濒危植物南川升麻传粉生物学的研究

南川升麻（ＣｉｍｉｃｉｆｕｇａｎａｎｃｈｕａｎｅｎｓｉｓＨｓｉｓｏ）的繁育系统以异交为主,传粉昆虫主要为蝇类,盛花时的访花频率平均每花每天１１次,雄蕊脱落后约０６次;单穗升麻（Ｃ．ｓｉｍｐｌｅｘＷｏｒｍｓｋ）以虫媒为主,风也可以帮助其花粉在近距离传播。单穗升麻的传粉昆虫有蝇类和蜂类,盛花时的访花频率蝇类为１．４次,蜂类为１．２次。南川升麻和单穗升麻都是靠大的花序和气味来吸引传粉昆虫,报酬是退化雄蕊基部分泌的蜜液。自然条件下南川升麻每个柱头上平均有４枚花粉,结籽率平均为６４％,而单穗升麻每个柱头上平均有１７枚花粉,结籽率平均为４５９％。南川升麻有性生殖中传粉的限制是其致濒的重要因素之一。     

地下结实植物白番红花的繁育系统与传粉生物学

地下结实是植物用来防御不利环境的一种策略, 研究地下结实植物的繁殖特性, 可以揭示它们的繁殖对策多样性, 对于探讨环境选择压力对其繁育系统及后代适合度的影响具有重要意义。白番红花(Crocus alatavicus)是一种分布在天山西部亚高山带、具地下芽和地下结实特性的早春短命植物。我们采用野外观测和统计分析方法, 对该物种的繁育系统与传粉生物学及其对亚高山环境的适应进行了研究。研究结果表明: 白番红花具有先花后叶的特性, 于4月上中旬始花, 呈爆发式开花式样; 花白色, 无花蜜无气味; 开花时, 下位子房位于地下, 花蕾在地上开放并随光照变化而开闭; 单花花期为6–9 d, 花萎蔫时花粉活性仍保持在75.39±5.69%, 柱头可授期为8 d。人工授粉实验结果显示, 该物种属于兼性异交繁育系统, 且具有自主自花授粉能力。白番红花属于泛化传粉系统, 鲁熊蜂 (Bombus lucorum)、老条蜂 (Anthophora senilis)和黄腹地花蜂 (Andrena capillosa)是有效传粉昆虫, 通过采食花粉进行传粉, 访花频率分别为0.50±0.27次•花–1•h–1、0.18±0.08次•花–1•h–1和0.13±0.05次•花–1•h–1。在天山西部亚高山早春环境中, 白番红花不仅利用其开花式样、泛化传粉系统及早春空白生态位来提高传粉效率, 而且通过自交亲和及主动自花授粉等繁育系统特征来弥补传粉昆虫少及访花频率低的不足, 从而保障繁殖成功。     

Pollinator aggregative and functional responses to flower density: does pollinator response to patches of plants accelerate at low‐densities?

Plant reproduction is often reduced at low densities, due to reduced pollinator visitation rates. Recent theory suggests that a disproportionate increase in pollinator visits to patches of plants as heterospecific plant density increases (i.e. if visitation is a sigmoid function of patch density) can rescue sparse populations of a focal plant species from reduced reproductive success or population decline. A field experiment was performed to determine the shape of the pollinator visitation response to patches of differing density of the common weed Brassica rapa . Both the aggregative and functional response for the entire pollinator community were saturating rather than sigmoid, indicating that pollinator response does not accelerate when density increases. The results for the entire pollinator community were consistent among temporal and spatial replicates. Aggregative response curves for specific pollinator taxa were either linear (bombyliid flies) or saturating (syrphid flies, solitary bees, and Lepidoptera). Functional responses for these taxa were saturating (syrphid flies and solitary bees) or flat (bombyliid flies and Lepidoptera). Individual pollinators visited more plants during foraging bouts in high-density patches, but visits per plant decreased. Seeds per fruit and seeds per flower increased with increasing density. There is no evidence that pollinators disproportionately visit denser patches, or that the conditions for this mechanism of pollination facilitation are likely to be met in this generalist pollinator system.     

