千岛湖岛屿社鼠的扩散特征

2009年7月—11月,2010年3月—11月对千岛湖两个岛屿上的社鼠(Niviventer confucianus)种群进行标志重捕,通过分析扩散个体的性别、年龄及扩散距离等,探讨陆桥岛屿环境下社鼠的扩散特征。研究结果显示:岛屿环境下社鼠的扩散率为37.96%,不同季节社鼠的扩散率存在差异,社鼠倾向于在春季发生扩散,尤其是3月份,社鼠扩散个体数最多;对于整个捕获史而言,雌雄扩散个体数存在极显著的差异(x~2=12.542,df=1,P0.001),雄性个体更倾向于发生扩散;而在繁殖高峰期,当怀孕鼠存在时,雄性扩散数亦大于雌性,两者存在显著差异(x~2=4.504,df=1,P=0.034)。扩散个体体重的季节差异不显著;扩散与社鼠的年龄密切相关,社鼠更加倾向于在亚成年阶段发生扩散;另外,家群大小对社鼠扩散个体数量也有显著影响,家群越大,扩散个体越多;对扩散距离进行分析发现存在显著的性别差异(t=-9.229,df=50,P0.001),雌性个体的平均扩散距离为(282.97±16.14)m,显著大于雄性的(146.70±6.80)m,而扩散距离与年龄、体重、最大活动距离均无显著相关性。     

湖北石首散养麋鹿种群的调控机制:密度制约下种群产仔率下降

为了探讨散养麋鹿(Elaphurus davidianus)种群密度制约的调控机制,1993–2013年,我们以湖北石首麋鹿国家级自然保护区围栏内的散养麋鹿种群为研究对象,采用分区直接计数法统计麋鹿种群数量,计算种群增长率、死亡率、存活率和产仔率等参数,对麋鹿种群的发展是否受到密度制约影响以及作用于哪些种群参数进行了研究。结果表明:石首麋鹿保护区散养麋鹿种群的发展过程可分为5个阶段,分别为稳定增长阶段(1993–1997年)、快速增长阶段(1998–2006年)、缓慢增长阶段(2007–2009年)、迅速下降阶段(2010年)和种群恢复阶段(2011–2013年)。1993–1997年,种群增长率为16.60±3.10(%),而死亡率为4.34±0.93(%);1998–2006年,种群增长率增加为28.98±3.62(%),死亡率为4.35±2.31(%);2007–2009年,种群的增长率下降为7.36±1.64(%),而死亡率增加为6.32±2.85(%);2010年种群暴发传染性疾病,数量急剧下降;2011–2013年,种群增长率增加为10.95±4.04(%),而死亡率下降为5.70±2.03(%)。Pearson相关性检验结果显示:种群密度与增长率呈极显著负相关(r=–0.612,P=0.0050.01),与产仔率也呈极显著的负相关(r=–0.902,P=0.0000.01),与死亡率的相关性不显著(r=0.425,P=0.0620.05)。独立样本t检验结果显示,2010年之前(1993–2009年)和之后(2011–2013年)的成、幼体存活率分别为95.40±1.56(%)、95.79±1.80(%)和96.67±0.92(%)、94.04±2.20(%),两者差异不显著(成体:t=–0.503,df=8,P=0.6280.05;幼体:t=0.558,df=8,P=0.5920.05),这说明密度制约因素未对石首麋鹿保护区散放麋鹿种群的存活率产生明显影响。从2003年起,种群受到密度制约机制的调控,主要表现为产仔率下降,同时也受到了洪水、疾病和人类干扰等环境因素的影响。针对目前石首麋鹿保护区散养麋鹿种群面临的密度制约和环境容纳量等问题,我们提出了应对策略。     

