1,720,967 research outputs found
Fish and their Scales: On the Power Laws of Aggregation, Size Distribution and Trophic Interaction
No full textPower law relationships are ubiquitous in ecology, and complex systems in general, andcan be used as metrics to describe many aspects of ecosystem structure and function.While ecological interactions and processes predominantly occur at the individual levelof biological organisation, currently, most ecological studies aim to estimate “typical”ecosystem behaviour over large spatial and temporal scales. This disconnect resultsin the under- appreciation of ecosystem dynamics that are potentially important fordeveloping ecological theory and ecosystem modelling. The research presented hereinaims to estimate within-ecosystem dynamics, as quantified by power law relationships,to test whether expected ecological dynamics can be captured effectively at smaller scales.I show that Taylor’s power law, a metric of aggregation, varies systematically, bothspatially and temporally within the North Sea fish community, with the abiotic environmentwhen populations were considered as cohorts of individual body sizes. By combiningestimates of the power law distribution of body size in fish with stable isotopes that can beused to infer trophic interactions, I show that seasonal trends in fish movement patternsand the incorporation of pulsed phytoplankton production can be quantified in a highlydynamic estuarine environment. Estimates of the in situ community predator-prey massratio, which describes trophic behaviour, and the apparent trophic transfer efficiency arethen derived and shown to exhibit strong seasonal variation, indicative of an estuarinefood web that is temporally variable. Finally, I quantify the degree of individual specialisation,a mechanism by which intraspecific competition is modulated, in the diet of a commerciallyimportant but over-exploited fish species to inform conservation efforts.This work shows that ecological dynamics can be captured by a range of ecosystemmetrics and that, therefore, small scale behaviours can be tested for empirically to direct ecosystem models and theory.<br/
Individual trophic specialization in juvenile European seabass: implications for the management of a commercially important species
No full textIndividual differences in diet can play an important role defining a population's ecological niche and its role within food webs and habitats, but individual trophic specialization is rarely considered in a fisheries context. Stocks of European seabass, Dicentrarchus labrax, have declined in recent years, and policy has focused on managing fishing effort. Inshore nursery grounds represent a critical habitat in terms of recruitment to standing stocks, and improved understanding of the ecology of juvenile seabass at the level of the individual may assist the development of management strategies aimed at maximizing their survival and growth. We quantified levels of individual trophic specialization in juvenile seabass using stomach contents and stable isotope analyses at a monthly resolution over an annual cycle. We found significant, seasonally varying levels of individual specialization in stomach contents, with reduced specialization observed in the spring. This was corroborated by stable isotope analyses, where isotopic variance among seabass individuals was significantly higher compared to that in two other concurrently sampled, sympatric bentho-pelagic predators. Our findings suggest that juvenile seabass form trophic-generalist populations composed of specialized individuals. Considering variation in individual behaviours may improve management strategies aimed at protecting the vulnerable life stages of this commercially important species
Taylor’s power law captures the effects of environmental variability on community structure: an example from fishes in the North Sea
No full textTaylor’s power law (TPL) describes the relationship between the mean and variance in abundance of populations, with the power law exponent considered a measure of aggregation. However the usefulness of TPL exponents as an ecological metric has been questioned, largely due to its apparent ubiquity in various complex systems. The aim of this study was to test whether TPL exponents vary systematically with potential drivers of animal aggregation in time and space, and therefore capture useful ecological information of the system of interest. We derived community TPL exponents from a long term, standardised and spatially dense data series of abundance and body size data for a strongly size-structured fish community in the North Sea. We then compared TPL exponents between regions of contrasting environmental characteristics. We find that, in general, TPL exponents vary more than expected under random conditions in the North Sea for size-based populations compared to communities considered by species. Further, size-based temporal TPL exponents are systematically higher (implying more temporally-aggregated distributions) along hydrographic boundaries. Time-series of size-based spatial TPL exponents also differ between hydrographically distinct basins. These findings support the notion that TPL exponents contain ecological information, capturing community spatio-temporal dynamics as influenced by external drivers
Stable isotopes demonstrate seasonally stable benthic-pelagic coupling as newly-fixed nutrients are rapidly transferred through food chains in an estuarine fish community
Get PDFSeasonal differences in the availability of resources potentially result in food web architecture also varying through time. Stable isotope analyses are a logistically simple but powerful tool for inferring trophic interactions and food web structure, but relatively few studies quantify seasonal variations in food web structure or nutrient flux across multiple trophic levels. We determined the temporal dynamics in stable isotope compositions (carbon, nitrogen and sulfur) of a fish community from a highly seasonal, temperate estuary sampled monthly over a full annual cycle. Sulfur isotope values in fish tissues discriminated among consumers exploiting pelagic and benthic resources but showed no seasonal variation. This implied limited change in the relative consumption of pelagic and benthic resources by the fish community over the study period despite major seasonal changes in phytoplankton biomass. Conversely carbon and nitrogen isotope values exhibited seasonality marked by the commencement of the spring phytoplankton bloom and peak chlorophyll concentration, with δ13C values following expected trends in phytoplankton growth physiology and variation in δ15N values coinciding with changes in major nitrogen sources to plankton between nitrate and ammonium. Isotope shifts in fish muscle were detected within two weeks of the peak spring phytoplankton bloom, suggesting a rapid trophic transfer of carbon and nitrogen along food chains within the estuarine food web during periods of high production. We therefore caution against the assumption that temporal averaging effectively dampens isotopic variability in tissues of higher trophic level animals in highly dynamic ecosystems such as temperate estuaries. This work highlights how stable isotope analyses can be combined with environmental data to gain broader understanding of ecosystem functioning, while emphasising the need for temporally appropriate sampling in stable isotope-based studies
Tracing basal resource use across sea-ice, pelagic, and benthic habitats in the early Arctic spring food web with essential amino acid carbon isotopes
Get PDFA 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
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Two Functional Epithelial Sodium Channel Isoforms Are Present in Rodents despite Pronounced Evolutionary Pseudogenization and Exon Fusion
Get PDFThe epithelial sodium channel (ENaC) plays a key role in salt and water homeostasis in tetrapod vertebrates. There are four ENaC subunits (α, β, γ, δ), forming heterotrimeric αβγ- or δβγ-ENaCs. While the physiology of αβγ-ENaC is well understood, for decades the field has stalled with respect to δβγ-ENaC due to the lack of mammalian model organisms. The SCNN1D gene coding for δ-ENaC was previously believed to be absent in rodents, hindering studies using standard laboratory animals. We analysed all currently available rodent genomes and discovered that SCNN1D is present in rodents but was independently lost in five rodent lineages, including the Muridae (mice and rats). The independent loss of SCNN1D in rodent lineages may be constrained by phylogeny and taxon-specific adaptation to dry habitats, however habitat aridity does not provide a selection pressure for maintenance of SCNN1D across Rodentia. A fusion of two exons coding for a structurally flexible region in the extracellular domain of δ-ENaC appeared in the Hystricognathi (a group that includes guinea pigs). This conserved pattern evolved at least 41 Ma ago and represents a new autapomorphic feature for this clade. Exon fusion does not impair functionality of guinea pig (Cavia porcellus) δβγ-ENaC expressed in Xenopus oocytes. Electrophysiological characterisation at the whole-cell and single-channel level revealed conserved biophysical features and mechanisms controlling guinea pig αβγ- and δβγ-ENaC function as compared to human orthologues. Guinea pigs therefore represent commercially available mammalian model animals that will help shed light on the physiological function of δ-ENaC
Variations on the Author
Get PDF“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
Get PDFWe 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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