西双版纳地区鞘花的繁殖物候特征及影响因素

桑寄生植物作为关键种和关键性食物资源在生态系统中扮演着重要角色,其鞘花的繁殖物候特征不仅会影响自身的繁殖适合度而且还会影响依赖于其获取食物资源的动物。为了解鞘花的繁殖物候特征及其影响因素,探究其与寄主植物和种子散布者之间的相互作用关系。该研究以西双版纳地区分布的鞘花为对象,通过定期观测鞘花和其寄主植物木荷的繁殖物候,测量它们的生物学特性和温湿度等环境因子,并分析鞘花在个体水平和种群水平上的繁殖物候特征以及寄主植物和温湿度对其繁殖物候的影响。结果表明:(1)鞘花的开花物候属于集中大量开花模式,整个种群的花期和果期的持续时间分别约为20 d和72 d,花期和果期的同步性指数都较高,6月中旬鞘花果实被取食的数量和速率最大,之后逐渐降低。(2)鞘花的始花期与木荷的始花期相关性较高,花期和果期与木荷的繁殖物候基本重叠。(3)每月开花和果熟的个体数量与同期和前一个月的平均温度和相对湿度的相关关系均不显著。总之,桑寄生植物的繁殖物候特征可能受到较多因素的影响,若想全面了解半寄生植物的繁殖物候特征,就要综合考虑生物和非生物等多种因子的共同作用。     

Host-mediated effects on the reproductive phenological asynchrony of a generalist mistletoe in China

一种泛性桑寄生植物繁殖物候异步性的寄主介导效应 寄主介导效应被认为会导致半寄生性的桑寄生植物的繁殖物候异步性，并由此为与桑寄生植物互惠共生的传粉者和种子散布者提供更长时间的食物资源供应，但目前关于此方面的研究还缺乏相关的实证数据。本研究以广泛分布于中国西南西双版纳地区的一种泛性桑寄生科植物五蕊寄生(Dendrophthoe pentandra)为材料，每周监测其开花、结果物候，检测了其开花和结果物候是否呈季节性格局，量化了五蕊寄生繁殖物候的异步程度，并检测了影响该植物始花期早晚的因素。最后，本研究还检验了五蕊寄生繁殖物候的异步性随寄主种类数量变化的效应。研究结果表明：(i)在连续两年的物候观测中五蕊寄 生的花期和果期都呈单峰分布格局；(ii)始花期显著受到植物大小和光照强度的影响，即冠幅越大和受光程度越高的植物个体有更早的始花期和更长的花期和果期；(iii)不同的寄主种类对五蕊寄生的繁殖物候有显著的影响，但与假设相反的是，随着寄主种类数量的增加，五蕊寄生繁殖物候的异步性没有显著提高。这项研究表明，在解释泛性桑寄生植物的繁殖物候异步性及寄主种类的数量对其影响的生态学意义还需进行更深入的探究。     

苏铁类植物传粉生物学研究进展(综述)

苏铁类植物是现存最古老的种子植物,研究其传粉特点,对于研究种子植物的起源与演化、植物与动物的协同进化以及苏铁类植物的繁殖机制、濒危机制有重要意义。本文从苏铁雌雄株开花物候学、传粉媒介及传粉机制等方面,对苏铁类植物传粉生物学相关研究进行综述,并提出今后该类植物传粉生物学研究的建议：对更多苏铁属种类未知的传粉机制进行研究;更广泛地应用排除法研究苏铁类特别是苏铁属植物的传粉媒介,进一步探讨传粉昆虫与苏铁类的共生关系问题。     

