Spatial synchrony through density-independent versus density-dependent dispersal

Many theoretical studies support the notion that strong dispersal fosters spatial synchrony. Nonetheless, the effect of conditional vs. unconditional dispersal has remained a matter of controversy. We scrutinize recent findings on a desynchronizing effect of negative density-dependent dispersal based on spatially explicit simulation models. Keeping net emigration rates equivalent, we compared density-independent and density-dependent dispersal for different types of intraspecific density regulation, ranging from under-compensation to over-compensation. In general, density-independent dispersal possessed a slightly higher synchronizing potential but this effect was very small and sensitive compared to the influence of the type of local density regulation. Notably, consistent outcomes for the comparison of conditional dispersal strategies strongly relied on the control of equivalent emigration rates. We conclude that the strength of dispersal is more important for spatial synchrony than its density dependence. Most important is the mode of intraspecific density regulation.     

Sex‐specific growth in chicks of the sexually dimorphic Black‐tailed Godwit

Sexual size dimorphism (SSD) is common in birds and has been linked to various selective forces. Nevertheless, the question of how and when the sexes start to differentiate from each other is poorly studied. This is a critical knowledge gap, as sex differences in growth may cause different responses to similar ecological conditions. In this study, we describe the sex‐specific growth – based on body mass and five morphometric measurements – of 56 captive Black‐tailed Godwit Limosa limosa limosa chicks raised under ad libitum food conditions, and conclude that all six growth curves are sex‐specific. Females are the larger sex in terms of body mass and skeletal body size. To test whether sex‐specific growth leads to sex‐specific susceptibility to environmental conditions, we compared the age‐specific sizes of male and female chicks in the wild with those of Black‐tailed Godwits reared in captivity. We then tested for a relationship between residual growth and relative hatching date, age, sex and habitat type in which the wild chicks were born. Early‐hatched chicks were relatively bigger and in better condition than late‐hatched chicks, but body condition and size were not affected by natal habitat type. Female chicks deviated more negatively from the sex‐specific growth curves than male chicks for body mass and total‐head length. This suggests that the growth of the larger females is more susceptible to limiting environmental conditions. On average, the deviations of wild chicks from the predicted growth curves were negative for all measurements, which suggests that conditions are limiting in the current agricultural landscape. We argue that in estimating growth curves for sexually dimorphic species, it is critical first to make accurate sex and age determinations.     

典型草原区鹰隼类密度对啮齿动物密度的数值响应

捕食者与猎物的关系是动物生态学研究的热点之一,捕食者应对猎物密度的变化往往呈现出特定的数值响应特征。为研究典型草原区鹰隼类对其猎物——啮齿动物密度变化的数值响应关系,于2005年7月在内蒙古自治区锡林郭勒盟阿巴嘎旗白音图嘎苏木选取15个实验样地,采用标准夹线法调查了啮齿类密度,同时采用目视方法调查了鹰隼类密度。本次实验共捕获鼠类2 675只,主要为布氏田鼠(Lasiopodomys brandtii),观察到鹰隼类活动450只次。回归分析结果表明,鼠类密度和鹰隼类密度的数值反应关系符合S型曲线,可用Gompertz方程W=22.765 e-3.735 e-0.078 t来拟合,拟合优度R2达0.984,表明鼠类密度对鹰隼类密度有显著影响,验证了Holling所提出的脊椎动物捕食者和猎物数量关系属于S型反应曲线的观点。从本文的结果看,鹰隼类数量对鼠类数量的反应可分为三个阶段:(1)平缓期,随着鼠类密度的逐渐增加,鹰隼类活动频次增长非常缓慢;(2)快速反应期,当鼠类密度达到5只/hm2时,鹰隼类活动频次随鼠类密度的增加迅速增长,期间出现一个增长拐点值;(3)稳定平台期,当鼠类的密度达到40只/hm2左右时,鼠类密度虽然继续增加,但鹰隼类活动频次保持稳定,不再增加。本研究可为草原鼠害的天敌控制方法提供参考。     

A stochastic discrete generation birth,continuous death population growth model and its approximate solution

