The biennial life strategy in a random environment

In a previous paper (J. Math. Biol. 26, 199–215 (1988)) we calculated the mean and variance of the long-run geometric growth rate of a discrete-time population model with two age classes in a random environment. The formula which was used in that paper as the starting point for the computation of the variance represents only the contribution of the one-period variances. Here we supplement these results by a calculation of the exact variance. All qualitative conclusions reached before are unaffected.     

One- and multi-locus multi-allele selection models in a random environment

Summary We deduce conditions for stochastic local stability of general perturbed linear stochastic difference equations widely applicable in population genetics. The findings are adapted to evaluate the stability properties of equilibria in classical one- and multi-locus multi-allele selection models influenced by random temporal variation in selection intensities. As an example of some conclusions and biological interpretations we analyse a special one-locus multi-allele model in more detail.This work was supported in part by Stiftung Volkswagenwerk.     

Selection for biennial life histories in plants

The applicability of traditional models of life-history evolution is restricted because models assume constant environments without density-dependence. In these models the geometric growth rate () of a lineage is the natural choice for the fitness criterion. Because in growing populations is very sensitive to changes in generation time, biennials appear at a disadvantage when compared to species with annual reproduction. We propose an alternative fitness criterion for the situation in which recruitment is limited by both the availability of seeds and the (constant) rate at which safe sites for establishment are created by small-scale disturbances. Under the assumptions of the model the evolutionarily stable strategy is to maximize expected seed production, irrespective of the length of the life cycle. For monocarpic plants, this implies that delay of flowering is favourable if the increased seed production compensates for the death of rosettes.Publication of the Meijendel comité, New series No. 89.Nomenclature follows Heukels & van der Meijden (1983), Flora van Nederland, Wolters Noordhoff, Groningen.We would like to thank Prof. K. Bakker, Dr Nora Croin Michielsen, Dr E. van der Meijden and Dr M. Sabelis for their comments on a number of previous drafts. We are indebted to the Netherlands Foundation for Fundamental Research (B.I.O.N.) and to the Netherlands Organization for the Advancement of Pure Research (Z.W.O.) for research grants to T. J. de Jong and P. G. L. Klinkhamer, and to J. A. J. Metz, respectively.     

The stabilizing effect of a random environment

It is shown that the lottery competition model permits coexistence in a stochastic environment, but not in a constant environment. Conditions for coexistence and competitive exclusion are determined. Analysis of these conditions shows that the essential requirements for coexistence are overlapping generations and fluctuating birth rates which ensure that each species has periods when it is increasing. It is found that a species may persist provided only that it is favored sufficiently by the environment during favorable periods independently of the extent to which the other species is favored during its favorable periods.Coexistence is defined in terms of the stochastic boundedness criterion for species persistence. Using the lottery model as an example this criterion is justified and compared with other persistence criteria. Properties of the stationary distribution of population density are determined for an interesting limiting case of the lottery model and these are related to stochastic boundedness. An attempt is then made to relate stochastic boundedness for infinite population models to the behavior of finite population models.     

The evolution of dispersal in random environment

In this paper we introduce a stochastic model for a population living and migrating between s sites without distinction in the states between residents and immigrants. The evolutionary stable strategies (ESS) is characterized by the maximization of a stochastic growth rate. We obtain that the expectation of reproductive values, normalized by some random quantity, are constant on all sites and that the expectation of the normalized vector population structure is proportional to eigenvector of the dispersion matrix associated to eigenvalue one, which are, in some way, analogous to the results obtained in the deterministic case.     

An epidemic model in a patchy environment

An epidemic model is proposed to describe the dynamics of disease spread among patches due to population dispersal. We establish a threshold above which the disease is uniformly persistent and below which disease-free equilibrium is locally attractive, and globally attractive when both susceptible and infective individuals in each patch have the same dispersal rate. Two examples are given to illustrate that the population dispersal plays an important role for the disease spread. The first one shows that the population dispersal can intensify the disease spread if the reproduction number for one patch is large, and can reduce the disease spread if the reproduction numbers for all patches are suitable and the population dispersal rate is strong. The second example indicates that a population dispersal results in the spread of the disease in all patches, even though the disease can not spread in each isolated patch.     

