The vitality model: A way to understand population survival and demographic heterogeneity

A four-parameter model describing mortality as the first passage of an abstract measure of survival capacity, vitality, is developed and used to explore four classic problems in demography: (1) medfly demographic paradox, (2) effect of diet restriction on longevity, (3) cross-life stage effects on survival curves and (4) mortality plateaus. The model quantifies the sources of mortality in these classical problems into vitality-dependent and independent parts, and characterizes the vitality-dependent part in terms of initial and evolving heterogeneities. Three temporal scales express the balance of these factors: a time scale of death from senescence, a time scale of accidental mortality and a crossover time between evolving vs. initial heterogeneity. The examples demonstrate how the first-passage approach provides a unique and informative perspective into the processes that shape the survival curves of populations.     

The partitioning of density-dependent dispersal, growth and survival throughout ontogeny in a highly fecund organism

The way in which density‐dependent effects are partitioned amongst survival, growth and dispersal are key in determining the temporal and spatial dynamics of populations. Here we propose a mechanistic approach to understanding how the relative importance of these sources of density dependence can change over ontogeny through changes in dispersal abilities, energy stores and mortality risks. Whereas the potential for active dispersal typically increases over ontogeny as a function of body size, susceptibility to starvation and predation decreases. The joint effect of these mechanisms suggests a general model for the ontogenetic sequence of how density dependence is manifested, with density dependence early in ontogeny being primarily expressed as mortality on local spatial scales, whereas later stages respond to local density in terms of dispersal and potentially growth. Here we test this model by manipulating the densities of juvenile Atlantic salmon (Salmo salar L.) at two life‐history stages in the wild. Density‐dependent mortality during the early juvenile stage (i.e. fry at onset of exogenous feeding) was accompanied by no effects on body size and weak effects on dispersal. In contrast, dispersal of older juveniles (i.e. parr 2–3 months after onset of feeding) was strongly density‐dependent, with more individuals emigrating from high‐density release sites, and with no effect of initial density on mortality. This dispersal, however, appeared insufficient to produce an ideal free distribution within the study stream, as indicated by the effect of spatial variation in density on body size by the end of the first growth season. These results demonstrate that the way density‐dependent effects are partitioned amongst survival, growth and dispersal changes throughout ontogeny. Furthermore, these changes occur in correlation with changes in individual mortality risks and dispersal abilities, and suggest a general paradigm for the way in which juvenile density‐dependence is manifest in spatially structured populations of highly fecund organisms.     

哲罗鱼稚鱼最佳投喂策略

为探讨哲罗鱼稚鱼的最佳投喂策略,设置了饥饿再投喂试验、饥饿再投喂恢复试验以及日投喂频率试验.结果表明: 饥饿再投喂试验中,各饥饿组未表现出补偿生长现象.但在饥饿再投喂恢复试验中,各饥饿组表现出不同程度的补偿生长,其中S_1/2组(饥饿1/2 d投喂1/2 d)体质量的增加量与对照组接近,表现出完全补偿生长.表明在哲罗鱼早期稚鱼阶段(体质量0～2 g,水温9～15.3 ℃),S_1/2是可以考虑使用的投喂方法.日投喂频率试验中,T₃组(日投喂3次)体长、体质量的增加量以及特定生长率均最高,饵料转化率也相对较高.表明在哲罗鱼后期稚鱼阶段(体质量2～21 g,水温8.8～15.5 ℃),以日投喂3次为宜.     

哲罗鱼稚鱼最佳投喂策略

为探讨哲罗鱼稚鱼的最佳投喂策略,设置了饥饿再投喂试验、饥饿再投喂恢复试验以及日投喂频率试验.结果表明: 饥饿再投喂试验中,各饥饿组未表现出补偿生长现象.但在饥饿再投喂恢复试验中,各饥饿组表现出不同程度的补偿生长,其中S_1/2组(饥饿1/2 d投喂1/2 d)体质量的增加量与对照组接近,表现出完全补偿生长.表明在哲罗鱼早期稚鱼阶段(体质量0～2 g,水温9～15.3 ℃),S_1/2是可以考虑使用的投喂方法.日投喂频率试验中,T₃组(日投喂3次)体长、体质量的增加量以及特定生长率均最高,饵料转化率也相对较高.表明在哲罗鱼后期稚鱼阶段(体质量2～21 g,水温8.8～15.5 ℃),以日投喂3次为宜.     