人类活动对野化麋鹿生存的影响及保护对策

在经济较为发达的江苏沿海地区,人类活动给不断增长的野化麋鹿Elaphurus davidianus种群带来了新的威胁。了解其中的规律有助于缓和、消除这些威胁对野化麋鹿产生的负面影响。2017年1月—2019年12月,以江苏大丰麋鹿国家级自然保护区围栏外的野化麋鹿为研究对象,对发生的野化麋鹿救助案例进行统计,分析不同年份、不同季节、不同生境救助次数和救助数量的特点,探讨所救助麋鹿的年龄结构和性别特征,总结野化麋鹿最主要的威胁因素。结果表明:共发生野化麋鹿救助次数209次,救助数量409头。不同年份野化麋鹿的救助次数(OneWay ANOVA:F=12.516,P 0.01)和救助数量(F=4.691,P 0.05)均存在显著差异,并呈现逐年增加的趋势。不同生境野化麋鹿救助次数(K-W test:χ~2=28.862,P 0.01)和救助数量(χ~2=25.752,P 0.01)均存在极显著差异,其中养殖塘发生的救助次数和救助数量最多。秋季野化麋鹿救助次数和救助数量较多,成年雄性麋鹿更容易受困于人类设施。落水、缠网和交通事故等造成的受困、死亡比例最高。因此应该采取"有效清除栖息地四周的障碍物、科学预留供麋鹿使用的穿越通道、增设野化麋鹿逃生通道"等措施消除野化麋鹿生存的威胁,加强野化麋鹿巡护管理,推动完善生态补偿机制,最终减少人类活动对野化麋鹿生存造成的不利影响。     

海南文昌昌洒荒坡地生境中蜡皮蜥繁殖期家域

为掌握蜡皮蜥(Leiolepis reevesii)繁殖期家域大小、家域内是否存在核域,以及家域与核域的重叠程度,分别于2010年和2011年的3月至5月在海南文昌荒坡地生境中,应用无线电遥测技术对蜡皮蜥家域进行了研究,采用最小凸多边形、固定核域、线家域等方法分析了13只个体(10雄3雌)的家域、核域及其重叠度。雄性最小凸多边形(100%MCP)家域面积为(14 091.6±5 718.0)m2,显著大于雌性的(253.3±106.5)m2(t=4.064,df=11,P=0.002);雄性95%固定核域(FK)和75%FK面积为(10 707.8±2 388.5)m2和(3 282.7±1 022.8)m2,分别显著大于雌性的(379.1±74.1)m2(t=7.262,df=11,P0.001)和(172.1±37.9)m2(t=5.107,df=11,P0.001);雄性线家域为(205.8±52.5)m,显著大于雌性的(25.0±2.0)m(t=5.781,df=11,P=0.034);分析遥测个体位点利用方式,蜡皮蜥个体家域内核域明显,雄性核域为(1 380.5±429.1)m2,显著大于雌性的(80.2±18.5)m2(t=5.088,df=11,P0.001),且雄性核域占100%最小凸多边形家域面积的比例为10.9%±3.9%,显著低于雌性的33.3%±6.1%(t=﹣7.834,df=11,P0.001);雄性100%MCP面积不仅与头体长(SVL)之间线性相关显著(n=10,r=0.815,P=0.004),而且与体重(BM)之间也具有明显的线性相关(n=10,r=0.683,P=0.029);个体之间具有家域和核域重叠,雄性个体之间100%MCP家域重叠指数为0.26±0.17,显著低于雌性的0.66±0.02(t=﹣3.372,df=34,P=0.002),而雄性核域重叠面积占核域比例为2.50%±1.70%、重叠指数为0.02±0.02,雌性比例为0.34%±0.01%、重叠指数为0.01,表明蜡皮蜥具有明显的领域性,且雌性在繁殖季节其领域性明显高于雄性。     

华西蟾蜍年龄结构、体长和生长率的研究

本研究利用骨龄学方法研究了青藏高原东缘横断山脉区一个华西蟾蜍种群的年龄结构、体长、年生长率及性成熟年龄。采集的74个成体个体中(雄性47只,雌性27只),均能够在趾骨切片中观察到受抑制生长线。结果表明:两性的体长和年龄都成正相关关系(雌性:F1,26=4.87,r=0.40,P=0.04,雄性:F1,46=4.48,r=0.30,P=0.04)。雌性初始繁殖年龄为4龄,寿命至少为11龄;雄性分别为3龄和11龄。雌性和雄性的平均年龄存在显著差异(Z=2.27,P<0.01),雌性为(8.4±1.8)龄,雄性为(6.2±1.8)龄。雌性平均体长大于雄性(t=2.348,P<0.01),雌性为91.9 mm±7.2 mm,雄性为74.8 mm±5.5 mm。另外,雌性和雄性具有不同的生长模式,雌性生长率(r=2.48)大于雄性(r=2.32)。年龄和生长率对华西蟾蜍的性二型的解释有重要意义。     

