The Experts below are selected from a list of 288 Experts worldwide ranked by ideXlab platform
Caren B Cooper - One of the best experts on this subject based on the ideXlab platform.
-
Solar Noon and tactile cues synergistically regulate clutch size a new approach to investigations of avian life history theory
Ibis, 2013Co-Authors: Margaret A Voss, Caren B CooperAbstract:Life-history theory is central to our understanding of the evolutionary processes that drive adaptation. According to life-history theory, a trade-off between reproduction and survival means that organisms cannot maximize both at the same time (Gadgil & Bossert 1970, Charnov & Krebs 1974, Stearns 1976, 1989, Reznick 1985, Morris 1986). As Reznick (1985) stated while reviewing the costs of reproduction, ‘To be the best in all possible worlds is not biologically possible; to be well adapted to even one world requires compromise.’ Throughout the progression of thought in life-history theory, clutch size has been a trait of primary interest. For over half a century, it has been argued that diverse selection pressures operate on clutch size in birds (Ricklefs 2000) so as to optimize it, although the relative importance of each pressure remains unclear. A few examples of competing selection pressures on clutch size include the trade-offs between clutch size and number of clutches in a given year, clutch size and parental care, clutch size and access to food resources, clutch size and parental age, and the list goes on. A vast body of literature demonstrates the extent of these trade-offs and their importance in understanding emergent avian lifehistory patterns, yet we still do not understand how birds regulate or determine clutch size. Although avian clutch size often varies systematically and in predictable ways, we cannot adequately explain the emergent patterns. While investigations have explored possible roles of predation, food availability and seasonality (e.g. Beukeboom et al. 1988, Hochachka 1990, Crick et al. 1993) on variation in clutch size, additional insights may be found by asking how (mechanistically) clutch size is determined, rather than why (evolutionarily). Such a shift in question might change our perception of which traits selection might be acting upon to optimize clutch size. A paper by Sacha Haywood in this issue of Ibis brings us closer to resolving a fundamental problem in identifying the proximate selection pressures regulating clutch size. Haywood’s egg removal experiments with Common Swifts Apus apus nicely demonstrate that the trait (or suite of traits) under selection is not the number of eggs in a clutch, an ordinal trait measured quantitatively, but rather the physiological mechanisms controlling the endpoint of the laying sequence. Haywood presents evidence that there is a specific point in time, approximately Solar Noon on the day the first egg is laid, that plays a decisive role in determining how many subsequent eggs will be produced (Haywood 2013). Haywood builds his argument in two parts. First he explores the possibility that the tactile cue that stops the production of yolky follicles is invariant in its timing. In other words, the production of yolky follicles is halted by the stimulus of the brood patch coming in contact with the first egg laid. Invariance in the timing of this tactile cue means that a second mechanism must come into play to account for the observed variability in egg production. Second, he postulates a role for an internal circadian clock that might govern the ability of ovarian tissue to receive and respond to hormone fluxes, thereby allowing for temporal plasticity in follicular development and eventual disruption. In the case of the Common Swift, this competency to receive the hormonal signal develops over a period of 3–6 h before Solar Noon on the day the first egg is laid, at which point it becomes fully functional. With these two mechanisms, Haywood’s model accounts for variability in clutch size in a species that would otherwise seem to be physiologically constrained to a predetermined number of eggs. A key implication of Haywood’s findings is that the focal point of life-history theory with regard to clutch size might actually be a set of physiological processes and their underlying gene regulation, rather than a single quantitative characteristic (i.e. number of eggs produced). A strong argument for considering physiological processes as the target of selection that subsequently drives life-history trade-offs was outlined by Sinervo and Svensson (1998). Haywood’s study fits this paradigm shift in that it forces us to view clutch size, a common life-history variable, not as a single quantitative trait under selection pressure but rather as the product of several intersecting endocrine feedback loops. Furthermore, his experimental results set the stage for clarification of the differentiation between determinate layers with invariant clutch size and indeterminate layers (variable clutch size). *Corresponding author. Email: mav11@psu.edu