Resource competition induces heterogeneity and can increase cohort survivorship: selection-event duration matters

Determining when resource competition increases survivorship can reveal processes underlying population dynamics and reinforce the importance of heterogeneity among individuals in conservation. We ran an experiment mimicking the effects of competition in a growing season on survivorship during a selection event (e.g., overwinter starvation, drought). Using a model fish species (Poecilia reticulata), we studied how food availability and competition affect mass in a treatment stage, and subsequently survivorship in a challenge stage of increased temperature and starvation. The post-treatment mean mass was strongly related to the mean time to mortality and mass at mortality at all levels of competition. However, competition increased variance in mass and extended the right tail of the survivorship curve, resulting in a greater number of individuals alive beyond a critical temporal threshold ( $T^{*}$ ) than without competition. To realize the benefits from previously experienced competition, the duration of the challenge ( $T_{c}$ ) following the competition must exceed the critical threshold $T^{*}$ (i.e., competition increases survivorship when $T_{c} > T^{*}$ ). Furthermore, this benefit was equivalent to increasing food availability by 20 % in a group without competition in our experiment. The relationship of $T^{*}$ to treatment and challenge conditions was modeled by characterizing mortality through mass loss in terms of the stochastic rate of loss of vitality (individual’s survival capacity). In essence, when the duration of a selection event exceeds $T^{*}$ , competition-induced heterogeneity buffers against mortality through overcompensation processes among individuals of a cohort. Overall, our study demonstrates an approach to quantify how early life stage heterogeneity affects survivorship.     

Survival against the odds: ontogenetic changes in selective pressure mediate growth-mortality trade-offs in a marine fish

For organisms with complex life cycles, variation among individuals in traits associated with survival in one life-history stage can strongly affect the performance in subsequent stages with important repercussions on population dynamics. To identify which individual attributes are the most influential in determining patterns of survival in a cohort of reef fish, we compared the characteristics of Pomacentrus amboinensis surviving early juvenile stages on the reef with those of the cohort from which they originated. Individuals were collected at hatching, the end of the planktonic phase, and two, three, four, six and eight weeks post-settlement. Information stored in the otoliths of individual fish revealed strong carry-over effects of larval condition at hatching on juvenile survival, weeks after settlement (i.e. smaller-is-better). Among the traits examined, planktonic growth history was, by far, the most influential and long-lasting trait associated with juvenile persistence in reef habitats. However, otolith increments suggested that larval growth rate may not be maintained during early juvenile life, when selective mortality swiftly reverses its direction. These changes in selective pressure may mediate growth-mortality trade-offs between predation and starvation risks during early juvenile life. Ontogenetic changes in the shape of selectivity may be a mechanism maintaining phenotypic variation in growth rate and size within a population.     

Flow cytometric assessment of Escherichia coli and Salmonella typhimurium starvation-survival in seawater using rhodamine 123, propidium iodide, and oxonol.

The use of flow cytometry in microbiology allows rapid characterization of cells from a nonhomogeneous population. A method based on flow cytometry to assess the effects of lethal agents and the bacterial survival in starved cultures through the use of membrane potential-sensitive dyes and a nucleic acid marker is presented. The use of propidium iodide, rhodamine, and oxonol has facilitated the differentiation of cells of Escherichia coli and Salmonella typhimurium of various states of vitality following various treatments (heat, sonication, electroporation, and incubation with gramicidin) and during starvation in artificial seawater. The fluorescence intensity is directly correlated with viable cell counts for rhodamine 123 labelling, whereas oxonol and propidium iodide labelling is inversely correlated with viable counts. The distribution of rhodamine and oxonol uptake during starvation-survival clearly indicates that single-species starved bacteria are heterogeneous populations, and flow cytometry can be a fundamental tool for quantifying this heterogeneity.     

