Large‐brained mammals live longer

Many mammals have brains substantially larger than expected for their body size, but the reasons for this remain ambiguous. Enlarged brains are metabolically expensive and require elongated developmental periods, and so natural selection should have favoured their evolution only if they provide counterbalancing advantages. One possible advantage is facilitating the construction of behavioural responses to unusual, novel or complex socio‐ecological challenges. This buffer effect should increase survival rates and favour a longer reproductive life, thereby compensating for the costs of delayed reproduction. Here, using a global database of 493 species, we provide evidence showing that mammals with enlarged brains (relative to their body size) live longer and have a longer reproductive lifespan. Our analysis supports and extends previous findings, accounting for the possible confounding effects of other life history traits, ecological and dietary factors, and phylogenetic autocorrelation. Thus, these findings provide support for the hypothesis that mammals counterbalance the costs of affording large brains with a longer reproductive life.     

Seedling interactions in a tropical forest in Panama

Competition is believed to be a central force limiting local diversity and controlling the structure of plant communities. However, it has been proposed that the stressed understory environment limits total understory plant density to such low levels that competitive exclusion cannot be an important factor limiting the local diversity of understory plants. To evaluate the importance of inter-seedling competition, we performed a seedling competition experiment with five shade-tolerant species in a tropical moist forest in Panama. Three-month-old seedlings were transplanted into the forest singly or with their roots intertwined with a single conspecific or heterospecific seedling in all pairwise species combinations. If competition is important, performance (survival, stem height, and number of leaves after one and six years) would be expected to be lowest with a conspecific neighbor and greatest without a neighbor. The experiment was replicated in five 0.24-m² plots at each of 20 sites in tall secondary forest. To test whether seedling performance differed among treatments we fitted linear mixed models (LMM) and generalized linear mixed models (GLMM), treating species identity and microsite (site and plot) as random effects. The five shade-tolerant study species all experienced good establishment with relatively high survival and growth rates. The neighbor treatment consistently affected seedling performance, but the effect was always very small, both in absolute terms and relative to the much stronger species and microsite effects. Seedlings with a conspecific neighbor consistently performed worse than seedlings with a heterospecific neighbor, but having no neighbor generally did not cause superior performance relative to the other treatments. We conclude that direct competitive interactions are relatively unimportant among understory plants in humid tropical forests.     

黄土高原马栏林区不同森林类型的土壤肥力研究

用灰色关联分析法对黄土高原马栏林区主要森林类型优势层生长状况与土壤养分因子的关联性进行分析,并对土壤肥力进行评价。结果表明腐殖质层和有机质是影响森林乔木层生长的主导土壤因子,其次是全氮和碱解氮,然后依次为速效钾、速效磷、全磷、pH值。土壤肥力的综合评价排序总体结果显示,辽东栎占优势的林型肥力最高,油松林、山杨占优势的混交林居中,辽东栎+白桦混交林较差,而白桦占优势的混交林最差。人工油松林对土壤有一定的改良作用;而多数混交林的土壤肥力高于以其中某一树种占优势的林型,但以辽东栎为优势种的林型比辽东栎混交林土壤肥力高,且辽东栎的重要值百分数越大,其土壤肥力越高。     

生理信号回归问题的一种解法

一自适应在线过程可通过Kalman滤波表示为时间变多变量的的自回归模型。时变模型的参数的估计能被用以计算线相关的瞬时测量,此方法对生理信号的分析非常有用。本文着重讨论了在呼吸运动,心率波动,血压的分析中的应用。     

