槭叶铁线莲(Clematis acerifolia Maxim.)群落物种生态位研究

槭叶铁线莲（Clematis acerifolia）为太行山特有植物,但数量稀少且分布零散,其生存状况受到学者和政府部门的高度关注。本文通过对河北省易县葫芦峪沟谷新发现的槭叶铁线莲群落的典型样地调查,以物种重要值作为生态位计量指标,对各物种生态位宽度、生态位重叠和生态位相似性进行了定量分析,对槭叶铁线莲的生存安全状况进行了评估。结果表明：在调查样地中共记录到14科15属17种植物,群落物种组成较为简单,槭叶铁线莲在大部分调查样地中的重要值最大,占据优势地位,其他物种重要值相对较低;群落内所有物种中,槭叶铁线莲的生态位宽度最大（B_i=6.264）,绒毛绣线菊（Spiraea dasyantha）次之（B_i=5.144）,其他种类较小;所有物种组成的136个种对中,生态位完全重叠（Q_ik=1）、重叠程度较高（0.5≤Q_ik<1）和重叠程度较低（Q_ik<0.5）的种对比例分别为8.09%、16.91%和75.00%,生态位完全相似（C_ik=1）、相似程度较高（0.5≤C_ik<1）和相似程度较低（C_ik<0.5）的种对比例分别为8.09%、5.88%和86.03%,大部分物种之间生态位重叠程度和相似性都处于较低水平;槭叶铁线莲与其他物种构成的16个种对中,62.50%的种对生态位重叠程度较低（Q_ik<0.5）,81.25%的种对生态位相似性程度较低（C_ik<0.5）,反映出群落内各物种间对资源和空间的竞争较为温和,群落较为稳定,槭叶铁线莲在其分布生境中生存状况相对安全;本文研究表明,利用生态位分析方法可以作为珍稀濒危物种生存状态和安全风险评估的一种方法。     

Behavioural ecology at the spatial–social interface

Spatial and social behaviour are fundamental aspects of an animal's biology, and their social and spatial environments are indelibly linked through mutual causes and shared consequences. We define the ‘spatial–social interface’ as intersection of social and spatial aspects of individuals' phenotypes and environments. Behavioural variation at the spatial–social interface has implications for ecological and evolutionary processes including pathogen transmission, population dynamics, and the evolution of social systems. We link spatial and social processes through a foundation of shared theory, vocabulary, and methods. We provide examples and future directions for the integration of spatial and social behaviour and environments. We introduce key concepts and approaches that either implicitly or explicitly integrate social and spatial processes, for example, graph theory, density-dependent habitat selection, and niche specialization. Finally, we discuss how movement ecology helps link the spatial–social interface. Our review integrates social and spatial behavioural ecology and identifies testable hypotheses at the spatial–social interface.     

重庆特有极小种群植物缙云秋海棠生态位特征研究

该研究通过对重庆缙云山国家级自然保护区的缙云秋海棠(Begonia jinyunensis)及其伴生物种所在群落进行实地调查,并以样地作为一维资源轴,物种重要值作为生态位计测状态指标,采用Levins、Hurlbert、Pianka公式对缙云秋海棠种群的生态位特征进行分析,以阐明该群落物种间对资源的利用和竞争关系,为缙云秋海棠的保护提供依据。结果表明:(1)在群落中缙云秋海棠的Levins和Hurlbert生态位宽度均最大,分别为6.742 40和0.717 80,表明缙云秋海棠对环境资源的利用能力强,生态适应幅度也较大。(2)研究区内缙云秋海棠的伴生物种中生态位宽度(Ba)大于0.3的3种植物为石生楼梯草(Elatostema rupestre)、斜方复叶耳蕨(Arachniodes rhomboidea)、对马耳蕨(Polystichum tsus-simense),其Ba值分别为0.460 00、0.417 04、0.301 60,表明缙云秋海棠的3个主要伴生种在群落中具有较强的竞争力。(3)20个伴生物种中与缙云秋海棠生态位重叠值最高的是石生楼梯草(0.671 4),说明缙云秋海棠与石生楼梯具有相似的环境要求,资源不足时,两者可能存在比较激烈的竞争,其中有12个伴生物种(60%)与缙云秋海棠的生态位重叠值小于0.5,群落中大多数物种与缙云秋海棠的生态位重叠值均较低,说明物种之间对资源的需求不同,环境适应能力相似度低,群落中的种间竞争不激烈。研究认为,缙云秋海棠生态位宽度大,生境适宜生存,种间竞争不激烈,即目前生态位因素不是造成其处于濒危状态的主要原因;导致缙云秋海棠数量少,呈现岛屿状分布的主要原因可能是其生境遭到人为破坏。     

