From fiddler crabs to humans, animals perform repetitive displays showing neuromotor skill and vigour. Consistent repetition of identical notes (vocal consistency) facilitates the assessment of ...neuromotor skills and is important in communication in birds. Most birdsong research has focused on song diversity as a signal of individual quality, which seems contradictory as repetition is extremely common in most species. Here we show that consistent repetition within songs is positively correlated with reproductive success in male blue tits (Cyanistes caeruleus). A playback experiment shows that females are sexually aroused by male songs with high levels of vocal consistency, which also peaks seasonally during the fertile period of the female, supporting the role of vocal consistency in mate choice. Male vocal consistency also increases with subsequent repetitions of the same song type (a warm-up effect) which conflicts with the fact that females habituate to repeated song, showing decreased arousal. Importantly, we find that switching song types elicits significant dishabituation within the playback, supporting the habituation hypothesis as an evolutionary mechanism driving song diversity in birds. An optimal balance between repetition and diversity may explain the singing style of many bird species and displays of other animals.
The design and function of birds' nests Mainwaring, Mark C.; Hartley, Ian R.; Lambrechts, Marcel M. ...
Ecology and evolution,
October 2014, Letnik:
4, Številka:
20
Journal Article
Recenzirano
Odprti dostop
All birds construct nests in which to lay eggs and/or raise offspring. Traditionally, it was thought that natural selection and the requirement to minimize the risk of predation determined the design ...of completed nests. However, it is becoming increasingly apparent that sexual selection also influences nest design. This is an important development as while species such as bowerbirds build structures that are extended phenotypic signals whose sole purpose is to attract a mate, nests contain eggs and/or offspring, thereby suggesting a direct trade‐off between the conflicting requirements of natural and sexual selection. Nest design also varies adaptively in order to both minimize the detrimental effects of parasites and to create a suitable microclimate for parents and developing offspring in relation to predictable variation in environmental conditions. Our understanding of the design and function of birds' nests has increased considerably in recent years, and the evidence suggests that nests have four nonmutually exclusive functions. Consequently, we conclude that the design of birds' nests is far more sophisticated than previously realized and that nests are multifunctional structures that have important fitness consequences for the builder/s.
All birds construct nests in which to lay eggs and/or raise offspring. Traditionally, it was thought that natural selection and the requirement to minimize the risk of predation determined nest‐building behaviors and the design of completed nests. However, it is becoming increasingly apparent that sexual selection, ectoparasitism, and environmental conditions also influence nest design.
Electricity market reforms have pursued two goals, both aimed at increasing economic efficiency. The first is to ensure that suppliers minimize costs. The second is to make prices more reflective of ...marginal costs. We use data from Texas to examine whether post-reform retail prices have better reflected wholesale prices, and whether reform has reduced retailer costs. We find clear evidence of both outcomes in competitive market areas but not in non-competitive areas supplied by municipally-owned utilities or co-operatives.
Display omitted
•Greater political control allows more deviations between prices and marginal costs.•Competitive area residential and commercial prices better reflect costs.•Residential margins declined in competitive but not non-competitive areas.•More commercial to residential cross-subsidization in non-competitive areas
Microcavity polaritons are composite half-light half-matter quasiparticles, which have recently been demonstrated to exhibit rich physical properties, such as non-equilibrium condensation, parametric ...scattering and superfluidity. At the same time, polaritons have important advantages over photons for information processing, because their excitonic component leads to weaker diffraction and stronger interparticle interactions, implying, respectively, tighter localization and lower powers for nonlinear functionality. Here, we present the first experimental observations of bright polariton solitons in a strongly coupled semiconductor microcavity. The polariton solitons are shown to be micrometre-scale localized non-diffracting wave packets with a corresponding broad spectrum in momentum space. Unlike the solitons known in Bose condensed atomic gases, they are non-equilibrium and rely on a balance between losses and external pumping. Microcavity polariton solitons are excited on picosecond timescales, and thus have further benefits for information processing over light-only solitons in semiconductor cavity lasers, which have nanosecond response times.
