Effect of Moniliformis moniliformis density on distribution within the definitive host population (Rattus norvegicus)

The population dynamics of Moniliformis moniliformis was studied in ‘free-ranging’ laboratory rats, Rattus norvegicus, presented with different relative density levels of M. moniliformis in cockroaches, Periplaneta americana. Changes in selected population parameters of the negative binomial distribution were evaluated as indicators of changes in aggregation. A significant increase in the degree of aggregation of parasites occurred as a result of the increase in relative density of infective stages available to the rats. This increase in aggregation was due to the increase in over-dispersion that occurred in female rats only. The degree of aggregation in females was found to be significantly higher than that in males at both treatment levels. The best indicators of the degree of aggregation were found to be the ratio of the variance to the relative density and the ratio of the log-variance to log-relative density. Changes in k were not correlated with changes in over-dispersion or the relative density.     

青海湖裸鲤寄生对盲囊线虫的种群生态研究

对盲囊线虫的三期幼虫寄生在青海湖裸鲁的体腔,以扁平的透明薄囊包被,附于肠壁和肠系膜间,其种群平均密度随突主体长的增加呈指数形式增加,寄生虫种群在突主种群中呈聚集分布,且其聚集强度随寄生虫的种群平均密度增加而增加。这种分布形式与其第一中间突主锯缘真剑水蚤在青海湖中分布的不均匀性和鱼类宿主在生长过程中的食性分化有关。具体机制无法用数学模式描述,感染率的显著增加引起分布的聚集强度降低。     

海南苏铁种群结构与森林群落郁闭度的关系

海南苏铁(Cycas hainanensis)是古老的苏铁属植物, 为国家Ⅰ级重点保护植物, 也是IUCN红色名录的濒危物种。为研究海南苏铁在海南昌江保梅岭省级自然保护区的种群结构与森林郁闭度的关系, 本文通过样方法对海南苏铁种群及其所在群落进行调查, 分析了其群落结构和物种多样性, 以及其种群密度、年龄结构、存活曲线、空间分布格局与森林郁闭度的关系。结果表明: 海南苏铁所在群落垂直结构分为乔木上下2层、灌木层和草本层。海南苏铁所在群落物种多样性指数偏高, 群落内物种组成丰富; 各样方内海南苏铁数量分布不均, 经常群生于海拔500 m左右的林下、林缘间。海南苏铁种群结构属于增长型, 种群更新力强, 种群存活曲线趋近于Deevey-II型, 死亡率随着龄级增加而增加, 说明海南苏铁种群处于相对稳定的状态, 随着种群个体的生长发育, 其生存力逐渐下降; 海南苏铁种群空间分布格局呈聚集型, 聚集程度指标随着林分郁闭度变大而增加。曲线估计结果显示, 海南苏铁幼苗幼树在透光率36.11%-58.33%显著增加。综上所述, 昌江保梅岭地区的海南苏铁种群处于较为稳定的增长状态, 喜生长于海拔500 m左右、郁闭度为35%-60%的森林环境中。     

Spatial structure and regeneration of Tetramerista glabra in peat swamp rain forest in Indonesian Borneo

We examined the spatial structure and regeneration of Tetramerista glabra, a dominant canopy tree in peat swamp rain forest in Borneo (West Kalimantan, Indonesia). T. glabra has strong spatial structure that changes dramatically during the life cycle; seedlings were highly aggregated, saplings were random and trees were evenly distributed. Germination and seedling relative growth were highest within canopy gaps, but seedling densities were highest at gap edges. Concentration of seedlings in gap edges, rather than localized seed dispersal, was responsible for seedling patchiness. The slope of the relationship between relative growth rate and seedling height decreased from gap, to gap edge to understory habitats, suggesting that competition within the seedling layer is more important in gaps than in the understory. The processes that break down seedling aggregation, leading to over-dispersion of trees, must be density dependent, but remain unknown.     