气候变暖对植物、传粉者及其相互作用的影响

植物和传粉者之间的相互作用,构成了错综复杂的传粉网络。近20年来,以全球变暖为主要特征的气候变化对开花植物、传粉昆虫和植物-传粉者相互作用的影响已成为研究热点。这些研究有助于更好地预测气候变暖对传粉网络乃至整个生态系统功能的影响。本文综述了气候变暖对开花植物个体的繁殖过程(物候、花吸引、报酬特征)和传粉昆虫活动及其相互作用产生的影响,以及在群落水平上对植物-传粉者网络产生的影响。气候变暖影响开花植物的花报酬(花蜜量、花粉的数量与质量)以及繁殖成功;温度升高对传粉昆虫的影响主要包括决定花粉流的传粉行为和传粉成功率。因此,气候变暖背景下植物、传粉者及其相互作用的改变会导致传粉网络结构发生变化,而传粉网络通过缓冲机制减少植物-传粉者间的错配而产生的负面效应,以维持自身稳定性。总体上,目前对气候变暖背景下植物-传粉者网络的研究较为薄弱,今后的研究应进一步关注以下问题:(1)气候变暖影响植物与传粉者物候匹配程度的原因、机制以及影响因素;(2)进一步探究不同生态系统中植物-传粉者的相互作用;(3)从群落水平或生态系统水平对植物-传粉者相互作用网络开展长期性研究。     

植物与传粉者物候错配效应研究进展

开花植物与传粉者之间稳定互惠模式的建立是维持互作双方种群适合度的关键。在全球变化的背景下,植物与传粉者对温度、融雪、人类活动等外界扰动的响应差异,易于引起两者关键物候期的不同步发生,由此可能减少传粉互作的重叠时间,改变相互作用的成本和收益,进而对两者的种群动态产生潜在的深远影响（即物候错配效应）。近年来国内外对植物花期与传粉者活动物候的错配研究主要集中在两方面：一是物候错配现象发生的原因及机制;二是这种物候错配带来的生态后果,尤其是对互惠双方种群动态的影响。但由于研究方法及数据获取等方面的局限性,物候错配研究仍存在一些薄弱环节,如物候匹配模式对环境变化的响应机制、传粉效率对错配效应的调节影响、物候数据获取的独立性等。本文综述了植物-传粉者物候错配效应的最新研究进展,并对未来的研究展望进行初步探讨,以期为物种多样性、动植物种群动态的合理预测等方面的研究提供有益的参考。     

克隆生长对被子植物传粉过程的影响

克隆植物与其传粉者的相互作用是植物繁殖生态学的重要研究领域之一。植物克隆生长与有性繁殖通常相伴进行, 往往产生较大的花展示与复杂的克隆空间结构, 通过传粉过程对有性繁殖过程产生影响, 共同决定植物的适合度。本文回顾了克隆生长对被子植物传粉过程影响的国内外研究进展, 从植物克隆大小、花资源空间配置、克隆构型与种群遗传结构四个方面讨论了克隆生长对传粉过程的影响及其生态学与进化生物学意义。早期研究预期, 随着克隆增大, 同株异花授粉水平增加, 因而通过增大自交率或花粉阻塞效应降低植物的适合度。但是, 后来的一些模拟与野外实验研究发现, 传粉者在同一克隆内访问的花数量并不会随克隆增大而一直增加, 访花行为也主要发生在分株内; 而且分子标记的自交率组分分析也表明自交主要发生在分株内。另一方面, 人工模型模拟以及传粉者访问行为研究表明, 当花朵数量相同时, 与所有花集中生长在同一分株上相比, 将花朵分散在多个分株上的克隆生长方式不会增加, 反而降低了同株异花授粉的发生水平。如果花序内花雌雄同熟, 花朵同时提供与接收花粉, 克隆生长会使植物接收到更高比例的异交花粉, 在提高后代质量的同时不增加同株异花授粉概率。这是从传粉生物学角度对植物克隆生长习性进化的一个全新的解释。今后, 克隆植物传粉生物学研究需要针对传粉者与克隆生长之间的相互作用建立理论模型, 探究克隆大小、克隆构型、花资源空间配置模式对传粉者访问频率和行为、花粉散布、交配格局的影响。同时, 需要在自然种群中, 尤其是克隆与非克隆的近缘类群、同一物种克隆与非克隆种群开展比较研究, 利用更高效的分子标记来研究克隆生长的生态与进化意义。     

