Resource quality and spatial variation in sex ratios of a free-living solitary sawfly,Dineura virididorsata (Hym., Tenthredinidae)

The sex ratio in final-instar larvae of a birch-feeding, free-living solitary sawfly, Dineura virididorsata, was investigated in Finnish Lapland. The prepupal proportion of females, pooled over ten sites, was 56%, and at four individual sites the sex ratio was significantly female-biased. Larval survival from egg to prepupae did not differ between the sexes. This suggests a femalebiased primary sex ratio in the field. The sex ratio varied among the sites but not among host trees within sites. Contrary to previous results with hymenopterans, we did not find that differences in the sex ratio depended on forage quality: site-specific or tree-specific sex ratios did not correlate with the average prepupal weight. A literature search indicated that female-biased sex ratios are also common in other free-living sawflies. We are unable to explain sex ratios of Dineura virididorsata or other free-living sawflies with existing general models.     

Metapopulation dynamics with quasi-local competition

Stepping-stone models for the ecological dynamics of metapopulations are often used to address general questions about the effects of spatial structure on the nature and complexity of population fluctuations. Such models describe an ensemble of local and spatially isolated habitat patches that are connected through dispersal. Reproduction and hence the dynamics in a given local population depend on the density of that local population, and a fraction of every local population disperses to neighboring patches. In such models, interesting dynamic phenomena, e.g. the persistence of locally unstable predator-prey interactions, are only observed if the local dynamics in an isolated patch exhibit non-equilibrium behavior. Therefore, the scope of these models is limited. Here we extend these models by making the biologically plausible assumption that reproductive success in a given local habitat not only depends on the density of the local population living in that habitat, but also on the densities of neighboring local populations. This would occur if competition for resources occurs between neighboring populations, e.g. due to foraging in neighboring habitats. With this assumption of quasi-local competition the dynamics of the model change completely. The main difference is that even if the dynamics of the local populations have a stable equilibrium in isolation, the spatially uniform equilibrium in which all local populations are at their carrying capacity becomes unstable if the strength of quasi-local competition reaches a critical level, which can be calculated analytically. In this case the metapopulation reaches a new stable state, which is, however, not spatially uniform anymore and instead results in an irregular spatial pattern of local population abundance. For large metapopulations, a huge number of different, spatially non-uniform equilibrium states coexist as attractors of the metapopulation dynamics, so that the final state of the system depends critically on the initial conditions. The existence of a large number of attractors has important consequences when environmental noise is introduced into the model. Then the metapopulation performs a random walk in the space of all attractors. This leads to large and complicated population fluctuations whose power spectrum obeys a red-shifted power law. Our theory reiterates the potential importance of spatial structure for ecological processes and proposes new mechanisms for the emergence of non-uniform spatial patterns of abundance and for the persistence of complicated temporal population fluctuations.     

Spatial instabilities and local oscillations in a lattice gas Lotka–Volterra model

 We analyze the evolution of spatially inhomogeneous perturbations in a lattice gas model for a prey-predator population. Starting with the master equation of the model, decoupled by means of a mean field approximation, spatial instabilities are seen to take place in a region of the phase diagram. This is in qualitative agreement with local oscillations already observed in computer simulations. We determine the transition line that separates the homogeneous region from the inhomogeneous region and we study the spatio-temporal self-organized structures that appear inside the inhomogeneous region. Received 3 November 1995; received in revised form 26 January 1996     

