Risk-Sensitive Foraging in a Patch Departure Context: A Test with Worker Bumble Bees

Typically, tests of risk-sensitive foraging involve observinga subject's choices of alternative prey types differing in somecombination of mean and variance of expected foraging gain.Here, we consider the problem of risk-sensitive foraging whenthere is a single prey type. We observed worker bumble bees(Bombus occidentalis) foraging in an array of artificial 2-flowerinflorescences. After visiting the bottom flower in an inflorescenceand obtaining a reward of some size, the bee decides whetherto visit the top flower or to move to a new inflorescence (apatch departure). Here, risk-sensitive behavior is expressedas the forager's choice of patch departure threshold (PDT) ofreward obtained in the bottom flower. We measured the PDTs ofbees whose colony energy stores (and therefore energy requirements)had been manipulated (Enhanced or Depleted). Simulations ledus to predict that shortfall-minimizing bees should decreasetheir PDTs when their colony energy reserves were depleted,relative to when the reserves were enhanced. Bees did not usea strict patch departure threshold, but instead the probabilityof departure varied with nectar volume in the bottom flower.Colony energy stores did affect patch departure behavior, butthis effect was confounded by the order in which manipulationof colony reserves was applied. Further, simulations of observedbee patch departure decisions did not produce behavior expectedif the decisions were based on shortfall-minimization. We concludethat a bee's decision of when to leave an inflorescence is notpredicted by a static shortfall-minimizing model. Our resultsalso implicate an important interaction between learning andforaging requirements. We review risk-sensitivity in bees, anddiscuss why risk-sensitive foraging may be adaptive for bumblebees.     

Risk-Sensitive Foraging, Fitness, and Life Histories: Where Does Reproduction Fit into the Big Picture?

Risk-sensitive foraging may occur whenever feeding success hasnon-linear effects on fitness. Models of sensitivity to variationin amount of food obtained have concentrated on foraging inorder to survive even though feeding during growth, migration,or reproduction can have strong and non-linear effects on fitness.I illustrate how risk-sensitive foraging for reproduction coulddiffer from risk-sensitive foraging for survival using two simplemodels. Each model assumes that organisms must accumulate somethreshold amount of resources before they can reproduce. Inthe first model, additional resources above the threshold leadto increased reproductive success. Here variance in feedingsuccess can be advantageous even when the mean gain would alloworganisms to reproduce. In the second model, early breedingis superior to late breeding because recruitment rate declinesover time. Here a symmetrical distribution in foraging ratesresults in a skewed distribution of breeding times. Despitethis, variance in feeding success may be advantageous even whenthe seasonal decline in recruitment is linear. The advantageof risk is much larger if foragers can switch freely betweenfeeding options. These two models are united by "the bankruptcyeffect" because all failures to reproduce carry the same consequences.These simple models suggest that risk-prone foraging may belikely when factors other than survival are important for fitness.Finally, I advocate using a mix of modelling techniques, notethe implicitly risk-sensitive nature of stochastic dynamic programming,and speculate on potential connections between risk-sensitiveforaging and theories of life histories in variable environments.INTRODUCTION visit restaurants that provided twice     

An Introduction to Risk Sensitivity: The Use of Jensen's Inequality to Clarify Evolutionary Arguments of Adaptation and Constraint

I review the basic rationale for risk-sensitive foraging, andpresent a few of the most common expressions of risk-sensitivitytheory. A simple heuristic, the energy-budget rule, and thez-score model are explained. These functional models of risksensitivity assume or explicitly model fitness as a nonlinearfunction of an animal's energy state. For such nonlinear relationships,Jensen's inequality predicts that the fitness realized by ananimal with a more constant energy state may be higher or lowerthan the fitness resulting from a variable energy state withthe same mean, depending on the shape of the fitness function.Predictive functional models of behavior, like the energy-budgetrule and the z-score model, depend on specific features of thefunction relating energy state to fitness, which may or maynot be general features for most organisms. While behavioralecologist have studied the functional significance of animalresponses to variation in foraging rewards, psychologists havelong studied the psychological mechanisms by which preferencesfor variable or constant rewards are expressed. Jensen's inequalityis applied here too; psychologists propose nonlinearities inthe perception and processing of information. The growing numberof different relationships that might account for risk-sensitivebehavior is a potential source of confusion. I advocate "returningto the basics," i.e., that hypotheses to explain risksensitivebehavior should specify precisely the assumed nonlinear relationships.     

