Occurrence of the Parasitic Dinoflagellate Amoebophrya ceratii in Chesapeake Bay Populations of Gymnodinium sanguineum

Chesapeake Bay populations of the red-tide dinoflagellate Gymnodinium sanguineum were regularly infected by the parasitic dinoflagellate Amoebophrya ceratii during the summers of 1988–1991. Infections developed inside the nucleus of G. sanguineum and were always lethal to the host. Parasite generation time was ? 40 h at 23° C, with the intracellular, trophont phase lasting 39.5 ± 0.3 h, and the extracellular, vermiform stage persisting for ? 20 min. Near surface accumulations of G. sanguineum sometimes exceeded 1,000 cells/ml; however, host abundance was relatively low when integrated over the surface mixed layer of each station (mean = 12.2 cells/ml ± 2.96 SE; n = 60). Parasitized hosts were encountered in 75% of the samples where host abundance was ≥ 1 per ml, and epidemic outbreaks (20–40% hosts infected) were observed on several occasions. Epidemic infections were generally located several meters below surface accumulations of G. sanguineum and were always restricted to a narrow region near the pycnocline. Consequently, integrated station values for parasite prevalence were low, with an average 2.7% (± 0.31 SE; n = 60). Parasite induced mortality removed up to 8% of G. sanguineum populations per day, but averaged < 2% of host biomass throughout the Bay. Thus, parasitism by A. ceratii does not appear to be a major factor regulating G. sanguineum bloom in the main stem of Chesapeake Bay.     

Population dynamics: Limits of predictability

Problems related to the complex pattern of ecosystem dynamics are discussed. Examples of studies on the complex population dynamics are considered, including those of plankton populations in a spatially heterogeneous environment and of an agroecosystem invaded by pests resistant to Bt toxins produced by genetically modified insecticidal crops.     

The dispersion of age differences between partners and the asymptotic dynamics of the HIV epidemic

In this paper, the effect of a change in the distribution of age differences between sexual partners on the dynamics of the HIV epidemic is studied. In a gender- and age-structured compartmental model, it is shown that if the variance of the distribution is small enough, an increase in this variance strongly increases the basic reproduction number. Moreover, if the variance is large enough, the mean age difference barely affects the basic reproduction number. We, therefore, conclude that the local stability of the disease-free equilibrium relies more on the variance than on the mean.     

Epidemic progression on networks based on disease generation time

We investigate the time evolution of disease spread on a network and present an analytical framework using the concept of disease generation time. Assuming a susceptible–infected–recovered epidemic process, this network-based framework enables us to calculate in detail the number of links (edges) within the network that are capable of producing new infectious nodes (individuals), the number of links that are not transmitting the infection further (non-transmitting links), as well as the number of contacts that individuals have with their neighbours (also known as degree distribution) within each epidemiological class, for each generation period. Using several examples, we demonstrate very good agreement between our analytical calculations and the results of computer simulations.     

AN ANALYSIS OF PROCEDURES FOR IMPLEMENTING THE DYNAMIC RESPONSE METHOD

Abstract: A new method, the dynamic response method, was developed (DeMaster et al. 1982) in an attempt to use time series data on relative population sizes to satisfy the requirements of the Marine Mammal Protection Act of 1972 for maintaining an optimum sustainable population of marine mammals. Three methods of implementing this approach were studied, using a computer simulation of stochastic population growth with density-dependence operating on first-year survival in the form of a generalized-logistic function. Methods developed by Gerrodette (1988) and Boveng et al. (1988) appeared to be less sensitive than desirable when used with the simulated population data. The third method, developed in this study, offers better protection against Type II error (failing to identify populations in the optimum sustainable population range), particularly when combined with Gerrodette's (1988) approach.     

Population dynamics and the color of environmental noise: A study on a three-species food chain system

In the present study, the effect of red, white and blue environmental noise on population dynamics in a simple three-species food chain system was analyzed. The colored noise was superimposed on the three-species food chain model first put forth by Rosenzweig in different ways and the resulting power spectra were investigated. We showed that the amplitude of environmental noise, the trophic level at which a population is positioned and whether a population is directly affected by environmental noise, are all important with respect to the way in which a population responds to noise with different colors. For the deterministic case, all population dynamics are red irrespective of the system dynamics. When all species are sensitive to environmental noise, the top predators dynamics always remain red regardless of the color of the noise and its amplitude, whereas the dynamics of the intermediate species turn blue under disturbances of any color with high amplitude, and those of the basal species may become blue only under blue noise. If only one species is sensitive to environmental noise, the dynamics of the insensitive species are always red, irrespective of the color of the noise and its amplitude. Unlike previous results obtained by studying single-species models, our results have almost nothing to do with deterministic system dynamics. In other words, changing the deterministic system dynamics from stable via periodic to chaotic does not qualitatively change the outcome. Our results are of importance in determining how we interpret the ubiquitous red power spectrum of natural ecological time series.     

