1,721,028 research outputs found
Life, death and fighting at high latitudes: a review
No full textIn earth's history, having two frozen polar regions is unusual. Not only do these regions experience extreme light climates and associated primary productivity, but freezing sea temperatures and seasonally intense UV irradiation. At these high polar latitudes severe wind speeds, wave action, ice scour and anchor ice (as well as massive fresh water runoff and localised anoxia in the arctic) make the nearshore environment the most disturbed anywhere. On land, in fresh water and in the intertidal zone there are few colonist species but just a few meters deeper in the sea there can be rich, diverse and abundant benthos even in shallow water. The severity of the physical environment is reflected in the interactions in the biological sphere. Amongst the most abundant shallow water benthos are lithophyllic polychaetes, bryozoans and sponges and in these communities its overgrow or be overgrown. The organisation of sessile animals is extremely hierarchical: at any given locality one species is overgrown by all others and one species overgrows all others - everyone else occupies a rank in between.
With no keystone predators to remove competitive dominant species only the catastrophically destructive power of ice and waves prevents monoculture of certain species. In ice-sheletered areas, such as crevices the end point of classically envisaged 'succession' can be seen. In these shallow water environments many animal populations display exactly the converse of characters typically associated with the polar regions. The most abundant species of many clades are the rarer broadcast spawners with pelagic larvae, that grow and reproduce fast (for polar animals) are small and have but brief lifespans. Many of these contrasts can be seen in the representatives of just one phylum - the Bryozoa. Rather than the predicted K selected species of deeper waters the shallows are ruled by lightly calcified pioneers. Here ecological and evolutionary success have become very much decoupled. A ~2°C rise, predicted in polar waters, could be enough to transform this unique zone
Antarctic sea ice losses drive gains in benthic carbon drawdown
No full textClimate forcing of sea-ice losses from the Arctic and West Antarctic are blueing the poles. These losses are accelerating, reducing Earth’s albedo and increasing heat absorption [1]. Subarctic forest (area expansion and increased growth) and ice-shelf losses (resulting in new phytoplankton blooms which are eaten by benthos) are the only significant described negative feedbacks acting to counteract the effects of increasing CO2 on a warming planet, together accounting for uptake of ∼107 tonnes of carbon per year [2]. Most sea-ice loss to date has occurred over polar continental shelves, which are richly, but patchily, colonised by benthic animals. Most polar benthos feeds on microscopic algae (phytoplankton), which has shown increased blooms coincident with sea-ice losses [3]. Here, growth responses of Antarctic shelf benthos to sea-ice losses and phytoplankton increases were investigated. Analysis of two decades of benthic collections showed strong increases in annual production of shelf seabed carbon in West Antarctic bryozoans. These were calculated to have nearly doubled to >2x105 tonnes of carbon per year since the 1980s. Annual production of bryozoans is median within wider Antarctic benthos [4], so upscaling to include other benthos (combined study species typically constitute ∼3% benthic biomass) suggests an increased drawdown of ∼2.9x106 tonnes of carbon per year. This drawdown could become sequestration because polar continental shelves are typically deeper than most modern iceberg scouring, bacterial breakdown rates are slow, and benthos is easily buried. To date, most sea-ice losses have been Arctic, so, if hyperboreal benthos shows a similar increase in drawdown, polar continental shelves would represent Earth’s largest negative feedback to climate change
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
A general ecology of bryozoans at Signy Island, Antarctica
No full textSIGLEAvailable from British Library Document Supply Centre- DSC:DX187210 / BLDSC - British Library Document Supply CentreGBUnited Kingdo
Body and resource size at the land–sea interface