小峰熊蜂访花偏爱性

传粉昆虫在访花时,通常会表现出对某一类型花的偏爱性。本研究利用人工制作的大小、颜色、形态和气味不同的9种类型的花来研究小峰熊蜂Bombus hypocrita的访花偏爱性。结果表明：当增加花的大小、形态、气味等附加特征数时,小峰熊蜂的偏爱性程度与花朵附加特征数有显著相关性（P<0.01）。当花朵颜色由2种增加到4种,熊蜂对紫色花的偏爱性程度降低,但花朵颜色的种类与小峰熊蜂的访花偏爱性没有相关性（P>0.05）,花颜色的种类对熊蜂访紫色花的偏爱性影响不大。大小为5 cm的紫花被访次数（108±9次）明显高于大小为3 cm的紫花被访次数（40±4次）（P<0.01）,说明熊蜂明显喜欢访大花瓣的紫花。完全盛开的紫花被访次数（129±13次）显著高于刚绽放的花被访次数（26±3次）（P<0.01）,说明熊蜂喜欢访盛开的紫花。柠檬味的紫花被访次数（63±8次）明显低于草莓味的紫色花被访次数（88±2次）（P<0.05）,说明熊蜂喜欢访草莓味的花朵。     

Trapline foraging by bumblebees: I. Persistence of flight-path geometry

By setting out arrays of potted plants of Penstemon strictus,I tested whether freely foraging bumblebee (Bombus spp. ) workerswould establish regular foraging routes that reflected the geometryof the array. They did, passing through an asymmetrical arrayin a pattern that minimized interplant flight distances. Afterthe array was changed to a symmetrical pattern, however, theexperienced bees continued to show their previous asymmetricalflight patterns. New bees without experience on the asymmetricalarray showed no asymmetry on the symmetrical array. I term thispersistence of flight-path geometry "trapline holdover, " anddiscuss its implications for the study of animals' learningand foraging behavior.     

Context-Sensitivity in Crab Foraging Studies

Initial work examining crab foraging from optimality premisesexplored fundamental foraging scope (the capacity of animalsto graze), often within an abstract experimental context. Anemergent theme involves explicit consideration of biologicalconstraints (e.g., predation risk) and environmental factors(e.g., substrate type) which, by modulating grazing capacity,determine the realized foraging pattern seen in nature. We briefly review two studies that illustrate the contemporaryfocus on realized foraging pattern. One defines field grow-outtechniques for bivalves (raised in mariculture and resourceenhancement programs) that minimize losses from predators suchas the portunid crab, Ovalipes ocellatus. By focusing on marginalregions of predator: prey interaction (in this case, foragingon low densities of clams planted in heterogenous substrates),the study yielded novel insight into limits on portunid crabforaging on infaunal clams. The second study analyses the foragingperformance of a deposit feeding ocypodid crab, Scopimera inflata,over different temporal and spatial scales. We demonstrate thatwhereas S. inflata performs sub-optimally at micro-scales (secondsto minutes; mm to cm), the crabs nearly optimize performanceover macro-scales (days to years; cm to m). Continued research on the fundamental foraging scope of crabsis warranted, but should be explicitly referenced to naturalhistorical context and, in particular, to the forager's ontogeneticstage. We also perceive a need for collaborative research incorporatingbehavioral, physiological, and biochemical facets in an integratedexperimental setting. This would ensure that context does notbias information, as can occur in studies that emphasise a particularresearch perspective, methodological approach, or scale at whichforaging is analysed.     