Density independent population dynamics by Trichoderma virens in soil and defined substrates

Classical models of population dynamics predict that with increasing initial population densities the per capita growth will diminish. Observations over a broad range of initial densities with a wild-type and a genetically engineered strain of the filamentous fungus, Trichoderma virens (Arx), in soil and autoclaved soil differed from these predictions. The per capita growth response of T. virens in vitro was found to be density dependent on potato dextrose agar, but density independent on water agar. Further experiments with a defined, carbon-free medium (Vogel's medium) and, with the same medium containing sucrose, indicated that density dependent per capita growth occurred in the nutrient-rich medium but not the oligotrophic medium. This hypothesis was tested and supported experimentally through observation of density dependent per capita growth after adding nutrients to autoclaved soil. Development of better models of population dynamics will be important to predict successfully the likelihood and extent of establishment after field release of microorganims.     

杭州石荠苎(Mosla hangchowensis)种群密度制约实验的统计分析

本文研究了我国特有、分布区极狭窄的一年生草本植物——杭州石荠苎(Mosla hangchowensis)种群的密度制约规律。结果表明：在生长季内,种群的死亡率与密度密切相关。种群的最适密度为200～1000株/m²左右。不同密度种群的平均株高、开花数等性状随时间的动态关系均符合“logistic”模型。高密度种群中60%左右的个体能完成生活史;低密度种群中80%以上的个体能完成生活史。种群密度较高制约杭州石荠苎的植株形态和繁殖投资。     

蒙古栎次生林群落结构及优势种群点格局分析

为探求大小兴安岭过渡区物种共存、生物多样性保护与维持机制,以黑龙江中央站黑嘴松鸡国家级自然保护区蒙古栎天然次生林25 hm²固定样地调查数据为基础,从群落物种组成、结构特征、径级结构以及优势种群的空间点格局分析对该样地进行分析。结果表明：样地内共有胸径≥1 cm的维管植物10种,活立木共 34 778株,平均密度1 392株·hm^-2。其中,重要值大于10%的物种共计4种,依次为蒙古栎（Quercus mongolica Fisch.ex Ledeb.）、黑桦（Betula dahurica Pall.）、白桦（Betula platyphylla Suk.）、兴安落叶松（Larix gmelinii（Rupr.）Kuzen）,占全样地的89.65%。该样地的Shannon-Wiener多样性H′、Simpson多样性D、Pielou均匀度指数J分别为1.577、0.760、0.685。表明该群落稀有物种较少,常见种比例较大,群落结构较为简单。样地内所有树种平均胸径10.77 cm。群落内总径级分布呈“倒J型”,符合典型异龄林的分布特征。黑桦、白桦径级分布近似“倒J型”,属于增长种群,蒙古栎种群径级结构为双峰型。兴安落叶松种群径级近似正态分布,有随演替进行逐渐消失的趋势,属于该群落的衰退种。在CSR模型下,4种优势种群的空间格局主要表现为聚集分布,且聚集程度随尺度增加聚集程度减弱,最终呈现随机或均匀分布趋势。在NS模型下,除兴安落叶松外,其余3种植株在小尺度（0~5 m）表现聚集性,可能是受种子的扩散限制的影响。对比4种优势种群,聚集强度表现为黑桦＞白桦＞蒙古栎＞兴安落叶松,因此我们推断群落内不同种群的聚集强度不仅与研究尺度相关,与种群的多度也存在一定的相关关系。     

Seasonal changes in the invertebrate community of small shallow ephemeral pans at Bain's Vlei, South Africa

Changes in invertebrate population numbers and composition were monitored in six small shallow ephemeral pans during four consecutive inundations of spring, summer and autumn 1988/1989. The community was generally characterized by crustaceans and was invaded by insect larvae in summer. Community changes and succession were prominent in spring but less so in summer and autumn. Large pans supported more species than small pans. During longer inundation there was less difference between the initial and the final population composition than during shorter inundation, although the total population density did not increase significantly. This indicated that population composition stabilized as inundation lengthened. Population changes of six representative taxa were not correlated to changes in the physical and chemical characteristics of the water.     

