Relationships between the floral neighborhood and individual pollen limitation in two self-incompatible herbs

Local flower density can affect pollen limitation and plant reproductive success through changes in pollinator visitation and availability of compatible pollen. Many studies have investigated the relationship between conspecific density and pollen limitation among populations, but less is known about within-population relationships and the effect of heterospecific flower density. In addition, few studies have explicitly assessed how the spatial scales at which flowers are monitored affect relationships. We investigated the effect of floral neighborhood on pollen limitation at four spatial scales in the self-incompatible herbs Armeria maritima spp. maritima and Ranunculus acris spp. acris. Moreover, we measured pollen deposition in Armeria and pollinator visits to Ranunculus. There was substantial variation in pollen limitation among Armeria individuals, and 25% of this variation was explained by the density of compatible and heterospecific flowers within a 3 m circle. Deposition of compatible pollen was affected by the density of compatible and incompatible inflorescences within a 0.5 m circle, and deposition of heterospecific pollen was affected by the density of heterospecific flowers within a 2 m circle. In Ranunculus, the number of pollinator visits was affected by both conspecific and heterospecific flower densities. This did not, however, result in effects of the floral neighborhood on pollen limitation, probably due to an absence of pollen limitation at the population level. Our study shows that considerable variation in pollen limitation may occur among individuals of a population, and that this variation is partly explained by floral neighborhood density. Such individual-based measures provide an important link between pollen limitation theory, which predicts ecological and evolutionary causes and consequences for individual plants, and studies of the effects of landscape fragmentation on plant species persistence. Our study also highlights the importance of considering multiple spatial scales to understand the spatial extent of pollination processes within a population.     

Reproduction of an early-flowering Mediterranean mountain narrow endemic (Armeria caespitosa) in a contracting mountain island

Reproduction at population lower edges is important for plant species persistence, especially in populations on contracting high-mountain islands. In this context, the ability of plants to reproduce in different microhabitats seems to be important to guarantee seed production in stressful environments, such as Mediterranean high mountains. We hypothesised that the warmer and drier conditions at the lower edge would be deleterious for the reproduction of Armeria caespitosa, an early-flowering plant. In addition, reproductive plasticity along this mountain gradient may also be microhabitat-dependent. We studied factors affecting the reproductive success of A. caespitosa , an endemic of the Spanish Sistema Central. We considered a complex set of predictors, including phenology, plant size and environmental factors at different scales using generalised estimating equations and generalised linear models. Microhabitat, together with the position in the altitudinal gradient and inter-annual variability affected the reproduction of A. caespitosa . In addition, individuals with longer flowering periods (duration of flowering) had significantly lower fruit set and a higher number of unviable seeds; delayed flowering peaks favoured the production of both viable and unviable fruits. Microhabitat variability over an altitudinal range is relevant for the reproduction of A. caespitosa, and is more important at the lower edge of the altitudinal range, where the species faces the most adverse conditions. In addition, the ability to reproduce in different microhabitats might increase the chances of the species to cope with environmental uncertainties under on-going climate warming. Finally, reproduction of this early-flowering plant is constrained by summer drought, which might shape its reproductive phenology.     

Pollination efficiency and reproductive patterns in relation to local plant density,population size,and floral display in the rewarding Listera ovata (Orchidaceae)

Pollination efficiency and reproductive success vary strongly among populations of most animal‐pollinated plant species, depending on their size and local density, whereas individual plants within populations experience varying levels of reproductive output as a result of differences in floral display. Although most orchid species have been shown to be severely pollination limited, few studies have investigated the impact of the above‐mentioned factors on pollination success and reproduction, especially in rewarding species. In this study, the impact of population size, local density of flowering plants, and floral display on the rates of pollinia export and fruit production was investigated in 13 natural populations of the rewarding terrestrial orchid Listera ovata. In addition, an emasculation experiment was set up to examine how floral display and local density of flowering plants affected the relative importance of cross‐ vs. geitonogamous pollination in determining fruit set. In the studied populations, pollination efficiency, pollen removal, and fruit set increased with increasing population size until a threshold value of 30–40 flowering plants was reached, above which pollination efficiency and reproductive output decreased again. On average, plants with large floral displays showed higher proportional pollinia removal and fruit set compared with smaller plants. Fruit production was also significantly and positively related to local plant density, whereas emasculation did not affect the relationship between local plant density and fruit set, suggesting that geitonogamous pollination did not affect the outcome of female function. The results of this study are discussed in the light of the flowering mechanism of the species and its generalized pollination system. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 157 , 713–721.     

