Spatial patterns in mesic savannas: the local facilitation limit and the role of demographic stochasticity

We propose a model equation for the dynamics of tree density in mesic savannas. It considers long-range competition among trees and the effect of fire acting as a local facilitation mechanism. Despite short-range facilitation is taken to the local-range limit, the standard full spectrum of spatial structures obtained in general vegetation models is recovered. Long-range competition is thus the key ingredient for the development of patterns. The long time coexistence between trees and grass, and how fires affect the survival of trees as well as the maintenance of the patterns is studied. The influence of demographic noise is analyzed. The stochastic system, under the parameter constraints typical of mesic savannas, shows irregular patterns characteristics of realistic situations. The coexistence of trees and grass still remains at reasonable noise intensities.Comment: 12 pages, 7 figure

Online games: a novel approach to explore how partial information influences human random searches

Many natural processes rely on optimizing the success ratio of a search process. We use an experimental setup consisting of a simple online game in which players have to find a target hidden on a board, to investigate the how the rounds are influenced by the detection of cues. We focus on the search duration and the statistics of the trajectories traced on the board. The experimental data are explained by a family of random-walk-based models and probabilistic analytical approximations. If no initial information is given to the players, the search is optimized for cues that cover an intermediate spatial scale. In addition, initial information about the extension of the cues results, in general, in faster searches. Finally, strategies used by informed players turn into non-stationary processes in which the length of each displacement evolves to show a well-defined characteristic scale that is not found in non-informed searches.Comment: 17 pages, 10 figure

Nagel scaling and relaxation in the kinetic Ising model on a n-isotopic chain

The kinetic Ising model on a n-isotopic chain is considered in the framework of Glauber dynamics. The chain is composed of N segments with n sites, each one occupied by a different isotope. Due to the isotopic mass difference, the n spins in each segment have different relaxation times in the absence of the interactions, and consequently the dynamics of the system is governed by multiple relaxation mechanisms. The solution is obtained in closed form for arbitrary n, by reducing the problem to a set of n coupled equations, and it is shown rigorously that the critical exponent z is equal to 2. Explicit results are obtained numerically for any temperature and it is also shown that the dynamic susceptibility satisfies the new scaling (Nagel scaling) proposed for glass-forming liquids. This is in agreement with our recent results (L. L. Goncalves, M. Lopez de Haro, J. Taguena-Martinez and R. B. Stinchcombe, Phys. Rev. Lett. 84, 1507 (2000)), which relate this new scaling function to multiple relaxation processes.Comment: 4 pages, 2 figures, presented at Ising Centennial Colloquium, to be published in the Proceedings (Brazilian Journal of Physics.

From car to bike. Marketing and dialogue as a driver of change

The Paris Climate Agreement has sent a key message to the international community regarding the need to increase efforts to move towards a low-carbon economy and help slow climate change, while underpinning global long-term economic growth and sustainable development. COP 21 recognizes the social, economic and environmental value of voluntary mitigation actions and their co-benefits for adaptation, health and sustainable development. In this framework, the PTP Cycle project, running from 2013 to 2016 and funded by the European Commission through the Intelligent Energy Europe program, introduces a non-market approach through voluntary participation in the adoption of sustainable transport modes such as cycling, based on marketing to potential customers through Personalized Travel Plans. The medium-sized city of Burgos (Spain) and the cities of Ljubljana, Riga, Antwerp and London (boroughs of Haringey and Greenwich) developed a new policy instrument (Personalized Travel Plans) in order to increase bike patronage. Beyond potential savings of CO2, the results show that PTP as a form of Active Mobility Consultancy is a suitable instrument to influence modal shift to public transport, walking and cycling, and to address the challenges of climate change, while fostering sustainable transportation by changing mobility behaviour. These results, matching with the state-of-the-art of studies and pilot applications in other countries, allows deriving differentiated results for medium-size and large urban areas

Minimal mechanisms for vegetation patterns in semiarid regions

The minimal ecological requirements for formation of regular vegetation patterns in semiarid systems have been recently questioned. Against the general belief that a combination of facilitative and competitive interactions is necessary, recent theoretical studies suggest that, under broad conditions, nonlocal competition among plants alone may induce patterns. In this paper, we review results along this line, presenting a series of models that yield spatial patterns when finite-range competition is the only driving force. A preliminary derivation of this type of model from a more detailed one that considers water-biomass dynamics is also presented. Keywords: Vegetation patterns, nonlocal interactionsComment: 8 pages, 4 figure

Vegetation pattern formation in semiarid systems without facilitative mechanisms

Regular vegetation patterns in semiarid ecosystems are believed to arise from the interplay between long-range competition and facilitation processes acting at smaller distances. We show that, under rather general conditions, long-range competition alone may be enough to shape these patterns. To this end we propose a simple, general model for the dynamics of vegetation, which includes only long-range competition between plants. Competition is introduced through a nonlocal term, where the kernel function quantifies the intensity of the interaction. We recover the full spectrum of spatial structures typical of vegetation models that also account for facilitation in addition to competition.Comment: 21 pages, 3 figure