240 research outputs found
Optimal methods for fitting probability distributions to propagule retention time in studies of zoochorous dispersal
Background: Propagule retention time is a key factor in determining propagule dispersal distance and the shape of
“seed shadows”. Propagules dispersed by animal vectors are either ingested and retained in the gut until defecation or
attached externally to the body until detachment. Retention time is a continuous variable, but it is commonly measured
at discrete time points, according to pre-established sampling time-intervals. Although parametric continuous
distributions have been widely fitted to these interval-censored data, the performance of different fitting methods
has not been evaluated. To investigate the performance of five different fitting methods, we fitted parametric probability
distributions to typical discretized retention-time data with known distribution using as data-points either the
lower, mid or upper bounds of sampling intervals, as well as the cumulative distribution of observed values (using
either maximum likelihood or non-linear least squares for parameter estimation); then compared the estimated and
original distributions to assess the accuracy of each method. We also assessed the robustness of these methods to
variations in the sampling procedure (sample size and length of sampling time-intervals).
Results: Fittings to the cumulative distribution performed better for all types of parametric distributions (lognormal,
gamma and Weibull distributions) and were more robust to variations in sample size and sampling time-intervals.
These estimated distributions had negligible deviations of up to 0.045 in cumulative probability of retention times
(according to the Kolmogorov–Smirnov statistic) in relation to original distributions from which propagule retention
time was simulated, supporting the overall accuracy of this fitting method. In contrast, fitting the sampling-interval
bounds resulted in greater deviations that ranged from 0.058 to 0.273 in cumulative probability of retention times,
which may introduce considerable biases in parameter estimates.
Conclusions: We recommend the use of cumulative probability to fit parametric probability distributions to propagule
retention time, specifically using maximum likelihood for parameter estimation. Furthermore, the experimental
design for an optimal characterization of unimodal propagule retention time should contemplate at least 500 recovered
propagules and sampling time-intervals not larger than the time peak of propagule retrieval, except in the tail of
the distribution where broader sampling time-intervals may also produce accurate fitsPeer reviewe
Migratory Birds as Global Dispersal Vectors
Propagule dispersal beyond local scales has been considered rare and unpredictable. However, for many plants, invertebrates, and microbes dispersed by birds, long-distance dispersal (LDD) might be regularly achieved when mediated by migratory movements. Because LDD operates over spatial extents spanning hundreds to thousands of kilometers, it can promote rapid range shifts and determine species distributions. We review evidence supporting this widespread LDD service and propose a conceptual framework for estimating LDD by migratory birds. Although further research and validation efforts are still needed, we show that current knowledge can be used to make more realistic estimations of LDD mediated by regular bird migrations, thus refining current predictions of its ecological and evolutionary consequences.Peer reviewe
Argon assisted chemical vapor deposition of CrO: an efficient process leading to high quality epitaxial films
A comparative study of the structural, microstructural and magnetic
properties of CrO thin films grown onto (110) and (100) TiO rutile
single crystal substrates by chemical vapor deposition (CVD), using CrO as
chromium precursor and either oxygen or argon as carrier gas is presented. Our
results show that growth under argon carrier gas leads to high quality CrO
epilayers with structural and magnetic properties similar to those obtained
using the more standard oxygen carrier gas. Furthermore, we interpret the
larger magnetic coercivity observed for the (110) oriented films in terms of
their microstructure, in particular of the highest strain and edge roughness of
the building structures of the CrO epilayers, which are settled by the
substrate crystallographic orientation.Comment: 27 pages, 2 tables, 8 figure
A synthesis of Eurasian Curlew (Numenius arquata arquata) demography and population viability to inform its management
The European population of Eurasian Curlew Numenius arquata arquata, a nearthreatened
wader subspecies, has undergone pronounced population declines over the
past 30 years. To assess the demography and viability of its global population, we surveyed
studies quantifying demographic rates (productivity and survival) and complemented
this review with new estimates of survival probability at the flyway scale. Then,
using a demographic model, we estimated population growth rates while accounting for
the range of variation of demographic parameters, and compared these estimates
(expected based on demographic rates) with those observed based on population censuses.
