Emigration and Density Dependence in Yellowstone Bison

Abstract: Understanding the relative importance of density-dependent and density-independent feedback on population growth is essential for developing management strategies to conserve wildlife. We examined a 99-year time series of annual counts and removals for 2 bison (Bison bison) herds occupying northern and central Yellowstone National Park in the western United States. Yellowstone's aggressive management intervention effectively recovered bison from 46 animals in 1902 to > 1,500 animals in 1954. Supplemental feeding of the northern herd facilitated rapid growth (r = 0.16) during 1902 to 1952. Augmentation of the central herd with 71 animals also led to rapid growth over 1936 to 1954 (r = 0.10). In 1969, manipulative management ceased in the park, and we detected evidence of density-dependent changes in population growth rates for both herds during 1970 to 2000 as numbers increased to >3,000 animals. The central herd showed evidence of a constant density-dependent response over 1970 to 2000. In contrast, density dependence had a stronger effect on the northern herd's growth rate during 1970 to 1981 than during 1982 to 2000. We found evidence to suggest that these trends resulted from pulses of emigration from the central herd to the northern range beginning in 1982 in response to resource limitation generated by an interaction between density and severe snow pack. Corroborative evidence supporting this interpretation included 1) the annual growth of the central herd was negatively correlated with snow pack but that of the northern herd was not, 2) growth rates of the central and northern herds were uncorrelated during 1970 to 1981 but significantly and negatively correlated during 1982 to 2000, and 3) the northern herd could not have sustained the high removals experienced during 1984 to 2000 without immigration. Density-related emigration from the central herd to the northern range may be fueling bison emigration onto private and public lands where large-scale removals occur, exacerbating the brucellosis controversy for natural resource managers.     

Winter Forage Selection in White-Tailed Deer at High Density: Balsam Fir is the Best of a Bad Choice

Abstract: We assessed winter forage selection by white-tailed deer (Odocoileus virginianus) on Anticosti Island, Quebec, Canada, using cafeteria-feeding trials. Winter habitat on Anticosti is degraded and free-ranging deer at high densities consume 70% balsam fir (Abies balsamea) and 20% white spruce (Picea glauca), even though spruce is much more available than fir. Deer ate 89.9% balsam fir and 10.1% white spruce when the availability of both trees was equal. Deer did not eat shredded twigs more than intact twigs. Fiber content and condensed tannins were greater in white spruce than in balsam fir. Deer preference for fir was not based on texture but, more likely, on plant constituents, so we concluded that deer will nearly eliminate fir before they use any significant amount of white spruce. Management actions, therefore, need to be undertaken to enhance balsam fir regeneration.     

茂兰喀斯特森林林隙幼苗出现的时空格局

通过4次对茂兰自然保护区喀斯特森林林隙内种子的天然萌发情况进行观测,分析了林隙内幼苗的萌发数量、存活率及幼苗出现的时空分布格局。结果发现：林隙中大多数萌发的幼苗存活率均较高,平均存活率达50%以上,林隙的形成,不但提高了喀斯特森林树种的萌发率,也提高了幼苗的存活率。林隙中心、近中心、林隙边缘各区域幼苗的密度存在显著的空间差异,山拐枣（Poliothyrsis sinensis）、多脉榆（Ulmus castaneifolia）等树种在林隙中心幼苗密度最大,圆果化香（Platycarya longipes）、翅荚香槐（Cladrastis platycarpa）、圆叶乌桕（Sapium rotundifolium）、掌叶木（Handeliodendron bodinieri）、黄连木（Pistacia chinen-sis）和云贵鹅耳枥（Carpinus pubescens）等树种在林隙近中心幼苗密度最大,而樟叶槭（Acercinnamomifolium）、球核荚蒾（Viburnumpropinquum）、小叶青冈（Cyclobalanopsis myrsinaefolia）、轮叶木姜子（Litsea verticillata）等则在林隙边缘光照较弱的地方生长良好。幼苗出现的时间分布特征明显,整个观察期幼苗都持续萌发,但大多数树种幼苗出现在第2观测期（3月）,幼苗出现数目从第2次到后面的几次观察期显著下降。林隙3个区域幼苗出现不是同步的,林隙中心的幼苗出现最快,与其它两个部位相比,林隙边缘的幼苗出现有滞后现象。研究结果表明林隙中心的环境条件有利于种子萌发,但林隙近中心却更利于幼苗存活。     