湖北石首麋鹿国家级自然保护区麋鹿种群动态

为实现麋鹿回归大自然的目标,1993年和1994年,湖北石首麋鹿国家级自然保护区(以下简称石首麋鹿保护区)分别从北京麋鹿苑引入麋鹿30头(8♂,22♀)和34头(10♂,24♀)建立了繁殖种群。自2000年6月开始,作者每月一次(7-10d)实地监测石首麋鹿保护区内、外的麋鹿种群动态。到2006年产仔季节结束后,该保护区内的麋鹿种群达522头,2006年产仔前性比为1∶1.22。用指数增长模型拟合种群增长曲线,1998年后石首麋鹿保护区内的麋鹿种群呈指数增长(Nt=84e0.226t),其瞬时增长率为0.226;1998年夏季长江暴发特大洪灾,石首麋鹿保护区内的部分麋鹿逃逸到长江南岸,形成了自然野化麋鹿种群。该自然野化种群比保护区内麋鹿种群增长快,其瞬时增长率达到0.267。湖北石首和江苏大丰两个国家级自然保护区内麋鹿种群的出生率和增长率差异显著,而两地的死亡率无显著差异。石首麋鹿保护区内的麋鹿种群年均出生率(26.8%,P=0.010)和年均增长率(21.7%,P=0.038)均显著地高于江苏大丰国家级自然保护区内麋鹿种群的年均出生率(21.6%)和年均增长率(17.0%)。由于生境退化和人为干扰,当前石首麋鹿保护区内的麋鹿种群增长已开始出现密度制约迹象,亟待采取有效措施来改善麋鹿的生存繁衍条件。     

洞庭湖区麋鹿再野化初期秋冬季生境选择

深入了解生境特征和生境选择的季节性差异是开展野生动物生境有效管理的前提。2016年3月, 原国家林业局和湖南省人民政府启动了麋鹿(Elaphurus davidianus)再野化项目, 来自江苏大丰的16头麋鹿(其中11头安装了GPS卫星跟踪颈圈)在湖南东洞庭湖国家级自然保护区君山后湖放归野外。冬季气候寒冷、食物匮乏, 濒危物种个体野放后能否在冬季找到适宜生境是再野化项目能否成功的关键。2016年10月至2017年1月, 借助GPS卫星和地面跟踪信息, 我们采用样方法对再野化麋鹿种群秋、冬季生境选择进行了研究, 测定了生境类型、食物丰富度、草本盖度、乔木盖度、距水源距离、距道路距离、距居民点距离、距隐蔽物距离、隐蔽级等9种生境因子。结果显示: (1)再野化麋鹿种群在秋、冬季对生境类型的选择差异极显著。冬季麋鹿偏好选择水塘、随机利用草本沼泽、避免利用灌草丛; 而秋季对生境类型无明显偏好。(2)再野化麋鹿秋冬季对食物丰富度、草本盖度、乔木盖度、距道路距离、距居民点距离、距隐蔽物距离和隐蔽级的选择差异极显著; 仅在距水源距离上的差异不显著。(3)秋季再野化麋鹿倾向于选择隐蔽级低、食物丰富度高、草本盖度高、距隐蔽物距离近的生境。其生境利用样方与对照样方在隐蔽级上的差异极显著; 在食物丰富度、草本盖度、距隐蔽物距离上的差异显著; 在距水源距离、乔木盖度、距道路距离、距居民点距离上的差异不显著。(4)冬季再野化麋鹿倾向于选择距水源近、食物丰富度高、草本盖度高的生境。其生境利用样方与对照样方在食物丰富度、草本盖度、距水源距离上的差异极显著; 在距道路距离、距居民点距离、距隐蔽物距离、隐蔽级上的差异不显著。研究结果揭示了洞庭湖区再野化麋鹿种群秋冬季生境选择偏好, 为再野化麋鹿种群保护及其生境修复提供了基础数据。     

