Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session F10: Focus Session: Evolutionary and Ecological Dynamics II |
Hide Abstracts |
Sponsoring Units: DBIO GSNP Chair: Pankaj Mehta, Boston University Room: 201 |
Tuesday, March 4, 2014 8:00AM - 8:36AM |
F10.00001: Environmental vs. demographic variability in stochastic lattice predator-prey models Invited Speaker: Uwe C. Tauber In contrast to the neutral population cycles of the deterministic mean-field Lotka-Volterra rate equations, including spatial structure and stochastic noise in models for predator-prey interactions yields complex spatio-temporal structures associated with long-lived erratic population oscillations. Environmental variability in the form of quenched spatial randomness in the predation rates results in more localized activity patches. Population fluctuations in rare favorable regions in turn cause a remarkable increase in the asymptotic densities of both predators and prey [1]. Very intriguing features are found when variable interaction rates are affixed to individual particles rather than lattice sites. Stochastic dynamics with demographic variability in conjunction with inheritable predation efficiencies generate non-trivial time evolution for the predation rate distributions, yet with overall essentially neutral optimization [2].\\[4pt] [1] U. Dobramysl and U.C.T., Phys. Rev. Lett. {\bf 101}, 258102 (2008);\\[0pt] [2] U. Dobramysl and U.C.T., Phys. Rev. Lett. {\bf 110}, 048105 (2013); J. Stat. Mech. P10001 (2013). [Preview Abstract] |
Tuesday, March 4, 2014 8:36AM - 8:48AM |
F10.00002: Stochastic recruitment leads to symmetry breaking in foraging populations Tommaso Biancalani, Louise Dyson, Alan McKane When an ant colony is faced with two identical equidistant food sources, the foraging ants are found to concentrate more on one source than the other. Analogous symmetry-breaking behaviours have been reported in various population systems, (such as queueing or stock market trading) suggesting the existence of a simple universal mechanism. Past studies have neglected the effect of demographic noise and required rather complicated models to qualitatively reproduce this behaviour. I will show how including the effects of demographic noise leads to a radically different conclusion. The symmetry-breaking arises solely due to the process of recruitment and ceases to occur for large population sizes. The latter fact provides a testable prediction for a real system. [Preview Abstract] |
Tuesday, March 4, 2014 8:48AM - 9:00AM |
F10.00003: Ising-like patterns of spatial synchrony in population biology Andrew Noble, Alan Hastings, Jon Machta Systems of coupled dynamical oscillators can undergo a phase transition between synchronous and asynchronous phases. In the case of coupled map lattices, the spontaneous symmetry breaking of a temporal-phase order parameter is known to exhibit Ising-like critical behavior. Here, we investigate a noisy coupled map motivated by the study of spatial synchrony in ecological populations far from the extinction threshold. Ising-like patterns of criticality, as well as spinodal decomposition and homogeneous nucleation, emerge from the nonlinear interactions of environmental fluctuations in habitat quality, local density-dependence in reproduction, and dispersal. In the mean-field limit, the correspondence to the Ising model is exact: the fixed points of our dynamical system are given by the equation of state for Weiss mean-field theory under an appropriate mapping of parameters. We have strong evidence that a quantitative correspondence persists, both near and far from the critical point, in the presence of fluctuations. Our results provide a formal connection between equilibrium statistical physics and population biology. [Preview Abstract] |
Tuesday, March 4, 2014 9:00AM - 9:12AM |
F10.00004: A Computational Approach to Competitive Range Expansions Markus F. Weber, Gabriele Poxleitner, Elke Hebisch, Erwin Frey, Madeleine Opitz Bacterial communities represent complex and dynamic ecological systems. Environmental conditions and microbial interactions determine whether a bacterial strain survives an expansion to new territory. In our work, we studied competitive range expansions in a model system of three \textit{Escherichia coli} strains. In this system, a colicin producing strain competed with a colicin resistant, and with a colicin sensitive strain for new territory. Genetic engineering allowed us to tune the strains' growth rates and to study their expansion in distinct ecological scenarios (with either cyclic or hierarchical dominance). The control over growth rates also enabled us to construct and to validate a predictive computational model of the bacterial dynamics. The model rested on an agent-based, coarse-grained description of the expansion process and we conducted independent experiments on the growth of single-strain colonies for its parametrization. Furthermore, the model considered the long-range nature of the toxin interaction between strains. The integration of experimental analysis with computational modeling made it possible to quantify how the level of biodiversity depends on the interplay between bacterial growth rates, the initial composition of the inoculum, and the toxin range. [Preview Abstract] |
Tuesday, March 4, 2014 9:12AM - 9:24AM |