种植密度对苜蓿生长及生物量的影响

种植密度作为影响作物产量和品质的重要因素, 会造成植物对于光照、水分和养分的竞争。为研究种植密度对苜蓿生长与产量的影响, 在日光温室环境下, 以紫花苜蓿(Medicago sativa)为材料, 设置25、100、400、800、1 500、2 000株·m ^-2, 共6个种植密度, 对紫花苜蓿的种群密度和生长状况进行了观测。结果表明, 各处理播种后15天的平均种植密度分别为25、100、373、745、1 255、1 938株·m ^-2; 随着紫花苜蓿的生长, 除了低密度(25、100株·m ^-2)处理没有发生植株数量的变化外, 其余4个密度处理植株数量均有所减少, 即发生不同程度的自疏, 至第二茬收获时(播种后第187天)种群数量分别减少为297、571、759、839株·m ^-2。植株个体的株高、基径和分枝数量随着现存密度的增加呈指数下降; 个体生物量与现存密度的关系满足竞争密度效应的幂函数关系, 即随着密度的增加而减小。紫花苜蓿单位面积地上生物量符合最终产量恒定法则, 然而, 随着密度的增加, 地下生物量有先增加后减小的趋势。     

Analysis of stability of neural network with inhibitory neurons

Phase coding in a neural network composed of neural oscillators with inhibitory neurons was studied based on the theory of stochastic phase dynamics. We found that with increasing the coupling coefficients of inhibitory neural oscillators, the firing density in excitatory population transits to a critical state. In this case, when we increase the inhibitory coupling, the firing density will come into dynamic balance again and tend to a fixed value gradually. According to the phenomenon, in the paper we found parameter regions to exhibit those different population states, called dividing zones including flat fading zone, rapid fading zone and critical zone. Based on the dividing zones we can choose the number ratio between inhibitory neurons and excitatory neurons in the neural network, and estimate the coupling action of inhibitory population and excitatory population. Our research also shows that the balance value, enabling the firing density to reach the dynamic balance, does not depend on initial conditions. In addition, the critical value in critical state is only related to the number ratio between inhibitory neurons and excitatory neurons, but is independent of inhibitory coupling and excitatory coupling.     

基于地形起伏度的中国西南地区人口集疏格局演化研究

中国西南地区复杂的地形起伏造就了人口分布的区域差异,研究地形起伏度与区域人口增减以及集疏格局演化的关系,有利于深入理解人口的分布规律和流动趋势,从而为增进对区域人地关系的认识,实现人口、资源、环境可持续利用提供科学依据。以西南地区DEM数据和人口统计数据为基础,采用人口密度、人口集聚度以及人口商度等指标,结合GIS空间分析方法,定量研究了西南地区1995—2010年期间地形起伏度与人口集疏格局演化的关系。结果表明:(1)西南地区县域尺度上的地形起伏度主要以中小起伏为主,其中小起伏(0—200m)占30.34%,中起伏(200—400m)占30.33%,且地形起伏度的空间分布特征与区域地貌类型分布状况基本一致,即小起伏主要出现在四川盆地盆中区域、广西丘陵以及青藏高原高原面,中起伏主要集中分布在云贵高原境内,大起伏和极大起伏主要分布在横断山区、青藏高原东南部边缘以及川西高原地区。(2) 1995—2010年间,西南地区人口"西疏东密"的集疏格局未发生明显变化,地形起伏度的整体格局根本上决定了区域人口格局的形成。人口流动主要发生在中小起伏地区,且流出人口比例逐渐占据主导地位;而地形起伏度较大的高山以及高原边缘地区多为人口稳定区域。(3)地形起伏度差异决定了西南地区高度集聚和极端稀疏两种人口格局并存的现状。平原、丘陵、低山等起伏较小的地区人口增长迅速;而地形起伏度大的高山以及高原边缘地区人口增减变化不显著。     

Strategies of mate finding in the European field cricket (Gryllus campestris) at different population densities: a field study

Abstract. 1. Members of a field population of Gryllus campestris L. varied in their walking and calling activity. In both sexes, some individuals occupied burrows whereas others walked around in the observation area. Males at burrows could be either silent or calling.
2. In the course of one summer, population density decreased and the initial balanced sex ratio changed to a large surplus of males.
3. At high population density, there were equal numbers of non-calling males at burrows, calling males at burrows and walking males, while walking females predominated over females at burrows. Non-calling males at burrows achieved more encounters with females than did calling and walking males. Females met males by walking through the population and by waiting at burrows. Thus, calling and phonotaxis were not essential for mate finding and calling was less effective than previously thought.
4. At low population density calling males predominated. Calling males at burrows achieved the most encounters with females. Females met males only by walking around in the population area. Calling was thus more important in mate finding than at high population density.
5. Changes in sex ratio and population density may cause the flexibility in mate finding behaviour of individual crickets.     