The foraging behavior of granivorous rodents and short-term apparent competition among seeds

The foraging behavior of a predator species is thought to bethe cause of short-term apparent competition among those preyspecies that share the predator. Short-term apparent competitionis the negative indirect effect that one prey species has onanother prey species via its effects on predator foraging behavior.In theory, the density-dependent foraging behavior of granivorousrodents and their preference for certain seeds are capable of inducing short-term apparent competition among seed species.In this study, I examined the foraging behavior of two heteromyidrodent species (family Heteromyidae), Merriam's kangaroo rats(Dipodomys merriami) and little pocket mice (Perognathus longimembris).In one experiment I tested the preferences of both rodent speciesfor the seeds of eight plant species. Both rodent species exhibiteddistinct but variable preferences for some seeds and avoidanceof others. However, the differences in preference appearedto have only an occasional effect on the strength of the short-term apparent competition detected in a field experiment. In anotherexperiment, I found that captive individuals of both rodentspecies had approximately equal foraging effort (i.e., timespent foraging) in patches that contained a highly preferredseed type (Oryzopsis hymenoides) regardless of seed density and the presence of a less preferred seed type (Astragalus cicer)in the patches. The rodents also harvested a large proportionof O. hymenoides seeds regardless of initial seed density;this precluded a negative indirect effect of A. cicer on O.hymenoides. But there was a negative indirect effect of O.hymenoides on A. cicer caused by rodents having a lower foragingeffort in patches that only contained A. cicer seeds than inpatches that contained A. cicer and O. hymenoides seeds. Theindirect interaction between O. hymenoides and A. cicer thusrepresented a case of short-term apparent competition thatwas non-reciprocal. Most importantly, it was caused by theforaging behavior of the rodents.     

Cue use affects resource subdivision among three coexisting hummingbird species

Competition for food can influence the coexistence of speciesvia habitat selection, and learned behavior can influence foragingdecisions. I investigated whether learned behavior and competitionact together to influence species interactions between threecoexisting hummingbird species: black-chinned (Archilochusalexandri), blue-throated (Lampornis clemenciae), and magnificent(Eugenes fulgens) hummingbirds. I found that color cue useby individuals affects not only their foraging choices butalso population-level responses to competition. I presented hummingbirds two types of habitats (rich and poor feeders).All birds shared a preference for the rich feeders, but shiftedpreference toward poor feeders in response to competition.I used color cues to manipulate the amount of information availableto birds and examined the effects of two information states(complete or incomplete) on their foraging choices. I examined hummingbirds' preferences for the rich feeders when both competitordensities and information varied. To relate foraging choicesto energetic intake, I also analyzed energy gained during asingle foraging bout. Males of all species exhibited strongpreferences for rich feeders when they foraged with complete information and low competitor densities. Without complete information,the two subordinate species (black-chinned and magnificent)shifted preference away from rich feeders in response to highdensities of the dominant species (blue-throated). Each subordinatespecies shifted in a unique way: black-chinned hummingbirdsreduced foraging efficiency, while magnificent hummingbirdsreduced foraging time. Birds foraging with complete information remained selective on rich feeders even at high competitor densities.Thus, learned information affected competitive interactions(for rich feeders) among these species.     

大叶铁线莲访花昆虫调查及盗蜜昆虫行为研究

大叶铁线莲Clematis heracleifolia DC. 的花朵大多下垂,需要传粉昆虫为其传粉,目前尚无关于其访花昆虫研究的报道。 通过2年的野外观察研究,共观察到27种昆虫访问大叶铁线莲。 发现有盗蜜行为的昆虫7种, 其中1种同时具有初级盗蜜和次级盗蜜行为,2种具有初级盗蜜行为,4种具有次级盗蜜行为;黄胸木蜂Xylocopa appendiculata Smith是主要的盗蜜昆虫,其盗蜜行为影响了其它昆虫的访花行为,对大叶铁线莲的传粉造成一定的影响。 在其余20种访花昆虫中,双带弄蝶Lobocla bifasciata (Bremer et Grey)、贡尺蛾Gonodontis aurata Prout、熊蜂Bombus sp.和姬蜂虻Systropus sp.是优势种; 而小青花金龟Oxycetonia jucunda Faldermann和日本条螽Ducetia japonica (Thunberg)访花频率最低,且访花目的只是取食花朵。 通过对大叶铁线莲访花昆虫的调查和盗蜜昆虫行为的研究,为大叶铁线莲的传粉生物学和保护提供参考依据。     

