1,721,112 research outputs found
Trends and global prospects of the Earth’s aquatic ecosystems
No full textThe Earth's organisms have depended on water since they
arose 3.5 billion years ago. In the last 10000 years, human
development of stone tools, learning of food cultivation,
growth of civilizations and trade, and migration among
others have increasingly impinged on aquatic ecosystems.
During the last century, the human population has tripled,
and water use for human purposes increased six-fold.
Approximately half of all available fresh water is now used to meet human ends, twice what it was 40 years ago (World Water Council [WWC] 2000), and by 2025, the withdrawal
of water is projected globally to increase by at least 50%
(Martinez Austria & van Hofwegen 2006)
Tracing basal resource use across sea-ice, pelagic, and benthic habitats in the early Arctic spring food web with essential amino acid carbon isotopes
Full text linkA rapidly warming Arctic Ocean and associated sea-ice decline is resulting in changing sea-ice protist communities, affecting productivity of under-ice, pelagic, and benthic fauna. Quantifying such effects is hampered by a lack of biomarkers suitable for tracing specific basal resources (primary producers and microorganisms) through food webs. We investigate the potential of ẟ13C values of essential amino acids (ẟ13CEAA values) to estimate the proportional use of diverse basal resources by organisms from the under-ice (Apherusa glacialis), pelagic (Calanus hyperboreus) and benthic habitats (sponges, sea cucumber), and the cryo-pelagic fish Boreogadus saida. Two approaches were used: baseline ẟ13CEAA values, i.e. the basal resource specific ẟ13CEAA values, and ẟ13CEAA fingerprints, or mean-centred baseline ẟ13CEAA values. Substantial use of sub-ice algae Melosira arctica by all studied organisms suggests that its role within Arctic food webs is greater than previously recognised. In addition, ẟ13CEAA fingerprints from algae-associated bacteria were clearly traced to the sponges, with an individually variable kelp use by sea cucumbers. Although mean-centred ẟ13CEAA values in A. glacialis, C. hyperboreus, and B. saida tissues were aligned with microalgae resources, they were not fully represented by the filtered pelagic- and sea-ice particulate organic matter constituting the spring diatom-dominated algal community. Under-ice and pelagic microalgae use could only be differentiated with baseline ẟ13CEAA values as similar microalgae clades occur in both habitats. We suggest that ẟ13CEAA fingerprints combined with microalgae baseline ẟ13CEAA values are an insightful tool to assess the effect of ongoing changes in Arctic basal resources on their use by organisms
Report on Botanical Explorations in Arctic America, 1946-48
Full text linkBrief account, in general terms, of the author\u27s field-trips in the northern Quebec, Southampton Island, and Baker Lake (Keewatin) regions, summer 1946; in the northwestern part of Mackenzie District, summer 1947; and in Fairbanks, Alaska, 1948, whence he made high altitude, aerological, bacteriological, collecting flights to the North Pole. Includes remarks on the vegetation in regions visited in 1946 and 1947
Current status and future trends in kelp forest ecosystems
No full text[Extract] Kelp forests dominate shallow rocky coasts of the world's cold-water marine habitats. They are comprised primarily of brown algae in the order Laminariales and produce one of the largest biogenic structures found in benthic marine systems. Kelp forest ecosystems include structure-producing kelps and their associated biota such as marine mammals, fishes, crabs, sea urchins, lobsters, molluscs, other algae and epibiota that collectively make this one of the most diverse and productive ecosystems of the world (Mann 1973, 2000; Dayton 1985a, b). Economically, kelp forest ecosystems have been significant to maritime peoples for thousands of years (Simenstad et al. 1978; Erlandson 2001). The aim of this chapter is to review how kelp forest ecosystems have changed at very large spatial scales over very long periods of time (decades to millennia). This perspective then provides a strong basis for assessing how different modern kelp ecosystems are from those in the past, and thus in turn allows an appreciation of possible future states
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
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