Assessment of predation risk via illumination level: facultative central place foraging in the cricetid rodent Phyllotis darwini

It is well known that the risk of predation affects prey decision making. However, few studies have been concerned with the cues used by prey to assess this risk. Prey animals may use indirect environmental cues to assess predation hazard since direct evaluation may be dangerous. I studied the assessment of predation risk, manipulated via environmental illumination level, and the trade-off between foraging and predation hazard avoidance in the nocturnal rodentPhyllotis darwini (Rodentia: Cricetidae). In experimental arenas I simulated dark and full moon nights (which in nature correlate with low and high predation risk, respectively) and measured the immediate responses of animals to flyovers of a raptor model. Second, varying illumination only, I evaluated patch use, food consumption, central place foraging, and nocturnal variation of body weight. During flyover experiments, animals showed significantly more evasive reactions under full moon illumination than in moonless conditions. In the patch use experiments, rodents significantly increased their giving-up density and decreased their total food consumption under moonlight. On dark nights, rodents normally fed in the food patch, but when illumination was high they became central place foragers in large proportion. Moreover, the body weight of individuals decreased proportionately more during bright nights. These results strongly suggest thatP. darwini uses the level of environmental illumination as a cue to the risk of being preyed upon and may sacrifice part of its energy return to avoid risky situations.     

Patch Size and Connectivity Thresholds for Butterfly Habitat Restoration

Abstract:  Recovery of endangered species in highly fragmented habitats often requires habitat restoration. Selection of restoration sites typically involves too many options and too much uncertainty to reach a decision based on existing reserve design methods. The Fender's blue butterfly (  Icaricia icarioides fenderi ) survives in small, isolated patches of remnant prairie in Oregon's Willamette Valley—a habitat for which <0.5% of the original remains. Recovery of this species will require considerable habitat restoration. We investigated the potential of biologically based rules of thumb and more complex models to serve as tools in making land acquisitions. Based on Fender's blue dispersal behavior and demography, we have estimated that restored patches should be <1 km from existing habitat and at least 2 ha. We compared these rules to the results of two modeling approaches: an incidence function model and a spatially explicit simulation of demography and dispersal behavior. Not surprisingly, the simple rules and complex models all conclude that large (>2 ha) connected (<1 km) patches have the highest restoration value. The dispersal model, however, suggests that small, connected patches have more restoration value than large, isolated patches, whereas the incidence function model suggests that size and connectivity are equally important. These differences stem from model assumptions. We used incidence functions to predict long-term, stochastic, steady-state conditions and dispersal simulations to predict short-term (25-year) colonization dynamics. To apply our results in the context of selecting restoration sites on the ground, we recommend selecting nearby sites when short-term colonization dynamics are expected to be an important aspect of a species' biology.     

Male age structure influences females’ mass change during rut in a polygynous ungulate: the reindeer (Rangifer tarandus)

The manipulation of the sex ratio and age structure in many managed ungulate populations calls for a better understanding of their potential consequences on females’ condition and behavior during rut. During 1996–2002, we manipulated the male age structure and male percentage (nine treatments during 7 years) within an experimental herd of semidomestic reindeer (Rangifer tarandus) and investigated their influence on both the body mass change and the behavior of females during rut. On average, the females lost body mass (−0.95±SE 0.18 kg) during rut, which we contend to reflect somatic costs. The females’ losses increased as the percentage of male decreased, but this was certainly ascribed to one treatment with high male percentage (27.7%) as compared to the others (ranging from 3.9 to 12.2%). Female losses were highest for treatments including both young and adult males as compared to only adult or only young males, and higher for treatments including only young compared to only adult males. This is supported by (1) the higher female harassment frequency when females are exposed to only young or a mixture of young and adult males as compared to only adults, (2) the higher female harassment frequency by young males as compared to adults in the mixed treatments, and (3) the reduced females’ feeding activity in treatments including both young and adult males. We conclude that the male age structure during rut will influence the females’ behavior and mass change and may have implications for females’ life history and for population dynamics.     

