1,720,972 research outputs found
IL DELFINO COMUNE DEL MEDITERRANEO: RICOSTRUZIONE DELLA STORIA ECOLOGICA ED EVOLUTIVA ATTRAVERSO I REPERTI OSTEOLOGICI
No full textIl delfino comune (Delphinus delphis, Linnaeus, 1785) è una delle specie più enigmatiche del Mar Mediterraneo. Un tempo ampiamente diffusa, alla fine degli anni '60 ha subìto un declino significativo in gran parte del bacino. Le ragioni e i meccanismi alla base di questo declino rimangono in gran parte sconosciuti o poco compresi. Tuttavia, è stata identificata una serie di potenziali cause, tra cui le campagne di abbattimento, la morte accidentale in attrezzi da pesca, la ridotta disponibilità di prede e il degrado dell'habitat. Le stime attuali ottenute da indagini e campagne di monitoraggio suggeriscono la completa assenza o la quasi scomparsa dei delfini comuni dalle aree storicamente note per ospitare popolazioni consistenti. L'Unione Internazionale per la Conservazione della Natura ha designato la sottopopolazione di delfino comune del Mediterraneo come "Endangered".
Abbiamo ricostruito la poco conosciuta storia naturale di questa specie utilizzando reperti museali osteologici degli ultimi due secoli. L'approccio multidisciplinare, che consiste nell'analisi genetica del DNA antico, nella morfometria geometrica dei crani e nell'analisi degli isotopi stabili del collagene, ha permesso di comprendere meglio l'ecologia della popolazione storica di delfino comune del Mediterraneo. I principali risultati della ricerca includono: i) l'approccio integrato molecolare/morfometrico ha permesso di identificare con successo gli esemplari museali a livello specie-specifico e di evidenziare errori di identificazione nelle collezioni museali e nella letteratura storica, i quali rappresentano un bias nell'identificazione delle specie di delfini mediterranei e nella conoscenza della loro storia demografica ed ecologica; ii) le analisi genomiche preliminari hanno evidenziato la perdita della diversità genetica di D. delphis nel corso degli ultimi decenni; ii) i risultati dell'analisi degli isotopi stabili (δ13C e δ15N) indicano diversi modelli ecologici e/o trofici del delfino comune mediterraneo nel corso del tempo, suggerendo un possibile spostamento della nicchia ecologica nel corso degli ultimi secoli. In conclusione, i risultati suggeriscono che il declino del delfino comune sia stato innescato da un insieme di fattori di natura antropogenica che hanno portato non solo alla competizione con l’uomo, ma anche a una competizione interspecifica con altre due specie ampiamente diffuse nel Mediterraneo: Stenella coeruleoalba e Tursiops truncatus
Unveiling the enigmatic natural history of Mediterranean Common Dolphin (Delphinus delphis Linnaeus, 1758): Ecological and evolutionary insights for conservation challenges
No full textThe Mediterranean population of common dolphin (Delphinus delphis) presents an enigmatic natural history. Once widely prevalent, it faced a significant decline across most of the basin by the late 1960s (Bearzi et al., 2003). The precise reasons and mechanisms behind this decline remain largely unknown or poorly understood. However, a range of potential causes has been identified, encompassing deliberate culling, accidental deaths in fishing gear, reduced prey availability, and habitat degradation (Bearzi et al., 2008; Bearzi, Holcer, & Notarbartolo di Sciara, 2004; Piroddi et al., 2011). Present estimates derived from surveys and monitoring campaigns suggest either a complete absence or a near disappearance of common dolphins from areas historically known to harbor substantial populations. The International Union for Conservation of Nature has designated the Mediterranean population of common dolphins as Endangered (Bearzi et al., 2021).
We reconstructed the little-known natural history of this population using Mediterranean museum skeletal specimens from the last two centuries. A multidisciplinary analytical approach, consisting of genetic analysis on ancient DNA, skull geometric morphometry, and collagen stable isotope analysis, in addition to data from strandings and historical documentation, has enabled a better understanding of the ecology of the historical Mediterranean common dolphin population.
The main results are: i) the incorrect taxonomic attributions in museum collections and historical literature represent a low but significant bias in the identification of Mediterranean dolphin species and in the knowledge of their demographic and ecological history over the past decades and centuries; ii) 10% of museum specimens show a discrepancy between morphology and genetics and these could potentially represent evidence of interspecific hybridization events between the Delphinus delphis and other species more common in the basin, such as Stenella coeruleoalba and Tursiops truncatus; iii) the Mediterranean common dolphin population shows significant spatial heterogeneity in the ecological, trophic and distribution patterns
in the Pelagos Sanctuary (NW Mediterranean Sea): does landscape matter?
