Is there an influence of historical events on contemporary fish species richness in rivers? Comparisons between Western Europe and North America

Freshwater fish species richness on 132 West European and North American rivers is analysed using eleven variables related to contemporary ecology (nine) and history (two). This is done in order to examine the relative and joint effects of both historical and ongoing processes on the contemporary richness of these two regional fish faunas. Relationships are quantified by simple and stepwise multiple regression procedures. Species-area curves are presented for the fish faunas within both continents. We show that ecological factors statistically explain most of the variation in freshwater fish species richness for both continents. Effects of historical factors are shown to be statistically significant, but add only a little to the variance already explained by ecological factors. Our analyses further indicate that rivers (which flow directly into the ocean) support fewer species of fish than do similarly sized tributaries. The immigration-extinction hypothesis appears to provide a plausible explanation for this observed pattern. The fact that in our final model, a continental effect is still highly significant, leads us not to exclude the possibility of some other historical influences in generating different overall species richness levels on the two continents.     

Scale-dependent mechanisms in the population dynamics of an insect herbivore

A multiscale approach has lead to significant advances in the understanding of species population dynamics. The scale-dependent nature of population processes has been particularly clearly illustrated for insect herbivores. However, one of the most well-studied insect herbivores, the galling sawfly Euura lasiolepis, has to date been examined almost exclusively at fine spatial scales. The preference-performance, plant vigour and larval survival hypotheses are well supported by this species. Here, we test these hypotheses at a spatial scale larger than that previously considered, i.e. across a landscape in northern Arizona represented by an altitudinal gradient encompassing a series of drainages. We also develop a qualitative model for understanding the population dynamics of E. lasiolepis based on patterns of survival and mortality found in this study and previous ones. Gall density was highly variable across the altitudinal gradient, not explained by host plant variables, and thus a poor surrogate fot population abundance. These findings for the first time fail to support the plant vigour and preference hierarchy hypotheses for E. lasiolepis. Dispersal limitation most likely explains the lack of support for these hypotheses at this scale. By contrast, sawfly survival, gall abortion, parasitism and larval mortality were well explained by host plant quality variables and altitude. The larval survival hypothesis was well supported and is thus comparatively scale-invariant. A qualitative model developed here highlighted the importance of both willow water status and disturbance in determining host plant quality, as well as an apparent trade off between shoot length and plant moisture status in determining vital rates across the altitudinal gradient. This study thus demonstrated for the first time the scale-dependent nature of mechanisms underlying the population dynamics E. lasiolepis, and identified the interaction between parasitism and altitude as a novel mechanism underlying spatial patterns in the survival and mortality patterns of this species.     

具休眠体淡水水生生物分布假说的研究进展

淡水水生生物的分布模式一直是进化和生物地理学研究中的热点问题, 特别是对具休眠体水生生物的研究, 早在达尔文时代就开始探讨具休眠体淡水水生生物分布的原因。根据对文献的整理, 可以将具休眠体淡水水生生物分布模式归纳为三种假说: 随机分布(Everything is Everywhere, EIE)假说、独占(Monopolisation)假说和局域特有(Moderate Endemicity, ME)假说。通过对三种假说的定义, 研究进展和形成不同模式的原因等进行分析, 提出了在研究时需注意是否存在隐存种、季节变化引起基因型变化、研究区域是否覆盖了本物种的所有分布范围、地理环境及地质事件与分布模式之间的关系等问题, 以便更准确的研究具休眠体淡水水生生物分布模式。     

小型哺乳动物种群周期性波动的外因调节假说

对小型哺乳动物种群数量周期性波动的外因调节假说进行介绍 ,概述了食物假说、捕食假说和复合因子假说的主要内容和研究进展。在少数生存环境严酷的小型哺乳动物种群中 ,食物假说能解释它们的周期性数量波动现象 ,可能作为调节因子起作用 ,但难以说明低数量期的确切机制 ,对于大多数小型哺乳动物而言 ,它更可能作为限制因子。捕食假说解释了北欧芬诺斯坎底亚地区某些种群的周期性波动 ,尤其是捕食的间接效应已引起许多学者的关注 ,但也有不支持该假说的证据。对于复合因子假说 ,近年颇受学者重视 ,其中验证食物和捕食交互及累加作用的实验证据较多 ,有的研究还包括气候、种间竞争、空间或社会行为等因素。有关复合因子的实验研究 ,尽管工作是困难和艰巨的 ,花费也是巨大的 ,但所得结果却极有价值 ,为深入理解种群动态调节理论提供了一个合理而有效的手段     