江西九连山亚热带常绿阔叶林优势种空间分布格局

于江西九连山国家自然保护区设置4 hm2亚热带常绿阔叶林固定监测样地,用样方法对亚热带常绿阔叶林进行调查分析。应用点格局方法分析生境异质性是否影响树木分布并分析优势种红钩栲(Castanopsis lamontii)、米槠(Castanopsis carlesii)、罗浮柿(Diospyros morrisiana)和细枝柃(Eurya loquaiana)分布格局,对比存在生境异质性和排除生境异质性两种情况下优势树种不同生长阶段(幼树、小树、成年树)的空间分布格局以及不同生长阶段之间的空间关联性,探讨生境异质性之外的其它种群分布影响因子。结果表明:1)生境异质性效应显著影响九连山树木分布,4个优势树种在大尺度上存在明显的生境偏好;2)用完全随机零模型不排除生境异质性时,4个优势种总体及其不同生长阶段在0—30 m所有尺度上主要呈现聚集分布;3)用异质性随机零模型排除生境异质性后,4个优势种及其不同生长阶段的聚集程度显著下降,只在小尺度上(0—5 m)呈现聚集分布;4)4个优势种的幼树与小树均表现显著的正相关。红钩栲的成年树与幼树及成年树与小树总体表现不相关。米槠的成年树与幼树总体以无相关为主;成年树与小树之间总体呈正相关。小乔木罗浮柿的成年树与幼树之间在小尺度上(0—5 m)表现负相关或无相关,在较大尺度范围上总体表现正相关关系;小树与成年树在研究尺度上表现出正相关。灌木细枝柃的成年树与幼树,成年树与小树及小树与幼树之间在研究尺度范围内均呈现正相关关系;5)研究发现九连山优势乔木物种通过密度制约和Janzen-Connell效应释放空间,为其他物种共存提供条件,而优势灌木物种细枝柃没有表现出这两个效应。     

Control of growth and differentiation of the wing imaginal disk of Precis coenia (Lepidoptera: Nymphalidae)

During the last larval instar, the wing imaginal disks of Precis coenia grow continuously. The rate of disk growth is not disk-autonomous but closely matches the rate of somatic growth of the larva, so that the size of the disks is a function of the size of the body, irrespective of the growth rate of the larva. When larvae are starved, their wing disks cease growth within 4 h, which indicates the existence of an efficient coupling mechanism between the growth of the soma and growth of the imaginal disks. Disk growth is inhibited by juvenile hormone in a dose-dependent manner. In the presence of the hormone the wing disks stop growing even while the larva continues to grow normally. During the last larval instar the wing imaginal disks also undergo a complex differentiation, consisting of the development of the lacunae and tracheation that define the future adult wing venation system. In normally growing larvae, differentiation of the wing disk is tightly correlated with wing size. Differentiation and size can be dissociated by starvation. If larvae are starved at any time after differentiation has begun, differentiation continues at a normal rate, even though the wing disk does not grow. Differentiation does not begin spontaneously in larvae that are starved before differentiation has begun. These findings indicate that the initiation of differentiation and its continuation are controlled independently. Juvenile hormone inhibits differentiation in a dose-dependent manner. Upon treatment with juvenile hormone, the stage of differentiation becomes fixed. These findings indicate that continued differentiation of the wing disk can only occur in the absence of juvenile hormone. Although the circulating level of juvenile hormone may be elevated during starvation, it is unlikely that this elevation is responsible for the observed effect of starvation on growth and differentiation of the disk.     