-
Solar Noon and tactile cues synergistically regulate clutch size: a new approach to investigations of avian life‐history theory
Ibis, 2013Co-Authors: Margaret A Voss, Caren B CooperAbstract:Life-history theory is central to our understanding of the evolutionary processes that drive adaptation. According to life-history theory, a trade-off between reproduction and survival means that organisms cannot maximize both at the same time (Gadgil & Bossert 1970, Charnov & Krebs 1974, Stearns 1976, 1989, Reznick 1985, Morris 1986). As Reznick (1985) stated while reviewing the costs of reproduction, ‘To be the best in all possible worlds is not biologically possible; to be well adapted to even one world requires compromise.’ Throughout the progression of thought in life-history theory, clutch size has been a trait of primary interest. For over half a century, it has been argued that diverse selection pressures operate on clutch size in birds (Ricklefs 2000) so as to optimize it, although the relative importance of each pressure remains unclear. A few examples of competing selection pressures on clutch size include the trade-offs between clutch size and number of clutches in a given year, clutch size and parental care, clutch size and access to food resources, clutch size and parental age, and the list goes on. A vast body of literature demonstrates the extent of these trade-offs and their importance in understanding emergent avian lifehistory patterns, yet we still do not understand how birds regulate or determine clutch size. Although avian clutch size often varies systematically and in predictable ways, we cannot adequately explain the emergent patterns. While investigations have explored possible roles of predation, food availability and seasonality (e.g. Beukeboom et al. 1988, Hochachka 1990, Crick et al. 1993) on variation in clutch size, additional insights may be found by asking how (mechanistically) clutch size is determined, rather than why (evolutionarily). Such a shift in question might change our perception of which traits selection might be acting upon to optimize clutch size. A paper by Sacha Haywood in this issue of Ibis brings us closer to resolving a fundamental problem in identifying the proximate selection pressures regulating clutch size. Haywood’s egg removal experiments with Common Swifts Apus apus nicely demonstrate that the trait (or suite of traits) under selection is not the number of eggs in a clutch, an ordinal trait measured quantitatively, but rather the physiological mechanisms controlling the endpoint of the laying sequence. Haywood presents evidence that there is a specific point in time, approximately Solar Noon on the day the first egg is laid, that plays a decisive role in determining how many subsequent eggs will be produced (Haywood 2013). Haywood builds his argument in two parts. First he explores the possibility that the tactile cue that stops the production of yolky follicles is invariant in its timing. In other words, the production of yolky follicles is halted by the stimulus of the brood patch coming in contact with the first egg laid. Invariance in the timing of this tactile cue means that a second mechanism must come into play to account for the observed variability in egg production. Second, he postulates a role for an internal circadian clock that might govern the ability of ovarian tissue to receive and respond to hormone fluxes, thereby allowing for temporal plasticity in follicular development and eventual disruption. In the case of the Common Swift, this competency to receive the hormonal signal develops over a period of 3–6 h before Solar Noon on the day the first egg is laid, at which point it becomes fully functional. With these two mechanisms, Haywood’s model accounts for variability in clutch size in a species that would otherwise seem to be physiologically constrained to a predetermined number of eggs. A key implication of Haywood’s findings is that the focal point of life-history theory with regard to clutch size might actually be a set of physiological processes and their underlying gene regulation, rather than a single quantitative characteristic (i.e. number of eggs produced). A strong argument for considering physiological processes as the target of selection that subsequently drives life-history trade-offs was outlined by Sinervo and Svensson (1998). Haywood’s study fits this paradigm shift in that it forces us to view clutch size, a common life-history variable, not as a single quantitative trait under selection pressure but rather as the product of several intersecting endocrine feedback loops. Furthermore, his experimental results set the stage for clarification of the differentiation between determinate layers with invariant clutch size and indeterminate layers (variable clutch size). *Corresponding author. Email: mav11@psu.edu
Margaret A Voss - One of the best experts on this subject based on the ideXlab platform.