Spatial ecology of mating success in a sexually polymorphic plant

The spatial context of reproduction is of crucial importance to plants because of their sessile habit. Since pollen and seed dispersal is often restricted, mating success is likely to depend on the quantity and quality of mates in local neighbourhoods. Here we use neighbourhood models to investigate the spatial ecology of pollination and mating in Narcissus assoanus, a sexually polymorphic plant with two mating morphs that differ in style length. By mapping individuals in eight populations from southwestern France, we investigated the influence of the density and morph identity of plants at different spatial scales on variation in female fertility. By using inferences on the expected patterns of pollen transfer based on floral morphology, we were able to predict the quantitative relations between local morph ratios and variation in fertility. Our analyses revealed differences in the spatial clustering of morphs and in their response to plant density and morph identity within local neighbourhoods. Mating success in N. assoanus was characterized by both density- and frequency-dependent processes, a condition that may be a general feature of the spatial ecology of plant mating.     

CONSEQUENCES OF FLORAL VARIATION FOR MALE AND FEMALE REPRODUCTION IN EXPERIMENTAL POPULATIONS OF WILD RADISH,RAPHANUS SATIVUS L

We documented effects of floral variation on seed paternity and maternal fecundity in a series of small experimental populations of wild radish, R. sativus. Each population was composed of two competing pollen donor groups with contrasting floral morphologies and several designated maternal plants. Progeny testing with electrophoretic markers allowed us to measure paternal success. Realized fecundity by each maternal plant and the fraction of those seeds attributable to each pollen donor group were used as outcome variables in path analysis to explore relationships between floral characters (petal size, pollen grain number per flower, and modal pollen grain size), pollinator visitation patterns, and reproductive success. A wide range of pollinator taxa visited the experimental populations, and patterns of discrimination appeared to vary among them. The impact of visitation on male and female reproduction also varied among taxa; visits of small native bees significantly increased paternal success, while those of honey bees reduced male fitness. Only visits by large native bees had discernible effects on recipient fecundity, and, overall, fecundity was not limited by visitation. Maternal plants bearing large-petalled flowers produced fewer flowers during the experiment, reducing their total seed production. In these small populations, postpollination processes (at least in part, compatibility) significantly influenced male and female reproductive success. Variation in pollinator pools occurring on both spatial and temporal scales may act to preserve genetic variation for floral traits in this species.     

Patterns and sources of variation in pollen deposition and pollen tube formation in flowers of the endemic monoecious shrub Cnidoscolus souzae (Euphorbiaceae)

Pollen deposition and pollen tube formation are key components of angiosperm reproduction but intraspecific variation in these has rarely been quantified. Documenting and partitioning (populations, plants and flowers) natural variation in these two aspects of plant reproduction can help uncover spatial mosaics of reproductive success and underlying causes. In this study, we assess variation in pollen deposition and pollen tube formation for the endemic monoecious shrub Cnidoscolus souzae throughout its distribution range in Mexico, and determine how this variation is structured among populations, plants and flowers. We also infer the relative importance of pollen quantity and quality in determining pollination success in this species. While we found no evidence suggesting that pollen receipt limits C. souzae reproduction across 19 populations, we did find extensive variation in pollen load size and pollen tube number per flower. Total variation in pollen receipt and pollen tube number was mostly explained by intra‐individual and among‐population variance. Furthermore, pollen load size had a stronger effect on the number of pollen tubes at the base of the style than pollen germination rate, suggesting that pollen quantity may be more important than quality for pollen tube success in C. souzae. Our results suggest that both small within‐plant flower differences and broad‐scale differences in community attributes can play an important role in determining pollination success. We emphasise the need to evaluate patterns and sources of variation in pollen deposition and pollen tube formation as a first step in understanding the causes of variation in pollination success over broad spatial scales.     

