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Search Results: 1 - 10 of 27259 matches for " Martin Stevens "
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The unsuitability of html-based colour charts for estimating animal colours – a comment on Berggren and Meril? (2004)
Martin Stevens, Innes C Cuthill
Frontiers in Zoology , 2005, DOI: 10.1186/1742-9994-2-14
Abstract: Colour matching experiments with printed charts involving 11 subjects showed that the choices made by individuals were significantly different between charts that had exactly the same RGB values, but were produced from different printers. Furthermore, individual matches tended to vary under different lighting conditions. Spectrophotometry of the colour charts showed that the reflectance spectra of the charts varied greatly between printers and that equal steps in RGB space were often far from equal in terms of reflectance on the printed charts.In addition to outlining theoretical criticisms of the use of colour charts, our empirical results show that: individuals vary in their perception of colours, that different printers produce strikingly different results when reproducing what should be the same chart, and that the characteristics of the light irradiating the surface do affect colour perception. Therefore, we urge great caution in the use of colour charts to study animal colour signals. They should be used only as a last resort and in full knowledge of their limitations, with specially produced charts made to high industry standards.The use of colour charts to estimate or categorise the colours of animal signals is a technique utilised in numerous studies [e.g. [1-5]]. In particular, a recent proposal [1] argues that researchers could produce custom-made charts, designed from the HTML colour code (the standard for colour representation on the World Wide Web). In this paper we present theory and data showing why the use of such charts to estimate colour is seriously flawed and only should be undertaken as a last resort.A major problem with using colour charts is one frequently stressed: that human vision differs markedly from most animals other than Old World primates [6-11]. Signals are often aimed at specific animals, and it has long been realised that there is an association between the evolution of a particular signal and the receivers' visual system [12], an
Color change and camouflage in juvenile shore crabs Carcinus maenas
Martin Stevens,Alice E. Lown
Frontiers in Ecology and Evolution , 2014, DOI: 10.3389/fevo.2014.00014
Abstract: Camouflage is perhaps the most widespread anti-predator defense in nature, with many different types thought to exist. Of these, resembling the general color and pattern of the background (background matching) is likely to be the most common. Background matching can be achieved by adaptation of individual appearance to different habitats or substrates, behavioral choice, and color change. Although the ability to change coloration for camouflage over a period of hours or days is likely to be widely found among animals, few studies have quantified this against different backgrounds. Here, we test whether juvenile shore crabs (Carcinus maenas) are capable of color change for camouflage by placing them on either black or white (experiment 1) or red and green (experiment 2) backgrounds. We find that crabs are capable of significant changes in brightness, becoming lighter on white backgrounds and darker on black backgrounds. Using models of predator (avian) vision, we show that these differences are large enough in many individuals to lead to perceptible changes in appearance. Furthermore, comparisons of crabs with the backgrounds show that changes are likely to lead to significant improvements in camouflage and potentially reduced detection probabilities. Crabs underwent some changes on the red and green backgrounds, but visual modeling indicated that these changes were very small and unlikely to be detectable. Our experiment shows that crabs are able to adjust their camouflage by changes in brightness over a period of hours, and that this could influence detection probability by predators.
A Quantitative, Non-Destructive Methodology for Habitat Characterisation and Benthic Monitoring at Offshore Renewable Energy Developments
Emma V. Sheehan,Timothy F. Stevens,Martin J. Attrill
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0014461
Abstract: Following governments' policies to tackle global climate change, the development of offshore renewable energy sites is likely to increase substantially over coming years. All such developments interact with the seabed to some degree and so a key need exists for suitable methodology to monitor the impacts of large-scale Marine Renewable Energy Installations (MREIs). Many of these will be situated on mixed or rocky substrata, where conventional methods to characterise the habitat are unsuitable. Traditional destructive sampling is also inappropriate in conservation terms, particularly as safety zones around (MREIs) could function as Marine Protected Areas, with positive benefits for biodiversity. Here we describe a technique developed to effectively monitor the impact of MREIs and report the results of its field testing, enabling large areas to be surveyed accurately and cost-effectively. The methodology is based on a high-definition video camera, plus LED lights and laser scale markers, mounted on a “flying array” that maintains itself above the seabed grounded by a length of chain, thus causing minimal damage. Samples are taken by slow-speed tows of the gear behind a boat (200 m transects). The HD video and randomly selected frame grabs are analysed to quantify species distribution. The equipment was tested over two years in Lyme Bay, UK (25 m depth), then subsequently successfully deployed in demanding conditions at the deep (>50 m) high-energy Wave Hub site off Cornwall, UK, and a potential tidal stream energy site in Guernsey, Channel Islands (1.5 ms?1 current), the first time remote samples from such a habitat have been achieved. The next stage in the monitoring development process is described, involving the use of Remote Operated Vehicles to survey the seabed post-deployment of MREI devices. The complete methodology provides the first quantitative, relatively non-destructive method for monitoring mixed-substrate benthic communities beneath MPAs and MREIs pre- and post-device deployment.