青藏高原及周边高山地区的植物繁殖生态学研究进展

青藏高原及周边高山地区孕育了极为丰富的植物多样性资源, 研究该地区植物如何顺利完成繁殖过程有助于我们理解植物对典型高山环境的进化和适应机制。该文综述了青藏高原地区高山植物在资源分配、繁殖方式、花部特征演化等方面的研究进展, 包括全球气候变化对植物繁殖特征的影响, 以及一些新技术和新方法在本研究领域的应用。在高山地区限制性环境中, 随海拔升高, 繁殖分配通常表现出增大的趋势, 其中投入到雄性资源的比例上升, 但具体的资源分配模式还要取决于植株的交配系统、个体大小、生活史特征、遗传特性以及环境中的资源有效性等。面对资源和传粉的双重限制, 植物在不同繁殖方式之间存在权衡, 当传粉者稀少时, 克隆繁殖和自交有利于繁殖保障; 而有性繁殖和异交能够提高种子的质量和后代的遗传多样性, 从而在复杂多变的气候条件下有利于种群的维持。因此, 不同繁殖方式的结合以及泛化的传粉互作网络可能是应对高山限制性环境的最优选择。花部特征的演化主要受到当地传粉者的选择压力, 但是外来传粉者、植食者、盗蜜者以及非生物环境(如温度、雨水和紫外辐射等)对花部性状的影响越来越受到重视。近年来, 青藏高原因其脆弱性和对气候变化的高度敏感性而在全球气候变化研究中备受关注, 以全球变暖和氮沉降增加为显著特征的全球气候变化正在直接或间接地影响着该地区高山植物的繁殖特征。气候变化影响植物和传粉者的物候并引起物种的迁移, 最终将导致植物与传粉者的时空不匹配。植物通过改变花部特征(花展示、花冠结构、花报酬的数量和质量)来响应气候变化, 这可能会改变其传粉者的类型、数量和访花行为, 从而最终影响植物的繁殖成功。3D打印和高通量测序等新技术和新方法的应用有助于促进植物繁殖生态学研究的进一步发展。3D打印的花能够精确控制其形态构造, 可以用于研究精细的花部特征变化对于传粉者行为的影响, 在此基础上与人工饲养的传粉者结合使用, 有助于进一步研究传粉者介导的花部特征演化。随着高通量测序技术的发展, 植物繁殖生态学领域, 尤其是花部特征演化的许多重要问题的潜在机制得以深入研究。该文最后提出了目前研究中需要注意的问题以及值得深入研究的发展方向。     

青藏高原及周边高山地区的植物繁殖生态学研究进展

青藏高原及周边高山地区孕育了极为丰富的植物多样性资源,研究该地区植物如何顺利完成繁殖过程有助于我们理解植物对典型高山环境的进化和适应机制。该文综述了青藏高原地区高山植物在资源分配、繁殖方式、花部特征演化等方面的研究进展,包括全球气候变化对植物繁殖特征的影响,以及一些新技术和新方法在本研究领域的应用。在高山地区限制性环境中,随海拔升高,繁殖分配通常表现出增大的趋势,其中投入到雄性资源的比例上升,但具体的资源分配模式还要取决于植株的交配系统、个体大小、生活史特征、遗传特性以及环境中的资源有效性等。面对资源和传粉的双重限制,植物在不同繁殖方式之间存在权衡,当传粉者稀少时,克隆繁殖和自交有利于繁殖保障;而有性繁殖和异交能够提高种子的质量和后代的遗传多样性,从而在复杂多变的气候条件下有利于种群的维持。因此,不同繁殖方式的结合以及泛化的传粉互作网络可能是应对高山限制性环境的最优选择。花部特征的演化主要受到当地传粉者的选择压力,但是外来传粉者、植食者、盗蜜者以及非生物环境(如温度、雨水和紫外辐射等)对花部性状的影响越来越受到重视。近年来,青藏高原因其脆弱性和对气候变化的高度敏感性而在全球气候变化研究中备受关注,以全球变暖和氮沉降增加为显著特征的全球气候变化正在直接或间接地影响着该地区高山植物的繁殖特征。气候变化影响植物和传粉者的物候并引起物种的迁移,最终将导致植物与传粉者的时空不匹配。植物通过改变花部特征(花展示、花冠结构、花报酬的数量和质量)来响应气候变化,这可能会改变其传粉者的类型、数量和访花行为,从而最终影响植物的繁殖成功。3D打印和高通量测序等新技术和新方法的应用有助于促进植物繁殖生态学研究的进一步发展。3D打印的花能够精确控制其形态构造,可以用于研究精细的花部特征变化对于传粉者行为的影响,在此基础上与人工饲养的传粉者结合使用,有助于进一步研究传粉者介导的花部特征演化。随着高通量测序技术的发展,植物繁殖生态学领域,尤其是花部特征演化的许多重要问题的潜在机制得以深入研究。该文最后提出了目前研究中需要注意的问题以及值得深入研究的发展方向。     

