1,058 research outputs found
A possible dearth of hot gas in galaxy groups at intermediate redshift
We examine the X-ray luminosity of galaxy groups in the CNOC2 survey, at
redshifts 0.1 < z < 0.6. Previous work examining the gravitational lensing
signal of the CNOC2 groups has shown that they are likely to be genuine,
gravitationally bound objects. Of the 21 groups in the field of view of the
EPIC-PN camera on XMM-Newton, not one was visible in over 100 ksec of
observation, even though three of the them have velocity dispersions high
enough that they would easily be visible if their luminosities scaled with
their velocity dispersions in the same way as nearby groups' luminosities
scale. We consider the possibility that this is due to the reported velocity
dispersions being erroneously high, and conclude that this is unlikely. We
therefore find tentative evidence that groups at intermediate redshift are
underluminous relative to their local cousins.Comment: 16 pages, 5 figures, reference added in section 1, typos corrected,
published in Ap
Habitable Climates: The Influence of Eccentricity
In the outer regions of the habitable zone, the risk of transitioning into a
globally frozen "snowball" state poses a threat to the habitability of planets
with the capacity to host water-based life. We use a one-dimensional energy
balance climate model (EBM) to examine how obliquity, spin rate, orbital
eccentricity, and ocean coverage might influence the onset of such a snowball
state. For an exoplanet, these parameters may be strikingly different from the
values observed for Earth. Since, for constant semimajor axis, the annual mean
stellar irradiation scales with (1-e^2)^(-1/2), one might expect the greatest
habitable semimajor axis (for fixed atmospheric composition) to scale as
(1-e^2)^(-1/4). We find that this standard ansatz provides a reasonable lower
bound on the outer boundary of the habitable zone, but the influence of
obliquity and ocean fraction can be profound in the context of planets on
eccentric orbits. For planets with eccentricity 0.5, our EBM suggests that the
greatest habitable semimajor axis can vary by more than 0.8 AU (78%!) depending
on obliquity, with higher obliquity worlds generally more stable against
snowball transitions. One might also expect that the long winter at an
eccentric planet's apoastron would render it more susceptible to global
freezing. Our models suggest that this is not a significant risk for Earth-like
planets around Sun-like stars since such planets are buffered by the thermal
inertia provided by oceans covering at least 10% of their surface. Since
planets on eccentric orbits spend much of their year particularly far from the
star, such worlds might turn out to be especially good targets for direct
observations with missions such as TPF-Darwin. Nevertheless, the extreme
temperature variations achieved on highly eccentric exo-Earths raise questions
about the adaptability of life to marginally or transiently habitable
conditions.Comment: References added, text and figures updated, accepted by Ap
Habitable Climates
According to the standard liquid-water definition, the Earth is only
partially habitable. We reconsider planetary habitability in the framework of
energy-balance models, the simplest seasonal models in physical climatology, to
assess the spatial and temporal habitability of Earth-like planets. We quantify
the degree of climatic habitability of our models with several metrics of
fractional habitability. Previous evaluations of habitable zones may have
omitted important climatic conditions by focusing on close Solar System
analogies. For example, we find that model pseudo-Earths with different
rotation rates or different land-ocean fractions have fractional habitabilities
that differ significantly from that of the Earth itself. Furthermore, the
stability of a planet's climate against albedo-feedback snowball events
strongly impacts its habitability. Therefore, issues of climate dynamics may be
central in assessing the habitability of discovered terrestrial exoplanets,
especially if astronomical forcing conditions are different from the moderate
Solar System cases.Comment: Accepted by ApJ. Several references added. 41 pages, 11 figures, 2
table
Habitable Climates: The Influence of Obliquity
Extrasolar terrestrial planets with the potential to host life might have
large obliquities or be subject to strong obliquity variations. We revisit the
habitability of oblique planets with an energy balance climate model (EBM)
allowing for dynamical transitions to ice-covered snowball states as a result
of ice-albedo feedback. Despite the great simplicity of our EBM, it captures
reasonably well the seasonal cycle of global energetic fluxes at Earth's
surface. It also performs satisfactorily against a full-physics climate model
of a highly oblique Earth-like planet, in an unusual regime of circulation
dominated by heat transport from the poles to the equator. Climates on oblique
terrestrial planets can violate global radiative balance through much of their
seasonal cycle, which limits the usefulness of simple radiative equilibrium
arguments. High obliquity planets have severe climates, with large amplitude
seasonal variations, but they are not necessarily more prone to global snowball
transitions than low obliquity planets. We find that terrestrial planets with
massive CO2 atmospheres, typically expected in the outer regions of habitable
zones, can also be subject to such dynamical snowball transitions. Some of the
snowball climates investigated for CO2-rich atmospheres experience partial
atmospheric collapse. Since long-term CO2 atmospheric build-up acts as a
climatic thermostat for habitable planets, partial CO2 collapse could limit the
habitability of such planets. A terrestrial planet's habitability may thus
depend sensitively on its short-term climatic stability.Comment: Minor changes, references added. 34 pages, 13 figures, accepted by
Ap
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Factors Affecting Incubation Patterns and Sex Roles of Black Oystercatchers in Alaska
Studies examining the effects of human disturbance on avian parental behavior and reproductive
success are fundamental to bird conservation. However, many such studies fail to also consider the influence of
natural threats, a variable environment, and parental roles. Our work examines interactive relationships of cyclical
(time of day, tide, temperature, seasonality) and stochastic (natural/human disturbance) processes with incubation
patterns (attendance, bout lengths, recess rates) of the Black Oystercatcher (Haematopus bachmani), a shorebird
of conservation concern. We used 24-hr-per-day video monitoring of 13 molecularly sexed breeding pairs to
systematically examine incubation, revealing previously undocumented information that may inform conservation
practices for the genus. Seven of 22 video-monitored nests failed, primarily from egg depredation by nocturnal
mammals. Analyses of 3177 hr of video footage indicated a near doubling of incubation-bout lengths at night,