黄山松种群结构与动态研究

以“空间代替时间”的方法,以种群径级结构代替年龄结构,采用静态生命表和生存分析的方法,探讨了天柱山国家森林公园黄山松种群结构和动态规律。结果表明,随海拔升高,黄山松种群密度增大,径级分布范围减小,种群存活曲线由Deevey-Ⅱ型之间过渡到Deevey—Ⅰ型,种群由稳定型过渡为增长型。表明由低海拔向高海拔,黄山松种群处于不同的演替和发展阶段。     

A conceptual model of the dynamics of the Syamozero Lake community

We present a conceptual mathematical model of the dynamics of a spatially heterogeneous population system whose prototype is the fish community of Lake Syamozero. Analysis of the solutions of this model is used to demonstrate that interactions between the predator and prey populations in two neighboring biotopes (the pelagic and coastal zones) may result in either undamped oscillations or steady states of the population sizes. The model population densities are of the same order of magnitude as the values obtained in long-term observations of the Syamozero biota. It is also demonstrated that the transition to steady states may be accompanied by long-term (dozens or hundreds of years) damped oscillations of the prey and predator population densities. Under natural conditions, long transitional periods may prevent fish communities from reaching stationary modes.     

DYNAMIC RESPONSE ANALYSIS. III. A CONSISTENCY FILTER AND APPLICATION TO FOUR NORTHERN ELEPHANT SEAL COLONIES

Dynamic response analysis, a technique for determining stock size relative to the maximum net productivity level (MNPL), was applied to northern elephant seal populations from the South Farallon Islands, Año Nuevo Island, San Nicolas Island and San Miguel Island. Pup counts were used as indices of population size. The application of dynamic response analysis presented here involved some methodological innovations. We present a moving interval method which involves calculating separate dynamic response analyses for intervals of various lengths ranging from four counts to the total number available for the colony. The sign of the second order polynomial regression coefficient computed from a particular interval was used to indicate the colony's apparent status (relative to its MNPL, += above MNPL, - = below MNPL) on that interval. Consistency in the sign of the second order coefficient, as the interval was moved along the trajectory, was used to determine the minimum reliable interval size. Each colony exhibited growth similar to that of a population below its MNPL. These results are consistent with recent natural history observations at San Nicolas, San Miguel and the South Farallon islands. Natural history observations at Año Nuevo Island suggest that the colony there is now at equilibrium. Thus, if our results from dynamic response analysis of the Ano Nuevo colony are correct, it appears that the MNPL may be close to the carrying capacity for these animals.     

Population dynamics of hypolimnetic rotifers in the Pluss-see (North Germany)

The hypolimnetic rotifer populations of the Pluss-see (Keratella hiemalis, Filinia terminalis, Filinia hofmanni) show similar patterns of changing population parameters indicating that they respond to particular environmental signals in the same way.     

Predator–vole interactions in northern Europe: the role of small mustelids revised

The cyclic population dynamics of vole and predator communities is a key phenomenon in northern ecosystems, and it appears to be influenced by climate change. Reports of collapsing rodent cycles have attributed the changes to warmer winters, which weaken the interaction between voles and their specialist subnivean predators. Using population data collected throughout Finland during 1986–2011, we analyse the spatio-temporal variation in the interactions between populations of voles and specialist, generalist and avian predators, and investigate by simulations the roles of the different predators in the vole cycle. We test the hypothesis that vole population cyclicity is dependent on predator–prey interactions during winter. Our results support the importance of the small mustelids for the vole cycle. However, weakening specialist predation during winters, or an increase in generalist predation, was not associated with the loss of cyclicity. Strengthening of delayed density dependence coincided with strengthening small mustelid influence on the summer population growth rates of voles. In conclusion, a strong impact of small mustelids during summers appears highly influential to vole population dynamics, and deteriorating winter conditions are not a viable explanation for collapsing small mammal population cycles.     

种群生存力分析（PVA）的方法与应用

随着人们对资源的加速利用,生境丧失和破碎化导致物种濒危问题日益严重.以岛屿生物地理学为理论起源的种群生存力分析（PVA）,通过分析和模拟种群动态过程并建立灭绝概率与种群数量之间的关系,为濒危物种保护提供了重要的理论依据和研究途径.在过去的几十年中,种群生存力分析已成为保护生物学中一项重要的研究内容.目前种群生存力分析发展稳定,但对其实际预测能力和准确性尚存质疑,应用方面也有待进一步发展.种群生存力分析的进一步完善还需要在理论和方法上的创新,特别是籍于景观生态学和可持续性科学的理念,将空间分析手段、经济社会因素纳入到物种和种群的预测和管理上,从而使其具有更完整的理论基础和更高的实用价值.为此,本文对种群生存力分析的历史、基本概念、研究方法、模型应用和准确性进行了综述,并提出了有关的研究展望.     