No full textBody size in animals varies with many parameters, amongst them taxonomic affiliation, lifestyle and ambient environment oxygen levels. Size has considerable implication to possibilities for animals; for example, parasites need to be small and top predators large. Body size and resource requirements (shell size) were investigated across the land–sea interface in hermit crabs (Crustacea: Malacostraca: Decapoda) and snails (Mollusca: Gastropoda: Prosobranchia). These are two of the few taxa to occur in the sea, on the shore and on land as residents. Both taxa are also appropriate for such an analysis as they are abundant, speciose, cohabit the same environments and are linked—gastropod shells are a critical resource to hermit crabs. Both the maximum and mean sizes of hermit crab species showed parabolic relationships with shore height, decreasing from the sublittoral and supralittoral to the eulittoral. Average maximum size of gastropods exhibited a similar intertidal minimum although variability was high. It is suggested that this pattern is robust: not only did two distantly related taxa show the same pattern, but neither region nor site contributed significantly to total variability. The mass of resources (gastropod shells) used by hermit crabs, however, showed a converse pattern. The smallest shells (relative to hermit crab body size) were used in the sublittoral and supralittoral. Response to environmental stress and predation pressure are offered as two alternate theories to explain the observed body dwarfism and resource gigantism in the intertidal zone
Ecology of subtropical hermit crabs in SW Madagascar: short-range migrations
No full textMany mobile animals migrate because of the different benefits provided by different localities in time and space. For hermit crabs, such benefits include resource (shell, water, food) acquisition and gamete release. One of the more successful crustacean land-invaders, Coenobita hermit crabs, undertake complex short-range migrations in SW Madagascar. Number of active hermit crabs was inversely related to wind strength and positively related to tidal range, emphasising that movement would conserve water. A circadian component was also recorded in the locomotory activity of Coenobita pseudorugosus and C. rugosus. Path linearity varied with many of the same parameters, but also with beach slope. Movement was primarily perpendicular to shore in small individuals, but the parallel proportion increased with hermit crab size and tidal range, probably driven mostly by shell and food searching. Despite the costs of movement and shell carriage in the terrestrial environment, C. pseudorugosus and C. rugosus were as fast as their marine counterparts. Their speeds varied principally with individual size and were approximately 20% faster without shells and about 20% slower when climbing up a 20° slope, compared to horizontal or downhill travel. Hermit crabs, which are highly numerous and speciose in SW Madagascar, do not seem to partition niches by differential movement patterns. Aside from provision of shells in middens and capturing large adults for bait or pets, human activity may have a profound effect on hermit crab movement: observations at rare uninhabited marine reserves like Nosy Ve show that considerable diurnal activity may take place despite the apparent hostility of the environment to an essentially marine animal
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
Epibiota and attachment substrata of deep-water brachiopods from Antarctica and New Zealand
No full textPrevalence (proportion of host organisms covered) and cover of encrusting epibiota were investigated for four Antarctic and two New Zealand species of deep-sea brachiopods. All epibiota was identified to the lowest possible taxonomic level, such that prevalence and dominance of each taxon could be assessed on different brachiopod species. Punctae had no detectable influence on fouling, whereas valve architecture and ornamentation were probably a major influence. Prevalence and percent cover of epibiota were found to decrease with depth (from 50-600 m) in the Antarctic terebratulid Liothyrella uva. A maximum of 5% epibiotic cover was recorded on the punctate terebratulids from beyond 160 m (Liothyrella uva, Magellania fragilis and Magellania joubini from Antarctica and Neothyris lenticularis from New Zealand). Epibiotic cover significantly increased with valve area to over 40% in the Antarctic inarticulate Neocrania lecointei and the New Zealand impunctate rynchonellid Notosaria nigricans. Bryozoans, foraminiferans and polychaetes were the most abundant colonizers, but there were also representatives present from seven other phyla. The epibiotic community structure of the terebratulids Liothyrella uva, Magellania joubini and Neothyris lenticularis, and the inarticulate Neocrania lecointei were broadly similar, suggesting a cosmopolitan nature to deep-sea brachiopod epibiota. The community on Magellania fragilis was notably different, in being almost entirely dominated by foraminiferans, but the reasons for this are unknown. Analyses of attachment substrata for the Antarctic terebratulid brachiopods indicated erect bryozoans were most commonly used, but that sponges, rocks and even echinoid spines were used. The substratum used by the majority of the New Zealand specimens was unknown, but this is possibly because N. lenticularis has been described as degenerating its attachment and becoming free-living with age
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