一类具有随机周期移民扰动的非线性人口发展方程随机周期解的存在唯一性

本文给出了一类具有随机周期移民扰动的非线性m增生人口发展方程随机周期解的存在性和唯一性结论。     

Molecular evolution and polymorphism in a random environment

A model of multi-allelic selection in a random environment, the SAS-CFF model, is examined for compatability with allele frequency and genetic distance data acquired by electrophoresis. The symmetric version of the model tends to predict higher than observed levels of polymorphism unless substantial positive autocorrelations in the environment are postulated. The actual allele frequency configurations observed in nature are in rough agreement with those predicted by the SAS-CFF model. An approximate analysis of the transient properties of the SAS-CFF model shows that, in broad outline, the behavior is quite similar to that of the neutral model.     

Predicting the population dynamics of the house dust mite Dermatophagoides pteronyssinus (Acari: Pyroglyphidae) in response to a constant hygrothermal environment using a model of the mite life cycle

A generalised model of the life cycle of a house dust mite, which can be tailored to any particular species of domestic mite, is presented. The model takes into account the effects of hygrothermal conditions on each life cycle phase. It is used in a computer simulation program, called POPMITE, which, by incorporating a population age structure, is able to predict population dynamics. The POPMITE simulation is adapted to the Dermatophagoides pteronyssinus (Acari: Pyroglyphidae) (DP) mite using published data on the egg development period, total development period, adult longevity, mortality during egg development, mortality during juvenile development, and fecundity of individual DP mites held at a range of constant hygrothermal conditions. An example is given which illustrates how the model functions under constant hygrothermal conditions. A preliminary validation of POPMITE is made by a comparison of the POPMITE predictions with published measurements of population growth of DP mites held at a range constant hygrothermal conditions for 21 days. The POPMITE simulation is used to provide predictions of population growth or decline for a wide range of constant relative humidity and temperature combinations for 30 and 60 days. The adaptation of the model to correctly take account of fluctuating hygrothermal conditions is discussed.     

On linear birth-and-death processes in a random environment

We study the probability of extinction for single-type and multi-type continuous-time linear birth-and-death processes in a finite Markovian environment. The probability of extinction is equal to 1 almost surely if and only if the basic reproduction number \(R_0\) is \(\le 1\) , the key point being to identify a suitable definition of \(R_0\) for such a result to hold.     

Coalescent theory for a completely random mating monoecious population

Consider a large random mating monoecious diploid population that has N individuals in each generation. Let us assume that at time 0 a random sample of ninfinity. It is then possible to obtain a generalization of coalescent theory for haploid populations if the distribution of G1 has a finite second moment and E[G(1)(3)]/N-->0 as N-->infinity.     

浅谈生物学实验教学改革策略

生物学实验教学具有重要地位和意义,针对当前实验教学存在问题,应从理念和实践两个层面采取有效策略来改革生物实验教学。如践行生物新课程实验标准,变验证性实验为探究性实验,着力培养学生创造性思维,重视实验课软硬件的建设与提升等。     

The minimisation of random events in the search for group structure

Summary An iterative species ranking and agglomerative clustering technique has been described. Its objectives were the minimisation of miselassification due to random species. occurrence and the demonstration of the changing role of specles in pattern formation.This work was supported by a grant from the National Science and Engineering Research Council of Canada.     

Systems microscopy: An emerging strategy for the life sciences

Dynamic cellular processes occurring in time and space are fundamental to all physiology and disease. To understand complex and dynamic cellular processes therefore demands the capacity to record and integrate quantitative multiparametric data from the four spatiotemporal dimensions within which living cells self-organize, and to subsequently use these data for the mathematical modeling of cellular systems. To this end, a raft of complementary developments in automated fluorescence microscopy, cell microarray platforms, quantitative image analysis and data mining, combined with multivariate statistics and computational modeling, now coalesce to produce a new research strategy, “systems microscopy”, which facilitates systems biology analyses of living cells. Systems microscopy provides the crucial capacities to simultaneously extract and interrogate multiparametric quantitative data at resolution levels ranging from the molecular to the cellular, thereby elucidating a more comprehensive and richly integrated understanding of complex and dynamic cellular systems. The unique capacities of systems microscopy suggest that it will become a vital cornerstone of systems biology, and here we describe the current status and future prospects of this emerging field, as well as outlining some of the key challenges that remain to be overcome.     

On a periodic-like behavior of a delayed density-dependent branching process

Most of natural populations seem to be regulated in their sizes in complex ways. Particularly, the sizes of some populations change in time or generation roughly periodically. There are many theoretical studies on such population dynamics. This paper develops stochastic population models for a periodic-like population dynamics. To see the nature of such mechanism, we consider simple models of a delayed density-dependent branching process, and present by numerical simulations how such a branching process shows periodic population changes. The effects of randomly changing stationary environments on the population dynamics are also considered.