1,721,046 research outputs found
Evidences of adaptive traits to rocky substrates undermine paradigm of habitat preference of the Mediterranean seagrass Posidonia oceanica
Full text linkPosidonia oceanica meadows are acknowledged as one of the most valuable ecosystems of the Mediterranean Sea. P. oceanica has been historically described as a species typically growing on mobile substrates whose development requires precursor communities. Here we document for the first time the extensive presence of sticky hairs covering P. oceanica seedling roots. Adhesive root hairs allow the seedlings to firmly anchor to rocky substrates with anchorage strength values up to 5.23 N, regardless of the presence of algal cover and to colonise bare rock without the need for precursor assemblages to facilitate settlement. Adhesive root hairs are a morphological trait common on plants living on rocks in high-energy habitats, such as the riverweed Podostemaceae and the seagrass Phyllospadix scouleri. The presence of adhesive root hairs in P. oceanica juveniles suggests a preference of this species for hard substrates. Such an daptation leads to hypothesize a new microsite driven bottleneck in P. oceanica seedling survival linked to substrate features. The mechanism described can favour plant establishment on rocky substrates, in contrast with traditional paradigms. This feature may have strongly influenced P. oceanica pattern of colonisation through sexual propagules in both the past and present
Turning casualty into opportunity: fragmenting dislodged colonies is effective for restoring reefs of a Mediterranean endemic coral
No full textWithin the framework of ecosystem-based management, restoration appears as a sensible option to counteract the global decline of coral reefs. Several techniques involving sexual and asexual coral propagules have been used for the restoration of reefs. Culturing of fragments has proved fruitful since it takes advantage of the capability of corals to asexually reproduce, providing a number of novel colonies that can be replanted. This method however, when using fragments detached from a colony, might be stressful for the wild donor. Astroides calycularis is an endemic and endangered Mediterranean scleractinian coral forming massive colonies mostly at shallow depth. It is subject to anthropogenic impact, particularly from damage due to accidental contacts by SCUBA divers, and it is expected to suffer from sea storms of increasing power under the projected climate change scenarios. Corals of opportunity (i.e. dislodged colonies found alive on the seabed) may be a useful resource for the restoration of A. calycularis reefs, given that the fragment-based transplant technique is effective for this species as it is for other massive corals. A one-year transplant experiment was carried out along an exposed rocky shore in NW Sicily (Mediterranean Sea) to test the feasibility of using fragments of corals of opportunity for restoration purposes. The transplants revealed high survival rates and higher number of new polyps than in control colonies. The original size of transplanted fragments did not influence their capability to bud new polyps and was not related to their survival rate. The applied technique provides the opportunity to restore rocky reefs, even the very shallow ones, through direct transplant of coral fragments, thus making reef restoration a feasible option in ecosystem-based management plans for this species
The role of Marine Protected Areas in influencing the invasion success of the alien crab Percnon gibbesi
No full textThe biotic resistance hypothesis states that pristine communities, with high species richness and functional diversity, are less prone to biological invasions than species-poor areas either this is natural or it is a result of human activities. Complex communities with high levels of biodiversity, such as those hosted by Marine Protected Areas, should offer fewer niche opportunities (e.g. resources and space) to invasive species thereby reducing both their establishment possibilities and success (i.e. settlement and/or expansion).
The present study aimed to evaluate the capacity of marine protected communities to provide a buffer against the establishment of one of the most invasive species in the Mediterranean Sea: the Percnidae crab Percnon gibbesi (H. Milne Edwards, 1853). Here, it was tested if predation provides a higher resistance to the invasion by P. gibbesi in protected native communities than in exploited ones. Specifically, this study aimed to compare (a) the abundance and diversity of predator assemblages of P. gibbesi, (b) the predation pressure on P. gibbesi and (c) the density of this species in protected and unprotected areas in the Mediterranean Sea. Tethering experiments were conducted in the field to assess the relative predation rate on two size classes of P. gibbesi, using long and short tethers, at two protected and two unprotected sites randomly chosen on the northern coast of Sicily (Southern Tyrrhenian Sea).
The abundance and diversity of predators of P. gibbesi and the relative predation rate on tethered crabs were higher at protected than unprotected sites, independent of crab size and tether length; the density of P. gibbesi was significantly lower in protected than unprotected areas.
The findings of this study, although restricted to a small spatial scale, support the existence of mechanisms for biotic resistance in Mediterranean protected native communities and provide experimental evidence that the restoration of predator assemblages confers better invasion resistance to marine protected areas against P. gibbesi invasion. More generally, the present study confirms that marine protected areas are an effective tool for ameliorating the impact of some biological invasions in the Mediterranean Sea
Sizing up the role of predators on Mullus barbatus populations in Mediterranean trawl and no-trawl areas
No full textFishing leads to drastic changes in ecosystems with a net loss of predatory biomass. This issue has been evidenced from historical ecological studies and from the evaluation of the effects of effective and large marine protected areas. In two fishery reserves off the northern Sicily coast the red mullet Mullus barbatus underwent an impressive biomass increment and a few piscivores fish species recovered after a trawl ban. The red mullet, more than 20% of all demersal fish in the untrawled areas, represented a huge food resource to its potential predators. By contrasting two trawled and two untrawled gulfs we figured out predator - prey relationships through the use of a combined approach based on trophic niche, stable isotopes data and biomass. We show that the white grouper Epinephelus aeneus and the black-bellied anglerfish Lophius budegassa are the most important predators of the red mullet with higher biomass in the untrawled areas. We also found a potential re-establishment of the trophic role for white grouper inside the untrawled areas. Our study highlights some of the benefits obtained from the use of large offshore marine protected areas as a tool for ecosystem restoration
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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