北京地区木本春季物候特征与生物学特性的关系

植物物候是植物生活史中的重要性状,也是指示气候与自然环境变化的重要指标,现已成为全球变化领域的研究热点之一。传统物候研究多假设物候由气候因素决定,如气温、降水、光照等,并主要从植物物候的年际变化角度探讨了气候因素对物候特征的影响。然而,不同物种的物候存在较大差异表明植物物候还与自身生物学特性（如系统发育和功能性状）有关,但植物生物学特性如何影响植物物候仍缺乏深入研究。基于北京地区44种木本植物1965-2018年的展叶始期和开花始期观测资料,以展叶始期和开花始期的3类物候特征（平均物候期、物候对温度的响应敏感度和物候期的积温需求）为例,探究植物物候特征与系统发育和功能性状的关系。首先,利用系统发育信号Blomberg’s K和进化模型检验植物物候特征是否具有系统发育保守性,并通过系统发育信号表征曲线直观表达植物物候特征的进化模式;之后,利用广义估计方程分析植物生活型、传粉型与物候特征的关系,以揭示不同植物的资源利用方式及生存策略的差异。研究发现：（1）除展叶始期的温度敏感度外,其余物候特征的进化均受随机遗传漂变和自然选择力的共同作用,可推断物候特征具有系统发育保守性,即亲缘关系越近的物种物候特征越相似。（2）开花始期的系统发育信号强度比展叶始期更大,表明繁殖物候的系统发育可能比生长物候更保守。（3）植物展叶始期及其积温需求与生活型密切相关。灌木比乔木的展叶时间早、积温需求少。植物开花始期与传粉型相关,风媒植物开花显著早于虫媒植物。研究成果有助于深入理解物候变化的生物学机制,对于丰富物候学的理论研究有重要意义,同时对植物保护也具有重要的指导价值。     

中国头细蛾属昆虫(鳞翅目,细蛾科)与大戟科植物互利共生关系研究进展

细蛾科头细蛾属昆虫与大戟科算盘子属、叶下珠属和黑面神属植物互利共生关系的发现为研究昆虫与植物协同演化过程提供了一个全新的模式。目前,国内对头细蛾与大戟科植物的互利共生关系了解和研究都很少。本文介绍了头细蛾的分类、生物学和形态适应;大戟科相关5属植物(算盘子属、叶下珠属、黑面神属、白饭树属和守宫木属)的生物地理学,开花生物学,花的结构与传粉系统的关系;寄主植物与传粉者的对应关系;互利共生关系的维持机制等。研究表明中国有丰富的头细蛾与大戟科植物资源,开展其互利共生关系的研究有重要科学意义。很多新的、复杂的头细蛾与大戟科植物的生态关系和大量的头细蛾种类有待我们去发现和研究。     

Host spatial structure and disperser activity determine mistletoe infection patterns

