1,721,057 research outputs found
Spatial variation in growth rate of early juvenile European plaice Pleuronectes platessa
No full textPatterns and causes of spatial variation in RNA-predicted growth rates in mid-August were examined in young-of-the-year European plaice Pleuronectes platessa (‘YOY plaice’) at 22 beaches along a 300 km stretch of coastline in west Scotland in 3 consecutive years. According to restricted maximum likelihood models, growth rates varied among beaches (25 km scale), but these spatial patterns were not consistent across years. We found no evidence for spatial variation in growth at the scale of subregions (50 km) or regions (100 km). Growth rate was positively correlated with total length, both within and among beaches and years. In general, YOY plaice in mid-August grew more slowly than estimated ad libitum laboratory rates. Average growth rates by beach and year were inversely related to intraspecific competitor densities, but not interspecific competitor densities (brown shrimp Crangon crangon) or 2 environmental productivity metrics (nearshore chlorophyll a concentration and lugworm Arenicola marina cast density). Physical beach characteristics also explained a significant source of spatial growth variation, with fish growing faster at beaches with larger tidal range and wave fetch. Therefore, the hypothesis of sub-maximum growth due to intraspecific competition (density-dependent growth) was supported, but additional, previously unexplored processes related to physical beach characteristics appear to have important influences on the spatial growth dynamics of YOY plaice
Decline in growth rate of juvenile European plaice (Pleuronectes platessa) during summer at nursery beaches along the west coast of Scotland
No full textThis study concludes that declines in growth rates of young-of-the-year European plaice (Pleuronectes platessa) (YOY plaice) during summer vary spatially and between years and that these dynamics are not driven by temperature, body size, or competition. RNA-predicted growth rates of YOY plaice on the west coast of Scotland declined linearly between mid-July and mid-September, with faster declines at beaches and in years where growth rates were initially high. Absolute growth estimates rarely approached ad libitum laboratory rates, and relative declines in growth rates were unrelated to temperature or body size allometry, indicating that maximum growth was rare. However, the absence of inverse relationships between spatial or temporal growth variation and YOY plaice or brown shrimp (Crangon crangon) densities suggests that competition did not limit growth. There were no consistent trends in morphometric condition factor, biochemical composition, or energy content during summer, indicating that apparent growth declines did not result from energy storage and did not result in depletion of energy stores. Influences of extrinsic factors (such as prey conditions, physical disturbance, and predator densities) on the diet, mediated by behavioral decisions to optimize growth with other ecological constraints, require further investigation as causes of growth variation in YOY plaice
Small-scale spatial and temporal heterogeneity in growth and condition of juvenile fish on sandy beaches
No full textTo characterize fine-grained heterogeneity in the functional role of sandy beaches as fish nurseries, we measured RNA concentration, DNA concentration and RNA-predicted growth rate in young-of-the-year European plaice Pleuronectes platessa L. (‘YOY plaice’) at beaches on the western side of the British Isles at small alongshore (100–500 m), temporal (days to weeks), depth (0.5–2 m below waterline) and inter-individual scales. We compared variations in these nucleic-acid-based metrics of condition and growth with a null metric (total length) considered to be less responsive to short-term changes in environmental conditions. All four metrics varied at small spatial and temporal scales, particularly RNA-based metrics of short-term condition and growth. A decline in condition and growth during summer was the most important source of temporal variation. Condition and growth also increased with depth below waterline. Alongshore variations within a beach were relatively small, but variance among stations on the same beach (500 m scale) was similar in magnitude to variance among beaches separated by 100 km. High variance in nucleic acid concentrations among samples resulted not only from technical error but also from inter-individual variation. Our application of high-resolution biochemical indices therefore demonstrates that functional roles of sandy beaches can be structured at remarkably small spatial (500 m) and temporal (days) scales, within a single beach
Predicting the effects of marine climate change on the invertebrate prey of the birds of rocky shores