This paper describes a single species growth model with a stochastic population size dependent number of births occurring at discrete generation times and a continuous population size dependent death rate. An integral equation for a suitable transformation of the limiting population size density function is not in general soluble, but a Gram-Charlier representation procedure, previously used in storage theory, is successfully extended to cover this problem. Examples of logistic and Gompertz type growth are used to illustrate the procedure, and to compare with growth models in random environments. Comments on the biological consequences of these models are also given.Currently at Department of Mathematics, University of MarylandWork partially supported by the Danish Natural Science Research Council and Monash University     

The evolution of aging and age-related physical decline in mice selectively bred for high voluntary exercise

We tested whether selective breeding for early-age high voluntary exercise behavior over 16 generations caused the evolution of lifelong exercise behavior, life expectancy, and age-specific mortality in house mice (Mus domesticus). Sixteenth-generation mice from four replicate selection lines and four replicate random-bred control lines were individually housed from weaning through death and divided between two activity treatments (either with or without running wheels). Thus, there were four treatment groups: selection versus control crossed with active versus sedentary. The effects of selective breeding on life expectancy and age-specific mortality differed between females and males. In females, sedentary selection mice had early and high initial adult mortality and thus the lowest increases in mortality with age. Active selection females had the lowest early adult mortality, had limited mortality during midlife, and exhibited rapid increases in mortality rates at the very end of life; thus, they had deferred senescence. Median life expectancy was greater for both groups of selection females than for the two complementary groups of control females. Like females, sedentary selection males had the highest early adult mortality, and slow but steadily increasing mortality over the entire lifetime. Unlike the active selection females, active control males had the lowest mortality across the lifespan (until the end of life). Interestingly, the males with the lowest median life expectancy were those in the active selection treatment group. In both sexes, running (km/week) decreased over the lifetime to very low and virtually equivalent levels at the end of life in control and selection mice. Overall, these results demonstrate an evolutionary cost of selective breeding for males, regardless of exercise level, but a benefit for females when they have an outlet for the up-selected behavior. We conclude that correlated evolution of senescence occurs in mice selectively bred for high voluntary wheel running; exercise per se is beneficial for control mice of both sexes, but the impact on the effect of selection depends on sex; and the behavioral effect of exercise selection at an early age declines throughout the life span, which demonstrates decreasing genetic correlations over age for the genes involved in increased exercise.     

Age and growth of Neotrygon picta, Neotrygon annotata and Neotrygon kuhlii from north-east Australia, with notes on their reproductive biology

Vertebral band formations were used to define age and growth in three Neotrygon species caught regularly as by-catch in prawn trawl fisheries in north-east Australia. Centrum edge and marginal increment ratio analyses were used to validate annual band formations. Age estimates ranged from 1 to 18 years, with the von Bertalanffy growth function considered to have the best fit to Neotrygon picta (males, W(D∞) = 271 mm, k = 0·12; females, W(D∞) = 360·5 mm, k = 0·08) and Neotrygon kuhlii (males, W(D∞) = 438·6 mm, k = 0·08; females, W(D∞) = 440·6 mm, k = 0·08) disc width (W(D))-at-age data. The Gompertz growth function had the best fit to Neotrygon annotata W(D)-at-age data (males, W(D∞) = 230·4 mm, k = 0·20; females, W(D∞) = 265·5 mm, k = 0·31). Age at sexual maturity ranged from 3 to 6 years, with N. picta having the smallest size at birth (100 mm W(D)), smallest W(D) at 50% maturity (W(D50): male, 172 mm, female, 180·7 mm) and lowest age at sexual maturity (3-4 years). This study helps redefine and improve the accuracy of fisheries-based risk assessments for these small species with relatively conservative life-history variables.     