Morphological variability and developmental instability in subpopulations of the Eurasian badger (Meles meles) in Denmark

Aim Local populations from different geographical regions may differ in the selection regimes to which they are exposed. Differences in environmental factors and population density may affect the relative importance of different selective forces (e.g. natural vs. sexual selection). We suggest a direction of investigation concerned with the developmental instability of morphological traits. The goal is to disclose putative small‐scale geographical differences in the evolutionary forces, which may be hard to detect. Location Craniometrical investigations were carried out on ninety‐eight skulls and teeth of the Eurasian badger (Meles meles) collected during the period 1995–97 from three different populations in Denmark. One of these thrives at low population density, whereas the two others are characterized by high local density. Methods The skulls were investigated for developmental instability (DI) using fluctuating asymmetry (FA) as its estimator. FA was measured on canines, molars, premolar teeth and other skull and mandible traits. For the statistical analyses, we applied nonparametric permutation tests. Results Evidence was found suggesting differentiation among populations in mean degree of FA, and the FA values measured on canines were higher in the high‐density populations. FA of the canines was significantly higher in males than females, in contrast to FA of the other traits. Evidence of a negative relationship between canine size and their FA was found, whereas no significant correlations were found between the molar and premolar teeth measures and their FA. Main conclusions Our results suggest that canines could be under directional selection stemming from intrasexual competition, which may be stronger in high‐density zones. The other teeth investigated seem to be under a stabilizing regime hence their FA is mainly affected by environmental stresses. The negative relationship between canine size and FA found in males suggests the capacity of badgers to respond in an evolutionary way to environmental changes, despite the low genetic variability previously found at the molecular level.     

Comparative studies on the influence of relative humidity and temperature on life table parameters of two populations of Cotesia flavipes (Hymenoptera: Braconidae)

Cotesia flavipes Cameron (Hymenoptera: Braconidae) is a gregarious larval koinobiont parasitoid of gramineous stemborers from the Indo-Australian region. More recently, it has been introduced into several countries in East and southern Africa for regulation of Chilo partellus (Swinhoe) (Lepidoptera: Crambidae). Establishment has varied from country to country and within country, suggesting that abiotic factors, such as temperature and relative humidity, may influence parasitoid performance. In this work, the effect of temperature and relative humidity on life table parameters of two populations of C. flavipes were measured. The results indicated that the factors and their interactions significantly affected the population growth of C. flavipes. The intrinsic rate of increase of the North Pakistan population of Cotesia flavipes was higher than that of the Indian population at all humidities at 28°C, but there were no differences at other temperatures or humidities.     

Population density does not influence male gonadal investment in the Least Killifish,Heterandria formosa

Comparative studies documenting a relationship between male gonadal investment and the degree of sperm competition (SC) have usually considered the association between these traits to be driven by qualitative differences in the mating system, such as whether spawning occurs in pairs or groups. However, ecological and demographic differences between conspecific populations may also generate variation in the importance of SC that can drive the evolution of male gonadal investment. In this study, we examined whether variation in population density, which is predicted to influence the level of SC in many animals, is correlated with male gonadal investment among populations of the least killifish, Heterandria formosa, a species with internal fertilization in which multiple mating is common. We complemented this field study by testing whether males respond plastically to experimentally increased levels of SC by increasing investment in testis. This experiment involved two treatments. In the first, we eliminated the potential for sperm competition (NSC) by housing a single male with a single female. In the second, we created a high risk of SC by housing five males with two females. In the field survey, we found significant differences among populations in density and relative testis mass. However, there was no evidence for a correlation between population density and relative testis mass. In our lab experiment, males did not adjust their gonadal investment in response to experiencing different levels of SC for 4 weeks. Our combined results indicate that gonadal investment in male H. formosa is not related to variation in population density.     

