Diffusion-driven instabilities and emerging spatial patterns in patchy landscapes

Spatial variation in population densities across a landscape is a feature of many ecological systems, from self-organised patterns on mussel beds to spatially restricted insect outbreaks. It occurs as a result of environmental variation in abiotic factors and/or biotic factors structuring the spatial distribution of populations. However the ways in which abiotic and biotic factors interact to determine the existence and nature of spatial patterns in population density remain poorly understood. Here we present a new approach to studying this question by analysing a predator–prey patch-model in a heterogenous landscape. We use analytical and numerical methods originally developed for studying nearest- neighbour (juxtacrine) signalling in epithelia to explore whether and under which conditions patterns emerge. We find that abiotic and biotic factors interact to promote pattern formation. In fact, we find a rich and highly complex array of coexisting stable patterns, located within an enormous number of unstable patterns. Our simulation results indicate that many of the stable patterns have appreciable basins of attraction, making them significant in applications. We are able to identify mechanisms for these patterns based on the classical ideas of long-range inhibition and short-range activation, whereby landscape heterogeneity can modulate the spatial scales at which these processes operate to structure the populations

Kolumbien - den Frieden gewinnen

Am 23. September 2015 unterzeichneten die kolumbianische Regierung und die Guerillagruppe FARC in Havanna ein Abkommen zur Etablierung einer "Sondergerichtsbarkeit für den Frieden". Damit rücken ein umfassendes Friedensabkommen und die Beendigung des Bürgerkriegs in greifbare Nähe. Das Friedensabkommen und seine Umsetzung müssen den ausgeprägten regionalen Unterschieden in Kolumbien Rechnung tragen. Auch wenn die Gewalt immer wieder die großen Städte erreichte, fand der Krieg vor allem im ländlichen Raum statt. Je nach Präsenz und Verankerung nichtstaatlicher Gewaltakteure sind die Herausforderungen für den Friedensprozess sehr unterschiedlich. Auch die Verfügbarkeit zentraler Ressourcen wie Drogen oder Land spielt eine wichtige Rolle. Das Abkommen zur "Sondergerichtsbarkeit für den Frieden" knüpft rechtlich und inhaltlich eng an vergleichbare Regelungen der Vergangenheit an. Juristisches Neuland ist die zentrale Rolle der Entschädigung der Opfer durch die Täter. Die Umsetzbarkeit wird von der Bewertung kolumbianischer und internationaler Gerichte abhängen. In den letzten Dekaden wurden in Kolumbien zahlreiche Reformen eingeleitet, um den strukturellen Ursachen der Gewalt zu begegnen. Dabei hat sich vor allem die Dezentralisierung als sehr ambivalent erwiesen. Die Aufwertung der Kommunen trug dazu bei, dass die bewaffneten Gruppen starkes Interesse an deren Kontrolle entwickelten. Über sechs Millionen Kolumbianerinnen und Kolumbianer sind intern Vertriebene und haben als Folge der Gewalt all ihr Hab und Gut verloren. Zudem hat der wirtschaftliche Wandel die traditionelle Landwirtschaft in vielen Regionen verdrängt. Diese Entwicklungen lassen sich auch nach Beendigung des Krieges nicht zurückdrehen. Die zentrale Herausforderung der nächsten Monate besteht darin, den Pakt zwischen Regierung und FARC in einen breiten gesellschaftlichen Konsens über die Zukunft des Landes zu übertragen. Während die Verhandlungen international viel Zustimmung erfahren haben, bleibt die öffentliche Meinung in Kolumbien tief gespalten

Dynamics and coexistence in a system with intraguild mutualism

It is a tenet of ecological theory that two competing consumers cannot stably coexist on a single limiting resource in a homogeneous environment. Many mechanisms and processes have since been evoked and studied, empirically and theoretically, to explain species coexistence and the observed biological diversity. Facilitative interactions clearly have the potential to enhance coexistence. Yet, even though mutual facilitation between species of the same guild is widely documented empirically, the subject has received very little theoretical attention. Here, we study one form of intraguild mutualism in the simplest possibly community module of one resource and two consumers. We incorporate mutualism as enhanced consumption in the presence of the other consumers. We find that intraguild mutualism can (a) significantly enhance coexistence of consumers, (b) induce cyclic dynamics, and (c) give rise to a bi-stability (a 'joint' Allee effect) and potentially catastrophic collapse of both consumer species.Fil: Assaneo, María Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física. Laboratorio de Sistemas Dinámicos; ArgentinaFil: Coutinho, Renato Mendes. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Lin, Yangchen. University of Cambridge; Estados UnidosFil: Mantilla, Carlos. Universidad de Carabobo.; VenezuelaFil: Lutscher, Frithjof. University of Ottawa; Canad