The social development of free-ranging infantLemur catta at Berenty reserve,Madagascar

The social development of 11 free-ranging infantLemur catta was examined over the first 16 weeks of the infants' lives. By 16 weeks, infants still occasionally suckled and were carried dorsally, but on the whole, they were independent of their mothers. Sex or mother's rank was not found to affect frequency or type of play behavior. Mother's rank had no effect on frequency of maternal rejections, from the nipple or from riding, but female infants were rejected slightly more frequently than males were. Mothers tended to reject infants more severely and more frequently from dorsal riding than from the nipple. Sex and rank differences were not found with respect to behaviors determined as measures of independence; however, lower-ranking infants engaged in significantly more dependent behaviors than higher-ranking young did. It may be necessary for the infant of a low-ranking mother to maintain closer proximity to its mother for a longer period of time during infancy because such infants may be subject to abuse by higher-ranking group members and, furthermore, may not be as readily rescued in a stressful or dangerous situation as a higher-ranking infant. Sex was not found to be a factor in terms of measures of dependence. The lack of sex differences in developmental behaviors in this species may be related to female dominance, as well as to the fact that, as adults, both sexes engage in aggressive territorial behavirs.     

Nested structure is dependent on visitor sex in the flower‒visitor networks in Kyoto,Japan

The characteristics of flower‒visitor networks, comprised of multiple species interacting with each other, predict ecological and evolutionary processes. Intraspecific and interspecific variations in interaction patterns should affect network structures. Because female and male visitors usually differ in flower‐visiting patterns due to mating strategy, visitor sex should affect nestedness, in which specialist species interact with a subset of species that interact with generalist species. I hypothesized that a network of male visitors and flowering plants would be more nested than a female network because males are less picky about which flowers they visit. To examine the effect of visitor sex on nestedness, I used museum specimens of insects and built 11 flower–visitor species networks, each composed of female and male subnetworks, and compared the strength of nestedness and related network metrics between the subnetworks. I found that male subnetworks were significantly more nested than female ones, and species networks were less nested than male or female subnetworks. The result may be attributable to the by‐chance selection of flowers by males. Because a nested structure is predicted to promote community stability in mutualistic flower–visitor networks, the greater nestedness of male subnetworks may suggest a positive effect of male visitors on pollination community stability.     