What processes and factors are responsible for species distribution are long-standing questions in ecology and a key element for conservation and management. Mistletoes provide the opportunity to study a forest species whose occurrence is expected to be constrained by multiple factors as a consequence of their life form. We studied the mistletoe Tristerix corymbosus (Loranthaceae) on its most common hosts species in northwest Patagonia. The seeds of this mistletoe are almost exclusively dispersed by the small arboreal and endemic marsupial Dromiciops gliroides (Microbiotheridae). We assessed the underlying causes of plant spatial patterns through point pattern analysis and we used different variables that characterize the neighborhood around each host to analyze the relative effect of host availability, potential for disperser movement and canopy light conditions. We found that potential hosts were strongly aggregated and that the three most common host species were distributed independent of each other. Considering all host species together, infected and non-infected host were individually aggregated but segregated from each other. The aggregated pattern of infected hosts could be explained in part by the template of potential hosts distribution, but was subsequently modulated by the activity of the mistletoe disperser. Potential for disperser movement, the proximity to reproductive mistletoes and habitat complexity, increased mistletoe infection probability. However, neighboring host availability decreased mistletoe infection probability, and tree DBH (used as surrogate for light conditions) had no detectable effect. Our results suggested that the distribution of mistletoe infection was determined by the structure of potential host populations and by the marsupial disperser activity. Compared to bird dispersed mistletoes, the scale of the infection was smaller and the proximity to reproductive mistletoes and habitat complexity were important for seed arrival and infection. The interplay between landscape structure and disperser activity determine the spatial structure of mistletoe future generations.     

Coevolution of mistletoes and frugivorous birds?*

Small frugivorous birds that feed largely on the fruits of stem-parasitic mistletoes have independently evolved in various parts of the world. Local populations of mistletoes may be dispersed almost exclusively by these birds. Four attributes of mistletoe dispersal systems may have enhanced the evolution of reciprocal dependence between mistletoes and specialized dispersers: (1) Safe sites for mistletoe seeds (i.e. the young branches of a compatible host) are precisely defined in space and time. (2) The viscidity of mistletoe seeds induces smaller dispersers to deposit seeds in safe sites. (3) Frugivores differ markedly in the efficiency with which they disperse mistletoe seeds to safe sites. (4) Relatively large viscid fruits and adaptive fruiting displays exclude or deter most members of the potential disperser guild. Some birds have anatomical adaptations as a result of dietary specialization on mistletoe fruit, and some mistletoes have fruiting displays that target specialized birds or a narrow disperser spectrum. Coevolution between guilds of mistletoes and specialized dispersers is therefore probable. The uncoupled selective pressures that might have driven their coevolution are the mistletoes’ provision of fruit crops that are unavailable to more generalized frugivores, in return for seed dispersal to the small stems most suitable for infection. As in other mutualistic seed dispersal systems, phylogenetic, ecological and life history factors constrain the evolution of monophyletic interdependence, resulting in varying degrees and patterns of reciprocal specificity between mistletoes and dispersers.     

Host compatibility interacts with seed dispersal to determine small-scale distribution of a mistletoe in Xishuangbanna,Southwest China

Aims Mistletoe infection between intra- and interspecific hosts can be restricted by seed dispersal, host–mistletoe compatibility and other factors, yet few studies have linked seed dispersal and seedling establishment together for understanding mistletoe plant distribution and demography together in different anthropogenic disturbance forest types at a local scale. The objectives of this study were to examine how three factors—seed disperser behavior, post-dispersal host compatibility and canopy cover—affect the spatial distribution of a generalist mistletoe Dendrophthoe pentandra (Loranthaceae) in plantation and rainforest within Xishuangbanna, Southwest China.Methods We observed mistletoe D. pentandra infection patterns at the scale of individual trees and sixteen 400-m 2 forest plots in adjacent plantation and rainforest within Xishuangbanna. To elucidate what determines infection patterns at different scales and in different forest types, we observed the behavior of major avian seed dispersers and carried out a seed inoculation experiment to examine how post-dispersal compatibility and light incidence affect the infection of different hosts.Important findings Dendrophthoe pentandra displayed an aggregated distribution and infected 10 species in our study site, with a significantly higher infection prevalence and intensity in the plantation than in the tropical forest. Different seed dispersers provided contrasting initial mistletoe templates: the specialist frugivore Dicaeum concolor (plain flowerpecker) preferred to fly between mistletoes in infected trees in the plantation and likely intensified existing infections. In contrast, the dietary generalist Pycnonotus jocosus (red-whiskered bulbul) was more likely to visit uninfected trees, thereby establishing new infections. Thus, seed dispersal appears to be an important determinant of the mistletoes distribution, with deposition patterns providing an initial distribution template and determining small-scale patterns. However, post-dispersal and abiotic factors revealed that different host compatibilities and levels of light incidence in different habitats affected the survival of D. pentandra seedlings. Hence, our findings suggest that seed dispersal interacts with host compatibility and canopy cover to determine establishment success, survival and the observed distribution patterns.     

