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.     

Predicting mistletoe seed shadow and patterns of seed rain from movements of the mistletoebird,Dicaeum hirundinaceum

Abstract At the scale of an individual host, mistletoes are aggregated in space, resulting from the preferential perching of mistletoe dispersers on previously infected plants. We hypothesized that the landscape scale movement patterns of mistletoe dispersers will also promote the aggregation of mistletoes. This hypothesis was tested by predicting the seed shadow for box mistletoe Amyema miquelii (Loranthaceae) and patterns of seed rain, by combining radiotelemetry data of mistletoebird Dicaeum hirundinaceum (Dicaeidae) movements with existing gut passage time data. Thirteen adult mistletoebirds had a mean home range of 20 ha, with core activity areas of approximately 1 ha, and birds more often used areas with high levels of mistletoe infestation. The predicted seed shadow of box mistletoe was leptokurtic, with a 12%, 35% and 23% probability of mistletoe seed being deposited 0 m (same host tree), 1–50 m and 51–100 m from the host tree, respectively. Although rare (3% probability), long distance dispersal of mistletoe (>500 m) can occur. The predicted patterns of seed rain were strongly aggregated, with birds dispersing large amounts of seed (>66 000 per ha) in areas with higher mistletoe infestation levels. The movements of mistletoe dispersers will therefore promote mistletoe aggregation at a landscape scale.     

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.     

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     

Uncorrelated mistletoe infection patterns and mating success with local host specialization in <Emphasis Type="Italic">Psittacanthus calyculatus</Emphasis> (Loranthaceae)

Mistletoe infection between conspecific and interspecific hosts can be restricted by seed dispersal, host-mistletoe compatibility and abiotic factors, yet no studies have linked mistletoe infection patterns and pollination together for understanding mistletoe distribution at a local scale. Psittacanthus calyculatus (Loranthaceae) is a hemiparasitic plant with a broad host range across its geographic distribution. The potential for local host adaptation has been shown using cross-inoculation experiments, in which plants of mistletoe seeds collected from a given host are more likely to survive when they are inoculated on conspecific host trees compared with those inoculated on other host provenances. Here we evaluate host adaptation by describing the local patterns of infection (prevalence and intensity) of P. calyculatus mistletoes on three native host tree species (Alnus acuminata, Quercus crassipes, Salix bonplandiana) and one introduced species (Populus alba) and carried out cross-pollination experiments to examine how pollination affects infection patterns of different host species. Mistletoe infection prevalence (proportion of infection) and infection intensity (mean number of mistletoes per tree) were in general disproportional with respect to the availability of native host tree species but higher to that of non-native host tree species. Cross-pollination experiments showed higher mating success on the native host tree species, suggesting higher local adaptation to specially Q. crassipes. The observed spatial distribution of host tree species and mistletoe infection along with the non-random mating could contribute to local genetic structuring of mistletoe populations.     

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.     

The Spatial Distribution of Mistletoe in a Southern Indian Tropical Forest at Multiple Scales

Taxillus tomentosus is a mistletoe of significant management concern in southern India. This mistletoe affects the productivity of several nontimber forest products, most significantly Amla (Phyllanthus emblica and Phyllanthus indofischeri), whose fruits provide an important source of income for indigenous forest communities. Management interventions are required to secure the continued viability of Amla and thereby its role in livelihoods. To enhance the scientific basis for management, we characterized the distribution of T. tomentosus at three scales, examined potential mechanisms underlying this distribution, and compared both with those documented in other habitats. Mistletoes were aggregated at all three scales: on individual trees, within forest plots of 500 m², and at scales of 3–4 km. Seed deposition patterns provide an initial distribution ‘template’ that largely determines patterns at tree and plot scales. This initial pattern is subsequently altered as variation in host suitability and mistletoe mortality from forest fires influence establishment success and postestablishment survival. Local prevalence of infection contributed most to infection spread, and areas of high infection prevalence are highlighted as appropriate foci for management intervention. Although novel underlying mechanisms and variation in the scale of aggregation have been identified, mistletoe distribution in a tropical forest appears to be shaped by similar forces as those documented previously in temperate systems.     