The influence of food abundance,food dispersion and habitat structure on territory selection and size of an Afrotropical terrestrial insectivore

Most tropical insectivorous birds, unlike their temperate counterparts, hold and defend a feeding and breeding territory year-around. However, our understanding of ecological factors influencing territory selection and size in tropical insectivores is limited. Here we examine three prominent hypotheses relating food abundance, food dispersion (spatial arrangement of food items), and habitat structure to territoriality in the Usambara Thrush Turdus roehli. We first compared leaf-litter macro-invertebrate abundance and dispersion, and habitat structure between territories and random sites. We then examined the relation between these same ecological factors and territory size. Invertebrate abundance and dispersion were sparsely and evenly distributed across our study system and did not vary between territories and random sites. In contrast, habitat structure did vary between territories and random sites indicating the Usambara Thrush selects territories with open understorey and closed overstorey habitat. Invertebrate abundance and dispersion within territories of the Usambara Thrush were not associated with habitat structure. We believe the most likely explanation for the Usambara Thrush’s preference for open understorey and closed overstorey habitat relates to foraging behavior. Using information-theoretic model selection we found that invertebrate abundance was the highest-ranked predictor of territory size and was inversely related, consistent with food value theory of territoriality.     

The evolution of adult light emission color in North American fireflies

Firefly species (Lampyridae) vary in the color of their adult bioluminescence. It has been hypothesized that color is selected to enhance detection by conspecifics. One mechanism to improve visibility of the signal is to increase contrast against ambient light. High contrast implies that fireflies active early in the evening will emit yellower luminescence to contrast against ambient light reflected from green vegetation, especially in habitats with high vegetation cover. Another mechanism to improve visibility is to use reflection off the background to enhance the light signal. Reflectance predicts that sedentary females will produce greener light to maximize reflection off the green vegetation on which they signal. To test these predictions, we recorded over 7500 light emission spectra and determined peak emission wavelength for 675 males, representing 24 species, at 57 field sites across the Eastern United States. We found support for both hypotheses: males active early in more vegetated habitats produced yellower flashes in comparison to later‐active males with greener flashes. Further, in two of the eight species with female data, female light emissions were significantly greener as compared to males.     

Grandmothers' longevity negatively affects daughters' fertility

The evolution of postmenopausal longevity in human females has been the subject of debate. Specifically, there is disagreement about whether the evolution of the trait should be understood as an adaptive or a neutral process, and if the former, what the selective mechanism is. There are two main adaptive proposals to explain the evolution of postreproductive longevity: the grandmother and the mother hypotheses. The grandmother hypothesis proposes that postreproductive longevity evolved because it is selectively advantageous for females to stop reproducing and to help raise their grandchildren. The mother hypothesis states that postmenopausal longevity evolved because it is advantageous for women to cease reproduction and concentrate their resources and energy in raising the children already produced. In this article, we test the mother and the grandmother hypotheses with a historical data set from which we bootstrapped random samples of women from different families who lived from the 1500s to the 1900s in the central valley of Costa Rica. We also compute the heritability of longevity, which allows us to determine if genes involved in longevity are nearly fixed in this population. Here we show that although longevity positively affects a woman's fertility, it negatively affects her daughter's fertility; for this reason, the heritability of longevity is unexpectedly high. Our data provide strong grounds for questioning the universality of the grandmother hypothesis and for supporting the mother hypothesis as a likely explanation for the evolution of human postreproductive longevity.     

小型哺乳动物种群周期性波动的自我调节假说

种群调节是种群生态学的一个核心问题。文章主要阐述了小型哺乳动物种群在其低数量期自我调节的4 种可能假说和相关的实验证据。其中, 有关衰老—母体效应假说近年已受到普遍重视, 而支持多态行为假说、社会生物学假说和远交假说的证据较少, 尚需更多的实验来加以验证。衰老—母体效应假说是在应激假说的基础上发展而成的。该假说认为, 母体质量会在整个高峰期的动物中发生改变, 并能够延续到衰减期和低数量期。在低数量期, 种群内的老年个体增多, 导致它们不能维持内分泌的自稳态, 可能通过影响后代的存活和生殖而维持低数量, 进而起到调节种群周期的作用。针对国际上研究的发展趋势, 我们还对未来的研究方向提出了一些建议。     