-
Solar Noon and tactile cues synergistically regulate clutch size a new approach to investigations of avian life history theory
Ibis, 2013Co-Authors: Margaret A Voss, Caren B CooperAbstract:Life-history theory is central to our understanding of the evolutionary processes that drive adaptation. According to life-history theory, a trade-off between reproduction and survival means that organisms cannot maximize both at the same time (Gadgil & Bossert 1970, Charnov & Krebs 1974, Stearns 1976, 1989, Reznick 1985, Morris 1986). As Reznick (1985) stated while reviewing the costs of reproduction, ‘To be the best in all possible worlds is not biologically possible; to be well adapted to even one world requires compromise.’ Throughout the progression of thought in life-history theory, clutch size has been a trait of primary interest. For over half a century, it has been argued that diverse selection pressures operate on clutch size in birds (Ricklefs 2000) so as to optimize it, although the relative importance of each pressure remains unclear. A few examples of competing selection pressures on clutch size include the trade-offs between clutch size and number of clutches in a given year, clutch size and parental care, clutch size and access to food resources, clutch size and parental age, and the list goes on. A vast body of literature demonstrates the extent of these trade-offs and their importance in understanding emergent avian lifehistory patterns, yet we still do not understand how birds regulate or determine clutch size. Although avian clutch size often varies systematically and in predictable ways, we cannot adequately explain the emergent patterns. While investigations have explored possible roles of predation, food availability and seasonality (e.g. Beukeboom et al. 1988, Hochachka 1990, Crick et al. 1993) on variation in clutch size, additional insights may be found by asking how (mechanistically) clutch size is determined, rather than why (evolutionarily). Such a shift in question might change our perception of which traits selection might be acting upon to optimize clutch size. A paper by Sacha Haywood in this issue of Ibis brings us closer to resolving a fundamental problem in identifying the proximate selection pressures regulating clutch size. Haywood’s egg removal experiments with Common Swifts Apus apus nicely demonstrate that the trait (or suite of traits) under selection is not the number of eggs in a clutch, an ordinal trait measured quantitatively, but rather the physiological mechanisms controlling the endpoint of the laying sequence. Haywood presents evidence that there is a specific point in time, approximately Solar Noon on the day the first egg is laid, that plays a decisive role in determining how many subsequent eggs will be produced (Haywood 2013). Haywood builds his argument in two parts. First he explores the possibility that the tactile cue that stops the production of yolky follicles is invariant in its timing. In other words, the production of yolky follicles is halted by the stimulus of the brood patch coming in contact with the first egg laid. Invariance in the timing of this tactile cue means that a second mechanism must come into play to account for the observed variability in egg production. Second, he postulates a role for an internal circadian clock that might govern the ability of ovarian tissue to receive and respond to hormone fluxes, thereby allowing for temporal plasticity in follicular development and eventual disruption. In the case of the Common Swift, this competency to receive the hormonal signal develops over a period of 3–6 h before Solar Noon on the day the first egg is laid, at which point it becomes fully functional. With these two mechanisms, Haywood’s model accounts for variability in clutch size in a species that would otherwise seem to be physiologically constrained to a predetermined number of eggs. A key implication of Haywood’s findings is that the focal point of life-history theory with regard to clutch size might actually be a set of physiological processes and their underlying gene regulation, rather than a single quantitative characteristic (i.e. number of eggs produced). A strong argument for considering physiological processes as the target of selection that subsequently drives life-history trade-offs was outlined by Sinervo and Svensson (1998). Haywood’s study fits this paradigm shift in that it forces us to view clutch size, a common life-history variable, not as a single quantitative trait under selection pressure but rather as the product of several intersecting endocrine feedback loops. Furthermore, his experimental results set the stage for clarification of the differentiation between determinate layers with invariant clutch size and indeterminate layers (variable clutch size). *Corresponding author. Email: mav11@psu.edu
-
Solar Noon and tactile cues synergistically regulate clutch size: a new approach to investigations of avian life‐history theory
Ibis, 2013Co-Authors: Margaret A Voss, Caren B CooperAbstract:Life-history theory is central to our understanding of the evolutionary processes that drive adaptation. According to life-history theory, a trade-off between reproduction and survival means that organisms cannot maximize both at the same time (Gadgil & Bossert 1970, Charnov & Krebs 1974, Stearns 1976, 1989, Reznick 1985, Morris 1986). As Reznick (1985) stated while reviewing the costs of reproduction, ‘To be the best in all possible worlds is not biologically possible; to be well adapted to even one world requires compromise.’ Throughout the progression of thought in life-history theory, clutch size has been a trait of primary interest. For over half a century, it has been argued that diverse selection pressures operate on clutch size in birds (Ricklefs 2000) so as to optimize it, although the relative importance of each pressure remains unclear. A few examples of competing selection pressures on clutch size include the trade-offs between clutch size and number of clutches in a given year, clutch size and parental care, clutch size and access to food resources, clutch size and parental age, and the list goes on. A vast body of literature demonstrates the extent of these trade-offs and their importance in understanding emergent avian lifehistory patterns, yet we still do not understand how birds regulate or determine clutch size. Although avian clutch size often varies systematically and in predictable ways, we cannot adequately explain the emergent patterns. While investigations have explored possible roles of predation, food availability and seasonality (e.g. Beukeboom et al. 1988, Hochachka 1990, Crick et al. 1993) on variation in clutch size, additional insights may be found by asking how (mechanistically) clutch size is determined, rather than why (evolutionarily). Such a shift in question might change our perception of which traits selection might be acting upon to