浙江省檫木林生境与生态位研究

植被生境是群落乃至整个生态系统的物质基础,生态位宽度、生态位重叠、种间关系在群落生态学研究领域也具有重要地位,因此在植被生境基础之上展开的生态位、种间关系研究对了解生态系统功能具有重要意义。主成分分析表明:土壤养分和海拔因子对檫木生长分布起着重要的限制性作用;通过重要值对环境因子趋势拟合得出檫木在浙江省的典型生境为:海拔400—800 m,坡度20°—40°,阴坡半阴坡,土壤厚度大且肥沃的区域;在出现檫木的189个监测样地中,共出现的乔木树种有149种,主要优势树种(以重要值排序)为杉木Cunninghamia lanceolata、马尾松Pinus massoniana Lamb.、木荷Schima superba、枫香Liquidambar formosana Hance、青冈Cyclobalanopsis glauca (Thunb) Oerst、苦槠Castanopsis sclerophylla、石栎Lithocarpus glaber(Thunb.) Nakai、檫木Sassafras tzumu (Hemsl.) Hemsl.等。生态位宽度大小依次为杉木、檫木、马尾松、木荷、枫香、青冈、苦槠、板栗Castanea mollissima等,可见杉木、檫木、马尾松、木荷对外部环境有较强的适应能力,在各个资源位中出现较多,对资源的利用优势比较明显,檫木的生态位宽度达到了61.65,仅次于杉木的89.64,甚至大于马尾松的57.28,也说明檫木能在研究区拥有较好的群落地位;檫木与野樱桃Cerasus serrula (Franch.) Yüet L的生态位重叠值高达0.9以上,和浙江楠Phoebe chekiangensisC. B. Shang、构树Broussonetia papyrifera、鸡爪槭Acer palmatum Thunb.的生态位重叠值分别达0.831、0.785、0.531,说明檫木和野樱桃、浙江楠、构树、鸡爪槭对生境要求比较相近,在生态资源充足的情况下可尝试混交造林;通过监测样地中11个优势树种的种间联结分析,显示檫木与杉木、马尾松、木荷的种间具有显著的正联结关系,与枫香、苦槠和青冈也存在正联结关系,可见在研究区内檫木能够与这些树种互相吸引。     

Sexually dimorphic transitions revealed in the relationships of yearling rhesus monkeys following the birth of siblings

We report here that in a large captive group of monkeys, Macaca mulatta,sudden sex-related changes occur in social interactions in one short phase of an infant’s development. Social interactions of 1-year-old animals (males, N =12; females, N =8) 6 weeks before the birth of siblings were compared with interactions occurring 6 weeks after the birth. On the day of the siblings’ birth, depression-like postures were seen in two yearling males (YMs); 10 YMs showed hyperactivity. In the postbirth period, YMs refocused their attentions away from their mother and toward other, often unrelated members of the group. Although YMs initiated disengagement of interactions with their mothers, there was evidence that mothers attempted to lessen this disengagement. The YMs had close relationships with specific (“preferred”) male individuals. These relationships (particularly those with adult males) became more pronounced following the birth of the sibling. The adult-male group also took an active role in maintaining interactions with YMs. The preferred partners in the YM-other male relationship before the birth of the sibling were, however, not always the same as those in the period after the birth. Dominance relationships and probably genetic factors determined patterns of interaction between YMs and their preferred male partners. Among yearling females (YFs), no dramatic changes in interactions with their mothers or with other group members were detected after their mothers gave birth. Relationships in YF-mother and YF-other-individual pairs (especially when the other individual was kin) seemed to be consolidated during the postbirth interval. There was little evidence of jealousy between the YFs and their younger siblings. Thus, sibling birth acted as a stimulus for the occurrence of sexually dimorphic interactions in yearlings. We suggest that in natural environments, social interactions in YFs promote relationships that will serve to integrate them into the matrilineal social structure, whereas comparable behavior in YMs encourages relationships with males that they may emigrate with into, or meet again in, nonnatal troops.     