The communal crop: modulation of sucrose response thresholds of pre-foraging honey bees with incoming nectar quality

We examined whether the quality (concentration) of incoming sucrose solutions returned by foraging honey bees affected the response thresholds of pre-foraging members of the colony. Six pairs of colonies were given ad libitum access to sucrose solution feeders. A colony from each pair was switched from 20–50% sugar concentration feeders while the other continued to have access to 20% sucrose feeders. Proboscis extension response (PER) scores to an increasing series of sucrose concentrations were significantly higher in pre-foragers of colonies foraging on 20% sucrose throughout compared to pre-foragers in colonies where foraging was switched to 50% sucrose. Although all colonies had honey stores, the concentration of sugar solution in non-foraging bees crops were significantly lower in bees from colonies foraging on 20% sucrose compared to those from colonies foraging on 50% sucrose. Because response thresholds to sugar of young bees were modulated by the concentration of sucrose solution returned to colonies, we repeated the 2000 study of Pankiw and Page that potentially confounded baseline response thresholds with modulated scores due to experience in the colony. Here, we examined PER scores to sucrose in bees within 6 h of emergence, prior to feeding experience, and their forage choice 2 to 3 weeks later. Pollen foragers had higher PER scores as newly emerged bees compared to bees that eventually became nectar foragers. These results confirm those of the 2000 study by Pankiw and Page. Combined, these experiments demonstrate that variation in pre-forager sucrose response thresholds are established prior to emerging as adults but may be modulated by incoming resources later on. Whether this modulation has long-term effects on foraging behavior is unknown but modulation has short-term effects and the potential to act as a means of communication among all bees in the colony.Communicated by M. Giurfa     

碳纤维增强复合材料的中低应变率力学性能试验研究

目的研究碳纤维增强复合材料的中低应变率力学性能。方法利用电子万能试验机和高速液压伺服材料试验机对[(±45°)]4s和[(±45°)]8两种铺层碳纤维增强复合材料进行常温下准静态和中低应变率力学性能试验,得到不同应变率下的应力应变曲线和失效参数。结果在应变率6.7×10-4~500 s-1范围内,两种铺层材料均具有明显的应变率强化效应,材料失效应力随应变率的提高而增大。两种铺层材料均发生纤维断裂失效和局部的分层失效,但[(±45°)]4s铺层发生燕尾形失效,[(±45°)]8铺层发生剪切失效。结论获得了碳纤维增强复合材料在不同应变率下的力学性能参数,可为复合材料飞机结构的抗冲击设计和仿真分析提供准确的材料参数。     

新冠肺炎疫情期间我国人群交通出行行为分析

为了解我国新型冠状病毒肺炎（COVID-19,简称“新冠肺炎”）疫情期间人群出行频次及交通方式,调查收集了2020年2月25日—3月14日我国31个省（自治区、直辖市）8 330名居民疫情期间的出行频次及交通方式等信息,并分析了其影响因素;对我国31个省（自治区、直辖市）按疫情严重程度进行等级划分,分析不同疫情等级下人群交通出行方式的差异,并与非疫情期间进行对比.结果表明:①新冠肺炎疫情期间调查人群中有75.1%的人有出行行为,其中,5.5%的人一天多次外出,17.6%的人每周出行频次不到一次.出行过程中乘坐公共交通和出租车这两类感染风险较高的交通工具的人数占比分别为6.3%和4.0%.②新冠肺炎疫情期间,我国居民的出行频次和交通方式可能受性别、年龄、城乡、片区等人口统计学变量以及当地或附近疑似/确诊病例情况的影响,还可能与所在省份疫情严重程度有关.西藏自治区、青海省等地区人群出行频次及交通方式受疫情影响变化相对较小,湖北省居民出行频次及交通方式与非疫情期间相比变化最大.③新冠肺炎疫情期间,我国成人居民选择步行和小轿车（出租车和私家车）出行的人数占比远高于非疫情期间,而选择公共交通和自行车或电动车等交通方式的人数占比与非疫情期间相比有所降低.研究发现,新冠肺炎疫情极大地改变了我国人群出行频次及交通方式.      

