fauna (that changes over time also due to the effect of colonizers) and the trophic role they play. This project focuses on the study of the fauna that develops on pig carcasses placed in a freshwater environment and of the trophic roles that characterize it. The use of Sus scrofa domesticus as an animal model represents an innovative element compared to previous publications concerning decompositions in Italian aquatic environments. The choice is motivated by the physiological and anatomical similarity of this animal with the human species, which could therefore allow a possible application of the obtained results in the forensic field. The degradation of 12 pig carcasses was studied during 4 experimental sessions distributed in the years 2018 and 2019. The carcasses were positioned in 3 sampling points along the perimeter of a small pond in the Modena Apennines located at an altitude of 865 m a.s.l.. Before the immersion of the carcasses, the community of the pond was studied with pre-operational samples for both years. The experimental sessions (spring-summer and late summer) were partially overlapped from a temporal point of view. The sampling of the fauna and the recording of the chemical-physical-environmental parameters were carried out at regular intervals of time, different according to the stage of degradation. The sampled fauna was morphologically determined in the laboratory at the species level. The averages of the various chemical-physical parameters (conductivity, pH, dissolved oxygen and water and air temperatures) calculated over the stages were evaluated according to the progress of the degradation (quantifiable with the stage number). The only parameter that has a good correlation coefficient is the temperature. A quantitative relationship between degradation rate and average water temperature was determined upon linear regression; it is observed that as the temperature increases, degradation occurs faster. A rich and diverse fauna, mostly represented by arthropods, was sampled from the carcasses. Considering the trophic roles in relation to the number of taxa and individuals sampled, it is generally appreciated that the presence of detritivores (collectors and fragmenters) is influenced by the stage. These in fact vary in number of individuals and taxa on the basis of trophic availability, which is in turn influenced by the stage of degradation and by competition with terrestrial fauna, when present. No relationship was observed between the Shannon, Margalef and Pielou indices and the temperature. This might be due to the sampling effort, i.e. the number of field visits made during the session, different for each stage, replica, session and year.
Succession of Species during the Degradation of Mammal Carcasses in a Northern Italy Freshwater Ecosystem
20-set-2021
PREVEDELLI, Daniela
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