44 research outputs found
Uncoupling the effects of seed predation and seed dispersal by granivorous ants on plant population dynamics
Secondary seed dispersal is an important plant-animal interaction, which is central to understanding plant population and community dynamics. Very little information is still available on the effects of dispersal on plant demography and, particularly, for ant-seed dispersal interactions. As many other interactions, seed dispersal by animals involves costs (seed predation) and benefits (seed dispersal), the balance of which determines the outcome of the interaction. Separate quantification of each of them is essential in order to understand the effects of this interaction. To address this issue, we have successfully separated and analyzed the costs and benefits of seed dispersal by seed-harvesting ants on the plant population dynamics of three shrub species with different traits. To that aim a stochastic, spatially-explicit individually-based simulation model has been implemented based on actual data sets. The results from our simulation model agree with theoretical models of plant response dependent on seed dispersal, for one plant species, and ant-mediated seed predation, for another one. In these cases, model predictions were close to the observed values at field. Nonetheless, these ecological processes did not affect in anyway a third species, for which the model predictions were far from the observed values. This indicates that the balance between costs and benefits associated to secondary seed dispersal is clearly related to specific traits. This study is one of the first works that analyze tradeoffs of secondary seed dispersal on plant population dynamics, by disentangling the effects of related costs and benefits. We suggest analyzing the effects of interactions on population dynamics as opposed to merely analyzing the partners and their interaction strength
Bees exposed to climate change are more sensitive to pesticides
Bee populations are exposed to multiple stressors, including land-use change, biological invasions, climate change, and pesticide exposure, that may interact synergistically. We analyze the combined effects of climate warming and sublethal insecticide exposure in the solitary bee Osmia cornuta. Previous Osmia studies show that warm wintering temperatures cause body weight loss, lipid consumption, and fat body depletion. Because the fat body plays a key role in xenobiotic detoxification, we expected that bees exposed to climate warming scenarios would be more sensitive to pesticides. We exposed O. cornuta females to three wintering treatments: current scenario (2007–2012 temperatures), near-future (2021–2050 projected temperatures), and distant-future (2051–2080). Upon emergence in spring, bees were orally exposed to three sublethal doses of an insecticide (Closer, a.i. sulfoxaflor; 0, 4.55 and 11.64 ng a.i./bee). We measured the combined effects of wintering and insecticide exposure on phototactic response, syrup consumption, and longevity. Wintering treatment by itself did not affect winter mortality, but body weight loss increased with increasing wintering temperatures. Similarly, wintering treatment by itself hardly influenced phototactic response or syrup consumption. However, bees wintered at the warmest temperatures had shorter longevity, a strong fecundity predictor in Osmia. Insecticide exposure, especially at the high dose, impaired the ability of bees to respond to light, and resulted in reduced syrup consumption and longevity. The combination of the warmest winter and the high insecticide dose resulted in a 70% longevity decrease. Smaller bees, resulting from smaller pollen–nectar provisions, had shorter longevity suggesting nutritional stress may further compromise fecundity in O. cornuta. Our results show a synergistic interaction between two major drivers of bee declines, and indicate that bees will become more sensitive to pesticides under the current global warming scenario. Our findings have important implications for pesticide regulation and underscore the need to consider multiple stressors to understand bee declines
Resonantly Damped Kink Magnetohydrodynamic Waves in a Partially Ionized Filament Thread
Transverse oscillations of solar filament and prominence threads have been
frequently reported. These oscillations have the common features of being of
short period (2-10 min) and being damped after a few periods. Kink
magnetohydrodynamic (MHD) wave modes have been proposed as responsible for the
observed oscillations, whereas resonant absorption in the Alfven continuum and
ion-neutral collisions are the best candidates to be the damping mechanisms.
Here, we study both analytically and numerically the time damping of kink MHD
waves in a cylindrical, partially ionized filament thread embedded in a coronal
environment. The thread model is composed of a straight and thin, homogeneous
filament plasma, with a transverse inhomogeneous transitional layer where the
plasma physical properties vary continuously from filament to coronal
conditions. The magnetic field is homogeneous and parallel to the thread axis.