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。     

A piece of the puzzle: a method for comparing pollination quality and quantity across multiple species and reproductive events

? Understanding how pollination affects plant reproductive success and how changes in pollination service affect plant populations, communities and ecosystems is of increasing concern. Yet supplemental hand-pollination traditionally used to assess pollen limitation is prohibitive for large-scale comparative work. Moreover, it does not differentiate between quality and quantity aspects of pollen limitation, and it may suffer from confounds of post-pollination processes such as resource availability to fill seeds. ? Here, we highlight pollen tubes as the functional link between pollen arrival and seed production and suggest that consideration of pollen tubes leads to a better depiction of limitation at the pre-zygotic (pollination) phase of sexual reproduction. ? We assessed the rigor of piecewise regression to analyze the relationship between the numbers of pollen grains and pollen tubes observed in nonmanipulated wilted flowers. We illustrate how parameters obtained from this analysis provide quantitative insight into the relative relevance of the quantity and quality of pollen receipt in limiting natural pollination success, and can facilitate comparisons among data sets. ? This nonmanipulative method opens up new opportunities for rigorous assessment of the relative importance of the quantity and quality of pollination in limiting plant reproduction, especially from a community-wide perspective.     

Effects of forest fragmentation on male and female reproductive success in<Emphasis Type="Italic"> Cestrum parqui</Emphasis> (Solanaceae)

In this paper we evaluate the effects of forest fragmentation on male (pollen removal, pollen load, and pollen tubes) and female reproductive success (fruit- and seed-set) of Cestrum parqui, a self-incompatible, pollination-specialist plant species. We also measure focal individual conspecific density to account for possible density-related effects that could influence the response variables. We calculate an index which incorporates male and female fitness and gives an integrated assessment of overall reproductive success. Forest fragmentation strongly affected the amount of pollen grains on stigmas and number of pollen tubes as well as seed-set, decreasing from continuous forest to small forest fragments, whereas focal individual conspecific density failed to explain any of the variability for the studied variables. Declines in overall reproductive success (i.e. male and female) in small forest fragments are ascribed to decreases in both the quality and quantity of pollination. Self-incompatibility coupled with a specialist pollination system may be particularly important traits determining the negative fragmentation effects observed in C. parqui. Logarithmic regression models described the behaviour of the variables along the fragmentation size gradient, allowing us to detect a threshold below which the effects of fragmentation begin to negatively affect reproductive success in C. parqui. Our results emphasize the importance of evaluating both components of the total plant fitness, as well as including simultaneously several aspects of pollination and reproduction processes when assessing the effects of forest fragmentation on plant reproductive success.     

Does Neighborhood Floral Display Matter? Fruit Set in Carpenter Bee‐pollinated Heterophragma quadriloculare and Beetle‐pollinated Lasiosiphon eriocephalus

Fruit set is pollen‐limited in the self‐incompatible tree Heterophragma quadriloculare (Bignoniaceae), pollinated by long‐distance flying carpenter bees, and in the self‐compatible shrub Lasiosiphon eriocephalus (Thymdeaceae), pollinated by weak‐flying, sedentary beetles. We studied a single H. quadriloculare population over high and low flowering years and found no difference in bee visitation rates between these years. For H. quadriloculare, neighborhood floral display did not make a significant contribution to reproductive success. We investigated dense and sparse L. eriocephalus populations in the same year. In the low density L. eriocephalus population, individual floral displays were higher than in the dense population, yet reproductive success was low, indicating that plant isolation was a major factor influencing fruit set. This result was due to the extremely low number of beetles per plant and per flower in this population. In the dense L. eriocephalus population, although the displays of individual neighbors were smaller and plants were closer, neighborhood floral display did not contribute significantly to reproductive success, whereas the effect of individual floral display was ambiguous. Species with self‐incompatible rather than self‐compatible breeding systems are expected to experience neighborhood effects on reproductive success; however, at the spatial scale and floral display levels of plants in this study, only individual floral display affected fruit set in H. quadriloculare, whereas neither individual nor neighborhood display influenced fruit set in L. eriocephalus. Therefore, pollinator type, pollinator behavior, and plant and population isolation, rather than breeding system alone, will determine if neighborhood floral display affects fruit set.     