Lattice gas cellular automata model for rippling and aggregation in myxobacteria

A lattice-gas cellular automaton (LGCA) model is used to simulate rippling and aggregation in myxobacteria. An efficient way of representing cells of different cell size, shape and orientation is presented that may be easily extended to model later stages of fruiting body formation. This LGCA model is designed to investigate whether a refractory period, a minimum response time, a maximum oscillation period and non-linear dependence of reversals of cells on C-factor are necessary assumptions for rippling. It is shown that a refractory period of 2-3 minutes, a minimum response time of up to 1 minute and no maximum oscillation period best reproduce rippling in the experiments of {\it Myxoccoccus xanthus}. Non-linear dependence of reversals on C-factor is critical at high cell density. Quantitative simulations demonstrate that the increase in wavelength of ripples when a culture is diluted with non-signaling cells can be explained entirely by the decreased density of C-signaling cells. This result further supports the hypothesis that levels of C-signaling quantitatively depend on and modulate cell density. Analysis of the interpenetrating high density waves shows the presence of a phase shift analogous to the phase shift of interpenetrating solitons. Finally, a model for swarming, aggregation and early fruiting body formation is presented

At Home and Abroad: The Use of Denial-of-service Attacks during Elections in Nondemocratic Regimes

In this article, we study the political use of denial-of-service (DoS) attacks, a particular form of cyberattack that disables web services by flooding them with high levels of data traffic. We argue that websites in nondemocratic regimes should be especially prone to this type of attack, particularly around political focal points such as elections. This is due to two mechanisms: governments employ DoS attacks to censor regime-threatening information, while at the same time, activists use DoS attacks as a tool to publicly undermine the government’s authority. We analyze these mechanisms by relying on measurements of DoS attacks based on large-scale Internet traffic data. Our results show that in authoritarian countries, elections indeed increase the number of DoS attacks. However, these attacks do not seem to be directed primarily against the country itself but rather against other states that serve as hosts for news websites from this country.publishe

A graphical theory of competition on spatial resource gradients

Resource competition is a fundamental interaction in natural communities.However little is known about competition in spatial environments where organisms are able to regulate resource distributions. Here, we analyze the competition of two consumers for two resources in a one-dimensional habitat in which the resources are supplied from opposite sides. We show that the success of an invading species crucially depends on the slope of the resource gradients shaped by the resident. Our analysis reveals that parameter combinations which lead to coexistence in a uniform environment may favor alternative stable states in a spatial system, and vice versa. Furthermore, differences in growth rate, mortality or dispersal abilities allow a consumer to coexist stationarily with - or even outcompete - a competitor with lower resource requirements. Applying our theory to a phytoplankton model, we explain shifts in the community structure that are induced by environmental changes

Faster movement in non-habitat matrix promotes range shifts in heterogeneous landscapes

Ecologists often assume that range expansion will be fastest in landscapes composed entirely of the highest‐quality habitat. Theoretical models, however, show that range expansion depends on both habitat quality and habitat‐specific movement rates. Using data from 78 species in 70 studies, we find that animals typically have faster movement through lower‐quality environments (73% of published cases). Therefore, if we want to manage landscapes for range expansion, there is a trade‐off between promoting movement with nonhostile matrix, and promoting population growth with high‐quality habitat. We illustrate how this trade‐off plays out with the use of an exemplar species, the Baltimore checkerspot butterfly. For this species, we calculate that the expected rate of range expansion is fastest in landscapes with ~15% high‐quality habitat. Behavioral responses to nonhabitat matrix have often been documented in animal populations, but rarely included in empirical predictions of range expansion. Considering movement behavior could change land‐planning priorities from focus on high‐quality habitat only to integrating high‐ and low‐quality land cover types, and evaluating the costs and benefits of different matrix land covers for range expansion