Stimulation of lipolysis enhances the rate of cholesterol efflux to HDL in adipocytes

Adipose tissue constitutes a major location for cholesterol storage and, as such, it may play a role in the regulation of circulating cholesterol levels. A possible metabolic link between the lipolytic activity of adipocytes and their ability to release cholesterol to reconstituted human high density lipoprotein, HDL, was investigated in 3T3-L1 adipocytes. In the presence of HDL, composed of human apoA-I and phosphatidylcholine, adipocytes release cholesterol in a lipoprotein-dose and time dependent fashion. β-adrenergic activation of the lipolysis promotes a 22% increase in the extent of cholesterol efflux to reconstituted discoidal HDL particles. Activation of lipolysis promotes a rapid decrease in the cholesterol content of the plasma membrane and a concomitant increase in lipid droplet cholesterol. This change is independent of the presence of HDL. Activation of the lipolysis does not affect the levels of ABCA1 and SR-BI. Therefore, the enhancement of cholesterol efflux is not due to the level of plasma membrane cholesterol, or to the levels of the cholesterol transporters ABCA1 and scavenger receptor SR-BI. Brefeldin A did not affect the rate of cholesterol efflux under basal lipolytic conditions, but it abolished the lipolysis-dependent enhancement of cholesterol efflux to HDL. This study suggests that activation of lipolysis is accompanied by an increase in BFA-sensitive vesicular transport that in turn enhances cholesterol efflux to HDL. The study supports a metabolic link between the lipolytic activity of adipocytes and the rate of cellular cholesterol efflux to HDL.     

Temporal consistency in the long-term spatial distribution of macroinvertebrate drift along a stream reach

Previous studies of the spatial pattern of stream invertebrate drift have focused on spatial variation at microhabitat scales or landscape scales, or temporal variation over diel or seasonal scales. None have examined consistency in spatial variation over longer time scales (>1 year). This study examined invertebrate drift density and composition at fixed locations (terminal ends of 10 riffles) each month at day and night along a 1 km reach of a 2nd order stream over a period of nearly 2 years. Consistent differences in the density of macroinvertebrate drift between riffles over 2 years were observed. The only habitat characteristic observed to be related to invertebrate drift density was the length and size of riffles above sampling sites, with larger and longer riffles producing the highest drift densities. Consistent differences in the supply of drifting macroinvertebrates along a stream reach may have implications for the supply of colonists to substrate patches and the profitability of feeding positions for drift-feeding fish and other predators. Handling editor: D. Dudgeon     

No evidence of genetic benefits from extra-pair fertilisations in female sand martins (Riparia riparia)

Genetic parentage studies of socially monogamous birds reveal a widespread prevalence of extra-pair paternity. Variation in extra-pair paternity among individuals may depend on how different individuals benefit from extra-pair fertilisations and on the opportunity to pursue extra-pair copulations. A long-term study of sand martins (Riparia riparia) in Hungary allowed us to examine patterns of extra-pair fertilisations in a large colony of over 3,000 breeding pairs with many known age individuals. We used multi-locus DNA fingerprinting to determine whether extra-pair fertilisations occur when females are paired to (1) presumably low quality mates, or (2) genetically similar or dissimilar mates, and whether extra-pair fertilisations result in offspring of higher quality. Extra-paternal young were found in 38% of 47 broods and comprised 19% of 190 offspring. Males that lost paternity did not differ significantly from others in age or body condition. Social mates of broods containing extra-pair offspring did not differ in genetic similarity from pairs without extra-pair offspring. Furthermore, there was no significant difference in body condition between extra-pair young and their maternal half-siblings. We were unable to assign paternity and therefore cannot exclude the possibility that extra-pair males differed from the within-pair males they cuckolded, in age, body condition or genetic similarity with the female. We found a positive relationship between paternity losses and breeding density, suggesting that low breeding density may constrain opportunities for seeking extra-pair copulations.     