Distribution, frequency and host patterns of European mistletoe (Viscum album subsp. album) in the major city of Lodz, Poland

The frequency of parasitism of the European mistletoe, Viscum album L. subsp. album, in the city of Lodz, a typical major city in Poland, was investigated. The infection prevalence and intensity of the mistletoe Viscum album subsp. album on its main host, Acer saccharinum as a function of host size was also investigated. The parasite showed a strong preference for alien, planted tree species (i.e. A. saccharinum, Populus×canadensis and Robinia pseudoacacia). In 2009–2011, V. album subsp. album was observed on 28 host taxa of trees and shrubs, which represents the highest diversity of host trees in a single locality in the Poland. Within the studied area 2147 trees were infested by mistletoe. The distribution of mistletoes (V. album subsp. album) among A. saccharinum hosts is significantly aggregated. The intensity of mistletoe infection in the silver maple trees was affected by the individual tree characteristics, such as the height of the tree. The overall level of aggregation as indicated by the variance to mean ratio of mistletoe numbers per host fell within the midrange of values found in other published studies of host-mistletoe interactions. The higher mistletoe infection prevalence in taller trees results from differential dispersal of mistletoe seeds to tall trees as well as differential survival of established mistletoes on tall trees. The incidence of mistletoe was higher in city centre (zone of high density development) than it was on the outskirts of a city (outer marginal zone). It was found that the abundant occurrence of mistletoe was recorded in the stands of increased nitrogen input, while other stands have little or no mistletoe infection present. Thus, this mistletoe species uses both passive and active uptake, which may be a selective advantage in a nutrient-poor environment or on a nutrient-deficient host species.     

Spatial Distribution of Oak Mistletoe as It Relates to Habits of Oak Woodland Frugivores

This study addresses the underlying spatial distribution of oak mistletoe, Phoradendron villosum, a hemi-parasitic plant that provides a continuous supply of berries for frugivorous birds overwintering the oak savanna habitat of California''s outer coast range. As the winter community of birds consuming oak mistletoe varies from group-living territorial species to birds that roam in flocks, we asked if mistletoe volume was spatially autocorrelated at the scale of persistent territories or whether the patterns predicted by long-term territory use by western bluebirds are overcome by seed dispersal by more mobile bird species. The abundance of mistletoe was mapped on trees within a 700 ha study site in Carmel Valley, California. Spatial autocorrelation of mistletoe volume was analyzed using the variogram method and spatial distribution of oak mistletoe trees was analyzed using Ripley''s K and O-ring statistics. On a separate set of 45 trees, mistletoe volume was highly correlated with the volume of female, fruit-bearing plants, indicating that overall mistletoe volume is a good predictor of fruit availability. Variogram analysis showed that mistletoe volume was spatially autocorrelated up to approximately 250 m, a distance consistent with persistent territoriality of western bluebirds and philopatry of sons, which often breed next door to their parents and are more likely to remain home when their parents have abundant mistletoe. Using Ripley''s K and O-ring analyses, we showed that mistletoe trees were aggregated for distances up to 558 m, but for distances between 558 to 724 m the O-ring analysis deviated from Ripley''s K in showing repulsion rather than aggregation. While trees with mistletoe were aggregated at larger distances, mistletoe was spatially correlated at a smaller distance, consistent with what is expected based on persistent group territoriality of western bluebirds in winter and the extreme philopatry of their sons.     