optimize clutch size. A paper by Sacha Haywood in this issue of Ibis brings us closer to resolving a fundamental problem in identifying the proximate selection pressures regulating clutch size. Haywood’s egg removal experiments with Common Swifts Apus apus nicely demonstrate that the trait (or suite of traits) under selection is not the number of eggs in a clutch, an ordinal trait measured quantitatively, but rather the physiological mechanisms controlling the endpoint of the laying sequence. Haywood presents evidence that there is a specific point in time, approximately Solar Noon on the day the first egg is laid, that plays a decisive role in determining how many subsequent eggs will be produced (Haywood 2013). Haywood builds his argument in two parts. First he explores the possibility that the tactile cue that stops the production of yolky follicles is invariant in its timing. In other words, the production of yolky follicles is halted by the stimulus of the brood patch coming in contact with the first egg laid. Invariance in the timing of this tactile cue means that a second mechanism must come into play to account for the observed variability in egg production. Second, he postulates a role for an internal circadian clock that might govern the ability of ovarian tissue to receive and respond to hormone fluxes, thereby allowing for temporal plasticity in follicular development and eventual disruption. In the case of the Common Swift, this competency to receive the hormonal signal develops over a period of 3–6 h before Solar Noon on the day the first egg is laid, at which point it becomes fully functional. With these two mechanisms, Haywood’s model accounts for variability in clutch size in a species that would otherwise seem to be physiologically constrained to a predetermined number of eggs. A key implication of Haywood’s findings is that the focal point of life-history theory with regard to clutch size might actually be a set of physiological processes and their underlying gene regulation, rather than a single quantitative characteristic (i.e. number of eggs produced). A strong argument for considering physiological processes as the target of selection that subsequently drives life-history trade-offs was outlined by Sinervo and Svensson (1998). Haywood’s study fits this paradigm shift in that it forces us to view clutch size, a common life-history variable, not as a single quantitative trait under selection pressure but rather as the product of several intersecting endocrine feedback loops. Furthermore, his experimental results set the stage for clarification of the differentiation between determinate layers with invariant clutch size and indeterminate layers (variable clutch size). *Corresponding author. Email: mav11@psu.edu
Joseph M. Piwowar - One of the best experts on this subject based on the ideXlab platform.
-
The effect of cloud and Solar zenith angle on spectral reflectance data collected in the field
2014 IEEE Geoscience and Remote Sensing Symposium, 2014Co-Authors: Patrick J. Bell, Joseph M. PiwowarAbstract:Remote sensing studies of vegetation are frequently supported by in situ spectral reflectance measurements. However, collecting these measurements in the field is frequently expensive, both in terms of time and financial commitments. While it is generally recommended that spectral reflectance measurements are acquired on clear, windless days within 2 hours of Solar Noon, such ideal weather conditions are often illusive, forcing the researcher into a decision whether to abandon their fieldwork or to try and extend their collection activities into less-than-ideal conditions. In this paper we measured the effects of variable atmospheric opacity (i.e. cloud cover) and Solar zenith angles on in situ spectral reflectance measurements and found that, with frequent instrument calibration, it is possible to collect useable spectra.
-
IGARSS - The effect of cloud and Solar zenith angle on spectral reflectance data collected in the field
2014 IEEE Geoscience and Remote Sensing Symposium, 2014Co-Authors: Patrick J. Bell, Joseph M. PiwowarAbstract:Remote sensing studies of vegetation are frequently supported by in situ spectral reflectance measurements. However, collecting these measurements in the field is frequently expensive, both in terms of time and financial commitments. While it is generally recommended that spectral reflectance measurements are acquired on clear, windless days within 2 hours of Solar Noon, such ideal weather conditions are often illusive, forcing the researcher into a decision whether to abandon their fieldwork or to try and extend their collection activities into less-than-ideal conditions. In this paper we measured the effects of variable atmospheric opacity (i.e. cloud cover) and Solar zenith angles on in situ spectral reflectance measurements and found that, with frequent instrument calibration, it is possible to collect useable spectra.
Mateusz Orzechowski - One of the best experts on this subject based on the ideXlab platform.
-
Effects of Soil Surface Irregularities on the Diurnal Variation of Soil Broadband Blue-Sky Albedo
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2015Co-Authors: Jerzy Cierniewski, Arnon Karnieli, Sławomir Królewicz, Jan Piekarczyk, Karolina Lewińska, Alexander Goldberg, Cezary Kazmierowski, Roman Wesolowski, Mateusz OrzechowskiAbstract:This paper quantitatively explores, in terms of roughness indices, the effect of soil surface irregularities on the diurnal variation of the broadband blue-sky albedo of a large range of soil properties. Field studies were carried out on cultivated and uncultivated soil surfaces in Poland and Israel that vary in roughness and brightness. It was found that these irregularities, formed by different agricultural equipment and modified by rain or sprinkler irrigation, can be quantified by two roughness indices. Soil roughness not only affects the overall level of the diurnal variation of the albedo, but also affects the intensity of the diurnal increase from the Solar zenith angle ( ${\thetab_{\mbi s}}$ ) at the local Noon to about $75^\circ - 80^\circ$ . The roughness indices are variables that precisely determine only the albedo at the local Solar Noon of soils with the same color value. If the contents of soil organic carbon (SOC) and calcium carbonate are treated as the dominant variables, combined with one of the indices, these three variables together would significantly describe the albedo at the local Solar Noon of all soil surfaces. The soils, with their high irregularities, showed almost no rising values of albedo at a ${\thetab_{\mbi s}}$ lower than 75 $^\circ$ , while the smooth soil surfaces exhibited a gradual increase of the albedo at these angles. It is concluded that the roughness indices provide sufficient means to accurately describe the diurnal variation of the albedo of a wide range of surfaces, disregarding other soil properties.