氮磷添加对栓皮栎不同地理种源幼苗温度耐性的影响

通过氮磷添加控制试验,对湖南城步(CB) 、湖北秭归(ZG)、河南内乡(NX)、河北临城(LC)和北京平谷(PG)5个种源的栓皮栎1年生幼苗的叶片温度耐性指标(耐寒性、耐热性及耐温范围)及相关生理指标(叶片养分浓度、非结构性碳水化合物及其组分和养分利用效率)进行测定,研究养分对植物种内不同地理种源的温度耐性影响.结果表明:不同种源的栓皮栎养分吸收与氮磷利用效率对氮磷添加存在显著差异但地理趋势不明显.PG在N、P及其二者复合添加的情况下均具有较高的氮磷利用效率,NX则在不同处理下磷利用效率均处于最低水平,CB在磷添加的情况下对磷的利用效率最高.与对照相比,养分(N、P或NP)添加能明显增加PG和LC的耐寒性,但N添加降低了NX的耐寒性.同时,养分添加在一定程度上增加了ZG、NX和LC的耐热性.耐温范围与耐寒性相反,表现为养分添加降低了PG和LC的温度耐受范围, 而增加了NX的温度耐受范围.偏相关分析表明,耐寒性与叶片可溶性糖浓度呈显著正相关;耐热性与叶片P呈显著负相关,与N/P呈显著正相关;叶片耐温范围与叶片物质浓度无显著相关性.因此,不同地理种源对养分利用程度及其效率可能与源生地土壤环境条件有关,表现出一定的局域适应特征,从而增加了温度耐性对养分响应的复杂程度.     

Part II: Fibroblasts preferentially migrate in the direction of principal strain

A growing body of evidence suggests that the sensory information from the cytoskeleton and integrins may be responsible for guiding migration during mechano- and haptotaxis. However, the dual function of these subcellular structures as mechano-sensors and -actuators is only partially understood. Using a new cell chamber described in the preceding companion paper (Ref to part I, Raeber et al. 2007a) we investigated the migration response of adhesion-dependent fibroblasts embedded 3-dimensionally within synthetic protease-sensitive poly(ethylene glycol) hydrogels to stepwise and cyclic mechanical loads. To that end, we developed a spatially and temporally resolved migration analysis technique capable of providing estimates of statistical cell migration parameters along and perpendicular to the main strain direction. Fibroblasts reoriented themselves in the direction of principal strain, increased their proteolytic migration activity and moved preferentially parallel to the principal strain axis. These results point to a possible correlation between planes of iso-strain and migration direction.     

The small-scale pattern of Cynodon dactylon in Mediterranean pastures

The abundance of Cynodon dactylon was recorded in 50 plots presenting different geomorphological conditions and along a transect of 16 500 2×2 cm contiguous quadrats within a small basin 330 m in length, in the granite pediment of the Sierra de Guadarrama (Central Spain). Soil analyses were undertaken on samples from the 50 plots and the soil information matrix obtained was analysed using Principal Components Analysis and Discriminant Analysis. Results showed that in the Mediterranean pastures Cynodon dactylon was restricted to deep, well developed soils with relatively high values of cations, conductivity and organic matter, and could be used as an indicator of such soil conditions in these grasslands. The spatial pattern of the species was analysed using New Local Variances which revealed the existence of a small-scale pattern, ranging from 8 to 18 cm, present at all levels of the analysis. The size of small-scale patterns was positively correlated with species abundance and was interpreted as a relation between plant vigour and favourable soil conditions.I would like to thank Professor González Bernáldez for his interest and encouragement.     

多通道局部场电位时变频谱的同步模式及其对行为事件的编码

用时变相干（time-varying coherence）频谱方法分析多通道局部场电位（local field potentials, LFPs）随时间变化的同步模式及其对行为事件的编码。实验数据为行为事件前后3秒的28通道LFPs。分别计算每个通道LFP的功率谱密度（power spectral density, PSD）及多通道LFPs各个特征频段的PSD,选取PSD分布集中的?兹频段为LFPs的特征频段;应用离散二进小波变换获取LFPs的?兹频段分量;从28通道LFPs中选取PSD最大的通道作为参考通道。选取计算窗口为50 ms,从初始点开始计算每个窗口中每个通道LFP及其?兹分量对参考通道的频谱相干分析。移动窗口步长为25 ms,获取多通道LFPs及其?兹分量的时变频谱相干动态分布。研究结果显示,?兹频段分量的PSD占LFPs总功率的71.95%,表明?兹分量是实验中多通道LFPs同步的特征频段;多通道LFPs的?兹分量频谱相干值随时间变化,行为事件点前后1 s的相干值具有显著差别（P＜0.05）,表明多通道LFPs的?兹频段时变频谱相干有效地编码了这一行为事件。