渗滤液浸沥下稳定化飞灰中重金属的浸出行为

稳定化飞灰与生活垃圾混合填埋过程中,在渗滤液浸沥作用下,存在稳定化飞灰中重金属溶出的风险.为探究渗滤液浸沥环境下稳定化飞灰中重金属的浸出行为,基于浸提实验,以填埋场早期、晚期渗滤液为浸提剂,研究了不同液固比（10：1、20：1、30：1、50：1、100：1、150：1、200：1）条件下磷酸稳定化飞灰、螯合剂稳定化飞灰中重金属（Cd、Cu、Zn、Pb、Cr、Ni）的浸出行为.结果表明：随着液固比的增加,浸出液中Cd、Cu和Zn浓度先上升后下降,在液固比20：1时达到最大值,Pb的浸出浓度随液固比的升高整体呈现缓慢增加的趋势,Cr、Ni浸出浓度变化较小,液固比对其影响不显著;Cd和Cu在早期渗滤液浸沥环境下更容易浸出,Zn、Pb、Cr、Ni在早期、晚期渗滤液浸沥环境下差别不大.在两种渗滤液浸沥环境下,螯合剂稳定化飞灰比磷酸稳定化飞灰具有更好的稳定性.     

对外援助能促进能源对外直接投资吗?——来自中国企业的微观证据

使用由多个数据库链接的微观数据,对中国对外援助能否促进中国企业的能源对外直接投资（Outward Foreign Direct Investment,OFDI）决策进行计量检验,结果发现：中国在东道国的援助活动显著增大了中国企业对东道国进行能源OFDI的概率,且当年援助的投资促进效应大于累计援助的促进效应,该结果在多种模型设定下均表现稳健;进一步检验中,研究发现中国对外援助对能源OFDI的促进效应在援助形式、用途和国家类别上存在广泛异质性,其中复合化和高级化的援助形式如技术援助和出口信贷,直接用于经济基础设施、能源产业发展、东道国政府财政的援助,以及援助“一带一路”沿线国家更能激发中国对外援助的能源OFDI促进效应。本文为中国对外援助能够带动中国能源OFDI提供了直接的微观证据,也为如何发挥对外援助的能源OFDI驱动效应提供了有益启示。     

农户规模经营意愿与行为的影响机制及差异——基于山东省3县379份农户调查问卷的实证

基于社会认知理论与计划行为理论构建分析框架,采用山东省五莲、东平和垦利等三县（区）的379份农户调查问卷数据,综合运用主成分分析法、Heckman二阶段模型和比较分析法,探究农户规模经营意愿与行为的主要影响因素及其作用机制与差异,为推进农地适度规模经营提供决策参考。结果表明：（1）案例区被调查农户对土地政策的认知程度普遍较低,且认知水平与结构均存在地域差异。（2）个体特征、资源禀赋和区位因素对规模经营意愿产生显著影响,而政策认知和社会保障因素的影响却不显著;所选四类因素均表现出了对规模经营行为的影响,其中影响力度较大且通过显著性检验的因素主要是“是否参加农业保险”和“新型经营主体认知程度”。（3）27.70%的受访农户存在规模经营意愿与行为不一致的情形,山区与平原农户规模经营的影响机制表现出一定差异,影响农户意愿与行为的因素也有较大不同。（4）建议深入了解农民的政策认知水平与结构、有针对性地加强宣传教育,因地制宜构建信息平台、降低农地流转交易成本,构建面向小农户的农业社会化服务体系,实现“土地+服务”的二元规模化。     

Interactions between engineered nanoparticles and dissolved organic matter: A review on mechanisms and environmental effects

Dissolved organic matter (DOM) is ubiquitous in the environment and has high reactivity. Once engineered nanoparticles (ENPs) are released into natural systems, interactions of DOM with ENPs may significantly affect the fate and transport of ENPs, as well as the bioavailability and toxicity of ENPs to organisms. However, because of the complexity of DOM and the shortage of useful characterization methods, large knowledge gaps exist in our understanding of the interactions between DOM and ENPs. In this article, we systematically reviewed the interactions between DOM and ENPs, discussed the effects of DOM on the environmental behavior of ENPs, and described the changes in bioavailability and toxicity of ENPs caused by DOM. Critical evaluations of published references suggest further need for assessing and predicting the influences of DOM on the transport, transformation, bioavailability, and toxicity of ENPs in the environment.