Profitability, encounter rates, and prey choice of African lions

The prey preferences of African lions (Panthera leo) in SerengetiNational Park, Tanzania, were examined in three ways. First,lion encounter rates with prey types were measured and comparedwith a random sample of the prey population. Lions encounteredmore wart hogs (Phacochoerus aethiopicus), Grant's gazelles(Gazella granti), wildebeests (ConnochaeUs taurinus), and zebras(Equus burchelli) than expected. Second, preferred prey typesof lions were identified using conditional logit analysis. Lionspreferred to hunt small prey groups, groups that were closerthan 200 m, and groups that contained wart hogs, wildebeests,or zebras. Third, a risk-minimization optimal foraging modeland a rate-maximization model were used to predict lion preferences.The foraging theory models predict that preferences should changewith season and with lion group size. Qualitative support wasfound for most of these predictions.     

地标对犬蝠空间记忆的影响

为了研究地标（landmarks）是否影响犬蝠（Cynopterus sphinx）的空间记忆,我们通过室内模拟试验研究犬蝠和地标在觅食过程中空间记忆形成的关系。实验组按照每天地标数分别为0、2、4、8、0的数目连续进行5天实验,对照组不设地标进行相同条件的实验。结果显示,两组犬蝠第一次取食所用的时间与实验天数之间极显著相关（Pearson Correlations: 实验组r=-0.593, P<0.01;对照组r=-0.581, P<0.01）;实验组取食成功率与实验天数之间无明显相关性（Pearson Correlations: r=0.177, P>0.05）;对照组取食成功率与实验天数之间显著相关（Pearson Correlations: r=0.445, P<0.05）。实验组与对照组犬蝠第一次取食的时间差异不显著（GLM: F_0.05,1=4.703, P>0.05）,两组间取食的成功率差异也不显著（GLM: F_0.05,1=0.849, P>0.05）。这些结果说明了随着时间增加,犬蝠对取食地的空间记忆逐渐形成,放置地标在犬蝠对取食地空间记忆形成的过程中无显著影响。     

Patch exploitation, group foraging, and unequal competitors

Charnov's (1976) marginal value theorem, MVT, addresses howlong a forager should stay in a patch of prey to maximize itsgain. Information-sharing models of group foraging suggest thatindividuals should join groups to improve their patch-findingrate. This is achievable if group members share informationabout the location of food patches. The determinants of theMVT are searching time and cumulative gain against time in apatch, those of the group foraging models are searching time,group size, and individual differences in ability to monopolizethe prey found. After combining the MVT and information-sharingmodels we explore the consequences of unequal competitors (good,G, and poor, P) foraging in groups. Under this domain G andP differ in their accumulated harvest against time in a patch.When the gain function of P is obtained by mere scaling of thatof G, optimal patch residence times for individuals of the twophenotypes do not differ. However, if the gain functions ofG and P cannot be derived from each other by a constant scalingmultiplier, the optimal patch times for G and P are not necessarilythe same. Under these conditions the model suggests that foraginggroups should become assorted by foraging ability.     