人为干扰对碧峰峡栲树次生林群落物种多样性及其优势种群生态位的影响

为进一步了解人为干扰对碧峰峡生态旅游区的生态环境及不同种群利用资源、占据生态空间的能力的影响,并为该区植物资源、大熊猫栖息地的保护及旅游可持续措施的制定提供依据,调查了人为干扰下碧峰峡栲树(Castanopsis fargesii)次生林物种多样性及其优势种群生态位的组成情况。结果表明:7200m2的样方中共记录到156个植物种,隶属于70科114属,其中乔木16科23属33种,灌木39科67属95种,草本38科42属47种;乔木层总体物种多样性水平在中度干扰下最低,在轻度及重度干扰下差异不大。灌木层总体物种多样性水平在中度干扰下最高,在轻度干扰下最低。而草本层物种多样性随着干扰强度的加深有明显降低趋势;随着人为干扰强度的增加,乔木层中优势种栲树的生态位宽度均为最大,与其他树种生态位重叠值在中度干扰下有所降低,枹栎(Quercus serrata)的生态位宽度会变小,山茶科(Theaceae)植物的生态位变宽,同时其生态位重叠值增大;在灌木层中,重度干扰下,菝葜(Smilax china)生态位宽度减小,栲树幼苗的生态适应范围也骤减,其他大多数物种在中度干扰下,生态位宽度最低;在草本层中,蕨类植物及皱叶狗尾草(Setaria plicata)在重度干扰下生态位宽度及重叠值均增高,其适应范围变广,种间竞争加剧。综合分析表明,群落各层次物种多样性水平对人为干扰的响应各不相同,其中人为干扰对灌木及草本层物种多样性影响最大。同时人为干扰会改变群落物种组成及种间原有的关系,特别是中度干扰会使群落间优势种地位增强,种间竞争关系加剧,导致其原有生境被破坏,不利于群落发展。因此强化景区保护及合理经营迫在眉睫。     

Proximal Spacing Between Individuals in a Group of Woolly Monkeys (Lagothrix lagotricha) in Tinigua National Park, Colombia

I studied proximal spacing within a group of woolly monkeys (Lagothrix lagotricha) during 7 months at Parque Nacional Tinigua, Colombia. I collected a total of 1188 instantaneous samples on focal individuals, recording the number and age/sex class of individuals that were in contact with, <2 m from, <5 m from the focal animal. The results indicate that proximate spacing reflects social affinities and is related to mother–infant relationship and social grooming. Subadult females and adult males are the sex/age classes with the lowest number of individuals in proximity. There are low proximity between adult females and between adult males and high frequencies of nearness between mother and offspring. Associations between males and females were usually low, but in some cases males showed preferences for a given female. There was a relatively gradual increase in spacing between mothers and their offspring as they became older. Old juvenile males were associated chiefly with other males—mostly subadults—whereas juvenile females maintained some proximity only to their mothers. There are also differences in spacing behavior according to different activity types.     

Selectable components of sex allocation in colonies of the honeybee (Apis mellifera L.)

Colonies of social insects that undergo fission as a componentof reproduction produce large excesses of males. Hypothesesto explain this phenomenon have assumed that the workers thatconstitute the entourage for the new queen (or queens) representinvestment in female reproductives. Selection for optimal colonysex allocation then leads to an increase in production of malesthat balances the investment in females based on their relativereproductive values. We show that the construction of comb dedicatedto the production of males (drone comb) versus workers (workercomb) is a component of sex investment under the control ofcolony workers. Relative comb construction was highly correlatedwith the relative investment in male and worker brood. Coloniesthat invested relatively more in their total numbers of malesinvested less in the dry weight of individual workers. Coloniesthat had more adult workers produced a greater number of malesand workers, but colony size did not affect the proportionalinvestment in drone comb or brood. Genetic variability was foundfor the number of adult workers in colonies, the amount of dronecomb produced, the amount of worker comb produced, and the dryweight of adult workers, suggesting that sex allocation is aselectable trait in honeybees.     

Resource competition between genetically varied and genetically uniform populations of Daphnia pulex (Leydig): does sexual reproduction confer a short‐term ecological advantage?