Implications of movement patterns of a dietary generalist for mistletoe seed dispersal

Mistletoes are dispersed primarily by frugivorous birds and have highly aggregated distributions at multiple scales. Mistletoe specialist frugivores have been found to intensify infections within infected hosts and stands, and this is considered the most likely mechanism underlying clumped mistletoe distributions at these scales. How these patchy infections first develop and whether seed dispersers also contribute to aggregated mistletoe distributions at landscape and regional scales have not been evaluated. Here we predict the mistletoe seed shadow of a dietary generalist (spiny‐cheeked honeyeater Acanthagenys rufogularis Aves: Meliphagidae), by combining our observations of movements via radio telemetry with previous data on gut passage times to estimate seed dispersal curves for individual birds. There was considerable variation in movements and inferred seed dispersal between individuals, with non‐breeding birds predicted to regularly transport Amyema quandang (Santalales: Loranthaceae) seeds up to 700 m; well beyond the boundaries of an existing mistletoe infection. As the first work to consider explicitly the distance component of mistletoe seed dispersal by dietary generalists, this study poses further questions about the relative seed dispersal roles of dietary generalists and mistletoe specialists. Moreover, our findings highlight considerable intraspecific variation in movement and foraging behaviour, suggesting gender and reproductive status of birds should be considered explicitly when quantifying seed dispersal services.     

Mistletoe Infection in an Oak Forest Is Influenced by Competition and Host Size

Host size and distance from an infected plant have been previously found to affect mistletoe occurrence in woody vegetation but the effect of host plant competition on mistletoe infection has not been empirically tested. For an individual tree, increasing competition from neighbouring trees decreases its resource availability, and resource availability is also known to affect the establishment of mistletoes on host trees. Therefore, competition is likely to affect mistletoe infection but evidence for such a mechanism is lacking. Based on this, we hypothesised that the probability of occurrence as well as the abundance of mistletoes on a tree would increase not only with increasing host size and decreasing distance from an infected tree but also with decreasing competition by neighbouring trees. Our hypothesis was tested using generalized linear models (GLMs) with data on Loranthus europaeus Jacq., one of the two most common mistletoes in Europe, on 1015 potential host stems collected in a large fully mapped plot in the Czech Republic. Because many trees were multi-stemmed, we ran the analyses for both individual stems and whole trees. We found that the probability of mistletoe occurrence on individual stems was affected mostly by stem size, whereas competition had the most important effects on the probability of mistletoe occurrence on whole trees as well as on mistletoe abundance. Therefore, we confirmed our hypothesis that competition among trees has a negative effect on mistletoe occurrence.     

Parasites boost productivity: effects of mistletoe on litterfall dynamics in a temperate Australian forest

The importance of litter in regulating ecosystem processes has long been recognised, with a growing appreciation of the differential contribution of various functional plant groups. Despite the ubiquity of mistletoes in terrestrial ecosystems and their prominence in ecological studies, they are one group that have been overlooked in litter research. This study evaluated the litter contribution from a hemiparasitic mistletoe, Amyema miquelii (Lehm. ex Miq.) Tiegh., in an open eucalypt forest (Eucalyptus blakelyi, E. dwyeri and E. dealbata), at three scales; the forest stand, single trees and individual mistletoes. Litter from mistletoes significantly increased overall litterfall by up to 189%, the amount of mistletoe litter being proportional to the mistletoe biomass in the canopy. The high litter input was due to a much higher rate of mistletoe leaf turnover than that of host trees; the host litterfall and rate of leaf turnover was not significantly affected by mistletoe presence. The additional litter from mistletoes also affected the spatial and temporal distribution of litterfall due to the patchy distribution of mistletoes and their prolonged period of high litterfall. Associated with these changes in litterfall was an increase in ground litter mass and plant productivity, which reflects similar findings with root-parasitic plants. These findings represent novel mechanisms underlying the role of mistletoes as keystone resources and provide further evidence of the importance of parasites in affecting trophic dynamics.     

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.     