Pollination and breeding systems of woody plant species in tropical dry evergreen forests,southern India

Tropical dry evergreen forests (TDEF) are a unique forest type found along the east coast of India. They mostly occur as small, isolated fragments of varying sizes (0.5 to ≈10 ha) and are considered as endangered forests types in peninsular India. Although plant diversity is well documented in these forests, there is a paucity of ecological studies vital for conservation and for planning restoration activities. We studied reproductive biology of 13 woody species: four trees, six shrubs, and three lianas in fragments of TDEF in southern India. The phenology of reproduction, floral biology, anthesis and sexual system of each species were recorded. The pollination mode was assessed through observations of the visitation frequency of pollinators and from the floral characters. The breeding system was determined by hand-augmented self- and cross-pollination experiments. The plants flowered during the dry season from January to July. Plants of nine species had both flowers and fruits at the same time. Twelve species were hermaphrodites and one was polygamo-dioecious. Flowers of 11 species opened at dawn and two at dusk. Four species were self-incompatible and six were self-compatible. Natural fruit set ranged from 10% to 56%, self-incompatible species having low fruit set. Cross-pollen augmentation increased fruit set, suggesting presence of outcrossing in all species. The majority of plants species (85%) had a generalized pollination system, receiving visits from diverse insects, such as social bees, solitary bees, wasps, moths and flies. However, only few of them were functionally important for the species. Two species namely: Capparis brevispina and C. zeylanica had butterflies and birds, respectively, as their main pollinators. Our data reveal that there is a predominance of outcrossing in plant species and a generalized pollination system in these forests. We suggest that restoration of TDEFs is crucial as habitats, not only for wild plants but also for pollinating insects.     

Change of floral orientation affects pollinator diversity and their relative importance in an alpine plant with generalized pollination system,Geranium refractum (Geraniaceae)

Floral orientation may affect pollinator attraction and pollination effectiveness, and its influences may differ among pollinator species. We, therefore, hypothesized that, for plant species with a generalized pollination system, changes in floral orientation would affect the composition of pollinators and their relative contribution to pollination. Geranium refractum, an alpine plant with downward floral orientation was used in this study. We created upward-facing flowers by altering the flower angle. We compared the pollinator diversity, pollination effectiveness, and pollinator importance, as well as female reproductive success between flowers with downward- and upward-facing orientation. Results indicated that the upward-facing flowers were visited by a wider spectrum of pollinators (classified into functional groups), with higher pollinator diversity than natural flowers. Moreover, due to influences on visitation number and pollen removal, the pollinator importance exhibited by the main pollinator groups differed between flower types. Compared with natural flowers, the pollination contribution of principal pollinators (i.e., bumblebees) decreased in upward-facing flowers and other infrequent pollinators, such as solitary bees and muscoid flies, removed more pollen. Consequently, stigmatic pollen loads were lower in upward- than in downward-facing flowers. These findings reveal that floral orientation may affect the level of generalization of a pollination system and the relative importance of diverse pollinators. In this species, the natural downward-facing floral orientation may increase pollen transfer by effective pollinators and reduce interference by inferior pollinators.     

珍稀濒危植物单性木兰传粉生态学研究

野外定位观测了单性木兰的花期物候、访花昆虫种类、访花频率、访花行为和同花期植物种类,并对其花粉散播距离和繁育系统进行了检测,旨在探讨制约单性木兰传粉过程的某些因素,为单性木兰的保护生物学提供科学依据。结果表明,单性木兰雄株和雌株在花期物候上存在差异,雌株在结实上存在明显的大小年现象。单性木兰以虫媒传粉为主,雄株访花昆虫30种,雌株访花昆虫仅14种,雌株和雄株共有的访花昆虫仅6种。单性木兰同花期植物共17种,其访花昆虫种类大部分与单性木兰的访花昆虫种类相同。蜂类和蝶类均非单性木兰的传粉者,其结实率低的原因不仅与访花昆虫种类少和访花频率少有关,更与其缺乏有效的传粉昆虫有关。     