The costs of phenotypic adaptation to repeatedly fluctuating temperatures in a soil arthropod

Costs of phenotypic adaptation to changing environments have often been studied in morphological structures. Such structures typically are irreversible for at least some stage in the organism's life. In this study we investigated whether recurrent and reversible adaptation to changes in the thermal environment incurs a cost in terms of some key life-history traits in the collembolan Orchesella cincta. We exposed juvenile O. cincta to two treatments differing in the frequency of temperature fluctuation but with equal total temperature sums. In the high frequency treatment temperature fluctuated daily between 10 and 20 °C, while in the low frequency treatment temperature fluctuated on a weekly schedule. During the treatments we measured juvenile growth rate and juvenile mortality, and after six weeks the animals were transferred to constant 15 °C and adult starvation resistance was assessed. We found no significant differences between the treatments in juvenile growth rate or juvenile survival. Also, adults that had grown up under high frequency temperature fluctuations did not suffer from reduced starvation resistance compared to animals growing under low frequency temperature fluctuations. This finding supports the hypothesis that selection minimizes the production costs of inducible phenotypes and suggests that the development of optimal phenotypes and evolution of temperature reaction norms are not constrained by such costs.     

Multistage density dependence in an amphibian

Density dependence is the major process keeping the sizes of natural populations within bounds. In organisms with complex life cycles, the stage at which density dependence occurs and whether it occurs in one or several life stages have important consequences for the dynamics of their populations. I manipulated density of pool frogs ( Rana lessonae) during the aquatic larval and the terrestrial juvenile stages and examined the effect on growth and survival until 1 year of age. High larval density, but not high juvenile density, led to smaller size at this age. Both larval and juvenile density led to reduced growth during the early juvenile stage, but the effect of the larval density appeared stronger than the effect of juvenile density. No density dependence in survival could be found. My results suggest that density dependence in both the larval and the terrestrial juvenile stage may play important roles in the regulation and dynamics of amphibian populations.     

Variation in tree growth,mortality and recruitment among topographic positions in a warm temperate forest

Questions: Do the population dynamics of trees differ among topographic positions and, if so, how does topographic position affect the population dynamics of species that are distributed in a topography‐specific manner? Which is the most important life stage in determining vegetation patterns? Location: Primary and secondary warm temperate evergreen broad‐leaved forest (40 ‐ 280 m a.s.l.) on the western part of Yakushima Island, Japan. Methods: Mortality, recruitment, DBH growth and distribution of stems (= 5 cm DBH) in a 2.62‐ha plot were surveyed in 1992 and 2002 to determine the relationships between population parameters and (1) topography and (2) distribution patterns of 17 common tree species. Results: Common species (n = 17) were classified into three distribution pattern groups: group A, distributed mainly on convex slopes; group B, on concave slopes, and group C, not aggregated with respect to topographic position. Stem mortality, recruitment and DBH growth were greater in group A than in group B within each topographic class. The hierarchy of stem mortality among topographic classes for groups A and B was convex > planar > concave. Stem recruitment density was relatively high on the convex and concave slopes, respectively, for groups A and B. Conclusions The topographical positions of adult trees were not always most suited for adult survival and growth. For group A, the distribution pattern of adults was determined in the juvenile stage, while this was not the case for group B. Studies of juvenile stages are important for understanding the demographic basis of vegetation distribution patterns.     

营养状态和代谢范围对锦鲫幼鱼群体行为的影响

为考察营养状态和代谢范围对鱼类群体行为的影响,研究以锦鲫(Carassius auratus)幼鱼为实验对象,在(25.4±0.2)℃条件下先测定其摄食代谢和能量代谢(标准代谢率, SMR;最大代谢率, MMR)计算代谢范围(AS=MMR–SMR),再测定5个“营养-AS”处理组的锦鲫鱼群体中的个体空间位置、摄食量及个体特征(如个体游泳速度和加速度)和群体特征(如个体游泳速度同步性、个体间距离、最近邻距离和群体极性)。研究发现:营养状态、饥饿、代谢范围、摄食和消化对鱼群中的个体空间位置均无影响。饥饿和消化对锦鲫群体的凝聚力并无影响,但饥饿降低该种鱼群体协调性的现象仅在消化期间存在,即群体中个体食物获取能力导致消化策略并非相同,由此引发个体游泳运动同步性更加紊乱,最终导致群体协调性下降。在正常营养状态的锦鲫群体中,群体前部的空间可赋予个体获得更多食物资源的生态收益,但饥饿消除该群体中个体空间分布生态收益的异质性。对照组摄食量与摄食水平与预测剩余的AS呈负相关,饥饿组摄食量与摄食水平与预测剩余的AS不相关。研究表明:在正常营养状态的锦鲫群体中,群体前部的空间可赋予个体获得更多食物资源的生态...     