阿根廷文化景观研究、项目和表现

旨在促进应用“文化景观”概念作为分析和开发阿根廷地域项目的工具。第1部分,力图总结有关文化景观的概念,术语名词的起源、传播以及其所暗含的可能性和矛盾性。第2部分,讨论这个概念成为项目工具的方式。第3部分中,强调了绘图在分析和项目中的核心作用。第4部分,以2个案例研究表明在前3个部分中阐述的问题。结论提出了这种开展项目的方式的潜能、挑战和矛盾。而只有针对地域特性的详细研究才能使找到一种回馈当地发展的管理方式成为可能。     

家蚕细胞周期蛋白基因BmCcnl1的克隆及表达分析

家蚕Bombyx mori由受精卵到完成胚胎发育孵化的过程中, 细胞进行大量的分裂和分化, 然而滞育性卵的胚胎细胞分化至G2期便停滞在此阶段。为了探索这一发育阶段细胞内的分子调控, 本研究以人Homo sapiens的细胞周期蛋白基因cyclin L1为模板, 成功克隆了家蚕同源基因BmCcnl1（GenBank登录号: FJ889988）。BmCcnl1基因开放阅读框（open reading frame, ORF）全长1 254 bp, 编码417个氨基酸。利用Protean软件分析得出BmCcnl1蛋白预测分子量为49 kDa, 等电点为9.84。利用DNA重组技术构建了BmCcnl1基因的重组表达载体pET-21d-BmCcnl1, 对其进行原核表达, 其表达的蛋白以包涵体形式存在。利用RT-PCR技术分析了BmCcnl1基因在胚胎发育过程中的转录水平, BmCcnl1基因在非滞育性卵的胚胎发育阶段基本保持相对稳定的转录表达, 而滞育性卵从蛾体产下经过72 h后已经检测不到BmCcnl1基因的转录。结果提示, BmCcnl1基因与胚胎期滞育及非滞育性卵的发育调控相关。对该基因的克隆和表达分析为今后研究家蚕胚胎发育及细胞周期调控奠定了基础。     

Rodent foraging is affected by indirect, but not by direct, cues of predation risk

We used foraging trays to determine whether oldfield mice, Peromyscuspolionotus, altered foraging in response to direct cues of predationrisk (urine of native and nonnative predators) and indirectcues of predation risk (foraging microhabitat, precipitation,and moon illumination). The proportion of seeds remaining ineach tray (a measure of the giving-up density [GUD]) was usedto measure risk perceived by mice. Mice did not alter theirGUD when presented with cues of native predators (bobcats, Lynxrufus, and red foxes, Vulpes vulpes), recently introduced predators(coyotes, Canis latrans), nonnative predators (ocelots, Leoparduspardalis), a native herbivore (white-tailed deer, Odocoileusvirginianus), or a water control. Rather, GUD was related tomicrohabitat: rodents removed more seeds from foraging trayssheltered beneath vegetative cover compared with exposed traysoutside of cover. Rodents also removed more seeds during nightswith precipitation and when moon illumination was low. Our resultssuggest that P. polionotus used indirect cues rather than directcues to assess risk of vertebrate predation. Indirect cues maybe more reliable than are direct scent cues for estimating riskfrom multiple vertebrate predators that present the most riskin open environments.     

感染稻水象甲的Wolbachia基因组中插入序列的鉴定与分析

共生细菌Wolbachia对宿主的生殖起多种调控作用。以往研究表明, Wolbachia基因组中广泛存在插入序列(insertion sequence, IS), 它们对宿主基因组的可塑性、 多样性和进化起重要作用。稻水象甲Lissorhoptrus oryzophilus Kuschel在东亚是一种外来水稻害虫, 在原产地北美营两性生殖, 而在所有入侵地均营孤雌生殖。本研究采用PCR法从河北唐海孤雌生殖型稻水象甲体内克隆获得了Wolbachia的2条IS序列, 即ISWosp4和ISWosp6; 从美国德克萨斯州两性生殖型稻水象甲成虫体内克隆获得了Wolbachia的2条IS序列, 即ISWosp3和ISWosp5。碱基序列比对显示: ISWosp3和ISWosp4属于IS3家族IS3组成员, ISWosp5为IS4家族IS231组成员, ISWosp6为IS5家族IS1031组成员。对这些IS的ORF结构、 所编码氨基酸序列的结构等进行了分析, 推测ISWosp5具有潜在转座活性。所得结果增进了我们对Wolbachia IS3, IS4和IS5家族插入序列的认识, 同时为今后从IS的角度探讨Wolbachia与稻水象甲生殖的关系奠定了基础。     