The effects of topical sodium cromoglicate on itch and flare in human skin induced by intradermal histamine: a randomised double-blind vehicle controlled intra-subject design trial
Alan M Edwards, Michael T Stevens, Martin K Church
BMC Research Notes , 2011, DOI: 10.1186/1756-0500-4-47
Abstract: SCG was introduced into the skin of healthy volunteers both by iontophoresis and by topical application using a new 4% cutaneous emulsion (Altoderm?). The skin was then challenged with intradermal histamine. Measurements were made of severity of itch, size of wheal and flare and change in blood fluxSCG significantly reduced the severity of itch (P = 0.0045) and flare (P = 0.0143) when delivered by iontophoresis. SCG 4% cutaneous emulsion significantly reduced severity of itch (P = 0.024) and flare (P = 0.015) in atopic subjects. Trend analysis showed increasing effect on itch with increased concentrations of SCG, which was significant (P = 0.046). There were no effects on wheal or blood flux.Topically applied SCG, administered in a new cutaneous emulsion base, significantly reduced the itch and flare caused by intradermal histamine. The effect was greatest in atopic subjects and increased with the concentration of SCG in the emulsion.ISRCTN35671014Itch is a prominent feature of many skin diseases, particularly atopic dermatitis and cutaneous mastocytosis. Itch can be triggered by local, systemic, peripheral or central stimuli. The transmission of itch to the brain is the function of a sub-population of the dense nerve network in the skin, unmyelinated C-neurons, which are histamine sensitive [1]. Intradermal injection of histamine into human skin results in a wheal, flare, erythema and itch. It therefore represents a useful model for investigating treatments that might reduce itch severity.Sodium cromoglicate (SCG), a chromone developed in the 1960's as an inhaled powder for the treatment of asthma [2] has subsequently been used for the treatment of allergic rhinitis, allergic conjunctivitis, food allergy and systemic mastocytosis. A number of studies have investigated the effect of topically applied SCG in atopic dermatitis [3-7]. Although variable effects have been reported, probably because of the hydrophilic nature of SCG that limits its penetration in intact sk
The function of animal ‘eyespots’: conspicuousness but not eye mimicry is key
Martin STEVENS,Abi CANTOR,Julia GRAHAM,Isabel S. WINNEY
Current Zoology , 2009,
Abstract: Many animals are marked with conspicuous circular features often called ‘eyespots’, which intimidate predators, preventing or halting an attack. It has long been assumed that eyespots work by mimicking the eyes of larger animals, but recent experiments have indicated that conspicuousness and contrast is important in eyespot function, and not eye mimicry. We undertake two further experiments to distinguish between the conspicuousness and mimicry hypotheses, by using artificial prey presented to wild avian predators in the field. In experiment 1, we test if eyespot effectiveness depends on the marking shape (bar or circle) and arrangement (eye-like and non-eye-like positions). We find no difference between shapes or arrangement; all spots were equally effective in scaring birds. In experiment 2, we test if the often yellow and black colors of eyespots mimic the eyes of birds of prey. We find no effect of shape, and no advantage to yellow and black spots over non-eye-like but equally conspicuous colors. The consistent finding is that eyespot function lies in being a conspicuous signal to predators, and not necessarily due to eye mimicry [Current Zoology 55 (5): –2009].
Ontology Design Patterns for bio-ontologies: a case study on the Cell Cycle Ontology
Aranguren Mikel Ega?a,Antezana Erick,Kuiper Martin,Stevens Robert
BMC Bioinformatics , 2008, DOI: 10.1186/1471-2105-9-s5-s1
Abstract: Background Bio-ontologies are key elements of knowledge management in bioinformatics. Rich and rigorous bio-ontologies should represent biological knowledge with high fidelity and robustness. The richness in bio-ontologies is a prior condition for diverse and efficient reasoning, and hence querying and hypothesis validation. Rigour allows a more consistent maintenance. Modelling such bio-ontologies is, however, a difficult task for bio-ontologists, because the necessary richness and rigour is difficult to achieve without extensive training. Results Analogous to design patterns in software engineering, Ontology Design Patterns are solutions to typical modelling problems that bio-ontologists can use when building bio-ontologies. They offer a means of creating rich and rigorous bio-ontologies with reduced effort. The concept of Ontology Design Patterns is described and documentation and application methodologies for Ontology Design Patterns are presented. Some real-world use cases of Ontology Design Patterns are provided and tested in the Cell Cycle Ontology. Ontology Design Patterns, including those tested in the Cell Cycle Ontology, can be explored in the Ontology Design Patterns public catalogue that has been created based on the documentation system presented (http://odps.sourceforge.net/). Conclusions Ontology Design Patterns provide a method for rich and rigorous modelling in bio-ontologies. They also offer advantages at different development levels (such as design, implementation and communication) enabling, if used, a more modular, well-founded and richer representation of the biological knowledge. This representation will produce a more efficient knowledge management in the long term.