黄山短尾猴社群中的架桥行为

2007年3~5月,采用随机取样法对黄山短尾猴(Macaca thibetana)YA1群架桥行为进行研究。结果表明,不同时间段架桥行为发生次数存在极显著差异(t=3.912,df=10,P<0.01)。成年组雄性个体是主要发起者(Z=-2.1888,P<0.05)和接受者(Z=-2.5238,P<0.05),但同年龄组不同性别个体发起次数(Z=-1.755,P>0.05)无显著差异,接受次数(Z=-2.201,P<0.05)差异显著。架桥行为多采用雄性婴幼猴(Z=-2.437,P<0.05)(F=6.735,df=2,P<0.05)作为媒介,母亲序位影响婴幼猴在架桥中被使用的次数(Z=-3.724,P<0.01)。不同序位雄性(F=2.947,df=4,P<0.05)和雌性个体(F=5.320,df=4,P<0.05)架桥行为发起模式主要是第Ⅰ类。雌性个体选择具有亲缘关系的个体作为架桥媒介(Z=-2.490,P<0.05),但雄性个体对母系亲属后代无明显选择性(Z=-0.866,P>0.05)。短期研究表明,黄山短尾猴社群中的架桥行为主要采用第Ⅰ类模式;亲缘关系不一定是影响架桥行为媒介选择的主要因素;架桥行为具有缓解群体间竞争压力的作用。     

Bechstein的蝙蝠，一个群居物种中的建群和扩散

群种群遗传模型认为建群和扩散是不同的行为。然而,建群和扩散是否真正反映自然界中不同的生物学过程是不清楚的。一个检测这个假设的可能是在严格的雌性个体恋家的物种中估计常染色体和线粒体的遗传结构模式,例如群居繁殖的Bechstein蝙蝠。在这个物种中,线粒体DNA只能当雌性个体建立新的群体的时候才能扩散,常染色体只能在雌性个体与出生于外群的单独生活的雄性个体交配的情况下在群体间传播。     

麋鹿沧桑命运与未来保护展望

麋鹿作为中国特有的鹿科动物,经历129年的保护努力,种群数量恢复到10000多头。因近亲繁殖严重,表面上看已无灭绝危险,但仍存在巨大隐忧。通过对麋鹿种群变迁、灭绝、重引入、恢复现状及四大种群(乌邦寺、南海子、大丰、石首野化种群)的发展趋势进行追踪分析,探究近千年来困扰麋鹿种群发展壮大的多重因素,提出种群保护与栖息地保护并重、强化疫病监测等保护对策,为麋鹿及其它大型陆生濒危哺乳动物突破种群发展瓶颈提供借鉴。     

荒漠孑遗植物裸果木种子时空扩散特性

裸果木(Gymnocarpos przewalskii)是亚洲中部荒漠区少有的第三纪孑遗物种,由于气候变化及人为干扰,其自然种群分布范围不断缩小。种子扩散作为植物生活史过程中的重要阶段,不仅对物种生存及其多样性至关重要,还影响物种分布范围和局部丰度。2015年和2016年分别在新疆哈密地区,采用布设种子收集器的方法,对其自然种群种子扩散的时空动态进行了定点连续观测。结果表明:该物种于当年6月上旬开始扩散,2015年略早于2016年。每年种子扩散持续时间约两个月,扩散趋势为单峰曲线,且呈集中大量扩散的模式,扩散高峰期与当年初次月降水高峰期吻合;在顺风的正南和东南方向上,种子扩散密度大且距离远;种子扩散主要集中在母株冠幅下,随着距母株距离的增加,种子扩散密度减少,二者间存在极显著的负相关性(P0.01),由于裸果木枝条繁多,对风力强度起到了一定的阻碍作用,可能是造成种子集中扩散在母株下的原因。裸果木种子扩散受外界环境(降水、风向)和自身因素等方面的影响,当种子在大量降水前完成扩散,将有利于种子在适宜的微生境萌发,是对多风、干旱的恶劣生境的一种长期适应。     

The seed dimorphism of Spergularia marina in relation to dispersal by wind and water

Summary The seeds of the halophyte Spergularia marina differ both within and between individuals in that they either possess or lack a membranaceous border. This paper presents a morphological study of the length, weight and area of the seed types, and their dispersal characteristics under experimental conditions of wind and water dispersal. The winged seeds are shown to be larger both by length and by weight. Their rate of descent increases with wing loading. If the wing is lacking, however, the rate of descent increases with weight only. The distance of dispersal is equal for both seed types except at low wind speeds, when the winged seeds disperse farther. If the seed wing is removed, the excised seeds have shorter dispersal distances. When dispersed by water, a difference in the distance seeds are dispersed can only be detected in the presence of vegetation. The winged seeds are more frequently trapped in the vegetation as compared to the unwinged seeds. The hypothesis that the seed dimorphism is an adaptation for differential dispersal distances is discussed.     