Both observed and expected average growth rates were negative but the observed
rates were higher than estimates from demographic models (λ = 0.98–0.99 compared
with 0.85–0.95). This discrepancy implies that there is geographical variation in the
demography of different populations that is not fully covered by current demographic
data, namely unstudied regions with higher productivity. According to our calculations,
at the flyway scale, productivity is currently c. 0.57 fledglings per pair per year, higher
than the average reported productivity of 0.29, but lower than the 0.68 needed to
achieve a stable global population size (λ = 1). Adult survival, estimated at 0.90, was
the most sensitive parameter determining population growth rates, but the low productivity
levels over the last few decades seems to be the most probable cause of population
declines. The negative population growth rates require immediate conservation actions
to preserve adult survival and increase the extremely low productivity in western and
northern European populations to values above 0.68 fledglings per pair per year. We
hope our synthesis on the demographic status of Curlew in Europe will encourage the
collection of more demographic data and allow concrete management goals at the flyway
scale to be established in order to recover the global population of this iconic species.Fédération Nationale des Chasseurs (Grant/Award Number: "FNC-PSN-PR11B-2013")
In Situ AFM Imaging of Adsorption Kinetics of DPPG Liposomes: A Quantitative Analysis of Surface Roughness
IF/00808/2013 (POPH, UE-FSE).
M.R. acknowledges the financial support from the project PTDC/FIS-NAN/0909/2014, FCT, Portugal.The adsorption of intact liposomes on surfaces is of great importance for the development of sensors and drug delivery systems and, also, strongly dependent on the surface roughness where the liposomes are adsorbed. In this paper, we analyzed, by using atomic force microscopy in liquid, the evolution of the morphology of gold surfaces and of poly(allylamine hydrochloride) (PAH) surfaces with different roughness during the adsorption of liposomes prepared with the synthetic phospholipid 1,2-dipalmitoyl-sn-glycero-3-[phospho-rac-(1-glycerol)]. Our results reveal the following. On smooth surfaces of Au only and Au with PAH, the liposomes open and deploy on the substrate, creating a supported-lipid bilayer, with the opening process being faster on the Au/PAH surface. On rough substrates of Au coated with polyelectrolyte multilayers, the liposomes were adsorbed intact on the surface. This was corroborated by power spectral density analysis that demonstrates the presence of superstructures with an average lateral size of 43 and 87 nm, in accordance with two and four times the mean liposome hydrodynamic diameter of about 21 nm. In addition, this work presents an adequate and effective methodology for analysis of adsorption phenomena of liposomes on rough surfaces.preprintepub_ahead_of_prin
Feeding Patterns of Potential West Nile Virus Vectors in South-West Spain
Background: Mosquito feeding behaviour determines the degree of vector–host contact and may have a serious impact on the risk of West Nile virus (WNV) epidemics. Feeding behaviour also interacts with other biotic and abiotic factors that affect virus amplification and transmission.
Methodology/Principal Findings: We identified the origin of blood meals in five mosquito species from three different wetlands in SW Spain. All mosquito species analysed fed with different frequencies on birds, mammals and reptiles. Both
‘mosquito species’ and ‘locality’ explained a similar amount of variance in the occurrence of avian blood meals. However,
‘season of year’ was the main factor explaining the presence of human blood meals. The differences in diet resulted in a marked spatial heterogeneity in the estimated WNV transmission risk. Culex perexiguus, Cx. modestus and Cx. pipiens were the main mosquito species involved in WNV enzootic circulation since they feed mainly on birds, were abundant in
a number of localities and had high vector competence. Cx. perexiguus may also be important for WNV transmission to
horses, as are Cx. pipiens and Cx. theileri in transmission to humans. Estimates of the WNV transmission risk based on mosquito diet, abundance and vector competence matched the results of previous WNV monitoring programs in the area. Our sensitivity analyses suggested that mosquito diet, followed by mosquito abundance and vector competence, are all
relevant factors in understanding virus amplification and transmission risk in the studied wild ecosystems. At some of the
studied localities, the risk of enzootic circulation of WNV was relatively high, even if the risk of transmission to humans and horses was less.
Conclusions/Significance: Our results describe for first time the role of five WNV candidate vectors in SW Spain. Interspecific and local differences in mosquito diet composition has an important effect on the potential transmission risk of WNV to birds, horses and humansPeer reviewe
Avaliação econômica da produção de nim para o uso no controle de Spodoptera frugiperda no milho.
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