Effectiveness of Mistletoe Seed Dispersal by Tyrant Flycatchers in a Mixed Andean Landscape

The dependence of mistletoes on few dispersers and the directed dispersal they provide is well known, yet no recent work has quantified either the effectiveness of these ‘legitimate’ dispersers, or the extent of redundancy among them. Here, I use the seed dispersal effectiveness (SDE) framework to analyze how birds (Mionectes striaticollis and Zimmerius bolivianus) contribute to mistletoe (Struthanthus acuminatus and Phthirusa retroflexa) infection in traditional mixed plantations within a humid montane forest in Bolivia. I calculated SDE for each bird–mistletoe pair and for the disperser assemblage, by estimating both the quantity and the quality of dispersal. The quantity of dispersal was measured as: (1) disperser abundance; (2) frequency of visits; and (3) number of seeds dispersed per visit, and the quality of dispersal was measured as: (1) germination percentage and speed of germination of seeds regurgitated by birds; and (2) the concordance of deposited seeds and seedling distribution patterns with adult mistletoe distribution at three scales (habitat, host, and microhabitat). Dispersers were not redundant: the more generalist species M. striaticollis dispersed more seeds, but provided lower quality seed dispersal, whereas the mistletoe specialist Z. bolivianus provided low‐quantity and high‐quality seed dispersal. Whereas S. acuminatus benefited more from the SDE of Z. bolivianus, P. retroflexa benefited from the complementary seed dispersal provided by both birds. These results demonstrate how sympatric mistletoes that share the same disperser assemblage may develop different relationships with specific vectors, and describe how the services provided by two different dispersers (one that provides high‐quality and one that provides high‐quantity dispersal) interact to shape spatial patterns of plants.     

Asymmetrical Dependence Between a Neotropical Mistletoe and its Avian Seed Disperser

The degree of interdependence among interacting species has major implications for our understanding of the coevolutionary process and biodiversity maintenance. However, the mutualism strength among fruiting plants and their seed dispersers remains poorly understood in tropical ecosystems. We evaluated simultaneously the effectiveness of the avian seed dispersers of the mistletoe Struthanthus flexicaulis (Loranthaceae) and the contribution of its fruits to their diets in a highland rocky savanna in southeastern Brazil. The mistletoe fruits are small lipid‐rich pseudoberries available throughout the year. Four passerine birds fed on fruits, but Elaenia cristata (Tyrannidae) was the most effective disperser, responsible for more than 96 percent of the dispersed seeds. This bird swallowed fruits whole, expelling and depositing undamaged seeds by regurgitation and bill wiping on perches. From 646 dispersed seeds, 56 percent were deposited on safe sites, thin live twigs of 38 susceptible host species. Elaenia cristata were predominantly frugivorous, feeding on typically ornithocoric fruits of at least 12 species, but also on arthropods. Although fruits represented 75 percent of the feeding bouts along the year, S. flexicaulis fruits represented only 34 percent of the E. cristata diet. Our results highlight the asymmetrical nature of this mutualistic interaction, with the mistletoe life cycle locally linked to one highly effective seed disperser that is more weakly dependent on mistletoes fruits as a food source. We suggest that merging the seed dispersal effectiveness framework with diet assessment of seed dispersers is needed to clarify the asymmetries in mutualistic pairwise interactions involving plants and their animal partners.     