Many models of slow, dense granular flows assume that the internal stresses are independent of the shearing rate. In contrast, logarithmic rate dependence is found in solid-on-solid friction, ...geological settings and elsewhere. Here we investigate the rate dependence of stress in a slowly sheared two-dimensional system of photoelastic disks, in which we are able to determine forces on the granular scale. We find that the mean (time-averaged) stress displays a logarithmic dependence on the shear rate for plastic (irreversible) deformations. However, there is no perceivable dependence on the driving rate for elastic (reversible) deformations, such as those that occur under moderate repetitive compression. Increasing the shearing rate leads to an increase in the strength of the force network and stress fluctuations. Qualitatively, this behaviour resembles the changes associated with an increase in density. Increases in the shearing rate also lead to qualitative changes in the distributions of stress build-up and relaxation events. If shearing is suddenly stopped, stress relaxations occur with a logarithmic functional form over long timescales. This slow collective relaxation of the stress network provides a mechanism for rate-dependent strengthening.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Data on the location and extent of protected areas, ecosystems, and species’ distributions are essential for determining gaps in biodiversity protection and identifying future conservation ...priorities. However, these data sets always come with errors in the maps and associated metadata. Errors are often overlooked in conservation studies, despite their potential negative effects on the reported extent of protection of species and ecosystems. We used 3 case studies to illustrate the implications of 3 sources of errors in reporting progress toward conservation objectives: protected areas with unknown boundaries that are replaced by buffered centroids, propagation of multiple errors in spatial data, and incomplete protected‐area data sets. As of 2010, the frequency of protected areas with unknown boundaries in the World Database on Protected Areas (WDPA) caused the estimated extent of protection of 37.1% of the terrestrial Neotropical mammals to be overestimated by an average 402.8% and of 62.6% of species to be underestimated by an average 10.9%. Estimated level of protection of the world's coral reefs was 25% higher when using recent finer‐resolution data on coral reefs as opposed to globally available coarse‐resolution data. Accounting for additional data sets not yet incorporated into WDPA contributed up to 6.7% of additional protection to marine ecosystems in the Philippines. We suggest ways for data providers to reduce the errors in spatial and ancillary data and ways for data users to mitigate the effects of these errors on biodiversity assessments. Efectos de Errores y Vacíos en Conjuntos de Datos Espaciales sobre la Evaluación del Progreso de la Conservación
Cardiopulmonary exercise testing (CPET) is increasingly used in the preoperative assessment of patients undergoing major surgery. The objective of this study was to investigate whether CPET can ...identify patients at risk of reduced survival after abdominal aortic aneurysm (AAA) repair.
Prospectively collected data from consecutive patients who underwent CPET before elective open or endovascular AAA repair (EVAR) at two tertiary vascular centres between January 2007 and October 2012 were analysed. A symptom-limited maximal CPET was performed on each patient. Multivariable Cox proportional hazards regression modelling was used to identify risk factors associated with reduced survival.
The study included 506 patients with a mean age of 73.4 (range 44–90). The majority (82.6%) were men and most (64.6%) underwent EVAR. The in-hospital mortality was 2.6%. The median follow-up was 26 months. The 3-year survival for patients with zero or one sub-threshold CPET value ( V˙O2 at AT<10.2 ml kg−1 min−1, peak V˙O2<15 ml kg−1 min−1 or V˙E/V˙CO2 at AT>42) was 86.4% compared with 59.9% for patients with three sub-threshold CPET values. Risk factors independently associated with survival were female sex hazard ratio (HR)=0.44, 95% confidence interval (CI) 0.22–0.85, P=0.015, diabetes (HR=1.95, 95% CI 1.04–3.69, P=0.039), preoperative statins (HR=0.58, 95% CI 0.38–0.90, P=0.016), haemoglobin g dl−1 (HR=0.84, 95% CI 0.74–0.95, P=0.006), peak V˙O2<15 ml kg−1 min−1 (HR=1.63, 95% CI 1.01–2.63, P=0.046), and V˙E/V˙CO2 at AT>42 (HR=1.68, 95% CI 1.00–2.80, P=0.049).
CPET variables are independent predictors of reduced survival after elective AAA repair and can identify a cohort of patients with reduced survival at 3 years post-procedure. CPET is a potentially useful adjunct for clinical decision-making in patients with AAA.