Small competitive advantages may suffice to compensate for a large disadvantage in intrinsic growth capacity. This well‐known principle from ecology has recently been applied to the enduring question of how sexual reproduction can persist in the face of invasion by female‐only parthenogens. Small competitive advantages resulting directly from sexual reproduction are predicted to cancel a two‐fold disadvantage in intrinsic growth capacity caused by males (which do not themselves produce offspring) comprising half the sexual population. In this paper we test the principal assumption of this theory, that the genetic variation produced by sexual reproduction confers a competitive advantage over self‐identical asexual invaders. We set up competition between a diverse clonal assembly of Daphnia pulex and genetically uniform populations from single clones. At young ages, the population comprising genetically varied Daphnia had significantly higher birth rates in competition with populations of genetically uniform Daphnia than in competition with itself, indicating competitive release and a Lotka–Volterra competition coefficient α₁₂ < 1. No such difference was apparent under conditions of greater food stress, possibly due to individuals channelling more energy into survival, or for old‐aged populations, possibly as a result of reduced selective pressures for high reproduction in old females. Mean birth rates differed between the clones at all ages in the presence of competition, providing evidence of variation in life history traits between clones. A Lotka–Volterra model predicted empirical estimates of α₁₂ = 0.896 (genetically uniform on varied) and α₂₁ = 1.010 (varied on uniform), which permits immediate coexistence of a sexual population of D. pulex even with an asexual lineage having twice the intrinsic growth capacity. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 85 , 111–123.     

马尾松人工林发育过程中林下灌草群落优势种生态位动态分析

该研究以贵州省孟关林场不同林龄马尾松人工林为研究对象并开展典型样地调查,采用空间代替时间的方法,根据Shannon、Levins公式和Pianka公式分析不同发育阶段林下灌草群落优势种生态位动态特征。结果表明:(1)同一优势种重要值在不同林分中存在差异,8a、18a林分中槲栎重要值分别为50.89%、47.32%,28a林分中铁仔重要值为50.49%,36a林分中菝葜重要值为50.62%,芒萁重要值在各发育阶段始终排第一。(2)槲栎和菝葜生态位宽度占绝对优势,南烛、茅栗随着年龄的递增生态位宽度值增大,芒萁生态位宽度值随林分林龄的增加而递增,边缘鳞盖蕨和野青茅随林分林龄的增加呈先增加后减少的趋势,灌草重要值与生态位宽度不存在绝对的正负关联关系,同一物种在不同时期对环境的适应及资源的利用能力不同。(3)槲栎与菝葜、铁仔与茅栗、乌蕨与边缘鳞盖蕨、野青茅与荩草等物种种对间表现出极强的生态学或生物学特性相似性,生态位宽度值大的物种与其他物种生态位重叠值并不同步。     

林窗尺度对马尾松人工林林下灌草层优势种生态位的早期影响北大核心CSCD

马尾松作为中国广泛栽植的乡土树种,其人工林群落结构简单和生物多样性低下是普遍存在的生态学问题。探究不同林窗尺度对马尾松人工林林下植被群落的影响,可为马尾松人工林近自然经营提供理论依据。该研究在45 a生马尾松人工林中分别设置A(50 m^(2))、B(100 m^(2))、C(200 m^(2))和D(667 m^(2))4种不同尺度的林窗,以不做任何处理的马尾松人工林作为对照(CK),探究采伐开窗后林窗内自然更新1 a后的灌草层植物组成、优势种生态位宽度和生态位重叠度分布特征。结果显示:(1)除100 m^(2)林窗下灌木层物种数与对照无显著差异外,其余林窗灌草层物种数均显著高于对照(P<0.05),且200 m^(2)林窗下灌草层物种数均最多,分别为35种和20种;4种林窗下灌草层物种丰富度指数较对照均显著增加(P<0.05),最大值均出现在200 m^(2)林窗下,其值分别为对照的1.5倍和2.6倍。(2)林窗增加了灌草层喜光植物种类,且在200 m^(2)林窗下种类最多,灌木层喜光植物有13种,草本层喜光植物有5种。(3)4种林窗下灌草层优势种中,喜光植物生态位宽度均较大,200 m^(2)林窗下灌草层生态位宽度平均值最小,其对资源利用程度低,重要值与生态位宽度之间无显著相关性(P>0.05)。(4)4种林窗下灌草层优势种间生态位重叠度指数均较小。667 m^(2)林窗下,灌草层优势种平均生态位重叠度指数最小,分别为0.029和0.024,200 m^(2)林窗下灌草层优势种高生态位重叠度占总数比例最大,分别为20%和23.8%。研究表明,采伐开窗促进了马尾松人工林林下植被发育,丰富了林下植物多样性,有利于马尾松林稳定持续发展,对精准提升马尾松人工林质量具有重要意义。     