Sex versus parasitism versus density

The Red Queen hypothesis predicts that sexual reproduction should be favoured when the risk of infection by parasites is high. However, this prediction may also be achieved independently by means of the reproductive assurance and the density-dependent transmission hypotheses because higher densities increase the chances of fertilization (i.e. mates are easier to find) and increase the risk of infection. Additionally, the Red Queen hypothesis makes a long-term prediction that infection should be genotype-specific, with time-lagged dynamics. In the present study, we attempt to consolidate these two predictions by investigating whether sexuality and parasitism alternate in a time-lagged fashion on an ecological time-scale. In a 3-year study, we examined the time-lagged dynamics between male frequencies, infection levels (by Centrocestus sp.), and snail densities of four natural populations of sexual and asexual Melanoides tuberculata snails. The results obtained provide no evidence of either prediction of the Red Queen hypothesis. We found partial support for reproductive assurance in a single population, and could not discriminate between the three hypotheses in another population. The remaining two populations did not support any of the hypotheses in question.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 537–544.     

Correlates of alternative migratory strategies in western bluebirds

Partial migration occurs when only some animals in a population migrate. While evidence suggests that migratory strategies are partially controlled by genes, individual and environmental conditions which alter the cost‐benefit trade‐off of migration among individuals are also likely to play a role. Three hypotheses have been advanced to explain condition‐dependent partial migration: the arrival time, dominance and body size hypotheses. In this study, we asked whether these hypotheses explained differences in migratory strategy among individuals in a partially migratory population of western bluebirds Sialia mexicana breeding in southern British Columbia, Canada. We used stable hydrogen isotope signatures in claw tissue to determine migratory strategy of individual bluebirds, and examined patterns of migration at both individual and population levels. The proportion of resident bluebirds varied significantly over the three years of the study, and across study sites. Several migrants switched to the resident strategy between years; however, we found no evidence of strategy switching in the opposite direction. Young birds were significantly more likely to be resident than older birds, a pattern which could arise if early arrival is particularly important for birds obtaining a territory for the first time. Furthermore, young females were the most likely of all sex–age classes to be resident, which may reflect a survival advantage of residency for young females. Finally, birds mated assortatively by migratory strategy and isotopic evidence suggests that members of a pair often wintered in the same place. Our results provided no support for the dominance or body size hypotheses, and only limited support for the arrival time hypothesis in bluebirds. However, taken together, we suggest that our findings indicate that social factors may influence migratory strategies in this system.     

Dexamethasone treatment supports age‐related maturation of the stress response in altricial nestling birds

In birds, the magnitude of the adrenocortical stress response can be down‐regulated during specific life‐history stages. Such modulation likely occurs when the effects of mounting robust corticosterone (Cort) elevations interfere with the normal progression of critical lifecycle activities (e.g. development, molt, migration, reproduction). The developmental hypothesis posits that altricial birds should display a ‘stress hyporesponsive period’ during the early post‐natal life stages, characterized by reduced adrenocortical stress responses compared to adult birds and a gradual age‐related increase. Such modulation would allow avoiding the potential deleterious effects that long‐term elevations of circulating Cort might exert on growth and development, when the physiological and behavioral abilities to cope with disturbance are limited. Two proximate hypotheses have been proposed to explain this age‐dependent pattern of Cort secretion. The ‘maturation hypothesis’ proposes a progressive age‐related growth, maturation and enhanced sensitivity to sensory input of the Hypothalamic‐Pituitary‐Adrenal (HPA) axis tissues, whereas the ‘negative feedback attenuation hypothesis’ proposes a gradual attenuation in the intensity of the negative feedback in the HPA axis. Here we tested these hypotheses by experimentally inducing negative feedback on the HPA axis via dexamethasone (DEX) treatment in nestling white storks Ciconia ciconia. Nestling age positively affected stress‐induced plasma Cort (STRESS‐Cort) levels during experimental handling and restraint, thus supporting the developmental hypothesis. DEX treatment significantly reduced STRESS‐Cort levels compared to saline (SAL) treatment, thus eliciting the expected negative feedback on the HPA axis. However, inter‐ and intra‐individual comparisons indicated no age effects on the intensity of the negative feedback exerted by DEX. Our results do not support the negative feedback attenuation hypothesis and suggest that progressive maturation of the HPA axis tissues is the proximate mechanism responsible for age‐related changes in the stress response during avian post‐natal development. We encourage further tests of the proposed proximate mechanisms during migration, breeding and molt.     

Is invasion success explained by the enemy release hypothesis?

