Spatial and spatiotemporal variation in metapopulation structure affects population dynamics in a passively dispersing arthropod

The spatial and temporal variation in the availability of suitable habitat within metapopulations determines colonization-extinction events, regulates local population sizes and eventually affects local population and metapopulation stability. Insights into the impact of such a spatiotemporal variation on the local population and metapopulation dynamics are principally derived from classical metapopulation theory and have not been experimentally validated. By manipulating spatial structure in artificial metapopulations of the spider mite Tetranychus urticae, we test to which degree spatial (mainland-island metapopulations) and spatiotemporal variation (classical metapopulations) in habitat availability affects the dynamics of the metapopulations relative to systems where habitat is constantly available in time and space (patchy metapopulations). Our experiment demonstrates that (i) spatial variation in habitat availability decreases variance in metapopulation size and decreases density-dependent dispersal at the metapopulation level, while (ii) spatiotemporal variation in habitat availability increases patch extinction rates, decreases local population and metapopulation sizes and decreases density dependence in population growth rates. We found dispersal to be negatively density dependent and overall low in the spatial variable mainland-island metapopulation. This demographic variation subsequently impacts local and regional population dynamics and determines patterns of metapopulation stability. Both local and metapopulation-level variabilities are minimized in mainland-island metapopulations relative to classical and patchy ones

Spatiotemporal variation in precipitation during rainy season in Beibu Gulf, South China, from 1961 to 2016

The spatiotemporal variation in precipitation is an important part of water cycle change, which is directly associatedwith the atmospheric environment and climate change. The high-resolution spatiotemporal change of precipitation is still unknown inmany areas despite its importance. This study analyzed the spatiotemporal variation in precipitation in Beibu Gulf, South China, during the rainy season (fromApril to September) in the period of 1961–2016. The precipitation datawere collected from 12 national standard rain-gauge observation stations. The spatiotemporal variation in precipitation was evaluated with incidence rate and contribution rate of precipitation. The tendency of variations was analyzed using the Mann–Kendall method. The precipitation in the rainy season contributed 80% to the total annual precipitation. In general, there was an exponential decreasing tendency between the precipitation incidence rate and increased precipitation durations. The corresponding contribution rate showed a downward trend after an initial increase. The precipitation incidence rate decreased with the rising precipitation grades, with a gradual increase in contribution rate. The precipitation incidence rate and contribution rate of 7–9 d durations showed the significant downward trends that passed the 95% level of significance test. The results provide a new understanding of precipitation change in the last five decades, which is valuable for predicting future climate change and extreme weather prevention and mitigation

Spatiotemporal variation of taxi demand

The growth of urban areas has made taxi service become increasingly more popular due to its ubiquity and flexibility when compared with, more rigid, public transportation modes. However, in big cities taxi service is still unbalanced, resulting in inefficiencies such as long waiting times and excessive vacant trips. This paper presents an exploratory taxi fleet service analysis and compares two forecast models aimed at predicting the spatiotemporal variation of short-term taxi demand. For this paper, we used a large sample with more than 1 million trips between 2014 and 2017, representing roughly 10% of Lisbon’s fleet. We analysed the spatiotemporal variation between pick-up and drop-off locations and how they are affected by weather conditions and points of interest. More, based on historic data, we built two models to predict the demand, ARIMA and Artificial Neural Network (ANN), and evaluated and compared the performance of both models. This study not only allows the direct comparison of a linear statistical model with a machine learning one, but also leads to a better comprehension of complex interactions surrounding different urban data sources using the taxi service as a probe to better understand urban mobility-on-demand and its needs.info:eu-repo/semantics/publishedVersio

Internal avalanches in a pile of superconducting vortices

Using an array of miniature Hall probes, we monitored the spatiotemporal variation of the internal magnetic induction in a superconducting niobium sample during a slow sweep of external magnetic field. We found that a sizable fraction of the increase in the local vortex population occurs in abrupt jumps. The size distribution of these avalanches presents a power-law collapse on a limited range. In contrast, at low temperatures and low fields, huge avalanches with a typical size occur and the system does not display a well-defined macroscopic critical current.Comment: 5 pages including 5 figure

Spatiotemporal variation of mammalian protein complex stoichiometries

Table reporting the summary of quantified complex members and their regulation. (XLSX 179 kb

Spatiotemporal variation of methane and other trace hydrocarbon concentrations in the valley of Mexico

Mexico City is the world's largest and most polluted urban center. We examine the distribution of methane and other hydrocarbons within the Valley of Mexico, using it as a model for the role developing megacities will play in the next century of geochemical cycling. Seventy-five whole air samples were analyzed with multivariate statistical techniques, including factor analysis using principal components. Methane concentrations are highly variable in space and time, due to air circulations and source distribution. Landfills and open sewage canals are major inputs. Emissions into and out from the valley are modeled to be ∼515 t per day. Per capita emission is 0.01 t per annum per person, consistent with the global average for human related anaerobic generation. Natural gas leaks are small, and likely to be higher in other developing megacities; Mexican natural gas use has been discouraged out of earthquake safety concerns. In contrast, liquefied petroleum gas loss constitutes the major emission of propane and butane estimated at a leak rate of 5-10%. Kyoto and other environmental conventions have ignored methane as a greenhouse gas. Our analysis underscores the need to consider methane and other hydrocarbons, and the urbanization process, in future emission protocols. © 2002 Elsevier Science Ltd. All rights reserved