No full textThe bottlenose dolphin (Tursiops truncatus Montagu, 1821) is a regularly observed species in the Mediterranean Sea, but its network organization has never been investigated on a large scale. We described the network macrostructure of the bottlenose dolphin (meta)population inhabiting the Pelagos Sanctuary (a wide protected area located in the north-western portion of the Mediterranean basin) and we analysed its connectivity in relation to the landscape traits. We pooled effort and sighting data collected by 13 different research institutions operating within the Pelagos Sanctuary from 1994 to 2011 to examine the distribution of bottlenose dolphins in the Pelagos study area and then we applied a social network analysis, investigating the association patterns of the photo-identified dolphins (806 individuals in 605 sightings). The bottlenose dolphin (meta)population inhabiting the Pelagos Sanctuary is clustered in discrete units whose borders coincide with habitat breakages. This complex structure seems to be shaped by the geo-morphological and ecological features of the landscape, through a mechanism of local specialization of the resident dolphins. Five distinct clusters were identified in the (meta)population and two of them were solid enough to be further investigated and compared. Significant differences were found in the network parameters, suggesting a different social organization of the clusters, possibly as a consequence of the different local specialization
Tracing time's footprints: exploring feeding ecology and historical changes of Mediterranean common dolphin (Delphinus delphis) over two centuries
No full textThe Mediterranean population of common dolphin (Delphinus delphis) presents an enigmatic natural history in the last centuries. Once widely prevalent in the 19th and early 20th, it faced a significant decline across most of the basin by the late 1960s. The causes and mechanisms behind this decline remain largely unknown and poorly understood. The IUCN has designated the Inner Mediterranean population of common dolphins as Endangered. Here, we analyzed stable isotopes of nitrogen and carbon (δ15N and δ13C) on skeletal remains collected in 22 Mediterranean natural history museums to investigate spatio-temporal trophic shifts and niche partitioning of the Mediterranean common dolphin over the past 200 years. We compared the isotope composition of historical common dolphins with those of the contemporary populations of Stenella coeruleoalba and Tursiops truncatus which co-occur in the Mediterranean occupying different habitats and trophic niches. We found that common dolphin individuals inhabiting the Mediterranean before 1970 occupied a significantly higher trophic level than the contemporary ones. The comparative analysis between dolphin species revealed that historically common dolphins occupied a well-defined isotopic niche separate from other species, while the contemporary populations shifted to overlap those of the striped dolphin. We cannot exclude that this significant ecological shift could be driven by habitat and trophic competition with human activities as prolonged and intense fishery stock exploitation has occurred in the basin. However, it appears that a key factor in the common dolphin's decline was competition with the striped dolphin, a widespread species in the region, that has effectively "squeezed" the common dolphin's habitat. This is the first long-term evidence of an ecological and/or trophic shift in the common dolphin Mediterranean population, which could be the starting point for understanding the causes and impacts of the species’ near-collapse in the Mediterranean
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Stima di abbondanza di Tursiops truncatus (Montagu, 1821) nel levante ligure ed evoluzione dei marcaggi naturali utili alla fotoidentificazione
No full textIl bacino ligure, pur facendo parte della più grande area marina protetta del Mar Mediterraneo, il Santuario Pelagos, risulta essere una regione in cui le attività umane stanno condizionando la presenza di numerose specie di Cetacei. Fra tutte Tursiops truncatus, in virtù della sua distribuzione limitata per lo più alle acque basse (<200 metri) è la specie maggiormente soggetta alle conseguenze dirette e indirette dell’impatto antropico.
Questo elaborato è stato condotto all’interno del più ampio progetto “Delfini Metropolitani” coordinato dall’Acquario di Genova. L’area di studio presa in esame è l’intero levante ligure con tre stazioni di ormeggio: Genova, Rapallo e Lerici. Tramite la tecnica della cattura-ricattura fotografica è stato possibile analizzare la distribuzione ed effettuare delle stime di abbondanza per il periodo di studio 2005 – 2012. Dai risultati e dal confronto con altri studi è emerso che il tursiope vive entro la piattaforma continentale e sembrerebbe che all’aumentare di quest’ultima aumenti la dimensione della popolazione. Per il periodo di studio considerato la popolazione non fa registrare trend demografici significativi, rimanendo costante fra 150 - 250 individui.
In questo elaborato si sono anche studiate le differenze fra maschi e femmine nell’evoluzione dei marcaggi naturali. I risultati preliminari hanno mostrato una differenza significativa fra i due sessi. Il maschio ha un valore maggiore come cambiamento rispetto alle femmine, questo è dovuto al fatto che gli individui maschi hanno interazioni spesso aggressive per poter accedere alle femmine.
Infine grazie all’analisi dell’evoluzione dei marcaggi naturali e delle differenze trovate, si è proposto un nuovo metodo per poter sessare gli animali. Questo qui proposto, comunque, è un metodo derivante da uno studio preliminare e si ha bisogno di successivi studi per testarne l’efficienza e l’affidabilità
Analysis of the social behaviour in regard to gender in Tursiops truncatus (eastern Mediterranean Sea)
No full textThe bottlenose dolphin Tursiops truncatus (Montagu, 1821) is a cosmopolitan species; it can be found in tropical and temperate waters worldwide. Its accessibility in nearshore waters has made it one of the best-studied cetaceans.
In the eastern Mediterranean Sea bottlenose dolphins have been studied since 2001 when the project “Delfini Metropolitani”, developed by Acquario di Genova, started; the study area runs from Genoa to La Spezia.
The bottlenose dolphin population inhabiting the study area is exposed to potential impact from human activities; this makes important to gather information on its ecology, social structure, abundance and demography.
The aims of the present study are to:
- assess the distribution;
- estimate the abundance using photographic mark-recapture technique;
- analyse the association pattern (in relation to gender);
- calculate the calving interval (the time elapsed between subsequent births).
Surveys were conducted using two inflatable boats; survey tracks and sighting waypoints were recorded by GPS. Photographic data were collected during the sightings and analysed using the photo-identification technique.
Data collected during this research provide that bottlenose dolphin distribution is confined to the continental shelf (concentrated within the 100 m isobaths) and that the highest amount of animals is located on the east side of the study area, as found by other researchers. According to our abundance estimates the population remained steady throughout the years. We discovered that calves significantly influence both group size and composition: groups are bigger when calves are present; larger groups contain a higher percentage of females while the percentage of males is lower. Analysing the social structure, we discovered that it’s characterized by: a good level of cohesion, weak and temporary bonds; long-term associations occur between members of the same sex; females live in bigger groups with other females and calves. These results are consistent with other studies.
Data collected during this research provide information available for comparisons of social ecology and behaviour between this population and others, living in the Pelagos Sanctuary as well as around the world. Such information might help in devising management protocols for this cetacean species contributing to its protection
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