Floral density,pollen limitation,and reproductive success in<Emphasis Type="Italic"> Trillium grandiflorum</Emphasis>

Decreases in floral density can disrupt mutualistic interactions between plants and their pollinators, and decrease reproductive success. I addressed the relationship between floral density and plant reproductive success using two experimental approaches: a pollen supplementation experiment in 12 populations of Trillium grandiflorum that naturally varied in floral density, and a transplant experiment in which floral density was manipulated in plots at four experimental sites. In the pollen supplementation experiments, the degree of pollen limitation, in terms of fruit set and seed set, decreased with floral density. Further, in the experimental sites, plant reproductive success increased asymptotically with floral density. These results demonstrate the value of simultaneously conducting experiments in both experimental sites and natural populations to understand how population density influences plant reproductive success. Factors that reduce the density of this perennial herb, such as habitat fragmentation and herbivory by white-tailed deer (Odocoileus virginianus), should be expected to limit its reproduction.Due to an error in the citation line, this revised PDF (published in December 2003) deviates from the printed version, and is the correct and authoritative version of the paper.     

Genetic rescue by distant trees mitigates qualitative pollen limitation imposed by fine‐scale spatial genetic structure

Restricted seed dispersal frequently leads to fine‐scale spatial genetic structure (i.e., FSGS) within plant populations. Depending on its spatial extent and the mobility of pollinators, this inflated kinship at the immediate neighbourhood can critically impoverish pollen quality. Despite the common occurrence of positive FSGS within plant populations, our knowledge regarding the role of long‐distance pollination preventing reproductive failure is still limited. Using microsatellite markers, we examined the existence of positive FSGS in two low‐density populations of the tree Pyrus bourgaeana. We also designed controlled crosses among trees differing in their kinship to investigate the effects of increased local kinship on plant reproduction. We used six pollination treatments and fully monitored fruit production, fruit and seed weight, proportion of mature seeds per fruit, and seed germination. Our results revealed positive FSGS in both study populations and lower fruit initiation in flowers pollinated with pollen from highly‐genetically related individuals within the neighbourhood, with this trend intensifying as the fruit development progressed. Besides, open‐pollinated flowers exhibited lower performance compared to those pollinated by distant pollen donors, suggesting intense qualitative pollen limitation in natural populations. We found positive fine‐scale spatial genetic structure is translated into impoverished pollen quality from nearby pollen donors which negatively impacts the reproductive success of trees in low‐density populations. Under this scenario of intrapopulation genetic rescue by distant pollen donors, the relevance of highly‐mobile pollinators for connecting spatially and genetically distant patches of trees may be crucial to safeguarding population recruitment.     

Morph-specific differences in reproductive success in the distylous Primula veris in a context of habitat fragmentation

Heterostylous self-incompatible plant species are particularly sensitive to habitat fragmentation and to disruption of pollination processes because of the need of intermorph cross-pollination for producing seeds. Heterostyly is characterized by sexual polymorphism through the occurrence of two (distyly) or three (tristyly) morph types that differ in floral traits (style length and anther position). We examined whether the long-styled (pin) and short-styled (thrum) morph types show differences in reproductive components and responses to habitat fragmentation in the distylous, self-incompatible perennial herb Primula veris. We documented reproductive components for pin and thrum individuals and their relationships with population size, plant density and morph ratio (pin frequency), in nine populations from Flanders (northern Belgium) located in fragmented habitats of the intensively used agricultural landscape. Seed abortion increased in small populations as a result of inbreeding depression. Fruit set increased with plant density. Seed set was positively related to pin proportion. Seed set was higher for pin than thrum in small populations, but lower in large populations. Two hypotheses can be considered to explain these morph-specific differences: a pollen transfer asymmetry, and a reproductive advantage for the partially self-compatible pin morph. Morph types appear to respond differently to habitat fragmentation constraints. A floral morph type showing partial self-compatibility may be favored in populations under pollination failure, because it can increase reproductive success and mating opportunities through intramorph crosses.     