Effects of Isolation on Stress Responses to Novel Stimuli in Subadult Chickens (Gallus gallus)

Extensive research has examined the effects of social isolation in neonatal and adult animal populations, but few studies have examined the effect of social isolation in early adulthood. Animals reaching reproductive age often experience extensive social changes as they leave their natal site, and a social stressor like isolation may uniquely affect this age group. Furthermore, adolescence is a time when sex differences in behavior become more pronounced. As such, the effects of social stressors are likely to vary by sex. In this study, we used noninvasive methods to evaluate stress responses to social change in male and female subadult chickens (Gallus gallus). Half of the birds experienced regular sessions of social isolation over the course of 2 wk, while the other half were never isolated. Subsequently, all of the animals were exposed to a suite of three novel probes, including an open‐field test. We monitored the birds’ behavioral (head movements) and physiological (fecal glucocorticoid metabolites, FGM) response to the tests. Our results indicate that, for subadult chickens, the effect of social isolation is sex dependent: Male FGM and behavioral responses did not change with subsequent experiences, in contrast to females. Females also exhibited more social reinstatement behavior compared to males. Our results are consistent with the expectations of differences between the sexes based on changes in the social environment due to sex‐biased dispersal patterns. For both sexes, the FGM and behavioral responses varied independently, which highlights the necessity for multiple measures of stress in animal populations.     

大兴安岭次生林区不同龄级落叶松(Larix gmelinii)生态位特征和竞争关系

生态位能够反映物种在群落中的功能地位,通过生态位可以定量地研究种内、种间、生境三者之间的相互关系。以大兴安岭次生林区优势种群落叶松（Larix gmelinii）为研究对象,运用Levins公式、Pianka指数和Hegyi单木竞争指数模型分析了该优势种的生态位特征、生态位宽度与重叠度以及重叠程度与竞争作用之间的关系。研究结果表明：随落叶松个体的发育其生态位呈先增大后减小的规律性变化;生态位宽度较大的落叶松个体间重叠程度往往也较高,生态位宽度与重叠度呈显著的线性正相关;落叶松个体间的生态位重叠程度与彼此之间的竞争作用无明显相关性、种群内存在互利性生态位重叠现象;生物个体间的竞争作用与研究尺度有关。     

Old,socially housed rhesus monkeys manipulate objects

Recent research has indicated that old, individually housed monkeys show little interest in novel objects. Yet unanswered is whether this effect is caused primarily by age or housing condition. The purpose of this study was to assess the role of social living in promoting responsiveness to objects. We measured the rates of object manipulation in older animals, assessed responsiveness over time to particular objects as a measure of habituation, and examined social influences on object use. Several social groups of rhesus monkeys that contained older adults were studied. These groups were housed in indoor pens or in an outdoor enclosure, and all monkeys had continuous access to a variety of objects in their home environment. In contrast to previous studies of individually housed monkeys, our group-housed monkeys showed sustained interest in objects. Old monkeys manipulated objects extensively, and this response was all the more significant, given that the objects were not novel. Monkeys housed in an outdoor enclosure showed object manipulation patterns that were not different from monkeys housed in indoor pens. However, females exhibited much higher object-related responses than males. Social facilitation played a role in the reactions of some monkeys to objects. Patterns of social facilitation as well as avoidance were present in two of the three indoor groups that were observed. Failure to manipulate objects in rhesus macaques appears to be more a function of individual housing than of old age. Factors such as environmental complexity, social needs, and early experience should be considered in order to understand why individually housed rhesus monkeys are unresponsive to objects. © 1993 Wiley-Liss, Inc.     