Relative importance of ballistic and ant dispersal in two diplochorous Viola species (Violaceae)

Viola is one of the diplochorous plant genera that disperse their seeds in two ways, ballistic and ant dispersal. We compared the seed dispersal of two major Viola species of northern Japan, V. selkirkii and V. verecunda. The mean weight of seed was less in V. verecunda (0.42 ± SD 0.03 mg) than in V. selkirkii (0.61 ± 0.12 mg). The elaiosome of V. selkirkii (0.02 ± 0.004 mg) was larger than in of V. verecunda (0.006 ± 0.0004 mg), whereas the lipid component of elaiosome was not remarkably different between the two species. In ballistic dispersal, the mean dispersal distance was 56.0 ± 17.5 cm in V. verecunda but only 38.3 ± 5.1 cm in V. selkirkii. In ant dispersal, the mean dispersal distance was 28.1 ± 24.9 cm in V. selkirkii and 36.1 ± 33.7 cm in V. verecunda; however, the seed removal frequency of V. selkirkii (15.5%) was much higher than that of V. verecunda (3.0%). These results suggest that V. selkirkii is more dependent on ant dispersal while V. verecunda is more dependent on ballistic dispersal. The effect of seed predation was very serious in both species. In the quadrat census, 99.0% of V. selkirkii seeds and 99.1% of V. verecunda seeds were damaged by ground beetles, spiders, ticks, and others which frequently devoured diaspores. An experiment with V. verecunda seeds demonstrated that the overdispersion of seeds on the forest floor enhanced the frequency of removal by ants and reduced seed damage by predators.     

Dung beetles as secondary seed dispersers in a temperate grassland

The two-phase dispersal event in which dung beetles move seeds after endozoochory is often assumed to be advantageous for plant regeneration. Because seeds are expected to end up in favourable and safe germination sites, it is considered as an example of directed dispersal. However, literature so far is restricted to tropical rain forest ecosystems, while data for temperate regions are lacking. In this study, the effect of dung beetles on seedling establishment of endozoochorically dispersed seeds is evaluated for a temperate grassland ecosystem. We performed a field experiment in which cages excluded dung beetles from horse and cattle dung samples with mixed-in grass seeds. Seed germination from these samples was significantly higher than that from samples which were accessible to dung beetles. This indicates that the effect of dung beetles on short-term seedling establishment was negative, which contrasts with the patterns found for large-seeded species used in tropical studies. This is most likely attributed to the lack of roller species and the larger depth at which tunneling Geotrupes species bury seeds.     

Dispersal and Burial Behavior in Larvae of <Emphasis Type="Italic">Chrysomya megacephala</Emphasis> and <Emphasis Type="Italic">Chrysomya albiceps</Emphasis> (Diptera,Calliphoridae)

Blowflies use discrete and ephemeral substrates to feed their larva. After they run out of food, the larvae begin to disperse in order to find adequate places for pupation or additional food sources, a process named post-feeding larval dispersal. Briefly state the aspects and why they are important were studied in a circular arena of 25 cm in diameter and covered with wood shavings to a height of 40 cm allowing post-feeding dispersal from the center of the arena. Larvae of both Chrysomya albiceps and C. megacephala were used in five experiments for each species. For each pupa location, determined as distance from the center, depth, and weight were evaluated. Statistical tests were done to verify the relation between weight, depth and distance for pupation and for larvae of two species shows that the media distance is significantly different for two species and for C. megacephala this distance is greater than the distance for C. albiceps. The depth too is different for each species, as the larvae of C. megacephala buries deeper than C. albiceps. With relation of weight, there is no statistic evidence that have any difference between weights for pupation for each species.     

Mating duration and Frequency in a Pine Sawfly

Newly emerged females of the European pine sawfly, Neodiprion sertifer Geoffroy (Hymenoptera: Diprionidae), were placed on pine twigs in the field and their behavior was recorded. Twenty to 25% of the females attracted wild males and mated on the day of release. One-third to one-half of these females remained and oviposited, while the rest disappeared from their twigs after mating. The mating frequency peaked at noon, and on average the mating lasted for 19 ± 13 (SD) min. Eleven to 30% of the females that remained on their twigs after mating remated, occasionally up to five times. Most released females disappeared from their twigs on the first day. Disappearances included both predation and dispersal. Only a few dispersals >5 m were recorded, because the sawflies were difficult to follow during flight. By color marking, dispersal up to 20 m was recorded.     