Spatiotemporal Variation of Risk Preceding Crashes on Freeways

Research into the application of freeway loop detector data for traffic safety has gained momentum in recent years. The incompleteness of data from loop detectors has been a common problem in both the development and the implementation of models. The effect of individual crash precursors, obtained one at a time from a series of loop detectors, on relative risk of crash occurrence was examined through within-stratum one-covariate logistic regression models. The hazard ratio (resultant change in log odds of observing a crash by changing the covariate by one unit) was used as the measure of risk. The log of coefficient of variation in speed expressed as percentage, standard deviation of volume, and average occupancy expressed as percentage were found to be the most significant individual covariates affecting the odds of crash occurrence at a crash site. It was also observed that these parameters calculated at a 5-min level (as opposed to a 3-min level) are more significantly associated with crash occurrence. Hazard ratios corresponding to these covariates observed at a series of stations during six 5-min slices were plotted as a contour variable. The location and time of measurements of these parameters with respect to the location and time of the crash were used as ordinate and abscissa, respectively, in the contour plots depicting spatiotemporal variation of crash risk. The chart corresponding to the log of coefficient of variation in speed demonstrated the most clear patterns of increasing risk as the time and location of the crash are approached. On the basis of these spatiotemporal patterns, a methodology with which to identify freeway black spots in real time is proposed. This information could be used by traffic management centers to take preventive measures to avoid crashes or to prepare law enforcement and emergency vehicles for the impending situation

Spatiotemporal variation in the demography of perennial plants

A major goal of ecological research is to understand how plant populations respond to spatial and temporal variation in environmental conditions. Short-lived species rapidly respond to changes in habitat conditions, but little is known about the effects on the population dynamics of long-lived plants. I analyzed the effects of varying habitat conditions on the population dynamics of two herbaceous perennials. One of the plants, Trifolium montanum, grows in nutrient-poor grasslands in a semi-natural landscape of central Europe, while the other plant, Heliconia metallica, grows in lowland rainforests in Amazonian Peru. During the last decades, changes in land use have resulted in a considerable loss of nutrient-poor grasslands in central Europe. I studied the effects of habitat degradation and fragmentation on the dynamics of the populations of the declining perennial plant Trifolium montanum L. in central Germany using matrix models. To assess the habitat quality in a site, I measured the leaf area index (LAI). The finite growth rate of a population strongly decreased with LAI. In unmanaged sites, population growth was <1, which was mostly due to lower survival and flowering of large plants. Management by clipping rapidly increased population growth because of a higher flowering probability of large plants. The number of seeds per fruithead was not related to LAI, but increased with local density, suggesting pollinator limitation in populations with a low density of flowering plants. In a common garden, the seed production of the offspring decreased with isolation, and in contrast to previous studies, also decreased with size and density of the population of origin. This might be due to increased inbreeding because of pollination between closely related neighboring plants in dense and large populations. In stochastic simulations, the median time to extinction of unmanaged populations of 100 flowering plants was about 50 years. However, small populations though managed were threatened by stochastic extinction and required a minimum number of 60 flowering plants to survive with 95% probability over the next 100 years. However, most populations of T. montanum in central Germany consist of less than 50 flowering plants. Many populations of other perennial plants of semi-natural grasslands might also be doomed because of the low quality of their habitats and their small size. However, the extinction process may take a long time in perennial plants, resulting in an extinction debt. The actual plant diversity of the remnant sites might thus be a misleading indicator of their conservation status. Large areas of tropical rainforests are still shaped by natural processes. Clonal herbs are an important component of the understory of these forests. However, very little is known about the population dynamics of these herbs. In a Peruvian floodplain forest, I analyzed the influence of seasonal and spatial environmental variation on the populations of the clonal herb Heliconia metallica Planchon & Linden ex Hooker over two wet and two dry seasons, using periodic matrix models. All populations increased in size during the wet and decreased during the dry season. Finite annual growth rates of non-flooded populations were 1 in recently formed gaps. The lower growth rate at non-flooded sites was due to lower survival of ramets during the dry season. In stochastic simulations, the extinction risk of the non-flooded populations of H. metallica was high, whereas that of flooded populations was low and decreased with the frequency of gap formation. Seed addition in unoccupied sites increased seedling recruitment, in particular in experimentally disturbed sites. The results indicate that the population dynamics of H. metallica are shaped by the interacting effects of seasonal flooding and of transient canopy gaps. Ramet survival and clonal growth are crucial for the persistence of populations of H. metallica in the forest understory, while the colonization of unoccupied sites is limited by insufficient dispersal of seeds to disturbed sites. The environmental differences between the wet and dry season affected the populations of H. metallica, and all populations decreased in size during the dry season. However, an increase in the length of the dry season has been observed in Amazon rainforests during the last decades. The results of this study suggest that the clonal life form of H. metallica enables populations to persist under variable light conditions, but might not be able to buffer the effects of drought stress during longer dry seasons. Climate change might cause a decrease in the regional abundance of the widespread clonal understory herbs of Amazon rainforests

Macroscopic Equations of Motion for Two Phase Flow in Porous Media

The established macroscopic equations of motion for two phase immiscible displacement in porous media are known to be physically incomplete because they do not contain the surface tension and surface areas governing capillary phenomena. Therefore a more general system of macroscopic equations is derived here which incorporates the spatiotemporal variation of interfacial energies. These equations are based on the theory of mixtures in macroscopic continuum mechanics. They include wetting phenomena through surface tensions instead of the traditional use of capillary pressure functions. Relative permeabilities can be identified in this approach which exhibit a complex dependence on the state variables. A capillary pressure function can be identified in equilibrium which shows the qualitative saturation dependence known from experiment. In addition the new equations allow to describe the spatiotemporal changes of residual saturations during immiscible displacement.Comment: 15 pages, Phys. Rev. E (1998), in prin