A recent trend in invasion ecology relates the success of non‐indigenous species (NIS) to reduced control by enemies such as pathogens, parasites and predators (i.e. the enemy release hypothesis, ERH). Despite the demonstrated importance of enemies to host population dynamics, studies of the ERH are split – biogeographical analyses primarily show a reduction in the diversity of enemies in the introduced range compared with the native range, while community studies imply that NIS are no less affected by enemies than native species in the invaded community. A broad review of the invasion literature implies at least eight non‐exclusive explanations for this enigma. In addition, we argue that the ERH has often been accepted uncritically wherever (i) NIS often appear larger, more fecund, or somehow ‘better’ than either congeners in the introduced region, or conspecifics in the native range; and (ii) known enemies are conspicuously absent from the introduced range. However, all NIS, regardless of their abundance or impact, will lose natural enemies at a biogeographical scale. Given the complexity of processes that underlie biological invasions, we argue against a simple relationship between enemy ‘release’ and the vigour, abundance or impact of NIS.     

中国人类化石的主要发现和理论探索(1922-2009)

文中简要回顾和总结近90年来中国古人类学的发展历程与脉络,重在梳理中国人类化石的发现、解剖特征、年代测定,以及建立在这些研究基础上所提出的主要理论学说,收尾于中国现代人类起源之论争.对中国古人类化石的形态学特征的比较研究导致为中国的人类进化提出新的假说-连续进化附带杂交说.这个假说同样获得古文化和古环境丰富信息的支持.     

生态学假说试验验证的原假说困境

试验方法是生态学假说的主要验证方法之一,但也存在由原假说引发的质疑.Quinn和Dunham(1983)通过对Platt(1964)的假说-演绎模型进行分析,主张生态学不可能存在可以严格被试验验证的原假说.Fisher的证伪主义与Neyman-Pearson(N-P)的非判决性使得统计学原假说不能被严格验证;而生态过程中存在的不同于经典物理学的原假说H₀(α=1,β=0)与不同的备假说H₁′(α′=1,β′=0)的情况,使得生态学原假说也很难得到严格的实验验证.通过降低P值、谨慎选择原假说、对非原假说采取非中心化和双侧验证可分别缓解上述的原假说困境.但统计学的原假说显著性验证(NHST)不应等同于生态学假说中有关因果关系的逻辑证明方法.因此,现有大量基于NHST的生态学假说的方法研究和试验验证的结果与结论都不是绝对的逻辑可靠的.     

Biogeographic bases for a shift in crop C : N : P stoichiometries during domestication

We lack both a theoretical framework and solid empirical data to understand domestication impacts on plant chemistry. We hypothesised that domestication increased leaf N and P to support high plant production rates, but biogeographic and climate patterns further influenced the magnitude and direction of changes in specific aspects of chemistry and stoichiometry. To test these hypotheses, we used a data set of leaf C, N and P from 21 herbaceous crops and their wild progenitors. Domestication increased leaf N and/or P for 57% of the crops. Moreover, the latitude of the domestication sites (negatively related to temperature) modulated the domestication effects on P (+), C (?), N : P (?) and C : P (?) ratios. Further results from a litter decomposition assay showed that domestication effects on litter chemistry affected the availability of soil N and P. Our findings draw attention to evolutionary effects of domestication legacies on plant and soil stoichiometry and related ecosystem services (e.g. plant yield and soil fertility).     

A unified view of the initiation of protein synthesis

The mechanism of the initiation of protein synthesis is discussed in terms of two different hypotheses in which each emphasized a different possible element of the process: the Shine-Dalgarno (SD) hypothesis ascribed an essential role to recognition of the SD segment by the ribosomal RNA; it is supported by a variety of experiments but conflicting evidence negates its obligatory nature. In contrast, our hypothesis highlighted the role of the structure of the mRNA and proposes that the initiation codon is selected by virtue of its unique accessibility. The rationale for the importance of accessibility in the selection of the initiation site is discussed. An analysis and a recapitulation of the initiation process and ribosomal specificity are presented. The apparent conflicts with the SD hypothesis are resolved in a unified mechanism where accessibility is the dominant factor.     

鸟类羽色多态现象：概念及其进化机制假说

多态现象对了解物种的遗传、变异和进化有着重要意义,鸟类羽色多态现象的进化机制,是多态现象研究中非常重要的内容。鸟类羽色多态现象的进化机制假说主要有：分化选择假说、异类选择假说和非随机性交配假说等。本文对鸟类羽色多态现象的概念和以上进化机制假说进行了综述,并针对鸟类羽色多态现象进化机制研究中存在争议的问题及研究的不足提出了自己的看法。