1,720,960 research outputs found
Intraspecific home range scaling: a case study from the owl limpet (Lottia gigantea)
No full textBackground: The owl limpet (Lottia gigantea) is an ectothermic invertebrate that inhabits the rocky intertidal zone where it territorially defends home ranges and grazes algae growing on the rocks. Among endothermic species, home range scales isometrically with body mass.Hypothesis: Home range area scales isometrically (scaling exponent ?1.0) across individuals of the owl limpet, spanning more than an order of magnitude in body mass.Field sites: Southern and central California rocky intertidal sites (n = 5; ?32.5–35.5?N).Methods: Measure home range area and body mass of individuals (n = 104). Determine the scaling exponent.Conclusions: Home range scaling across individuals of L. gigantea exhibits the same isometric relationship that is often found across endothermic species
Historical and recent processes shaping the geographic range of a rocky intertidal gastropod: phylogeography, ecology, and habitat availability
Full text linkFactors shaping the geographic range of a species can be identified when phylogeographic patterns are combined with data on contemporary and historical geographic distribution, range-wide abundance, habitat / food availability and through comparisons with co-distributed taxa. Here, we evaluate range dynamism and phylogeography of the rocky intertidal gastropod Mexacanthina lugubris lugubris across its geographic range - the Pacific coast of the Baja peninsula and southern California. We sequenced mitochondrial DNA (CO1) from ten populations and compliment these data with museum records, habitat availability and range-wide field surveys of the distribution and abundance of M. l. lugubris and its primary prey (the barnacle Chthamalus fissus). The geographic range of M. l. lugubris can be characterized by three different events in its history: an old sundering in the mid-peninsular region of Baja (~ 417,000 years ago) and more recent northern range expansion and southern range contraction. The mid-peninsular break is shared with many terrestrial and marine species, although M. l. lugubris represents the first mollusc to show it. This common break is often attributed to a hypothesized ancient seaway bisecting the peninsula, but for M. l. lugubris it may result from large habitat gaps in the southern clade. Northern clade populations, particularly near the historical northern limit (prior to the 1970’s) have high local abundances and reside in a region with plentiful food and habitat – which makes its northern range conducive to expansion. The observed southern range contraction may result from the opposite scenario, with little food or habitat nearby. Our study highlights the importance of taking an integrative approach to understanding the processes that shape the geographic range of a species via combining range-wide phylogeography data with temporal geographic distributions and spatial patterns of habitat / food availability
Lethal and sub-lethal responses of rocky shore gastropods to extreme temperatures
Full text linkIntertidal communities are more frequently experiencing extreme air and sea temperatures as a result of anthropogenic climate change, with heatwaves increasing in intensity and duration. Most studies exploring the thermal tolerances of intertidal species to extreme temperatures haven't directly studied early life stages. We explored whether locally extreme tide-out temperatures were lethally impacting premature Boreal (Littorina littorea and Steromphala cineraria) and Lustanian (Phorcus lineatus and Steromphala umbilicalis) intertidal gastropod species from southwest England. Two separate experiments tested lethal and sub-lethal responses to simulated local heatwave and cold spell temperatures. Two sensitive early size classes (new recruits and year 1+ juveniles) for each species were exposed to simulated extreme and ambient tide-out temperatures in replicated boulderfield (air) and rockpool (seawater) microhabitats per experiment. Realistic experimental temperatures were determined by EnvLogger temperature data recorded locally in sun-exposed, shaded and rockpool intertidal habitats. For each nine-day experiment, specimens were exposed for six hours daily to four laboratory thermal treatments simulating both ambient conditions and extreme temperature events. These experiments were designed to test the following questions: are premature trochids and littorinids more sensitive to extreme temperatures than adults, and is there a difference in response between species of Boreal and Lusitanian origin sampled from the same geographical region? We identified that the premature intertidal trochid species may not be more thermally sensitive than adults, although premature L. littorina may have a slightly lower lethal heat limit. Survivorship in extreme heatwave air temperatures (40.0–42.9 °C) was lowest for lowshore and highest for highshore species, relating directly to species' vertical shore zonation. There were minimal to zero mortalities in all other thermal treatments. Following stress-induced inactivity in the extreme heatwave air temperature treatment, S. cineraria and P. lineatus specimens all died. In contrast, L. littorea and S. umbilicalis specimens recovered in some instances. Intensifying and more frequent aerial heatwave events occurring unseasonably are likely to cause population declines, local extinctions or subtidal retreat for premature lowshore Boreal intertidal species, influencing recruitment to adult populations, especially where rockpools are not present to provide thermal refugia. Conversely, mid-highshore Lusitanian species are likely to be more resilient to high air temperatures during low tides. Cold spell temperatures did not lethally or sub-lethally impact any juvenile gastropod species, suggesting Lusitanean species will thrive as a result of increasingly milder winters
Impacts and effects of ocean warming on intertidal rocky habitats.
Full text link• Intertidal rocky habitats comprise over 50% of the shorelines of the world, supporting a diversity of marine life and providing extensive ecosystem services worth in the region of US$ 5-10 trillion per year. • They are valuable indicators of the impacts of climate change on the wider marine environment and ecosystems. • Changes in species distributions, abundance and phenology have already been observed around the world in response to recent rapid climate change. • Species-level responses will have considerable ramifications for the structure of communities and trophic interactions, leading to eventual changes in ecosystem functioning (e.g. less primary producing canopy-forming algae in the North-east Atlantic). • Whilst progress is made on the mitigation1 required to achieve goals of a lower-carbon world, much can be done to enhance resilience to climate change. Managing the multitude of other interactive impacts on the marine environment, over which society has greater potential control (e.g. overfishing, invasive non-native species, coastal development, and pollution), will enable adaptation1 in the short and medium term of the next 5-50 years
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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