We find that the kink mode is efficiently damped by resonant absorption for
typical wavelengths of filament oscillations, the damping times being
compatible with the observations. Partial ionization does not affect the
process of resonant absorption, and the filament plasma ionization degree is
only important for the damping for wavelengths much shorter than those
observed. To our knowledge, this is the first time that the phenomenon of
resonant absorption is studied in a partially ionized plasma.Comment: Submitted in Ap
The effect of the solar corona on the attenuation of small-amplitude prominence oscillations. I. Longitudinal magnetic field
Context. One of the typical features shown by observations of solar
prominence oscillations is that they are damped in time and that the values of
the damping times are usually between one and three times the corresponding
oscillatory period. However, the mechanism responsible for the attenuation is
still not well-known. Aims. Thermal conduction, optically thin or thick
radiation and heating are taken into account in the energy equation, and their
role on the attenuation of prominence oscillations is evaluated. Methods. The
dispersion relation for linear non-adiabatic magnetoacoustic waves is derived
considering an equilibrium made of a prominence plasma slab embedded in an
unbounded corona. The magnetic field is orientated along the direction parallel
to the slab axis and has the same strength in all regions. By solving the
dispersion relation for a fixed wavenumber, a complex oscillatory frequency is
obtained, and the period and the damping time are computed. Results. The effect
of conduction and radiation losses is different for each magnetoacoustic mode
and depends on the wavenumber. In the observed range of wavelengths the
internal slow mode is attenuated by radiation from the prominence plasma, the
fast mode by the combination of prominence radiation and coronal conduction and
the external slow mode by coronal conduction. The consideration of the external
corona is of paramount importance in the case of the fast and external slow
modes, whereas it does not affect the internal slow modes at all. Conclusions.
Non-adiabatic effects are efficient damping mechanisms for magnetoacoustic
modes, and the values of the obtained damping times are compatible with those
observed.Comment: Accepted in A&
Global patterns of phosphatase activity in natural soils
Soil phosphatase levels strongly control the biotic pathways of phosphorus (P), an essential element for life, which is often limiting in terrestrial ecosystems. We investigated the influence of climatic and soil traits on phosphatase activity in terrestrial systems using metadata analysis from published studies. This is the first analysis of global measurements of phosphatase in natural soils. Our results suggest that organic P (Porg), rather than available P, is the most important P fraction in predicting phosphatase activity. Structural equation modeling using soil total nitrogen (TN), mean annual precipitation, mean annual temperature, thermal amplitude and total soil carbon as most available predictor variables explained up to 50% of the spatial variance in phosphatase activity. In this analysis, Porg could not be tested and among the rest of available variables, TN was the most important factor explaining the observed spatial gradients in phosphatase activity. On the other hand, phosphatase activity was also found to be associated with climatic conditions and soil type across different biomes worldwide. The close association among different predictors like Porg, TN and precipitation suggest that P recycling is driven by a broad scale pattern of ecosystem productivity capacity
Seismology of Standing Kink Oscillations of Solar Prominence Fine Structures
We investigate standing kink magnetohydrodynamic (MHD) oscillations in a
prominence fine structure modeled as a straight and cylindrical magnetic tube
only partially filled with the prominence material, and with its ends fixed at
two rigid walls representing the solar photosphere. The prominence plasma is
partially ionized and a transverse inhomogeneous transitional layer is included
between the prominence thread and the coronal medium. Thus, ion-neutral
collisions and resonant absorption are the considered damping mechanisms.
Approximate analytical expressions of the period, the damping time, and their
ratio are derived for the fundamental mode in the thin tube and thin boundary
approximations. We find that the dominant damping mechanism is resonant
absorption, which provides damping ratios in agreement with the observations,
whereas ion-neutral collisions are irrelevant for the damping. The values of
the damping ratio are independent of both the prominence thread length and its
position within the magnetic tube, and coincide with the values for a tube
fully filled with the prominence plasma. The implications of our results in the
context of the MHD seismology technique are discussed, pointing out that the
reported short-period (2 - 10 min) and short-wavelength (700 - 8,000 km) thread
oscillations may not be consistent with a standing mode interpretation and
could be related to propagating waves. Finally, we show that the inversion of
some prominence physical parameters, e.g., Alfv\'en speed, magnetic field
strength, transverse inhomogeneity length-scale, etc., is possible using
observationally determined values of the period and damping time of the
oscillations along with the analytical approximations of these quantities.Comment: Accepted for publication in Ap
Swaying threads of a solar filament
From recent high resolution observations obtained with the Swedish 1 m Solar
Telescope in La Palma, we detect swaying motions of individual filament threads
in the plane of the sky. The oscillatory character of these motions are
comparable with oscillatory Doppler signals obtained from corresponding
filament threads. Simultaneous recordings of motions in the line of sight and
in the plane of the sky give information about the orientation of the
oscillatory plane. These oscillations are interpreted in the context of the
magnetohydrodynamic theory. Kink magnetohydrodynamic waves supported by the
thread body are proposed as an explanation of the observed thread oscillations.