Experimental manipulation of plant density and its effect on pollination and reproduction of two confamilial montane herbs

The density of a plant population is expected to influence reproductive success through changes in the quantity and quality of pollination service, or because both density and reproduction respond to quality of the local environment. We reported previously that seed set in sparse natural populations of Delphinium nuttallianum and Aconitum columbianum was lower than in nearby dense populations, whereas quantity of pollination service was equivalent. To explore the hypotheses that environmental quality or pollination quality are lower in sparse natural populations, leading to lower seed set, we manipulated density using arrays of potted plants. In three replicate experiments with D. nuttallianum, pollinator visitation rate and seed set were indistinguishable in sparse and dense arrays, consistent with the interpretation that environmental quality contributed to the earlier result in natural populations of this species. In three replicates with A. columbianum, visitation rate tended to increase with density, and seed set increased significantly, in contrast to our earlier result. One element of pollination quality, the degree of within-plant selfing, did not vary between sparse and dense arrays. These results highlight the complexity of mechanisms by which population parameters may influence plant reproductive success, and the temporal variation that characterizes pollination service.     

Effects of Local Plant Density and Incomplete Dichogamy on the Reproductive Success of the Rare Neotropical Palm Geonoma epetiolata

Density dependent processes are known to influence reproduction and establishment of plant populations. In this study, we evaluated the effects of local density and sexual expression on the reproductive success of the rare palm species Geonoma epetiolata in Costa Rica. We classified individuals in two density categories based on distances to the two nearest neighbors and recorded the occurrence of sexual overlap on each individual. Overlap between pistillate and staminate flowers in monoecious plants allows geitonogamous pollination, potentially reducing dependence on mates for reproduction. We measured plant size and light availability, and evaluated the influence of these variables on pollination success, fruit production, fruit abortion and seed mass. Pollination success significantly increased with density but there was no effect of sexual overlap. In contrast, there was no effect of density on the probability of initiated fruit, and a negative effect on fruit set. Fruit abortion was lowest in isolated plants with no sexual overlap. Plant size and light did not contribute to variation in reproductive success. In conclusion, the pollination advantage of plants in dense neighborhoods does not compensate reproductive losses incurred by fruit abortion, possibly due to mating among genetically related individuals. Geonoma epetiolata is threatened by habitat loss and poaching of seeds for the horticultural market. High fruit abortion rates associated with density in G. epetiolata suggest that seed collections from the remnant wild populations of this palm species may cause bottlenecks that further threaten population viability.     

Female and male fitness of a sexually deceptive orchid with a narrow distribution area: from phenotypic traits to spatial distribution patterns

• The Orchidaceae family presents one of the most extravagant pollination mechanisms: deception. While many studies on reproductive success have been performed on food‐deception orchids, less have been performed on sexually deceptive orchids. Here, we focused on Ophrys balearica P. Delforge, an endemic orchid of the Balearic Islands, to study its reproductive ecology, the spatio‐temporal variation of its reproductive success and the individual (floral display and geospatial position) and population parameters (patch size, shape and density) that affect its reproductive success.
• We performed hand‐pollination experiments, along with the recording of floral display parameters and GPS position of over 1,100 individuals from seven populations in two consecutive years. We applied, for the first time, GIS tools to analyse the effects of individual’s position within the population on the reproductive success. Reproductive success was measured both in male (removed pollinia) and female (fruit set) fitness.
• The results confirm that this species is pollinator‐dependent and mostly allogamous, but also self‐compatible. This species showed high values for the cumulative inbreeding depression index and high pollen limitation. Male fitness was almost equal to female fitness between years and populations, and reproductive success exhibited huge spatio‐temporal variation.
• Although we did not find strong correlations between floral display and reproductive success, patches with low‐plant density and individuals in the external portion of the population showed significantly higher plant fitness. These findings must be considered in conservation actions for endangered orchid species, especially considering that most orchids are strongly dependent on pollinators for their species’ fitness.

     

The plot thickens: does low density affect visitation and reproductive success in a perennial herb, and are these effects altered in the presence of a co-flowering species?