Reaching the canopy on the ground: incidence of infection and host-use by mistletoes (Loranthaceae and Viscaceae) on trees felled for timber in Amazonian rainforests

There is a profound absence of knowledge of infestation prevalence and host-use by mistletoes of mature South American tropical rainforests. In this study, we fill this gap using information gathered from felled trees at a logging concession area in Amazonian Brazil. We sampled individuals of 18 tree species, which occurred in two forest physiognomies; open forest with canopy interrupted by palm trees and closed, denser forest, with emergent trees. We hypothesized that infection incidence would be higher in open than in closed forest, irrespective of the mistletoe species involved. In addition, we expected that mistletoe parasitism would be higher on host species that were more abundant, taller, deciduous, and had less dense wood. We sampled 870 individual trees in both sites combined. All but one host species was infected by at least one species of mistletoe. We found 13 mistletoe species/morphospecies, Loranthaceae (7) and Viscaceae (6), parasitizing very different hosts. Mistletoe infection incidence was higher in the closed forest (10.3%) than in the open forest (5.4%). In the closed forest, host height influenced incidence positively, while deciduousness had a negative influence. Our results show that mistletoes are common in the canopy of pristine tropical forests and, contrary to expectations, that infection incidence was higher in the closed forest. The positive relation between infection incidence and host height in this forest type suggests that emergent trees have higher chances of being infected than individuals of correspondent species in the lower forest layers.     

桑寄生植物繁殖物候研究概述

桑寄生植物是一类自身可以进行光合作用的半寄生性灌木, 作为森林和林地的关键性资源可为鸟类等动物分类群提供重要的食物资源和巢址, 并影响当地的生物多样性。桑寄生植物隶属于檀香目, 包括5科88属约1,600种, 除极地、部分高寒和干旱沙漠地区外均有分布。桑寄生植物繁殖物候的研究对于了解“寄主植物-桑寄生植物-传粉/种子散布者系统”中物种相互作用网络的维持机制、生态系统结构的稳定性具有重要意义。本文综述了桑寄生植物在景观、群落和种群尺度上繁殖物候的表现类型, 发现桑寄生植物主要通过繁殖物候异步的方式延长物候期, 维持与传粉/种子散布者持久的互惠关系以保障自身种群的繁衍。该领域经过近年的发展, 已从单一地描述繁殖物候的表现类型到探究系统中寄主植物、传粉/种子散布者以及桑寄生植物自身生物学特性等因素的分析。通过前人的研究发现桑寄生植物繁殖物候对于该系统内相互作用的双方或多方有重要的适应意义, 今后首先应该对桑寄生植物的基础生物学背景进行研究, 然后还应加强实验验证, 进行多因素综合分析等来探讨桑寄生植物繁殖物候的生态学意义。     

Ecological assembly rules on arthropod community inhabiting mistletoes

1. The colonisation of a new habitat by a community is led by deterministic and stochastic processes at different spatio-temporal scales. Parasitic plants, such as mistletoe, represent a new habitat within forest canopy that is free to be colonised by many organisms. 2. This study investigates how ecological factors operating at forest and plant scales drive changes in both specialist (mistletoe-dwelling) and tourist (transient visitors) arthropod communities inhabiting European mistletoe, Viscum album subsp. austriacum, in a Mediterranean pine forest. The influence of elevation along a broad elevational gradient was tested by sampling arthropod communities dwelling in mistletoe plants and host pine branches and the effects of mistletoe plant size, distances to other mistletoes, and temporal variation in arthropod assemblages inhabiting mistletoes. 3. The diversity of the specialist community remained constant along the elevational gradient and over the summer period, while the tourist and pine-dwelling arthropod communities showed species turnover. Larger mistletoes were occupied by more species and individuals, whereas more isolated mistletoes presented the same equilibrium point as the more aggregated ones. Thus, mistletoe size is key to the composition of the arthropod community. 4. In conclusion, this study's findings indicate contrasting assembly rules for specialised and tourist arthropod communities associated with mistletoe. The specialist community was highly stable and followed a deterministic trophic sequence of colonisation as the assemblage rule: first, colonisation by the main specialist herbivore, Cacopsylla visci, and, second, by its predator Anthocoris visci. Meanwhile, the tourist community, being a subset of the arthropod assemblage of the pine, acts independent of mistletoe presence.     