漓江流域岩溶区檵木群落不同恢复阶段主要共有种生态位变化

以空间代替时间的方法选取典型样地,采用群落学调查对漓江流域岩溶区立地条件基本一致的檵木群落不同恢复阶段主要共有种的Levins生态位宽度和Pianka生态位重叠进行研究,揭示檵木群落恢复过程物种的环境资源利用状况和种间关系、种群动态及群落稳定性,为漓江流域岩溶石漠化生态系统的植被恢复和重建提供依据。结果表明:(1)檵木群落不同恢复阶段乔木层主要共有种为檵木、小巴豆,灌木层主要共有种为檵木、红背山麻杆、龙须藤、火棘、白饭树、白马骨、扁片海桐、皱叶雀梅藤、亮叶崖豆藤。(2)乔木层主要共有种的生态位宽度和生态位重叠随着檵木群落的恢复呈现增大的趋势,而灌木层主要共有种的生态位宽度和生态位重叠变化趋势则相反。(3)在乔灌阶段的乔木层和乔林阶段的灌木层主要共有种的生态位宽度均小于1.0,灌木层中主要共有种对间的低生态位重叠值(0～0.6)的种对数随着群落恢复增多,而高生态位重叠值(0.8～0.9)的种对数减少。(4)乔木层中的主要共有种檵木和小巴豆协同发展,在相当长的时间内将共同主导群落的整体恢复方向;灌木层中的主要共有种随着群落的恢复对环境资源需求进一步分化或者生态位进一步分离,檵木的优势地位进一步削弱。     

Do animals have culture?

Culture is probably not rare in animals, although hard experimental evidence is lacking. The strongest case for culture is found in the species most amenable to experimental manipulation, rather than in nonhuman primates. Human culture is much more likely to be cumulative than animal culture, but the reasons for this are not well established. At this point, there is no reason to assume that cumulative culture depends critically on teaching, imitation, language, or perspective‐taking. Currently, animals are being judged according to stricter criteria than humans.     

Primate Innovation: Sex,Age and Social Rank Differences

Analysis of an exhaustive survey of primate behavior collated from the published literature revealed significant variation in rates of innovation among individuals of different sex, age and social rank. We searched approximately 1,000 articles in four primatology journals, together with other relevant databases, for examples of innovation. The reported incidence of innovation is higher in males and adults, and lower in females and nonadults, than would be expected by chance given the estimated relative proportions of these groups. Amongst chimpanzees, the only species for which there are sufficient data to consider alone, there is a similar sex difference in the propensity to innovate, but no effect of age. Chimpanzees of low social rank are reported as innovators more frequently than high-ranking chimpanzees are. Male chimpanzees innovate more often than females in sexual, courtship, mating and display contexts; that is, in contexts likely to increase access to mates. The largest number of recorded observations are in the foraging context, wherein contrary to expectations, there is no evidence for female chimpanzees exhibiting more innovation than males. The study is the first extensive investigation of behavioral innovation in primates and provides evidence that much individual variation in the propensity to innovate can be explained in terms of sex, age, and social rank.     

The effects of sex ratio and density on the expression of gender in the polychaeteCapitella capitata

Summary Large natural populations of the marine polychaeteCapitella capitata (species type I) contain males, females, and occasionally, hermaphrodites. Environmental conditions control the occurrence of hermaphrodites. At low density or in groups with female-biased sex ratios, males develop into hermaphrodites, and hermaphrodites are common. Crosses suggest that females are heterogametic, and males and hermaphrodites are homogametic. Heterogametic females do not become hermaphrodites.This study shows that in homogametic individuals, environmental conditions determine not only the development of hermaphroditism but also the expression of initial gender. Homogametic individuals can express either male or female gender initially, and homogametic individuals of either gender can develop subsequently into simultaneous hermaphrodites. The choice of initial gender depends on isolation. Most homogametic juveniles become females if reared alone but males if reared with other conspecifics. Homogametic males readily develop into hermaphrodites if females are rare. In contrast, homogametic females rarely become hermaphrodites.