5,568 research outputs found
Response of Waterbirds to Salt Pond Enhancements and Island Creation in the San Francisco Bay
Historically, San Francisco Bay supported the largest salt pond complex on the Pacific coast of North America, and these areas have been used by large numbers of migrating and wintering waterbirds for more than a century. In 2003, salt ponds in the South San Francisco Bay were purchased with a goal of restoring 50-90% of the 6100 ha of former salt ponds to replace lost tidal marsh habitats. However, a major challenge for the restoration project has been maintaining the abundance of non-breeding waterbirds in a smaller footprint of managed ponds. Thus, in 2009-2010, Pond SF2 was enhanced with 30 islands of two different shapes and water control structures that provided muted tidal flows with shallow water depths predicted to benefit waterbirds. To assess how non-breeding waterbirds responded to these enhancements, a spatial grid (50 m x 50 m) was used to survey SF2 weekly from October to May 2010-2012, and examine waterbird use. Of the 262,932 non-breeding waterbirds observed, only 12-15% used the islands depending on tide. Island size, shape, or both predicted the presence or relative abundance of some foraging guilds, whereas island slope, perimeter, and distance to mudflat did not improve the model\u27s predictions of relative guild abundances. Results indicated that waterbirds were attracted to areas with shallow water depths; however, the constructed islands were not used by a large number of waterbirds
Arboreal twig-nesting ants form dominance hierarchies over nesting resources.
Interspecific dominance hierarchies have been widely reported across animal systems. High-ranking species are expected to monopolize more resources than low-ranking species via resource monopolization. In some ant species, dominance hierarchies have been used to explain species coexistence and community structure. However, it remains unclear whether or in what contexts dominance hierarchies occur in tropical ant communities. This study seeks to examine whether arboreal twig-nesting ants competing for nesting resources in a Mexican coffee agricultural ecosystem are arranged in a linear dominance hierarchy. We described the dominance relationships among 10 species of ants and measured the uncertainty and steepness of the inferred dominance hierarchy. We also assessed the orderliness of the hierarchy by considering species interactions at the network level. Based on the randomized Elo-rating method, we found that the twig-nesting ant species Myrmelachista mexicana ranked highest in the ranking, while Pseudomyrmex ejectus was ranked as the lowest in the hierarchy. Our results show that the hierarchy was intermediate in its steepness, suggesting that the probability of higher ranked species winning contests against lower ranked species was fairly high. Motif analysis and significant excess of triads further revealed that the species networks were largely transitive. This study highlights that some tropical arboreal ant communities organize into dominance hierarchies
Distinguishing Between CDM and MOND: Predictions for the Microwave Background
Two hypothesized solutions of the mass discrepancy problem are cold dark
matter (CDM) and modified Newtonian dynamics (MOND). The virtues and vices of
these very different hypotheses are largely disjoint, making the process of
distinguishing between them very dependent on how we weigh disparate lines of
evidence. One clear difference is the nature of the principal mass constituent
of the universe (CDM or baryons). This difference in the baryon fraction ( vs. 1) should leave a distinctive signature in the spectrum of
fluctuations in the cosmic microwave background. Here I discuss some of the
signatures which should be detectable in the near future. The most promising
appears to be the ratio of the amplitudes of the first two peaks relative to
the intervening trough.Comment: 8 pages, 1 figure, AASTeX. Accepted for publication in ApJ Letter
Fitting the radial acceleration relation to individual SPARC galaxies
Galaxies follow a tight radial acceleration relation (RAR): the acceleration
observed at every radius correlates with that expected from the distribution of
baryons. We use the Markov Chain Monte Carlo method to fit the mean RAR to 175
individual galaxies in the SPARC database, marginalizing over stellar
mass-to-light ratio (), galaxy distance, and disk
inclination. Acceptable fits with astrophysically reasonable parameters are
found for the vast majority of galaxies. The residuals around these fits have
an rms scatter of only 0.057 dex (13). This is in agreement with the
predictions of modified Newtonian dynamics (MOND). We further consider a
generalized version of the RAR that, unlike MOND, permits galaxy-to-galaxy
variation in the critical acceleration scale. The fits are not improved with
this additional freedom: there is no credible indication of variation in the
critical acceleration scale. The data are consistent with the action of a
single effective force law. The apparent universality of the acceleration scale
and the small residual scatter are key to understanding galaxies.Comment: 12 pages, 7 figures, 2 tables. Accepted for publication in A&A. The
same as the first version with typos corrected. A set of 175 figures is
available at http://astroweb.cwru.edu/SPARC
Polarization and Extent of Maser Emission from Late-Type Stars: Support for a Plasma Turbulence Model of Maser Production
The integrated spectrum of OH emission from late-type stars is often
circularly polarized, by as much as 50% in some cases. While the spectra are
partially polarized, the individual maser components revealed by VLBI are much
more so. Using VLBI observations of late-type stars from the literature, we
show that the difference in circular polarization between main lines correlates
with a difference in angular extent for a given object. This is a natural
result if turbulent magnetic fields are causing the masers to be polarized via
the Cook mechanism, and might serve as a good diagnostic for determining which
objects should be investigated in the search for magnetic fields around evolved
stars.Comment: 5 pages, 2 figs ApJL, accepte
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