Worldwide, invasive species are a leading driver of environmental change across terrestrial, marine, and freshwater environments and cost billions of dollars annually in ecological damages and ...economic losses. Resources limit invasive-species control, and planning processes are needed to identify cost-effective solutions. Thus, studies are increasingly considering spatially variable natural and socioeconomic assets (e.g., species persistence, recreational fishing) when planning the allocation of actions for invasive-species management. There is a need to improve understanding of how such assets are considered in invasive-species management. We reviewed over 1600 studies focused on management of invasive species, including flora and fauna. Eighty-four of these studies were included in our final analysis because they focused on the prioritization of actions for invasive species management. Forty-five percent (n = 38) of these studies were based on spatial optimization methods, and 35% (n = 13) accounted for spatially variable assets. Across all 84 optimization studies considered, 27% (n = 23) explicitly accounted for spatially variable assets. Based on our findings, we further explored the potential costs and benefits to invasive species management when spatially variable assets are explicitly considered or not. To include spatially variable assets in decision-making processes that guide invasive-species management there is a need to quantify environmental responses to invasive species and to enhance understanding of potential impacts of invasive species on different natural or socioeconomic assets. We suggest these gaps could be filled by systematic reviews, quantifying invasive species impacts on native species at different periods, and broadening sources and enhancing sharing of knowledge. A nivel mundial, las especies invasoras son un conductor importante del cambio ambiental en los ecosistemas terrestres, marinos y de agua dulce y cuestan anualmente billones de dólares en daños ecológicos y pérdidas económicas. Los recursos limitan el control de las especies invasoras y laplaneación de procesos es necesaria para identificar soluciones rentables. Por esto, los estudios cada vez consideran más los activos naturales espacialmente variables y socioeconómicos (p. ej.: la persistencia de especies, pesca recreativa) cuando se planea la asignación de acciones para el manejo de especies invasoras. Hay una necesidad por mejorar el entendimiento de cómo dichos activos están considerados en el manejo de especies invasoras. Revisamos más de 1600 estudios enfocados en el manejo de especies invasoras, incluyendo a la flora y fauna. Ochenta y cuatro de estos estudios estuvieron incluidos en nuestro análisis final porque están enfocados en la priorización de acciones para el manejo de especies invasoras. El 45% (n = 38) de estos estudios estuvo basado en los métodos de optimización espacial, y el 35% (n = 13) representó los activos espacialmente variables. En todos los 84 estudios de optimización considerados, el 27% (n = 23) justificaba explícitamente los activos espacialmente variables. Con base en nuestros hallazgos, exploramos los costos y beneficios potenciales para el manejo de especies invasoras cuando los activos espadalmente variables estén considerados explícitamente o no. Para incluir los activos espadalmente variables en los procesos de toma de decisiones que guían el manejo de especies invasoras hay una necesidad de cuantificar las respuestas ambientales a las especies invasoras y de mejorar el entendimiento de los impactos potenciales de las especies invasoras en diferentes activos naturales o socioeconómicos. Sugerimos que estos vacíos podrían llenarse con revisiones sistemáticas, la cuantificadón de los impactos de las especies invasoras sobre las especies nativas en diferentes periodos, y la ampliación de las fuentes y la mejora de las formas para compartir el conocimiento.
We propose a method of simultaneously calibrating the radial distortion function of a camera and the other internal calibration parameters. The method relies on the use of a planar (or, ...alternatively, nonplanar) calibration grid which is captured in several images. In this way, the determination of the radial distortion is an easy add-on to the popular calibration method proposed. The method is entirely noniterative and, hence, is extremely rapid and immune to the problem of local minima. Our method determines the radial distortion in a parameter-free way, not relying on any particular radial distortion model. This makes it applicable to a large range of cameras from narrow-angle to fish-eye lenses. The method also computes the center of radial distortion, which, we argue, is important in obtaining optimal results. Experiments show that this point may be significantly displaced from the center of the image or the principal point of the camera.
A key challenge in aquatic restoration efforts is documenting locations where ecological connectivity is disrupted in water bodies that are dammed or crossed by roads (road crossings). To prioritize ...actions aimed at restoring connectivity, we argue that there is a need for systematic inventories of these potential barriers at regional and national scales. Here, we address this limitation for the North American Great Lakes basin by compiling the best available spatial data on the locations of dams and road crossings. Our spatial database documents 38 times as many road crossings as dams in the Great Lakes basin, and case studies indicate that, on average, only 36% of road crossings in the area are fully passable to fish. It is therefore essential that decision makers account for both road crossings and dams when attempting to restore aquatic ecosystem connectivity. Given that road crossing structures are commonly upgraded as part of road maintenance, many opportunities exist to restore connections within aquatic ecosystems at minimal added cost by ensuring upgrade designs permit water flow and the passage of fish and other organisms. Our findings highlight the necessity for improved dam and road crossing inventories that traverse political boundaries to facilitate the restoration of aquatic ecosystem connectivity from local to global scales.
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