Carpenter Bee (Xylocopa micans) Risk Indifference and a Review of Nectarivore Risk-sensitivity Studies

This paper presents new results of risk-sensitive foraging studiesof the carpenter bee, Xylocopa micans, and reviews the workto date on risk sensitivity in nectarivores. In the field, nectarivoreschoose among alternative food sources (flowers) that differin the variabilities of their nectar rewards. In the lab, theforaging situation for carpenter bees was experimentally simplifiedby offering the bees a choice between either "low variance"or "high variance" artificial flowers. The two flower typesdiffered in their variabilities but offered the same expectedshortterm rates of net energy gain to test the predictions ofthe short-term rate maximization mechanism. Foragers were testedunder two energy budget conditions, hungry and well-fed, totest the predictions of the z-score model. Individual carpenterbees were indifferent to variability in both nectar volume andnectar sugar concentrations, and their risk-indifference wasunaffected by energy budget. These findings of risk indifferencesupport neither the variance discounting nor the z-score modelof risk sensitivity. Since the low and high variance flowertypes are equivalent for carpenter bees in short-term rate ofenergy gain, there can be no selection on carpenter bees tobe sensitive to variability based on differences in rate ofgain. Studies of risk sensitivity in honey bees and bumble beesusing variance in nectar concentration support this contention.These findings are compared with other nectarivore risk sensitivitystudies in order to highlight the most likely mechanisms underlyingaversion to variation in nectar rewards (short-term rate maximizing,the Weber-Fechner law of perception and learning non-empty flowers)and to suggest future research in the interplay of these threemechanisms.     

中国部分地区柑桔木虱体内感染Wolbachia的检测及其系统发育分析

Wolbachia是一种广泛分布于节肢动物体内的共生细菌, 该共生菌经寄主卵的细胞质传播并参与多种寄主生殖活动调控, 对节肢动物的物种进化有着重要意义并可能应用于害虫的生物防治。本研究以柑桔黄龙病（Huanglongbing, HLB）的主要传播媒介——柑桔木虱Diaphorina citri为研究对象, 通过Wolbachia的16S rDNA、 细胞分裂基因（ftsZ）、 表面蛋白基因（wsp）的特异引物对来自于中国广西北海、 广西柳州、 广东深圳、 广东阳春、 福建福州5个地区的柑桔木虱进行PCR扩增, 并对扩增产物进行克隆测序, 与GenBank中相关序列进行比对分析, 建立了柑桔木虱共生Wolbachia的系统发育树。结果显示上述5个地区的柑桔木虱均存在Wolbachia感染, 通过Wolbachia的16S rDNA, ftsZ基因和wsp基因DNA序列的系统发育分析表明, 5个地区的柑桔木虱体内的Wolbachia均属于B组; 基于wsp基因的系统发育分析进一步表明5个地区的亚洲柑桔木虱体内的Wolbachia属于B组的Con亚组, 且不同地区柑桔木虱体内的Wolbachia的16S rDNA, ftsZ基因和wsp基因序列差异不明显。研究结果为认识柑桔黄龙病传播媒介昆虫的进化及其综合防治提供了重要的参考依据。     

An evolutionary model of low mood states

It has been suggested that low mood in humans is an adaptive response to unfavourable circumstances, and that the anhedonia, pessimism and fatigue that often accompany it function to minimise risk until circumstances improve. While this is plausible, it would be possible to make the opposite prediction equally plausibly: individuals in bad circumstances should take greater risks in order to improve their situations. Here, I present a simple analytical model adapted from the risk-sensitive foraging literature. It shows that in dire states, individuals should be risk-prone, in poor states, risk-averse, and in good states, risk-prone again. I discuss how the various kinds of mood state observed in humans might be understood as mechanisms for adaptively adjusting behavioural risk-taking to the current situation.