A population dynamics model for annual plants subject to inbreeding depression

Summary We present a population dynamics model for annual plants subject to density dependent competition and a decline in mean individual fitness with inbreeding. An analysis of this model provides three distinct sets of parameter values that define the relative influence of inbreeding depression and density on population growth. First, a population with a relatively high finite rate of increase and a relatively small environmental carrying capacity can persist in spite of low levels of inbreeding depression. These types of population may occur during a bottleneck event that is caused by pure predation (or collecting) pressure rather than loss of habitat. Second, there can exist a minimum viable population size when the finite rate of increase is relatively low and the population is also affected by density: the growth or decline of the population will depend on the initial population size. Third, when the population is small enough to be simultaneously effected by density and by inbreeding depression, there can be no viable population.     

子午沙鼠种群数量动态及预测

子千沙鼠（Ｍｅｒｉｏｎｅｓ ｍｅｒｉｄｉａｎｕｓ）是荒漠和半荒漠地区常见的鼠种之一,作者于１９９１～、９９５年４～１０月每月中旬,在内蒙古达拉特旗中国农业守草原研究所鄂尔多斯沙地草场改良试验站,利用直线夹日法在站内的流动消逝天,半流动消逝一,固定沙地,丘间滩地,林地和农田中开展了种群数量调查。６ａ共布放１２４２４５闪日,捕获鼠７４９８只,其中子午沙鼠１４０８只,在各种鼠中占１８．７７％,居第二位。     

三化螟种群动态分析及防治

分析了 1 980～ 2 0 0 0年三化螟种群数量变动情况 ,发现年度间的变动不一致 ,有明显间歇性。认为冬春气候 (气温、雨量 )、耕作制度、天敌因素等与三化螟为害密切相关 ,并提出科学实用的防治方法     

自然种群中混沌的检测及其在种群动态研究中的意义

混沌现象广泛地存在于自然界,20世纪70年代以来,通过大量的生物模型模拟说明混沌也存在于生物系统中。几十年来生态学家一直在努力寻找混沌在自然生态系统存在的证据,但所获不多,这是源于自然的现实还是由于检测方法的不当和数据的局限?一直困扰着生态学家,自然界中对混沌的检测成为一个要点,也是一个难点。在概述混沌概念和性质的基础上,着重介绍目前在自然生态系统检测混沌的方法,对各种方法的应用条件和范围进行了概述。这些方法包括功率谱法、时间序列的自相关函数分析、模型参数估计、庞加莱截面法、全局和局域李雅普若夫特征指数的估计、吸引子关联维的确定、非线性预测。大量研究结果显示,虽然在自然界检测到的混沌的例子还不多,但其存在却是不容怀疑的。问题是什么样的系统在什么样的条件下会出现混沌?研究表明食物链的结构、种群的迁入和迁出、环境噪音都会对种群的复杂性动态特征产生影响。混沌动态可能对产生系统的多样性和适应性有利,它比随机系统对外界干扰的抵抗能力更强。自然界的变化和系统的维持是持续性和混沌相互矛盾统一的结果。害虫种群复杂性动态的研究为害虫的管理提供了更多的理论依据。混沌控制的理论和方法有可能为害虫管理提供新的思路和途径。在孤立的种群中,混沌会增加种群的灭绝概率,而在集合种群中,混沌动态降低了各局域种群的同步性和同时灭绝的倾向,所以混沌虽然能增加局域种群灭绝的概率,但却能减少整个集合种群灭绝的概率。系统结构及其时空动态与混沌及种群灭绝之间的关系,是保护生物学及生物多样性保护研究的一个重要方面。今后的研究应更多地从种群、群落、生态系统及景观不同层次上的时空动态入手,利用3S等信息技术和空间动态分析方法,研究复杂性动态产生的条件及其在系统调控中的作用机制。     

The effect of food quantity and quality on the growth,birth-rate and longevity of Daphnia hyalina Leydig

To study experimentally the relation between zooplankton and phytoplankton, laboratory cultures of Daphnia hyalina Leydig were set up. The combined influence of food quality and quantity on growth, birth-rate and longevity was measured. The effect of seven different food regimes was tested. Natural unfiltered lake water from the eutrophic lake Tjeukemeer was used in one regime. The food value of the natural unfiltered lake water appeared to be relatively low, which was most likely caused by the abundance of large sized algae in the lake water.