The influence of mistletoes on birds in an agricultural landscape of central Mexico

Mistletoes are hemiparasitic flowering plants that function as keystone resources in forests and woodlands of temperate regions, where a positive relationship between mistletoe density and avian species richness has been observed. Mistletoes have been less studied in tropical regions and the relationship between birds and mistletoes has seldom been explored in tropical agricultural systems. Therefore, we studied the presence of infected trees and infection prevalence (i.e., number of parasitized trees/total number of trees) by Psittacanthus (Loranthaceae) mistletoes in 23 hedgerows located in an agricultural landscape of central Mexico during the dry and rainy seasons, and investigated the relationship between bird species richness and abundance and the abundance of mistletoes. We found a mean of 74 mistletoe plants per 100-m transect of only one species, Psittacanthus calyculatus. Thirty-one percent of the trees surveyed were infected and tree species differed in infection prevalence, mesquite (Prosopis laevigata) being the most infected species with 86% of the surveyed trees infected. For both seasons, we found a positive and significant association between bird species richness and number of mistletoe plants. The same pattern was observed for total bird abundance. Many resident and Neotropical migratory birds were observed foraging on mistletoes. Our results show that mistletoes are important in promoting a higher bird species richness and abundance in tropical agricultural landscapes.     

Spatial autocorrelation and dispersal in mistletoes: field and simulation results

The infections of two species of mistletoes in Baja California, Mexico were investigated for spatial patterns of abundance, and for an effect of the dispersal patterns of mistletoe seeds on these spatial patterns. Mistletoe distributions were mapped and the dispersal of mistletoe seeds was observed. Most mistletoes seeds were dispersed locally to the parent tree or to nearby trees. While mistletoe distributions were highly clumped at the level of the individual tree, no spatial pattern was found above the scale of the individual tree. Infected trees were no more clumped than the overall host population, and infected trees had no more mistletoes on nearby surrounding trees than did uninfected trees. Trees showed no spatial autocorrelation in the number of mistletoes they supported. Simulations using a spatially explicit simulation model with local dispersal and stochasticity in seed dispersal, host mortality, and mistletoe mortality were used to interpret the field results. Simulation results suggest that dispersal patterns affect the overall level of variance in the number of mistletoes per tree but do not lead to spatial patterns in abundance above the scale of the tree. Thus, both simulation and field systems give the surprising result that local dispersal does not lead to spatial autocorrelation in the numbers of mistletoes per tree.Abbreviations AI = Arroyo Inspiracion - VSR = Valle San Rafael     

Mistletoes Play Different Roles in a Modular Host–Parasite Network

Antagonistic interactions between host plants and mistletoes often form complex networks of interacting species. Adequate characterization of network organization requires a combination of qualitative and quantitative data. Therefore, we assessed the distribution of interactions between mistletoes and hosts in the Brazilian Pantanal and characterized the network structure in relation to nestedness and modularity. Interactions were highly asymmetric, with mistletoes presenting low host specificity (i.e., weak dependence) and with hosts being highly susceptible to mistletoe‐specific infections. We found a non‐nested and modular pattern of interactions, wherein each mistletoe species interacted with a particular set of host species. Psittacanthus spp. infected more species and individuals and also caused a high number of infections per individual, whereas the other mistletoes showed a more specialized pattern of infection. For this reason, Psittacanthus spp. were regarded as module hubs while the other mistletoe species showed a peripheral role. We hypothesize that this pattern is primarily the result of different seed dispersal systems. Although all mistletoe species in our study are bird dispersed, the frugivorous assemblage of Psittacanthus spp. is composed of a larger suite of birds, whereas Phoradendron are mainly dispersed by Euphonia species. The larger assemblage of bird species dispersing Psittacanthus seeds may also increase the number of hosts colonized and, consequently, its dominance in the study area. Nevertheless, other restrictions on the interactions among species, such as the differential capacity of mistletoe infections, defense strategies of hosts and habitat types, can also generate or enhance the observed pattern. Abstract in Portuguese is available at http://www.blackwell‐synergy.com/loi/btp .