No full textBy the end of the 21st century models of climate change predict that the air temperature over most of the British Isles will increase by between 2 and 3 °C and sea-level will rise by 40–50 cm. Over that period it will become windier and mean wave height will increase, as will the frequency of storms. These changes in climate and weather will impact the intertidal zone of the UK and will cause distribution changes in many of the common invertebrate species that live there. Where these changes are severe they may well impact on patterns of distribution of ducks and wading birds. In the British Isles a number of organisms live close to their geographical limits of distribution. Some of these species might be expected to extend their range as climatic restraints are relaxed. Species currently limited by cool summers or winter cold will move northwards. In most cases the effects on the distribution of waterbirds will be small. For example, the replacement of the Northern Limpet Patella vulgata by the Southern Limpet P. depressa is unlikely to adversely affect Eurasian Oystercatchers Haematopus ostralegus. Of wider concern is the possibility that as climate warms the abundance and productivity of brown algae will decrease. This is likely to have two significant effects for waders. First, it would represent a loss of potentially rich feeding grounds for species such as Ruddy Turnstone Arenaria interpres that feed on small easily desiccated invertebrates living on or below the seaweed. Secondly, as algae die or are broken away the resulting debris is exported to sediment habitats where it considerably boosts the in situ production of bacteria at the base of the food web. An increase in sea-level will only have a major impact on the extent of rocky shore invertebrate communities where shore topography prevents the upward migration of the biota. Where a seawall limits shores, for example, biological production will be curtailed as the area available for colonization decreases. Increases in the size of waves and the frequency of storms will mimic increasing exposure and there will be a significant reduction in algal production in areas that are affected
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
Modelling the response of populations of competing species to climate change
No full textBiotic interactions will modulate species' responses to climate change. Many approaches to predicting the impacts of climate change on biodiversity so far have been based purely on a climate envelope approach and have not considered direct and indirect species interactions. Using a long-term observational data set (>30 years) of competing intertidal barnacle species, we built a hierarchy of age-structured two-taxa population models (Semibalanus balanoides vs. Chthamalus montagui and C. stellatus combined as one taxon) to test if the presence of a dominant competitor can mediate climatic influence on the subordinate species. Models were parameterized using data from populations on the south coast of southwest England and verified by hindcasting using independent north coast population data. Recruitment of the dominant competitor, S. balanoides, is driven by temperature. The mechanisms of competition explored included simple space preemption and temperature-driven interference competition. The results indicate that interspecific competition between juvenile barnacles is important in regulating chthamalid density but not that of the dominant competitor S. balanoides. Simulations were carried out using alternative future climate scenarios to predict barnacle population abundance over the next century. Under all emission scenarios, the cold-water S. balanoides is predicted to virtually disappear from southwest England by the 2050s, leading to the competitive release of Chthamalus throughout the entire region and thereby substantially increasing its abundance and occupied habitat (by increasing vertical range on the shore). Our results demonstrate that climate change can profoundly affect the abundance and distribution of species through both the direct effects of temperature on survival, and also by altering important negative interactions through shifting competitive balances and essentially removing dominant competitors or predators. Climate change impacts on organisms are unlikely to lead only to straightforward, easily predictable changes in population size and distribution. The complex, indirect effects of climate change need to be taken into account if we are to accurately forecast the long-term effects of global warming
Size variation of 0-group plaice: Are earlier influences on growth potential a contributing factor?
No full textOver a decade of sampling has shown that there are consistent differences in the sizes of 0-group plaice by late summer comparing 21 nursery sites on the Scottish west coast. However, when young fish were collected from two sites which produce particularly small and large fish and reared using a common garden design, growth rates between fish from the two sites were indistinguishable. Either there is little selection for fast or slow growth up to a few weeks post-settlement, or such effects do not persist sufficiently strongly to influence later growth. There were also no significant correlations between the time-series of fish size comparing sites, although within some sites there was evidence of inter-annual density-dependent effects. Any influences of offshore regional scale factors, such as sea temperature or pelagic primary productivity on growth thus appear to be heavily modified by local conditions on the nursery grounds. The field observations combined with the experimental results lead us to conclude that the size 0-group plaice attain in late summer is mainly controlled by post-settlement habitat quality
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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