corresponding to the increased risk of nighttime egg predation. Females had higher overall nest attendance (54%
vs. 42%) and longer mean incubation bouts than did males (88 min vs. 73 min). Uninterrupted incubation bouts
were over twice as long as bouts interrupted by disturbance. Incubating males departed nests substantially more
frequently because of nest-area disturbances than did females in one but not both years of our study. Our findings
suggest that the sexes incubate in different but complementary patterns, facilitating efficient egg care in a dynamic
environment with several nest threats. We emphasize the importance of considering natural influences when human
threats to shorebird reproductive behavior and success are evaluated.Keywords: Black Oystercatcher, Disturbance, Incubation behavior, Prince William Sound, sex roles, Video monitoring, Nest failure, Haematopu
Implanted Satellite Transmitters Affect Sea Duck Movement Patterns at Short and Long Timescales
Studies of the effects of transmitters on wildlife often focus on survival. However, sublethal behavioral changes resulting from radio-marking have the potential to affect inferences from telemetry data and may vary based on individual and environmental characteristics. We used a long-term, multi-species tracking study of sea ducks to assess behavioral patterns at multiple temporal scales following implantation of intracoelomic satellite transmitters. We applied state-space models to assess short-term behavioral patterns in 476 individuals with implanted satellite transmitters, as well as comparing breeding site attendance and migratory phenology across multiple years after capture. In the short term, our results suggest an increase in dispersive behavior immediately following capture and transmitter implantation; however, behavior returned to seasonally average patterns within ~5 days after release. Over multiple years, we found that breeding site attendance by both males and females was depressed during the first breeding season after radio-marking relative to subsequent years, with larger relative decreases in breeding site attendance among males than females. We also found that spring and breeding migrations occurred later in the first year after radio-marking than in subsequent years. Across all behavioral effects, the severity of behavioral change often varied by species, sex, age, and capture season. We conclude that, although individuals appear to adjust relatively quickly (i.e. within 1 week) to implanted satellite transmitters, changes in breeding phenology may occur over the longer term and should be considered when analyzing and reporting telemetry data
Spatially Explicit Network Analysis Reveals Multi‐Species Annual Cycle Movement Patterns of Sea Ducks
Conservation of long‐distance migratory species poses unique challenges. Migratory connectivity, that is, the extent to which groupings of individuals at breeding sites are maintained in wintering areas, is frequently used to evaluate population structure and assess use of key habitat areas. However, for species with complex or variable annual cycle movements, this traditional bimodal framework of migratory connectivity may be overly simplistic. Like many other waterfowl, sea ducks often travel to specific pre‐ and post‐breeding sites outside their nesting and wintering areas to prepare for migration by feeding extensively and, in some cases, molting their flight feathers. These additional migrations may play a key role in population structure, but are not included in traditional models of migratory connectivity. Network analysis, which applies graph theory to assess linkages between discrete locations or entities, offers a powerful tool for quantitatively assessing the contributions of different sites used throughout the annual cycle to complex spatial networks. We collected satellite telemetry data on annual cycle movements of 672 individual sea ducks of five species from throughout eastern North America and the Great Lakes. From these data, we constructed a multi‐species network model of migratory patterns and site use over the course of breeding, molting, wintering, and migratory staging. Our results highlight inter‐ and intra‐specific differences in the patterns and complexity of annual cycle movement patterns, including the central importance of staging and molting sites in James Bay, the St. Lawrence River, and southern New England to multi‐species annual cycle habitat linkages, and highlight the value of Long‐tailed Ducks (Calengula haemalis) as an umbrella species to represent the movement patterns of multiple sea duck species. We also discuss potential applications of network migration models to conservation prioritization, identification of population units, and integrating different data streams
Unexpected diversity in socially synchronized rhythms of shorebirds
The behavioural rhythms of organisms are thought to be under strong selection, influenced by the rhythmicity of the environment. Such behavioural rhythms are well studied in isolated individuals under laboratory conditions, but free-living individuals have to temporally synchronize their activities with those of others, including potential mates, competitors, prey and predators. Individuals can temporally segregate their daily activities (for example, prey avoiding predators, subordinates avoiding dominants) or synchronize their activities (for example, group foraging, communal defence, pairs reproducing or caring for offspring). The behavioural rhythms that emerge from such social synchronization and the underlying evolutionary and ecological drivers that shape them remain poorly understood. Here we investigate these rhythms in the context of biparental care, a particularly sensitive phase of social synchronization where pair members potentially compromise their individual rhythms. Using data from 729 nests of 91 populations of 32 biparentally incubating shorebird species, where parents synchronize to achieve continuous coverage of developing eggs, we report remarkable within-and between-species diversity in incubation rhythms. Between species, the median length of one parent's incubation bout varied from 1-19 h, whereas period length-the time in which a parent's probability to incubate cycles once between its highest and lowest value-varied from 6-43 h. The length of incubation bouts was unrelated to variables reflecting energetic demands, but species relying on crypsis (the ability to avoid detection by other animals) had longer incubation bouts than those that are readily visible or who actively protect their nest against predators. Rhythms entrainable to the 24-h light-dark cycle were less prevalent at high latitudes and absent in 18 species. Our results indicate that even under similar environmental conditions and despite 24-h environmental cues, social synchronization can generate far more diverse behavioural rhythms than expected from studies of individuals in captivity. The risk of predation, not the risk of starvation, may be a key factor underlying the diversity in these rhythms.</p
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