F10.00005: The effects of psammophilous plants on sand dune dynamics Golan Bel, Yosef Ashkenazy Sand dune dynamics involve physical processes in many temporal and spatial scales. Many physical and mathematical models have been developed to explain the interesting patterns of sand dunes. While many works have focused on the formation and patterns of sand dunes, the observed bi-stability of fixed and active sand dunes under the same climatic conditions has received little attention. Many of the models considered different types of sand dune cover (affecting dune activity); however, despite their important role in dune dynamics, to our knowledge, psammophilous plants (special plants that flourish in moving sand environments) have never been incorporated into mathematical models of sand dunes. Here, we propose a non-linear physical model for the role of psammophilous plants in the dynamics of sand dunes. The model exhibits complex bifurcation diagrams and dynamics, which explain observed phenomena, and predicts new dune stabilization scenarios. [Preview Abstract] |
Tuesday, March 4, 2014 9:24AM - 9:36AM |
F10.00006: The fate of complex ecologies: How do species organize? An exact method Ahmed Roman, Michel Pleimling Complex ecology models present a bridge between far from equilibrium physics and biology of populations. The May-Leonard, Rock-Paper-Scissor and Lotka-Volterra models have been extensively studied in an attempt to understand the dynamics of finite but large populations. In this talk we present a new theoretical technique which predicts the dynamics of these models for any complex ecology with interactions similar to the aforementioned models. This method has applications to real-world systems as it presents a simple method to predict correlations among two or more species in a complex ecology. We apply this method to the models mentioned and show that exact agreement between predictions and Monte-Carlo simulation data is obtained. This method could be applied to a wide variety of problems from economics to biology and game theory. [Preview Abstract] |
Tuesday, March 4, 2014 9:36AM - 9:48AM |
F10.00007: Collapse of biodiversity in fractured metacommunities Charles Fisher, Pankaj Mehta The increasing threat to global biodiversity from climate change, habitat destruction, and other anthropogenic factors motivates the search for features that increase the resistance of ecological communities to destructive disturbances. Recently, Gibson et al (\emph{Science} 2013) observed that the damming of the Khlong Saeng river in Thailand caused a rapid collapse of biodiversity in the remaining tropical forests. Using a theoretical model that maps the distribution of coexisting species in an ecological community to a disordered system of Ising spins, we show that fracturing a metacommunity by inhibiting species dispersal leads to a collapse in biodiversity in the constituent local communities. The biodiversity collapse can be modeled as a diffusion on a rough energy landscape, and the resulting estimate for the rate of extinction highlights the role of species functional diversity in maintaining biodiversity following a disturbance. [Preview Abstract] |
Tuesday, March 4, 2014 9:48AM - 10:00AM |
F10.00008: Flow-driven Delocalization of Populations with Heterogeneous Growth Rates Thiparat Chotibut, David Nelson, Sauro Succi Growth in controlled laboratory environments such as a Petri dish can be used to study the spatial evolutionary dynamics of microorganisms. However, natural populations often grow up in heterogeneous environments with spatially varying growth rates, and can be subjected to fluid advection as well. Using lattice Boltzmann simulations, we study single species population dynamics subject to constant flows under heterogeneous growth conditions. We show that quenched random growth rates lead to localized growth niches even in the presence of a background fluid flow. Non-equilibrium steady states when the flow velocity is weak exhibit a mixture of localized high-density growth niches and a low-density background mass distribution influenced by extended states of the linearized growth operator. At sufficiently strong advection, however, the growth niches suddenly delocalize to form elongated parallel streaks of order the system size along the flow direction. We discuss the localized and delocalized growth eigenfunctions, as well as a phase transition characterized by a diverging correlation length in the flow direction. [Preview Abstract] |
Tuesday, March 4, 2014 10:00AM - 10:12AM |
F10.00009: Correlation between stability and resilience in multiple deteriorating environments Lei Dai, Kirill Korolev, Jeff Gore The recovery rate and the basin of attraction are two important properties that describe the local and global stability of dynamical systems. The idea that loss of stability (i.e. slower recovery) may indicate loss of resilience (i.e. shrinking size of basin of attraction), especially in the context of providing warning signals as a system is close to bifurcations, has been demonstrated before transitions in many systems, such as ecosystems, the climate, neurons and power grids. However, most empirical studies focus on the observation of warning signals with respect to a particular type of environmental change. Here we measure the stability-resilience relationship of laboratory microbial populations in different deteriorating