Non-Hermitian Localization and Population Biology

The time evolution of spatial fluctuations in inhomogeneous d-dimensional biological systems is analyzed. A single species continuous growth model, in which the population disperses via diffusion and convection is considered. Time-independent environmental heterogeneities, such as a random distribution of nutrients or sunlight are modeled by quenched disorder in the growth rate. Linearization of this model of population dynamics shows that the fastest growing localized state dominates in a time proportional to a power of the logarithm of the system size. Using an analogy with a Schrodinger equation subject to a constant imaginary vector potential, we propose a delocalization transition for the steady state of the nonlinear problem at a critical convection threshold separating localized and extended states. In the limit of high convection velocity, the linearized growth problem in $d$ dimensions exhibits singular scaling behavior described by a (d-1)-dimensional generalization of the noisy Burgers' equation, with universal singularities in the density of states associated with disorder averaged eigenvalues near the band edge in the complex plane. The Burgers mapping leads to unusual transverse spreading of convecting delocalized populations.Comment: 22 pages, 11 figure

Stochastic models in population biology and their deterministic analogs

In this paper we introduce a class of stochastic population models based on "patch dynamics". The size of the patch may be varied, and this allows one to quantify the departures of these stochastic models from various mean field theories, which are generally valid as the patch size becomes very large. These models may be used to formulate a broad range of biological processes in both spatial and non-spatial contexts. Here, we concentrate on two-species competition. We present both a mathematical analysis of the patch model, in which we derive the precise form of the competition mean field equations (and their first order corrections in the non-spatial case), and simulation results. These mean field equations differ, in some important ways, from those which are normally written down on phenomenological grounds. Our general conclusion is that mean field theory is more robust for spatial models than for a single isolated patch. This is due to the dilution of stochastic effects in a spatial setting resulting from repeated rescue events mediated by inter-patch diffusion. However, discrete effects due to modest patch sizes lead to striking deviations from mean field theory even in a spatial setting.Comment: 47 pages, 9 figure

The Population Biology and Transmission Dynamics of Loa loa

Endemic to Central Africa, loiasis – or African eye worm (caused by the filarial nematode Loa loa) – affects more than 10 million people. Despite causing ocular and systemic symptoms, it has typically been considered a benign condition, only of public health relevance because it impedes mass drug administration-based interventions against onchocerciasis and lymphatic filariasis in co-endemic areas. Recent research has challenged this conception, demonstrating excess mortality associated with high levels of infection, implying that loiasis warrants attention as an intrinsic public health problem. This review summarises available information on the key parasitological, entomological, and epidemiological characteristics of the infection and argues for the mobilisation of resources to control the disease, and the development of a mathematical transmission model to guide deployment of interventions

Implications of fisheries during the spawning season for the sustainable management and recovery of depleted fish stocks: a conceptual framework

Fishing during the spawning season may negatively affects the reproductive potential and reproductive dynamics of exploited fish stocks due to a variety of mechanisms such as the disturbance of the natural spawning behaviour, effects on the age, size and sex composition of the spawning population and effects on the population genetics. The effect may differ between species in relation to the spawning strategy and population dynamic characteristics. Based on first principles of reproductive biology, population biology and fishing methods, a theoretical framework is developed on the effects of fishing during the spawning period. This framework is used to structure a review of the available scientific evidence. Implications of the findings on the recovery of depleted fish stocks and the sustainability of exploitation will be discussed and illustrated for a selection of North Sea fish stocks (flatfish, roundfish and pelagic)

Neurospora from natural populations: Population genomics insights into the Life history of a model microbial Eukaryote

The ascomycete filamentous fungus Neurospora crassa played a historic role in experimental biology and became a model system for genetic research. Stimulated by a systematic effort to collect wild strains initiated by Stanford geneticist David Perkins, the genus Neurospora has also become a basic model for the study of evolutionary processes, speciation, and population biology. In this chapter, we will first trace the history that brought Neurospora into the era of population genomics. We will then cover the major contributions of population genomic investigations using Neurospora to our understanding of microbial biogeography and speciation, and review recent work using population genomics and genome-wide association mapping that illustrates the unique potential of Neurospora as a model for identifying the genetic basis of (potentially adaptive) phenotypes in filamentous fungi. The advent of population genomics has contributed to firmly establish Neurospora as a complete model system and we hope our review will entice biologists to include Neurospora in their research

The contribution of statistical physics to evolutionary biology

Evolutionary biology shares many concepts with statistical physics: both deal with populations, whether of molecules or organisms, and both seek to simplify evolution in very many dimensions. Often, methodologies have undergone parallel and independent development, as with stochastic methods in population genetics. We discuss aspects of population genetics that have embraced methods from physics: amongst others, non-equilibrium statistical mechanics, travelling waves, and Monte-Carlo methods have been used to study polygenic evolution, rates of adaptation, and range expansions. These applications indicate that evolutionary biology can further benefit from interactions with other areas of statistical physics, for example, by following the distribution of paths taken by a population through time.Comment: 18 pages, 3 figures, glossary. Accepted in Trend in Ecology and Evolution (to appear in print in August 2011

An atlas of the growth, mortality and recruitment of Philippine fishes

Growth, Mortality, Recruitment, Size distribution, Population dynamics, Fishery biology, Stock assessment, Length, Philippines, Teleostei

Investigation of parental care in avocets from the perspectives of behavioural ecology and conservation biology

This research encompasses both basic (behavioural ecology) and applied (conservation biology) aspects of the biology of Avocets (Recurvirostra avosetta L.). My central question is whether adoption of alien young can be adaptive for adults and the adopted chicks. I evaluate proximate-level hypotheses by quantifying costs and/or bene�ts of both adopters and adoptees. I observed adoption of alien chicks in 19% of the families in 1998 and 1999. My �rst results suggest that adoption may be adaptive for both the adoptive adult and the adopted chick. This is because adopted chicks were more likely to �edge than their siblings remaining in their own family and the �edging success of the adopter adults' own chicks was higher than that of nonadoptive adults' chicks. In my applied research I collect data on avocet breeding biology to �nd out whether the current population increase in Hungary results from the reproductive output of the Hungarian population or is maintained by an in�ux of birds from coastal populations. I also use these data to design and implement e�ective conservation measures by which to further enhance the Hungarian population of the endangered Avocet. I successfully increased the hatching success of mainland nests by erecting a fence to keep ground predators away. The �edging success of chicks also increased after a predator control in the most a�ected areas. By providing information about the timing of nesting to nature conservation authorities I assured the successful breeding of one �fth of Hungary's avocet population on a �shpond in 1999