晋西黄土区典型乔灌木短期水分利用效率对环境因子的响应

为明确晋西黄土区植物的水分利用规律及对半干旱区的适应策略, 提高黄土地区植被建设效益, 该研究对该地区典型乔灌木短期水分利用效率随环境因子的变化进行了探究。以典型乔木油松(Pinus tabuliformis)、刺槐(Robinia pseudoacacia)及其林下灌木黄刺玫(Rosa xanthina)、杠柳(Periploca sepium)为研究对象, 测定叶片可溶性糖稳定碳同位素比值(δ¹³C_leaf)与枝条渗出液稳定碳同位素比值(δ¹³C_branch), 使用δ¹³C_leaf推导计算7-10月叶片尺度下植物短期水分利用效率(WUE_leaf)变化趋势, 使用δ¹³C_branch明确植物光合作用后分馏情况, 确定半干旱区植物在生长季的水分变化规律对环境因子变化的响应。结果表明: (1) 7-10月4种植物δ¹³C_leaf总体呈现降低趋势, δ¹³C_branch呈现先升高后降低趋势。δ¹³C_leaf在种间和生活型中均存在差异。具体表现为: 灌木>乔木, 常绿乔木(油松) >落叶乔木(刺槐)。研究过程中未发现明显的碳同位素在光合作用后发生分馏的情况。(2) 4种植物WUE_leaf在7-8月保持稳定, 9-10月逐渐升高。21.5 ℃、0.9 kPa、52.4%分别为WUE_leaf随温度(T_a)、饱和水汽压差(VPD)、相对湿度(RH)变化的突变点, 突变点之后4种植物WUE_leaf均表现出稳定的变化趋势, 不再随T_a、VPD、RH升高而降低。(3) WUE_leaf与T_a、RH、VPD之间存在显著负相关关系, T_a通过非气孔因素, 即酶的作用改变光合速率, 引起WUE_leaf变化。RH、VPD等水分因子则通过改变气孔开度, 影响蒸腾, 进而改变WUE_leaf。随着土壤含水量(SWC)的升高, WUE_leaf呈现先升高后降低的趋势。油松林和刺槐林在SWC分别达到15%-18%、13%-14%时, WUE_leaf达到最高值。经过混合线性模型(LMM)分析得到, 油松和刺槐WUE_leaf主导环境因子分别为RH和VPD, 黄刺玫和杠柳WUE_leaf主导环境因子均为T_a。该研究得到了黄土地区典型乔灌木生长季水分利用效率变化的规律和主要环境影响因子, 明确了黄土地区植物对气候因子变化的适应机制。     

Metrics that differentiate the origins of osmolyte effects on protein stability: a test of the surface tension proposal

Osmolytes that are naturally selected to protect organisms against environmental stresses are known to confer stability to proteins via preferential exclusion from protein surfaces. Solvophobicity, surface tension, excluded volume, water structure changes and electrostatic repulsion are all examples of forces proposed to account for preferential exclusion and the ramifications exclusion has on protein properties. What has been lacking is a systematic way of determining which force(s) is(are) responsible for osmolyte effects. Here, we propose the use of two experimental metrics for assessing the abilities of various proposed forces to account for osmolyte-mediated effects on protein properties. Metric 1 requires prediction of the experimentally determined ability of the osmolyte to bring about folding/unfolding resulting from the application of the force in question (i.e. prediction of the m-value of the protein in osmolyte). Metric 2 requires prediction of the experimentally determined ability of the osmolyte to contract or expand the Stokes radius of the denatured state resulting from the application of the force. These metrics are applied to test separate claims that solvophobicity/solvophilicity and surface tension are driving forces for osmolyte-induced effects on protein stability. The results show clearly that solvophobic/solvophilic forces readily account for protein stability and denatured state dimensional effects, while surface tension alone fails to do so. The agreement between experimental and predicted m-values involves both positive and negative m-values for three different proteins, and as many as six different osmolytes, illustrating that the tests are robust and discriminating. The ability of the two metrics to distinguish which forces account for the effects of osmolytes on protein properties and which do not, provides a powerful means of investigating the origins of osmolyte-protein effects.     

腐植酸生产菌株——链霉菌发酵条件研究

利用链霉菌ST菌株发酵生产腐植酸。在蔗渣发酵培养基的基础上,采用一次回归正交试验,对腐植酸发酵过程中接种量（I）、通气量（搅拌次数,A）、温度（T）及时间（D）4个因素对腐植酸产量的影响情况进行分析。结果表明发酵时间的影响最为显著,接种量影响显著;所得到的回归方程有效且可信度高,回归方程为Y=6．0356＋0．02501＋0．0033A＋0．0069T＋0．2425D,其中各因素均与腐植酸产量呈正相关性。该回归方程为腐植酸生产过程链霉菌ST菌株发酵条件的控制提供了很好的指导作用。     

昆虫发育进度的非正态描述──分段指数曲线

提出了分段连续指数曲线转化为多元线性回归方程的方法。利用取剩余平方和最小的方法确定未知折点。给出了在描述昆虫发育进度的模拟模型。