On the basis of this interpretation and by means of seismological arguments, we
give an estimation of the thread Alfv\'en speed and magnetic field strength by
means of seismological arguments.Comment: Accepted for publication in the Astrophysical Journa
Improved SOT (Hinode mission) high resolution solar imaging observations
We consider the best today available observations of the Sun free of
turbulent Earth atmospheric effects, taken with the Solar Optical Telescope
(SOT) onboard the Hinode spacecraft. Both the instrumental smearing and the
observed stray light are analyzed in order to improve the resolution. The Point
Spread Function (PSF) corresponding to the blue continuum Broadband Filter
Imager (BFI) near 450 nm is deduced by analyzing i/ the limb of the Sun and ii/
images taken during the transit of the planet Venus in 2012. A combination of
Gaussian and Lorentzian functions is selected to construct a PSF in order to
remove both smearing due to the instrumental diffraction effects (PSF core) and
the large-angle stray light due to the spiders and central obscuration (wings
of the PSF) that are responsible for the parasitic stray light. A
Max-likelihood deconvolution procedure based on an optimum number of iterations
is discussed. It is applied to several solar field images, including the
granulation near the limb. The normal non-magnetic granulation is compared to
the abnormal granulation which we call magnetic. A new feature appearing for
the first time at the extreme- limb of the disk (the last 100 km) is discussed
in the context of the definition of the solar edge and of the solar diameter. A
single sunspot is considered in order to illustrate how effectively the
restoration works on the sunspot core. A set of 125 consecutive deconvolved
images is assembled in a 45 min long movie illustrating the complexity of the
dynamical behavior inside and around the sunspot.Comment: 15 pages, 22 figures, 1 movi
Dissipative instabilities in a partially ionised prominence plasma slab: II. The effect of compressibility
This present study deals with the dissipative instability that appears in a compressible partially ionised plasma slab embedded in a uniform magnetic field, modelling the state of the plasma in solar prominences. In the partially ionised plasma, the dominant dissipative effect is the Cowling resistivity. The regions outside the slab (modelling the solar corona) are fully ionised, and the dominant mechanism of dissipation is viscosity. Analytical solutions to the extended magnetohydrodynamic (MHD) equations are found inside and outside of the slab and solutions are matched at the boundaries of the slab. The dispersion relation is derived and solutions are found analytically in the slender slab limit, while the conditions necessary for the appearance of the instability is investigated numerically for the entire parameter space. Our study is focussed on the effect of the compressibility on the generation and evolution of instabilities. We find that compressibility reduces the threshold of the equilibrium flow, where waves can be unstable, to a level that is comparable to the internal cusp speed, which is of the same order of flow speeds that are currently observed in solar prominences. Our study addresses only the slow waves, as these are the most likely perturbations to become unstable, however the time-scales of the instability are found to be rather large ranging from - seconds. It is determined that the instability threshold is further influenced by the concentration of neutrals and the strength of the viscosity of the corona. Interestingly, these two latter aspects have opposite effects. Our numerical analysis shows that the interplay between the equilibrium flow, neutrals and dispersion can change considerably the nature of waves. Despite employing a simple model, our study confirms the necessity of consideration of neutrals when discussing the stability of prominences under solar conditions
Physics of Solar Prominences: II - Magnetic Structure and Dynamics
Observations and models of solar prominences are reviewed. We focus on
non-eruptive prominences, and describe recent progress in four areas of
prominence research: (1) magnetic structure deduced from observations and
models, (2) the dynamics of prominence plasmas (formation and flows), (3)
Magneto-hydrodynamic (MHD) waves in prominences and (4) the formation and
large-scale patterns of the filament channels in which prominences are located.
Finally, several outstanding issues in prominence research are discussed, along
with observations and models required to resolve them.Comment: 75 pages, 31 pictures, review pape