早春短命植物黑鳞顶冰花的花粉呈现时序及其适应性

花粉的时序呈现是指植物花药按一定次序释放花粉的现象, 被认为是对传粉者访问频率的一种适应。在传粉者充足的环境中, 植物通过限制花粉1次被移出的数量, 使花粉供体能作为多个父本, 从而提高雄性适合度。该文从开花习性、花部特征、传粉者及繁育系统等方面对早春短命植物黑鳞顶冰花(Gagea nigra)的花粉呈现时序及其适应性进行研究, 结果表明, 黑鳞顶冰花单花期约5-7天; 白天开放, 晚上闭合, 花药次序开裂, 呈拉链式散粉, 散粉期4-6天。黑鳞顶冰花以异交为主, 部分自交亲和。蝇类和食蚜蝇为主要传粉者, 访花频率为(0.141±0.078) flower∙h^-1。在雄蕊的时序散粉过程中, 雌蕊持续生长, 经历了从低于雄蕊到等高、再到高于雄蕊阶段。在等高阶段, 单花早晚的开闭, 使得雌雄蕊紧靠在一起, 促成了自动自花授粉。在传粉者缺乏的环境中, 黑鳞顶冰花的花粉时序呈现延长了散粉期, 在等待传粉者和分摊风险方面具重要作用。这种花粉渐次呈现的策略, 在新疆的早春开花植物中可能广泛存在。     

Experimental reduction of pollinator visitation modifies plant–plant interactions for pollination

The strength of interactions between plants for pollination depends on the abundance of plants and pollinators in the community. The abundance of pollinators may influence plant associations and densities at which individual fitness is maximized. Reduced pollinator visitation may therefore affect the way plant species interact for pollination. We experimentally reduced pollinator visitation to six pollinator‐dependent species (three from an alpine and three from a lowland community in Norway) to study how interactions for pollination were modified by reduced pollinator availability. We related flower visitation, pollen limitation and seed set to density of conspecifics and pollinator‐sharing heterospecifics inside 30 dome‐shaped cages partially covered with fishnet (experimental plots) and in 30 control plots. We expected to find stronger interactions between plants in experimental compared to controls plots. The experiment modified plant–plant interactions for pollination in all the six species; although for two of them neighbourhood interactions did not affect seed set. The pollen limitation and seed set data showed that reduction of pollinator visits most frequently resulted in novel and/or stronger interactions between plants in the experimental plots that did not occur in the controls. Although the responses were species‐specific, there was a tendency for increasing facilitative interactions with conspecific neighbours in experimental plots where pollinator availability was reduced. Heterospecifics only influenced pollination and fecundity in species from the alpine community and in the experimental plots, where they competed with the focal species for pollination. The patterns observed for visitation rates differed from those for fecundity, with more significant interactions between plants in the controls in both communities. This study warns against the exclusive use of visitation data to interpret plant–plant interactions for pollination, and helps to understand how plant aggregations may buffer or intensify the effects of a pollinator loss on plant fitness.     

Plant species roles in pollination networks: an experimental approach

Pollination is an important ecosystem service threatened by current pollinator declines, making flower planting schemes an important strategy to recover pollination function. However, ecologists rarely test the attractiveness of chosen plants to pollinators in the field. Here, we experimentally test whether plant species roles in pollination networks can be used to identify species with the most potential to recover plant–pollinator communities. Using published pollination networks, we calculated each plant's centrality and chose five central and five peripheral plant species for introduction into replicate experimental plots. Flower visitation by pollinators was recorded in each plot and we tested the impact of introduced central and peripheral plant species on the pollinator and resident plant communities and on network structure. We found that the introduction of central plant species attracted a higher richness and abundance of pollinators than the introduction of peripheral species, and that the introduced central plant species occupied the most important network roles. The high attractiveness of central species to pollinators, however, did not negatively affect visitation to resident plant species by pollinators. We also found that the introduction of central plant species did not affect network structure, while networks with introduced peripheral species had lower centralisation and interaction evenness than networks with introduced central species. To our knowledge, this is the first time species network roles have been tested in a field experiment. Given that most restoration projects start at the plant community, being able to identify the plants with the highest potential to restore community structure and functioning should be a key goal for ecological restoration.     