Juvenile hormone titres and metabolism during starvation-induced supernumerary larval moulting of the tobacco hornworm, Manduca sexta L.

When tobacco hornworm (manduca sexta) larvae are starved for 5 days immediately after ecdysis to the 5th instar, then fed normal diet, they undergo a supernumerary moult instead of metamorphosis. During starvation the titre of juvenile hormone in the haemolymph increased to a maximum of 3 ng juvenile hormone I equivalents/ml (determined by the black Manduca larval bioassay) on the fourth day of starvation, then began a decline which continued through the subsequent feeding period. The changes in juvenile hormone titre were not attributable to changes in haemolymph volume during starvation (only a 5% decrease) and subsequent feeding. During starvation the esterase activity of the haemolymph declined 4-fold with a 2-fold larger decrease in the DFP-insensitive, presumably juvenile hormone specific, esterase activity. Both the total and the juvenile hormone-specific esterase activity then increased as a function of larval weight during the subsequent feeding period. As growth was slow in the prolongedly starved larvae, sufficient juvenile hormone was present at the time of prothoracicotropic hormone (PTTH) and ecdysteroid release at the beginning of the fourth day of feeding to prevent metamorphosis.     

Winter energy allocation and deficit of juvenile walleye pollock <Emphasis Type="Italic">Theragra chalcogramma</Emphasis> in the Doto area,northern Japan

Seasonal energy allocation and deficits of marine juvenile fishes have considerable effects on their survival. To explore the winter survival mechanism of marine fishes with low lipid reserves in their early life, juvenile walleye pollock Theragra chalcogramma were collected along the continental shelf of northern Japan over a 2-year period, and energy allocation and deficit patterns were compared between wild and laboratory-starved fish. Contrary to expectations, wild fish generally continued to accumulate protein mass and concurrently tended to reduce lipid mass from late autumn through winter. The most plausible explanation for the continuous structural growth is that juvenile pollock give priority to reducing mortality risk from size-selective predators under quasi-prey-limited conditions. Exceptionally, inshore small fish reduced both constituents during a winter. The inshore fish consumed 2.5 times more lipid energy than protein energy in November–December, but protein was more important than lipids as a source of energy in December–January and in February–March. However, dependence upon protein reserves was lower for the wild fish than for the laboratory-starved fish, suggesting milder nutritional stress of the wild fish than that observed in the starvation experiment. Moreover, the lipid contents of mortalities in the starvation experiment were mostly <1%, whereas few wild fish had such lipid contents in the field. These results suggest that juvenile pollock are able to avoid both starvation and predation by accumulating protein reserves.     

Dietary protein hydrolysate and trypsin inhibitor effects on digestive capacities and performances during early-stages of spotted wolffish: suggested mechanisms