environments (e.g. increasing death rate, nutrient limitation, etc.). We found that the loss of stability is correlated with loss of resilience before population collapsed in multiple scenarios of deterioration, but the warning signals increased with variable levels under different drivers. We mapped out the relationship between stability and resilience by tuning three drivers and also evaluated possible scenarios of environmental change where the positive correlation between the recovery rate and the basin of attraction may break down. Our results suggest the correlation between stability and resilience can be utilized to assess the fragility of dynamical systems under environmental changes; however, the stability-resilience relationship can be complex and will limit our assessment when multiple drivers are involved. [Preview Abstract] |
Tuesday, March 4, 2014 10:12AM - 10:24AM |
F10.00010: ABSTRACT WITHDRAWN |
Tuesday, March 4, 2014 10:24AM - 10:36AM |
F10.00011: Coarsening and biodiversity in cyclically competing species Ben Intoy, Michel Pleimling When four species compete stochastically in a cyclic way, the formation of two teams of mutually neutral partners is observed. We study through numerical simulations the extinction processes that can take place in this system both in the well mixed case as well as on different types of lattices [1]. The different routes to extinction are revealed by the probability distribution of the domination time, i.e. the time needed for one team to fully occupy the system. If swapping is allowed between neutral partners, then the probability distribution is dominated by very long-lived states where a few very large domains persist, each domain being occupied by a mix of individuals from species that form one of the teams. Many aspects of the possible extinction scenarios are lost when only considering averaged quantities as for example the mean domination time. We also discuss some results for a model where species, that compete in Rock-Paper-Scissor fashion, have mixed strategies rather than pure strategies. We compare the case with mixed strategy to the pure strategy case and look at similarities and differences.\\[0.2cm] [1] B. Intoy and M. Pleimling, J. Stat. Mech (2013) P08011. [Preview Abstract] |
Tuesday, March 4, 2014 10:36AM - 10:48AM |
F10.00012: Escaping an infestation of parasites by outrunning them: insights from a simple stochastic model Jiajia Dong, Brian Skinner, Nyles Breecher, Beate Schmittmann, Royce K.P. Zia Coexistence of multiple species abounds in ecological systems as a consequence of various interactions. Unlike predator-prey, the latter is not killed by the former in a parasite-host system. We study a simple lattice model, in which parasites wander randomly and die, giving birth only when they land on a square with the host. For a stationary host with certain boundary conditions, the stochastic process can be solved and the results match well to Monte Carlo simulations. In non-trivial stationary states, the characteristics of the ``parasite-cloud'' around the host are well understood. If the host moves with uniform velocity, solving the problem becomes much more challenging. Instead, we consider a stationary host with parasites performing \emph{biased} diffusion, for which our theoretical predictions (with no fitting parameters) also agree with simulation results. In the appropriate continuum limit, the two processes are identical but interesting differences emerge in our lattice model. The most notable phenomenon is that the stationary parasite population generally increases with the bias, reaching a maximum before vanishing at some critical value. These and other features will be illustrated by examples with realistic Verhulst factors, which model finite carrying capacities. [Preview Abstract] |
Tuesday, March 4, 2014 10:48AM - 11:00AM |
F10.00013: The Structure of Fitness Landscapes in Antibiotic-Resistant Bacteria Barrett Deris, Minsu Kim, Zhongge Zhang, Hiroyuki Okano, Rutger Hermsen, Jeff Gore, Terence Hwa To predict the emergence of antibiotic resistance, quantitative relations must be established between the fitness of drug-resistant organisms and the molecular mechanisms conferring resistance. We have investigated E. coli strains expressing resistance to translation-inhibiting antibiotics. We show that resistance expression and drug inhibition are linked in a positive feedback loop arising from an innate, global effect of drug-inhibited growth on gene expression. This feedback leads generically to plateau-shaped fitness landscapes and concomitantly, for strains expressing at least moderate degrees of drug resistance, gives rise to an abrupt drop in growth rates of cultures at threshold drug concentrations. A simple quantitative model of bacterial growth based on this innate feedback accurately predicts experimental observations without ad hoc parameter fitting. We describe how drug-inhibited growth rate and the threshold drug concentration (the minimum inhibitory concentration, or MIC) depend on the few biochemical parameters that characterize the molecular details of growth inhibition and drug resistance (e.g., the drug--target dissociation constant). And finally, we discuss how these parameters can shape fitness landscapes to determine evolutionary dynamics and evolvability. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700