Dominant network interactions are not correlated with resource availability: a case study using mistletoe host interactions

Network theory in ecology has been central to understanding species co‐occurrence patterns, specialization and community stability. However, network theory has traditionally focused on the ‘higher’ trophic level where exploitation of network ‘partners’ (i.e. individual interactions in response to resource availability) have remained underappreciated. In this study we tested how clumping and host availability influenced mistletoe–host interactions in a semi‐arid woodland, central Australia. We used a hierarchical approach that evaluated individual interactions by modifying the traditional randomization technique to simulate clumping and host exploitation. Using published literature we then compared our results with mistletoes from other genera. We found that mistletoes clump on fewer trees than predicted, even though interaction strength was no different from random expectations, and we found no evidence that common trees were heavily infected as predicted by the host availability hypothesis. The rate of host exploitation (measured as the proportion of trees infected) in semi‐arid Australia is similar to that for mistletoe genera in other parts of the world. We hypothesize that specific host trees act as a focal point for infection that facilitates the spread and overall population size of mistletoes. Overall our results indicate that resources, such as the number of trees in a mistletoe network, are less important than clumping of individual plants. We suggest that exploitation of available resources may play a similar role in other networks that extend beyond antagonistic relationships such as parasite or herbivore interactions.     

Mistletoe macroecology: spatial patterns in species diversity and host use across Australia

Mistletoes are parasitic plants, the spatial distributions of which are poorly understood on macroecological scales. Because of their highly unusual life history, investigating mistletoe macroecology may provide new insight into broad‐scale patterns in species distributions. We collated data on the spatial distribution and host use of 65 species of Loranthaceous mistletoes across the continent of Australia, and tested two predictions. First, we predicted mistletoe diversity would be unrelated to productivity (i.e. evapotranspiration and precipitation), as the parasitic lifestyle might relax environmental constraints on their distributions. Second, we predicted that mistletoe host ranges (number of infected host species) would increase in areas with more potential host species. The basis of this prediction is that greater host generality is likely to evolve in regions with greater host diversity because of greater unpredictability in encounter rates with particular host species. Conversely, in regions with fewer potential hosts, randomly dispersing mistletoe propagules are likely to repeatedly encounter particular host species, thus favouring the evolution of host specialization. The results were generally consistent with these predictions. Mistletoe diversity across Australia was weakly associated with environmental conditions, whereas mistletoe host ranges increased significantly with total plant diversity. Macroecological patterns in mistletoes are unusual. In contrast to non‐parasitic plants, mistletoe diversity is poorly correlated with productivity. Host ranges varied predictably across Australia, providing the first quantitative support for the hypothesis that mistletoes in diverse regions tend to be host generalists, whereas mistletoes in depauperate regions tend to be host specialists. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 459–468.     

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.     

Reduced mycorrhizae on Juniperus monosperma with mistletoe: the influence of environmental stress and tree gender on a plant parasite and a plant-fungal mutualism

Summary We examined how an important plant mutualist (fungal mycorrhizae) interacted with a common tree parasite, a xylem-tapping mistletoe (Phoradendron juniperium Engelm.) growing on one-seeded juniper (Juniperus monosperma Engelm.). We also examined how host tree gender and environmental stress might be involved in this interaction. Four major patterns were observed. First, the mycorrhizal levels of trees of both sexes were negatively correlated with mistletoe density. In comparisons of heavily and lightly infested trees at the stressful site, high mistletoe levels were associated with 27% less mycorrhizae on male trees and 38% less mycorrhizae on the roots of female trees. Second, the reduction of mycorrhizae on trees with high mistletoe levels was slightly but significantly greater for female trees than male trees. These results are consistent with the hypothesis that severe mistletoe infestation suppresses mycoresis and that this suppression is more severe in female trees because of their greater energetic investment in reproduction. Third, female junipers growing in the stressful ash and cinder fields averaged three-fold higher levels of mistletoe infestation than male trees. Fourth, no differences in mistletoe infestation were observed between male and female trees growing in the more favorable soils. Comparisons with other systems suggest that both mistletoes and herbivores have similar interactions with mycorrhizae.