蒙古扁桃的花部综合特征与虫媒传粉

连续2年对蒙古扁桃自然居群的传粉昆虫进行了观察,用重力玻片法检测。结果表明风媒导致的异株传粉作用可以忽略;蒙古扁桃花散布的气味、花蜜在诱导昆虫传粉中起主要作用;共发现访花昆虫17种,主要包括蜂类、蝇类、蝶类,以蜂类为主;昆虫访花频率与开花习性有关,访问者偏爱访问处于盛花期的花;蒙古扁桃趋向于虫媒的异花授粉,但缺乏忠实的传粉者。     

同域分布的紫堇属三种植物的繁育系统和传粉差异

为研究近缘物种之间繁育系统分化对传粉环境的适应性意义,本文针对湖北地区的3种紫堇属植物（紫堇Corydalis edulis Maxim.、尖距紫堇C.shearer S.Moore.和小花黄堇C.racemosa（Thunb.） Pers.）进行了传粉生态学研究,对比分析了它们在花部特征、分布模式、花期、交配系统、传粉系统等方面的差异。3种紫堇属植物常见伴生现象,花期有一定重叠;花色、距长、花蜜量等方面均有显著差异;尖距紫堇交配系统为自交不亲和、依靠传粉者异花授粉;而紫堇和小花黄堇交配系统为自交亲和,兼有自交和异交的混合交配系统。3个物种均由蜂类传粉,且花部性器官与传粉者的接触部位一致,但访花频率差异较大。在混合群落中,传粉者访花具有较高的忠实性,花部特征差异可能是传粉者选择性访花的原因。对于紫堇属3个物种,花部特征和交配系统的分化有助于其避免传粉过程的相互干扰,交配系统与传粉环境具有一定相关性,混合交配系统可能有利于提高植物对不同生境和气候的适应性。     

Pollination biology in the Snowy Mountains of Australia: Comparisons with montane Colorado,USA

Various aspects of the pollination biology of the alpine flora of Kosciusko National Park, NSW, were examined from late December 1983 until the end of March 1984, including flowering phenology, corolla tube lengths, flower colour, ultraviolet reflectance patterns, visitation rates to the flowers and proboscis lengths of the flower-visiting insects. An average of 5.3 species flowered in each of 13, 2 m×2 m montane plots and 5.6 species in the 13 alpine plots. The maximum number in flower simultaneously averaged 4.1 species in the montane and 3.3 in the alpine plots; flowering peaked in mid-January, Corolla tube lengths of the flora averaged 1.73 mm. The most common floral colour was white or predominantly white (40 species), followed by yellow (14 species). Only six of the 38 species (16%) examined had some type of reflectance pattern; the remaining species all absobed ultraviolet. Flies appeared to be the major pollinators. The insects collected in the study area comprised 60 species of Diptera, 33 species of Hymenoptera, and several species each of Lepidoptera and Coleoptera. On average, 14.4% of flowers watched during 379 observation periods (10 min each) were visited. On average, each plant species was visited by 6.4 species of flies, 2.4 species of bees, wasps or sawflies, one species of butterfly or moth and 0.3 species of beetles. Visitation rates increased over the growing season, and were significantly affected by ambient temperature (positively), light levels (positively) and wind speed (negatively). The maximum proboscis length for the 25 most common species of bees was 2.76 mm, but 18 of 51 species of flies had proboscis lengths longer than this. The mean proboscis length for all 25 species of bees was 1.68 mm, and for 51 species of flies was 2.31 mm. Proboscis lengths for flies were positively correlated with the average corolla length for the plant species they visited. For bees, however, the range in proboscis lengths was relatively small and did not show this pattern. There appear to be significant differences between the plant-pollinator community of alpine Australia and other alpine areas where bumblebees are common pollinators. These differences include shorter proboscis and corolla tube lengths, and perhaps an increased diversity and significance of flies as pollinators.     

Effect of habitat disturbance on pollination biology of the columnar cactus Stenocereus quevedonis at landscape‐level in central Mexico