The significance of ratios of detritus types and micro-organism productivity to competitive interactions between aquatic insect detritivores

Investigations of competitive interactions emphasize non-detrital resources, even though detritus is a major component of most food webs. Studies of competing species focus usually on single resource types, although consumers in nature are likely to encounter mixtures of resource types that may affect whether competition results in exclusion or coexistence. The invasive mosquito Aedes albopictus is capable of excluding the native mosquito Ochlerotatus triseriatus in competition for single detritus types in laboratory and field microcosms. In this study, we used nine ratios of two detritus types (animal and leaf) common in natural containers to test whether detritus ratios affect the outcome of competition. Under intraspecific and interspecific competition, A. albopictus attained higher survival and estimated population growth rate than did O. triseriatus. Unlike past studies, both species had positive growth and high adult survival, with little evidence of competitive effects, under one resource ratio (10:1 ratio of leaf : animal detritus) regardless of mosquito densities, suggesting potential coexistence. Path analysis showed that densities of larvae had negative effects on population growth for O. triseriatus but not for A. albopictus, indicating competitive superiority of A. albopictus. Population growth of both species was affected strongly by the direct paths from animal (positive) and leaf (negative) detritus, and the indirect effect of leaf detritus via bacterial production (positive). Field sampling established that detritus entered real tree holes in ratios similar to those in our experiment, suggesting that natural variation in detritus ratios may influence local coexistence of these species. Seasonal variation in ratios of plant and animal detritus indicated that temporal as well as spatial variation in inputs may be important for potential coexistence.     

The extended Moran effect and large-scale synchronous fluctuations in the size of great tit and blue tit populations

1. Synchronous fluctuations of geographically separated populations are in general explained by the Moran effect, i.e. a common influence on the local population dynamics of environmental variables that are correlated in space. Empirical support for such a Moran effect has been difficult to provide, mainly due to problems separating out effects of local population dynamics, demographic stochasticity and dispersal that also influence the spatial scaling of population processes. Here we generalize the Moran effect by decomposing the spatial autocorrelation function for fluctuations in the size of great tit Parus major and blue tit Cyanistes caeruleus populations into components due to spatial correlations in the environmental noise, local differences in the strength of density regulation and the effects of demographic stochasticity. 2. Differences between localities in the strength of density dependence and nonlinearity in the density regulation had a small effect on population synchrony, whereas demographic stochasticity reduced the effects of the spatial correlation in environmental noise on the spatial correlations in population size by 21.7% and 23.3% in the great tit and blue tit, respectively. 3. Different environmental variables, such as beech mast and climate, induce a common environmental forcing on the dynamics of central European great and blue tit populations. This generates synchronous fluctuations in the size of populations located several hundred kilometres apart. 4. Although these environmental variables were autocorrelated over large areas, their contribution to the spatial synchrony in the population fluctuations differed, dependent on the spatial scaling of their effects on the local population dynamics. We also demonstrate that this effect can lead to the paradoxical result that a common environmental variable can induce spatial desynchronization of the population fluctuations. 5. This demonstrates that a proper understanding of the ecological consequences of environmental changes, especially those that occur simultaneously over large areas, will require information about the spatial scaling of their effects on local population dynamics.     

戊四氮点燃癫痫大鼠空间学习记忆改变及海马突触素、突触后致密物PSD-95表达的变化

目的探讨戊四氮点燃癫痫对大鼠空间学习记忆的影响及可能的分子机制。方法戊四氮(pentylenetet-razol,PTZ)点燃建立慢性癫痫(chronic epileptic,CEP)模型,Morris水迷宫进行行为学检测,免疫组织化学方法观察大鼠海马CA1、CA3区突触素(synaptophysin,P38)和突触后致密物95(postsynaptic density 95,PSD-95)的表达,并用计算机图像分析系统对免疫反应结果进行处理。结果水迷宫试验检测癫痫组大鼠空间学习记忆能力受损;免疫组化结果表明其海马CA1、CA3区P38和PSD-95免疫反应产物较对照组明显减少(P<0.01,P<0.05)。结论戊四氮点燃癫痫大鼠伴有学习记忆功能减退,其海马神经元P38和PSD-95的表达减少可能参与了空间学习记忆受损。     

进展期胃癌p53表达与微血管密度及生物学行为的关系

目的探讨进展期胃癌生长过程中p53基因表达与微血管密度和生物学行为之间的关系。方法搜集有随访资料的胃癌标本107例,用免疫组化对突变型p53和CD34作了标记,用原位杂交对野生型p53作了检测。结果突变型p53在肿瘤不同侵犯深度、不同生长方式、不同淋巴结转移状态以及预后方面,存在显著差异(P<0.05),突变型p53与微血管密度显著相关(P<0.05),而野生型p53则与突变型p53相反。结论突变型和野生型p53在肿瘤生长过程中的表达不同,说明p53的不同功能状态在肿瘤的发展过程中发挥重要作用。