Effects of agri-environmental schemes on farmland birds: do food availability measurements improve patterns obtained from simple habitat models?

Studies evaluating agri‐environmental schemes (AES) usually focus on responses of single species or functional groups. Analyses are generally based on simple habitat measurements but ignore food availability and other important factors. This can limit our understanding of the ultimate causes determining the reactions of birds to AES. We investigated these issues in detail and throughout the main seasons of a bird's annual cycle (mating, postfledging and wintering) in a dry cereal farmland in a Special Protection Area for farmland birds in central Spain. First, we modeled four bird response parameters (abundance, species richness, diversity and “Species of European Conservation Concern” [SPEC]‐score), using detailed food availability and vegetation structure measurements (food models). Second, we fitted new models, built using only substrate composition variables (habitat models). Whereas habitat models revealed that both, fields included and not included in the AES benefited birds, food models went a step further and included seed and arthropod biomass as important predictors, respectively, in winter and during the postfledging season. The validation process showed that food models were on average 13% better (up to 20% in some variables) in predicting bird responses. However, the cost of obtaining data for food models was five times higher than for habitat models. This novel approach highlighted the importance of food availability‐related causal processes involved in bird responses to AES, which remained undetected when using conventional substrate composition assessment models. Despite their higher costs, measurements of food availability add important details to interpret the reactions of the bird community to AES interventions and thus facilitate evaluating the real efficiency of AES programs.     

中国鸦雀的系统分类研究

本文对我国的鸦雀,提出一个新的分类系统,列有4个亚属,14种;同时还报道一个新亚种,即黄嘴鸦雀贡山亚种。从鸦雀在国内外的分布情况及棕头鸦雀亚种组的形成,推测鸦雀的起源地可能是在我国西南区的横断山脉。     

崇明东滩湿地芦苇种群内功能性状及生态对策变异分析

植物种群功能性状及生态对策变异对其自身环境适应能力及群落结构具有重要影响。该文基于崇明东滩湿地芦苇(Phragmites australis)种群内3个小种群不同发育时期分株集合的多项性状指标,分析了其性状及生态对策变异,并基于CSR、LHS生态对策体系,对各小种群的生态对策进行了排序。结果表明, 3个芦苇小种群的21项性状指标及C、R对策得分均存在显著差异。在LHS体系中,以比叶面积(11.5 mm2/mg)、株高(175 cm)和花序干质量(4 g)为分界线,可对3个小种群进行区分。处于生殖生长期的芦苇分株具有更大的植株大小、更高的叶片干物质含量及S对策得分,而处于营养生长期的分株则具有较小的植株大小、较大的比叶面积及R对策得分。总体而言,崇明东滩湿地3个芦苇小种群间及各小种群内处于不同生长发育阶段的分株集合间,都存在显著的性状差异及生态对策差异,且二者的差异模式基本吻合。芦苇种内性状及生态对策变异特征,可为该区芦苇种群的生态保育和恢复实践提供重要的理论参考和技术支撑。     

Bacterial responses to natural organic inputs in a marine subAntarctic area

Quantitative investigations of bacteriological and organic matter parameters were conducted regularly at least once a week for a year at three subAntarctic benthic stations. The different bacteriological methods used (direct counts, viable counts and heterotrophic potentials) gave complementary results. Despite substantial differences in organic matter content of the different sediments, the bacterial communities were of similar density. Seasonal variations observed in the studied area were regular enough to allow a detailed analysis. A general scheme describing the reactions of the bacterial microflora to the different periods of organic input is discussed. This model, which includes three parts (lag phase, growing phase and return to the initial state), allows the interpretation of the bacterial responses observed during the benthic surveys.     

A microscopic model for the current-voltage behaviour of the Na,K-pump

The current voltage characteristic of the Na, K pump is described on the basis of a modified Post-Albers cycle. The voltage dependence of the rate constants is derived from the elementary chargetranslocations associated with the single reaction steps. Charge displacements result from movements of the sodium- or potassium-loaded binding sites, as well as from motions of polar groups in the pump molecule. If part of the transmembrane voltage drops between the alkali-ion binding sites and the aqueous solution, the binding constants become voltage-dependent. Depending on the values of the microscopic parameters, the current-voltage characteristic may assume a variety of different shapes. Saturating behaviour results when one or more voltage-independent reaction steps become rate limiting. Non-monotonic current-voltage curves exhibiting regions of negative pump conductance are predicted when, at least in one of the transitions, charge is moved against the direction of overall charge-translocation. The theoretical predictions are compared with recent experimental studies of voltage-dependent pump currents.     

Photon requirement for growth of the diatom Phaeodactylum tricornutum Bohlin (Bacillariophyceae)

Abstract Photon requirements for growth (φ_g^?1) of the diatom Phaeodactylum tricornutum were determined under nutrient-sufficient conditions at two photon flux densities corresponding to light limited and near-saturating conditions for growth. The value of φ_g^?1 based on assimilated carbon was light-dependent and varied from 8.8 to 14.0 mol photon mol C^?1 with the minimum value at the lowest photon flux density. These results are lower than might be predicted for microalgal growth based on the Z scheme of photosynthesis. Conversion of these values for carbon fixation to estimates based on oxygen evolution is problematical due to uncertainty over the appropriate assimilatory quotient (Q_a= mol O₂ mol C^?1). Minimum values based on oxygen evolution rates ranged from 6.2 to 7.6 mol photon mol O₂^?1 using a Q_a of 1.41 mol O₂ mol C^?1 obtained by Myers (1980). These estimates are similar to our previous measurements for photosynthesis and indicate a high efficiency for light energy transforming reactions during growth. The values of (φ_g^?1 obtained in this work indicate a number of inadequacies in our understanding of the energetics of microalgal growth and are inconsistent with our present knowledge of photosynthetic energy coupling in plant cells.     

Patch clamp study and kinetic modeling on the most abundant chloride channel on distal fibers of crayfish opener muscle

Whereas the inhibitory innervation of the deep extensor abdominal muscle in crayfish is mediated by a weakly acting common inhibitor, the opener muscle exhibits a stronger inhibition. In the present study the most abundant γ-aminobutyric acid-activated chloride channel on distal fibers of crayfish opener muscle was characterized by measuring the current responses after applying pulses of γ-aminobutyric acid to outside-out patches. The results were compared to those obtained earlier with the chloride channel on the deep extensor abdominal muscle of the same species. The double logarithmic plot of the dose-response relationship had a slope of n _H = 2.2 in contrast to n _H = 5.3 for the channel on the deep extensor abdominal muscle. The rise time of the current response declined to 1 ms at a γ-aminobutyric acid concentration of 50 mmol · l⁻¹. With lower concentrations the rise time increased to a maximal value of 280 ms. No peak of the rise time at low γ-aminobutyric acid concentrations, as observed for the channel on the deep extensor abdominal muscle, was obvious. The open and closed times were similar to those of the channel of the deep extensor abdominal muscle. Different reaction schemes were discussed to describe the kinetics of the chloride channel of the opener muscle. Accepted: 12 August 1996