Stenocereus quevedonis (‘pitire’) is a columnar cactus endemic to central Mexico, grown for its edible fruit. Phenology, pollination biology and behaviour of flower visitors of this species were compared in six conserved and disturbed sites, hypothesising that: (i) pitire pollination is self‐incompatible, requiring animal vectors; (ii) higher incidence of radiation on plants in cleared forest may lead to a higher number of flowers per pitire plant and longer blooming season, and disturbing and differential spatial availability of flower resources may determine differential attraction of pollinators to conserved and disturbed areas; (iii) if pitire pollination system is specialised, reproductive success would decrease with pollinator scarcity, or other species may substitute for main pollinators. In all sites, pitire reproduction started in January, flowering peak occurring in April, anthesis duration was 15 h and predominantly nocturnal (9 h), pollen was released at 23:00 h, nectar was produced throughout anthesis, and breeding system was self‐incompatible. Flower production per plant was similar in disturbed and conserved sites, but flower availability was higher (because of higher tree density) and longer in disturbed sites. Pollination is nocturnal, the most frequent legitimate pollinator being the bat Leptonycteris yerbabuenae; diurnal pollination is rare but possible, carried out by bee species. Fruit and seed set in control and nocturnal pollination treatments at disturbed sites were higher than in conserved sites. Frequency of L. yerbabuenae visits was similar among site types, but more visits of complementary nocturnal and diurnal pollinators were recorded in disturbed sites, which could explain differences in reproductive success.     

菊科12种外来植物的有性繁殖特征和入侵风险研究

菊科植物具有极强的有性繁殖能力,对外来菊科观赏植物的引进存在极高的入侵风险。本研究以武汉常见的菊科12种外来观赏植物为对象,通过有性繁殖特征调查,研究植株的花部特征、花粉活力、传粉系统、种子产量,分析各物种有性繁殖能力的差异,评估其入侵能力。结果显示,多数物种可在隔绝传粉者情况下结实;访花昆虫类型多样,共观察到26种访花昆虫,其中膜翅目蜂类是主要的传粉者;结实情况具有一定差异。综合考虑花粉活力、传粉情况和结实情况,认为黑心金光菊(Rudbeckia hirta L.)、松果菊(Echinacea purpurea(L.)Moench)、大花金鸡菊(Coreopsis grandiflora Hogg.)、蛇目菊(Sanvitalia procumbens Lam.)的有性繁殖竞争力较高,对本地传粉环境可能有较大影响。本研究对近缘物种有性繁殖特征的综合分析结果可为评估外来物种的入侵风险提供一定的参考。     

Pollination crisis in the butterfly-pollinated wild carnation Dianthus carthusianorum?

Knowledge of pollination services provided by flower visitors is a prerequisite for understanding (co)evolutionary processes between plants and their pollinators, for evaluating the degree of specialization in the pollination system, and for assessing threats from a potential pollination crisis. This study examined pollination efficiency and visitation frequency of pollinators--key traits of pollinator-mediated fecundity--in a natural population of the wild carnation Dianthus carthusianorum. The five lepidopteran pollinator species observed differed in pollination efficiency and visitation frequency. Pollinator importance, the product of pollination efficiency and visitation frequency, was determined by the pollinator's visitation frequency. Pollination of D. carthusianorum depended essentially on only two of the five recorded pollinator species. Seed set was pollen-limited and followed a saturating dose-response function with a threshold of c. 50 deposited pollen grains for fruit development. Our results confirm that D. carthusianorum is specialized to lepidopteran pollinators, but is not particularly adapted to the two main pollinator species identified. The local persistence of D. carthusianorum is likely to be at risk as its reproduction depends essentially on only two of the locally abundant, but generally vulnerable, butterfly species.     

The pollination of the gynomonoecious Bdallophytum oxylepis (Cytinaceae,Malvales)

Bdallophytum oxylepis is a rare and endemic species belonging to the Cytinaceae family, a root holoparasitic plant in which most resources are allocated to attracting pollinators. This species is gynomonoecious with intraindividual variation in flower size and sex. Moreover, the flowers exhibit sapromyophilous traits, as do other species of Bdallophytum. Firstly, this study aimed to determine whether all floral morphs can form seeds and be pollen donors (in the case of bisexual flowers). Secondly, as this species has floral traits hypothesized to adapt to particular types of pollen vectors (carrion flies), we also studied the pollination of B. oxylepis to confirm whether the syndromes correspond to what occurs in nature. Through pollination treatments, we determined that all floral morphs are functional. By monitoring the inflorescences, we found that pollination is specialized in the studied population. Stingless bees performed pollination, as they have a high visitation rate, frequency, and constancy, and they are unique visitors that deposit pollen on the stigmas. Thus, they appear to be effective pollinators rather than carrion flies, as predicted by the syndrome. As shown here, animal–plant interaction studies can help establish a basis for conserving rare species such as holoparasites. Moreover, knowledge about the reproductive aspects of B. oxylepis reveals essential clues about its life cycle and role in maintaining native pollinators with economic and cultural value, such as stingless bees.     