Optimization of growth conditions of the postharvest biocontrol agent Candida sake CPA-1 in a lab-scale fermenter

AIM: To maximize the growth (expressed as number of viable cells per millilitre) of the postharvest biocontrol agent Candida sake CPA(-1) at laboratory scale conditions. METHODS AND RESULTS: Growth conditons (aeration, agitation speed and inoculum size) were studied in batch conditions in a 5 l fermenter using molasses and urea as growth medium. Consumption of sugars and urea were analysed. Fed-batch studies were also carried out. Glucose and fructose were consumed during the exponential growth phase and were depleted after 18 h of growth. On the contrary, C. sake cells assimilated sucrose during the stationary phase. There was not growth improvement when fed-batch technology was used. Addition of an extra amount of glucose or molasses after 18 h of growth did not contribute to increase final population. CONCLUSIONS: Maximum growth (about 8 x 10(8 )CFU ml(-1)) was obtained at batch fermentation after 30 h growth at 400 rev min(-1), 150 l h(-1) of air and initial concentration of 106 CFU ml(-1). SIGNIFICANCE AND IMPACT OF THE STUDY: The results obtained in this study are an approach for further upscaling of C. sake production.     

The demography of slow aging in male and female Drosophila mutant for the insulin-receptor substrate homologue chico

Hypomorphic mutants affecting the Drosophila insulin/IGF signal pathway are reported to increase longevity in females but not in males. To understand this sex-difference, we conducted a large-scale demographic study with three new isogenic strains of alleles at chico, the insulin-receptor substrate homologue. We verify that female dwarf homozygotes (ch1/ch1) and normal-sized heterozygotes (ch1/+) are long-lived, as originally reported. We find for the first time that male heterozygotes are long-lived relative to wildtype, by about 50%. The life span of male ch1/ch1 is similar to that of wildtype but these dwarf males age at a slow demographic rate. The levels of demographic frailty and of age-independent mortality are elevated in ch1/ch1 males, counteracting the effect of slow aging upon life expectancy. Mortality deceleration occurs amongst the oldest-old wildtype adults, as seen in many organisms. Remarkably, in similarly sized cohorts of male and female ch1/ch1 and of male ch1/+ mortality deceleration is absent. Mortality deceleration is a phenotype of chico.     

GROWTH OF BOTTLENOSE DOLPHINS (TURSIOPS TRUNCATUS) FROM THE INDIAN RIVER LAGOON SYSTEM, FLORIDA, U. S. A.

Gompertz growth models were fitted to total lengths and ages from tooth sections of 199 stranded bottlenose dolphins ( Tursiops truncatus ) from the Indian River Lagoon system, eastern Florida. Based on the model, dolphins from this population are estimated to be born at 119 cm and reach asymptotic length at 250 cm. No apparent pubescent growth acceleration was noted for either sex. Males appeared to grow to slightly longer lengths than females. There were small size differences between Indian River dolphins and those in Texas and Sarasota, indicating general size similarities between North Atlantic and Gulf of Mexico bottlenose dolphins stocks.     

基因工程菌在活性污泥中的衰减及其影响因素

在间歇实验和连续运行的反应器中,考察了基因工程菌细胞密度在活性污泥中的衰减,进行了动力学模型拟合,求得模型参数,并分析了影响衰减的因素.结果表明,在间歇实验和连续运行反应器中,细胞密度在活性污泥中均呈现初期快速衰减而后趋于稳定的趋势.其衰减动力学可以用Logistic模型和Gompertz模型拟合,两个模型的拟合都有很好的相关性和显著性,拟合优度没有差异.在不同的条件下,间歇实验拟合得到的参数取值范围是：Logistic模型衰减系数r′=0.5～0.6 h^-1,稳定细胞密度K′=10⁴～10⁵ cfu·ml^-1;Gompertz模型初始衰减系数b=0.6～1.2 h^-1,比衰减系数a=0.02～0.09 h^-1.初始投加密度对衰减速率影响不大,但是显著影响稳定细胞密度.污泥浓度和温度对衰减速率和稳定密度均有显著影响. 污泥浓度越大,衰减越快,稳定密度越大;而温度越低,衰减越快,稳定密度也会越低.营养条件和微型动物捕食也是影响衰减的重要因素.基因工程菌在连续运行的膜生物反应器和活性污泥反应器中的细胞密度衰减,也可以用Logistic模型拟合,其参数在间歇实验的取值范围内.