-
Effects of Soil Surface Irregularities on the Diurnal Variation of Soil Broadband Blue-Sky Albedo
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2015Co-Authors: Jerzy Cierniewski, Arnon Karnieli, Cezary Kaźmierowski, Sławomir Królewicz, Jan Piekarczyk, Karolina Lewińska, Alexander Goldberg, Roman Wesołowski, Mateusz OrzechowskiAbstract:This paper quantitatively explores, in terms of roughness indices, the effect of soil surface irregularities on the diurnal variation of the broadband blue-sky albedo of a large range of soil properties. Field studies were carried out on cultivated and uncultivated soil surfaces in Poland and Israel that vary in roughness and brightness. It was found that these irregularities, formed by different agricultural equipment and modified by rain or sprinkler irrigation, can be quantified by two roughness indices. Soil roughness not only affects the overall level of the diurnal variation of the albedo, but also affects the intensity of the diurnal increase from the Solar zenith angle (θs) at the local Noon to about 75°- 80°. The roughness indices are variables that precisely determine only the albedo at the local Solar Noon of soils with the same color value. If the contents of soil organic carbon (SOC) and calcium carbonate are treated as the dominant variables, combined with one of the indices, these three variables together would significantly describe the albedo at the local Solar Noon of all soil surfaces. The soils, with their high irregularities, showed almost no rising values of albedo at a θs lower than 75°, while the smooth soil surfaces exhibited a gradual increase of the albedo at these angles. It is concluded that the roughness indices provide sufficient means to accurately describe the diurnal variation of the albedo of a wide range of surfaces, disregarding other soil properties.
Frederic Jacob - One of the best experts on this subject based on the ideXlab platform.
-
derivation of diurnal courses of albedo and reflected Solar irradiance from airborne polder data acquired near Solar Noon
Journal of Geophysical Research, 2005Co-Authors: Frederic Jacob, Albert OliosoAbstract:[1] Knowledge of the diurnal course of land surface albedo is needed for monitoring radiative transfers between soil, vegetation, and atmosphere. These transfers are of interest for crop monitoring, hydrological cycle modeling, weather forecast, and climate modeling. The required absolute accuracy ranges between 0.02 and 0.05. At the present time, it is possible to derive the diurnal course of albedo from geostationary satellites. Sun-synchronous sensors, with higher spatial resolutions, allow retrieving surface radiative properties by both discriminating different types of land cover and capturing the subclass variability. However, the current possibilities for deriving the diurnal course of albedo from Sun-synchronous observations are empirical or mathematically complex. We proposed in this paper a physically based method, which is candidate for operational use along with multiangular Sun-synchronous sensors, under clear-sky conditions. This method uses both reciprocal kernel-driven bidirectional reflectance distribution function (KD BRDF) models and narrowband to broadband (NTB) conversion. It was implemented and validated using the Alpilles-RESEDA database which was collected over agricultural areas. The implementation was performed using the 20 m spatial resolution airborne POLDER data acquired near midday. The validation was conducted using field measurements of albedo, recorded over the diurnal cycle. The retrievals of the diurnal course of albedo were good, with errors ranging from 0.026 to 0.029. Better results were observed for instantaneous values at Solar Noon and times close to satellite overpasses as well as for the daily mean value, with errors ranging between 0.014 and 0.022. Among the selected reciprocal KD BRDF models, Li-Ross systematically provided the best results, regardless of considered albedo product. Further, using instantaneous values at times close to satellite overpasses, in place of the daily mean value, did not yield significant differences, with errors ranging around 0.01. Finally, we assessed the interest of deriving the diurnal course of reflected Solar irradiance by using the several albedo products aforementioned. For the environmental conditions of the Alpilles-RESEDA experiment, the resulting differences were not significant, with accuracies better than 20 W m−2.