Defeating Crypsis: Detection and Learning of Camouflage Strategies
Jolyon Troscianko, Alice E. Lown, Anna E. Hughes, Martin Stevens
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0073733
Abstract: Camouflage is perhaps the most widespread defence against predators in nature and an active area of interdisciplinary research. Recent work has aimed to understand what camouflage types exist (e.g. background matching, disruptive, and distractive patterns) and their effectiveness. However, work has almost exclusively focused on the efficacy of these strategies in preventing initial detection, despite the fact that predators often encounter the same prey phenotype repeatedly, affording them opportunities to learn to find those prey more effectively. The overall value of a camouflage strategy may, therefore, reflect both its ability to prevent detection by predators and resist predator learning. We conducted four experiments with humans searching for hidden targets of different camouflage types (disruptive, distractive, and background matching of various contrast levels) over a series of touch screen trials. As with previous work, disruptive coloration was the most successful method of concealment overall, especially with relatively high contrast patterns, whereas potentially distractive markings were either neutral or costly. However, high contrast patterns incurred faster decreases in detection times over trials compared to other stimuli. In addition, potentially distractive markings were sometimes learnt more slowly than background matching markings, despite being found more readily overall. Finally, learning effects were highly dependent upon the experimental paradigm, including the number of prey types seen and whether subjects encountered targets simultaneously or sequentially. Our results show that the survival advantage of camouflage strategies reflects both their ability to avoid initial detection (sensory mechanisms) and predator learning (perceptual mechanisms).
Color contrast and stability as key elements for effective warning signals
Lina María Arenas,Jolyon Troscianko,Martin Stevens
Frontiers in Ecology and Evolution , 2014, DOI: 10.3389/fevo.2014.00025
Abstract: Vivid warning signals (aposematism) have evolved repeatedly throughout the animal kingdom. However, relatively few studies consider what makes an effective signal, in terms of preventing attack and promoting avoidance learning by predators. Signal form varies substantially among and sometimes within species, but there has also been apparent convergence on relatively few main color types. We aimed to determine why warning signals often combine red, orange, yellow, and black colors, and specifically to determine whether these colors provide highly salient and reliable visual signals under a range of environmental conditions. Using digital image analysis, we modeled ladybird (ladybug) coloration to an avian visual system. We calculated the contrast of several different ladybird species against an average green background, based on predicted opponent color channel responses in bird vision. Our results suggest that longwave colors (i.e., red, orange) are more contrasting than colors such as blue, against green natural backgrounds. Moreover, these colors yield relatively unchanging (stable) signals throughout the day and under different weather conditions. These analyses show how aposematic signals have evolved under selection to be more effective by being more conspicuous and reliable to the visual system of their potential avian predators.
Innovations in Leadership Development: Centering Communities of Color  [PDF]
Ann Curry-Stevens
Open Journal of Leadership (OJL) , 2018, DOI: 10.4236/ojl.2018.74016
Abstract: With innovative funding from a large local foundation, communities of color in Portland, Oregon developed an array of leadership programs to serve communities of color. This article shares the models they developed, including overviews of curriculum, theories of change, and concrete evidence-based gains achieved by the programs. Innovations include a leadership model that is rooted in community leadership, and the emergence of community priorities to guide the programs, alongside culturally-specific programs that are effective in reaching and supporting the participation of emerging and existing leaders of color. Community priorities included advocacy engagement that resulted in achieving real gains during the yearlong program, and preparing leaders to engage in racial equity work in public and institutional policy after graduation. Highlighted are the distinct assets of culturally specific programs that were perceived to be responsible for achieving significant gains. Conclusions emphasize the importance of culturally specific leadership programs for reaching and centering leaders of color and the ways that such investments hold potential to lead equity efforts in the community and in organizations. Avenues for strengthening programs and their evaluation conclude the article.
A Novel Behavioral Fish Model of Nociception for Testing Analgesics
Ana D. Correia,Sérgio R. Cunha,Martin Scholze,E. Don Stevens
Pharmaceuticals , 2011, DOI: 10.3390/ph4040665
Abstract: Pain is a major symptom in many medical conditions, and often interferes significantly with a person’s quality of life. Although a priority topic in medical research for many years, there are still few analgesic drugs approved for clinical use. One reason is the lack of appropriate animal models that faithfully represent relevant hallmarks associated with human pain. Here we propose zebrafish ( Danio rerio) as a novel short-term behavioral model of nociception, and analyse its sensitivity and robustness. Firstly, we injected two different doses of acetic acid as the noxious stimulus. We studied individual locomotor responses of fish to a threshold level of nociception using two recording systems: a video tracking system and an electric biosensor (the MOBS system). We showed that an injection dose of 10% acetic acid resulted in a change in behavior that could be used to study nociception. Secondly, we validated our behavioral model by investigating the effect of the analgesic morphine. In time-course studies, first we looked at the dose-response relationship of morphine and then tested whether the effect of morphine could be modulated by naloxone, an opioid antagonist. Our results suggest that a change in behavioral responses of zebrafish to acetic acid is a reasonable model to test analgesics. The response scales with stimulus intensity, is attenuated by morphine, and the analgesic effect of morphine is blocked with naloxone. The change in behavior of zebrafish associated with the noxious stimulus can be monitored with an electric biosensor that measures changes in water impedance.
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