Intrinsic and extrinsic determinants of mountain pine beetle population growth

1 Mountain pine beetle Dendroctonus ponderosae populations have large, economically significant outbreaks. Density dependence and environmental variability are expected to have important effects on their dynamics. We analysed time series data from an outbreak in the 1930s to determine the relative importance of population density and environmental variability on local population growth rates.
2 Resource depletion occurred rapidly at the scale of 0.4 ha and population growth rates were strongly density dependent. Annual environmental changes did not have detectable effects on population growth rates, leading to the conclusion that intrinsic processes influenced local population density more than extrinsic factors during this outbreak.
3 Our calculated value of r _max (1.16) does not suggest intrinsically cyclic population dynamics. Our estimate of r _max and density dependence will be useful in developing applied models of mountain pine beetle outbreaks, and the subsequent evaluation of management strategies.     

Changes with aging in the levels of amino acids in rat CNS structural elements I. Glutamate and related amino acids

Glutamate and related amino acids were determined in 53 discrete brain areas of 3-and 29-month-old male Fischer 344 rats microdissected with the punch technique. The levels of amino acids showed high regional variation-the ratio of the highest to lowest level was 9 for aspartate, 5 for glutamate, 6 for glutamine, and 21 for GABA. Several areas were found to have all four amino acids at very high or at very low level, but also some areas had some amino acids at high, others at low level. With age, in more than half of the areas, significant changes could be observed, decrease occurred 5 times more frequently than increase. Changes occurred more often in levels of aspartate and GABA than in those of glutamate or glutamine. The regional levels of glutamate and its related amino acids show severalfold variations, with the levels tending to decrease in the aged brain.     

Annual Changes in Meiobenthos Community Structure in Alekseev Bight, Sea of Japan

We performed a comparative analysis of the taxonomical composition and population density of the meiobenthos and substrate types of Alekseev Bight, Sea of Japan, throughout the period when a plantation for mariculture of Japanese scallop was exploited in the bight and for a decade after the plantation had been removed. We found that silting of substrates in the bight decreased and the number of taxonomical groups that constituted the meiobenthos increased. The nematodes that, earlier, dominated the meiobenthos in terms of population density were later exceeded by foraminiferans, the species diversity of which increased. Changes are revealed in the composition of the dominant species of these groups.     

不同水位梯度下的小叶章种群密度

通过人工试验控制水位条件,研究了在不同水位梯度条件下,小叶章种群密度的动态变化,并分析了不同时期小叶章种群密度与水位梯度之间的相关关系。结果表明,小叶章群落中,0~20 cm的水位梯度条件下,小叶章种群密度的季节动态呈比较明显的双峰型曲线。而小叶章-苔草群落中,在-10、0和30 cm水位梯度,小叶章种群密度季节动态曲线为双峰型。小叶章群落不同水位梯度的季节动态曲线显示,除10和20 cm的水位梯度,种群密度具有随着水位梯度的升高而降低的趋势。而小叶章-苔草群落小叶章种群密度最大值出现在0 cm水位梯度,种群密度与水位梯度之间关系复杂,没有简单的线性规律。两个群落均在10 cm水位具有明显的变化:试验初期种群密度显著快速增长,而后趋缓,再增长。小叶章种群密度与水位梯度之间存在着显著负相关性,利用两者之间的拟合方程可以估测不同水位梯度条件下的小叶章种群密度。     

Body temperature in arboreal and nonarboreal anuran amphibians: Differential effects of a small change in water vapor density

1. 1.|Body temperatures (T_b) and contaneous evaporative water loss rates (CWL) were measured in tree frogs (Hyla cinerea) and toads (Bufo valliceps) exposed to cyclical ramp changes in water vapor density (WVD) between 7.5 and 9.8 gm⁻³ (1 cycle h⁻¹ at an air temperature of 27.0°C.

2. 2.|CWL was 3.3 times greater in toads than in tree frogs.

3. 3.|T_b in toads cycled directly with WVd; WVD accounted for 98% of the variation in toad T_b.

4. 4.|T_b in tree frogs was independent of WVD, probably due to changes in skin resistance to water loss.