Effect of parasitism on flight behavior of the soybean aphid, Aphis glycines

Many aphid species possess wingless (apterous) and winged (alate) stages, both of which can harbor parasitoids at various developmental stages. Alates can either be parasitized directly or can bear parasitoids eggs or larvae resulting from prior parasitism of alatoid nymphs. Winged aphids bearing parasitoid eggs or young larvae eventually still engage in long-distance flights, thereby facilitating parasitoid dispersal. This may have a number of important implications for biological control of aphids by parasitoids. In this study, we determined the effect of parasitism by Aphelinus varipes (Hymenoptera: Aphelinidae) on wing development and flight of the soybean aphid, Aphis glycines (Hemiptera: Aphididae). We also quantified the influence of aphid flight distance on subsequent A. varipes development. Parasitism by A. varipes was allowed at different A. glycines developmental stages (i.e., alatoid 3rd and 4th-instar nymphs, alates) and subsequent aphid flight was measured using a computer-monitored flight mill. Only 35% of aphids parasitized as L3 alatoid nymphs produced normal winged adults compared to 100% of L4 alatoids. Flight performance of aphids parasitized as 4th-instar alatoid nymphs 24 or 48 h prior to testing was similar to that of un-parasitized alates of identical age, but declined sharply for alates that had been parasitized as 4th-instar alatoid nymphs 72 and 96 h prior to testing. Flight performance of aphids parasitized as alate adults for 24 h was not significantly different from un-parasitized alates of comparable ages. Flight distance did not affect parasitoid larval or pupal development times, or the percent mummification of parasitized aphids. Our results have implications for natural biological control of A. glycines in Asia and classical biological control of the soybean aphid in North America.     

Research progress in avian dispersal behavior

Dispersal, defined as a linear spreading movement of individuals away from others of the population is a fundamental characteristic of organisms in nature. Dispersal is a central concept in ecological, behavioral and evolutionary studies, driven by different forces such as avoidance of inbreeding depression, density-dependent competition and the need to change breeding locations. By effective dispersal, organisms can enlarge their geographic range and adjust the dynamic, sex ratio and genetic compositions of a population. Birds are one of the groups that are studied intensively by human beings. Due to their diurnal habits, diverse life history strategies and complex movement, birds are also ideal models for the study of dispersal behaviors. Certain topics of avian dispersal including sex-biased, asymmetric dispersal caused by differences in body conditions, dispersal processes, habitat selection and long distance dispersal are discussed here. Bird-ringing or marking, radio-telemetry and genetic markers are useful tools widely applied in dispersal studies. There are three major challenges regarding theoretical study and methodology research of dispersal: (1) improvement in research methodology is needed, (2) more in-depth theoretical research is necessary, and (3) application of theoretical research into the conservation efforts for threatened birds and the management of their habitats should be carried out immediately. __________ Translated from Acta Ecologica Sinica, 2008, 28(4): 1354–1365 [译自: 生态学报]     

Sex-biased dispersal in eastern chipmunks, Tamias striatus

I investigated the effect of male mate competition and inbreeding avoidance on natal dispersal of chipmunks by longitudinally monitoring known individuals from 1986 to 1990. Natal males exhibited greater absolute and effective dispersal distances but dispersed at the same proportion as natal females. Recruitment of juvenile males was negatively affected by density of resident males, but there was no evidence of local mate competition among male kin. Analysis of the spatial distribution of neighbors showed that natal males settled farther from their mothers than did their female siblings and farther than unrelated juvenile males. In addition, mothers apparently tolerated daughters as close neighbors and occasionally shared den sites with grandprogeny. Sexually mature males were never neighbors of their mothers and were never observed at maternal mating bouts. Males may disperse to improve reproductive opportunities by avoiding competition with resident males, and by increasing access to unrelated females. Maternal tolerance of daughters but not sons may result in the close affiliation between mothers and daughters, and indirectly contribute to dispersal of natal males. Hence male-biased dispersal could be a consequence of mate competition and maternal avoidance of incestuous matings. This revised version was published online in July 2006 with corrections to the Cover Date.     

Observations of predator-prey interaction on dispersal of an oligochaete prey,Limnodrilus hoffmeisteri

Clumped patches of the oligochaete, Limnodrilus hoffmeisteri, were subjected to predation by the leech, Erpobdella punctata to determine how the dispersion pattern might change. Two separate experiments showed that worms left the patch in 39% and 48% greater numbers when the leech predator was present. This suggests that L. hoffmeisteri uses a antipredatory strategy of dispersal rather than clumping.