Plants may experience reduced reproductive success at low densities, due to lower numbers of pollinator visits or reduced visit quality. Co-occurring plant species that share pollinators have the potential to facilitate pollination by either increasing numbers of pollinator visits or increasing the quality of visits, but also have the potential to reduce plant reproductive success through competition for pollination. I used a field experiment with a common distylous perennial (Piriqueta caroliniana) in the presence and absence of a co-flowering species (Coreopsis leavenworthii) in plots with one of four different distances between conspecific plants. I found strong negative effects of increasing interplant distance (related to conspecific density) on several components of P. caroliniana reproductive success: pollinator visits to plants per plot visit, visits received by individual plants, conspecific pollen grains on stigmas, outcross pollen grains on stigmas, and probability of fruit production. Although P. caroliniana and C. leavenworthii share pollinators, the co-flowering species did not affect visitation, pollen receipt or reproductive effort in P. caroliniana. Pollinators moved very infrequently between species in this experiment, so floral constancy might explain the lack of effect of the co-flowering species on P. caroliniana reproductive success at low densities. In co-occurring self-incompatible plants with floral rewards, reproductive success at low density may depend more on conspecific densities than on the presence of other species.     

Spatially inconsistent direct and indirect effects of herbivory on floral traits and pollination success in a tropical shrub

Investigations on plant–animal interactions have traditionally focused on single interactions at a time (e.g. herbivory, pollination), yet plant fitness is generally influenced in complex ways by several interactions operating concurrently, and very little is known on the degree of spatial consistency of the direct and indirect effects that link different interactions. This paper evaluates experimentally whether direct and indirect effects of herbivory on male and female flower size and pollination success of the monoecious tropical shrub Cnidoscolus aconitifolius (Euphorbiaceae) remain consistent at three distant regions in Yucatan (southeastern Mexico). Plants were subjected to different levels of leaf defoliation, and treatment effects on floral traits (corolla area, corolla tube length, pollen production), and male and female components of pollination success (percent pollen removal, number of pollen tubes) were subsequently measured to evaluate the indirect effect of herbivory on plant reproductive success via pollination. Defoliation had significant direct effects on floral traits, but its indirect effects differed between the male and female components of pollination success. Moreover, the relationships between defoliation, floral traits and male and female pollination success varied spatially (i.e. between regions), although they were frequently more spatially‐consistent for male success than for female success. Results from this study stress the importance of explicitly testing for spatial variation in direct and indirect effects arising from plant‐animal interactions.     

Effects of population size on reproductive success of the endangered and endemic species Primula merrilliana

The reproductive ability related to the population size of the endangered and endemic species Primula merrilliana Schltr.was investigated.In 26 populations observed,only four contain more than 500 flowering individuals,whereas most of them(53.8%) consist of less than 100 flowering individuals.Though the ratio of pin and thrum plants keeps its balance at 1:1 for all populations,the frequency of pin and thrum flowers was significantly biased in most small populations.Population size strongly affected reproductive success; plants in small populations produced significantly fewer flowers and fruits per plant and fewer seeds per fruit,and therefore fewer seeds per plant.The floral density was another important factor that influenced the reproductive success of P.merrilliana,because four main reproductive success parameters (fruits per plant,seeds per fruit,seeds per plant,and the proportion of flowers setting fruit) were all positively correlated with floral density.The size of plants and the number of leaves per plant (measure of habitat quality) were not influenced by the variation of population size,suggesting that the reduced fecundity in small populations may not be a consequence of lower habitat quality,inbreeding depression and pollen limitation as a result of less attractiveness in small populations are therefore likely explanations for these patterns.     

Allee effects within small populations of Aconitum napellus ssp. lusitanicum, a protected subspecies in northern France

Plants growing at low density can suffer from Allee effects as a result of pollen limitation. Previous studies of Allee effects have focused on the effects of variation among populations in size or density on reproduction. Here, the effects of plant distribution within populations on fitness components are explored in a rare plant, Aconitum napellus ssp. lusitanicum, and ecological and genetic mechanisms underlying these effects are identified. To detect pollen limitation, seed production was compared under natural versus hand-supplemented pollinations on inflorescences of different sizes in natural patches differing both in flower density and in isolation from other patches. Germination rate and juvenile survival of seeds produced in low- and high-density patches were also compared. Pollen-supplemented flowers always produced more seeds than open-pollinated flowers, especially among small plants and plants growing at low density. Offspring produced in low-density patches exhibited lower fitness that those produced in high-density patches. This could have been caused by post-fertilization mechanisms, including inbreeding depression or differential maternal resource allocation. These results show that Allee effects on fitness components (ecological and genetic Allee effects) occur within A. napellus populations at different spatial scales. The spatial distribution of plants seems to be a crucial factor affecting reproductive output and fitness.