Growth rate is dependent upon adequate provision of amino acids especially in newly-hatched fish which experience very high growth rate. The replacement of a fraction of protein content by partially hydrolyzed (pre-digested) proteins was carried out and the digestive capacities and performances of larval/juvenile spotted wolffish (Anarhichas minor) were measured. The goal of this study was to verify whether the scope for growth is principally dictated by the proteolytic capacity of the digestive system by examining the effect of protein hydrolysates (PH) and trypsin inhibitor dietary inclusion on protein digestion/assimilation capacities, growth and survival. Four experimental diets were examined: C (control) I (supplemented with 750 mg/kg soybean trypsin inhibitor (SBTI)) H (supplemented with 20% PH) and HI (supplemented with 20% PH and 750 mg/kg SBTI). Protein hydrolysate supplementation gave significantly higher body mass than control at day 15 post-hatching. Unexpectedly, at day 30 and 60, fish administered diet HI (containing trypsin inhibitor) were heavier than the other groups. Suggested mechanisms are presented and discussed. The main conclusions of this study are that wolffish larval stage lasts roughly 15 days and that juvenile growth is linked to proteolytic capacity, but also very likely to absorption capacity of peptides and amino acids.     

Nutritional and gonadal effects on the intra-acinar profiles of low-Km and high-Km aldehyde dehydrogenase activity in rat liver

Total and low-Km aldehyde dehydrogenase (ALDH) activity was measured in 50-150 ng microdissected liver tissue samples of the entire sinusoidal length. High-Km ALDH activity was calculated by subtracting the low-Km ALDH values from the total ALDH activity. Enzyme activity was measured by a microchemical assay, using the oil-well technique with luminometric determination of NADH. The intra-acinar profiles of high-Km and low-Km ALDH activity could be demonstrated graphically for both male and female rats after 84 h of starvation, and after starvation and refeeding for 6 nights. In addition, the ALDH distribution patterns of juvenile, castrated, and castrated and testosterone-treated rats were determined. It could be demonstrated that starvation, and starvation followed by refeeding, lead to changes in enzyme activity which parallel the loss and regain of liver- and body-weight. The nutritional factors do not essentially alter the normal intra-acinar profiles. In juvenile rats, ALDH is lower by 30% in comparison with the controls, but sex-differences in the distribution profiles are not yet present. Castration has no effect on the amount of enzyme activity but the sex specific distribution profiles are less marked. The main effect of testosterone treatment is an elevation of low-Km ALDH in the perivenous zone. The characteristics of the intra-acinar profiles of high-Km and low-Km ALDH activity are discussed with respect to hepatic acetaldehyde oxidation and alcoholic liver damage.     

不同体质量和饥饿程度对红鳍东方鲀幼鱼游泳能力的影响

为了考察不同体质量和饥饿程度红鳍东方鲀(Takifugu rubripes)幼鱼的游泳能力,利用行为生态学方法测定了不同体质量(0.22—3.31 g)和饥饿天数(1d、3d、6d和9d)下红鳍东方鲀幼鱼的绝对临界游速(U_crit,cm/s)、相对临界游速(U_crit’,体长/s,BL/s)、偏好游速(U_pref,cm/s)、6个流速区域(2—36 cm/s)下停留时间百分比(P_t,%)、偏好区域平均流速(V_mean,cm/s)和总游泳距离(D_1h,m)等游泳行为指标。结果显示,体质量和饥饿显著影响红鳍东方鲀幼鱼的U_crit、U_crit’、P_t、V_mean和D_1h。随体质量增加,实验鱼的U_crit、U_pref、V_mean和D_1h均逐渐升高,而U_crit...     

Some aspects of infanticide and intermale competition among langurs,Presbytis entellus,at Dharwar,India

Conspecific infanticides by male langurs depresses population growth in their densely populated habitats. An infanticidal model developed from demographic parameters obtained in the Dharwar study area predicts an almost stable population. On the other hand, a non-infanticidal model predicts a population growth by 2.6% per year. The effect of frequent troop usurpation and infanticide on the control of population growth must be strong if the natality rate is high. For subadult and juvenile surplus males, it must be difficult to survive and to mature in the all-male party in its poor habitat. However, from calculations for living adult males and the number of troops at Dharwar, most adult males are thought to be able to obtain a troop within five years of first challenge of usurpation. Dominant males do not always take over a troop containing more females than do subordinate males. These simple assessments require further intensive field studies to determine the precise differences between infanticidal and non-infanticidal populations and whether or not dominant males make a greater genetic contribution than subordinate males to subsequent generations.