Role of honey bees (Hymenoptera: Apidae) in the pollination biology of a California native plant, Triteleia laxa (Asparagales: Themidaceae)

A central focus of pollination biology is to document the relative effectiveness of different flower visitors as pollinators. Ongoing research seeks to determine the role that introduced honey bees (Apis mellifera L.) play in the pollination of both invasive and native plants. Here we report on the importance of A. mellifera as pollinators of a California native plant, Triteleia laxa Bentham. In observation plots and transect censuses, A. mellifera overwhelmingly dominated the T. laxa flower visitor assemblage. We believe the proximity to agriculture, where A. mellifera density is higher relative to areas far from agriculture, contributes to the discrepancy between A. mellifera abundance at the two sites. Although A. mellifera were inferior flower visitors qualitatively (visited less flowers per minute), they were the most frequent interactors with flowers. Furthermore, the proportion of visits to flowers on the same plant among flower visitor species did not differ, suggesting a general mechanism by which insects forage at T. laxa flowers and that A. mellifera do not cause more deleterious geitonogamy than do native pollinators. Flower visitation rates as a function of floral display size did not differ between A. mellifera and other flower visitors. The difference in the magnitude of flower visitation (largely by A. mellifera) between sites is consistent with a difference in seed set between sites. These results suggest that non-native A. mellifera bees can play an important role in the pollination of native plant species.     

Effective pollinators of Asian sacred lotus (Nelumbo nucifera): contemporary pollinators may not reflect the historical pollination syndrome

Background and Aims

If stabilizing selection by pollinators is a prerequisite for pollinator-mediated floral evolution, spatiotemporal variation in the pollinator assemblage may confuse the plant–pollinator interaction in a given species. Here, effective pollinators in a living fossil plant Nelumbo nucifera (Nelumbonaceae) were examined to test whether beetles are major pollinators as predicted by its pollination syndrome.

Methods

Pollinators of N. nucifera were investigated in 11 wild populations and one cultivated population, and pollination experiments were conducted to examine the pollinating role of two major pollinators (bees and beetles) in three populations.

Key Results

Lotus flowers are protogynous, bowl shaped and without nectar. The fragrant flowers can be self-heating during anthesis and produce around 1 million pollen grains per flower. It was found that bees and flies were the most frequent flower visitors in wild populations, contributing on average 87·9 and 49·4 % of seed set in Mishan and Lantian, respectively. Beetles were only found in one wild population and in the cultivated population, but the pollinator exclusion experiments showed that beetles were effective pollinators of Asian sacred lotus.

Conclusions

This study indicated that in their pollinating role, beetles, probable pollinators for this thermoregulating plant, had been replaced by some generalist insects in the wild. This finding implies that contemporary pollinators may not reflect the pollination syndrome.     

Relationships between species’ floral traits and pollinator visitation in a temperate grassland

Knowledge about plant–plant interactions for pollinator service at the plant community level is still scarce, although such interactions may be important to seed production and hence the population dynamics of individual plant species and the species compositions of communities. An important step towards a better understanding of pollination interactions at the community level is to assess if the variation in floral traits among plant species explain the variation in flower visitation frequency among those species. We investigated the relative importance of various floral traits for the visitation frequency of all insects, and bumblebees and flies separately, to plant species by measuring the visitation frequency to all insect-pollinated species in a community during an entire flowering season. Visitation frequency was identified to be strongly positive related to the visual display area and the date of peak flowering of plant species. Categorical variables, such as flower form and symmetry, were important to the visitation frequency of flies only. We constructed floral similarity measures based on the species’ floral traits and found that the floral similarity for all species’ traits combined and the continuous traits separately were positively related to individual visitation frequency. On the other hand, plant species with similar categorical floral traits did not have similar visitation frequencies. In conclusion, our results show that continuous traits, such as flower size and/or density, are more important for the variation in visitation frequency among plant species than thought earlier. Furthermore, differences in visitation frequency among pollinator groups give a poor support to the expectations derived from the classical pollination syndromes.     

Fly pollination of Linum lewish (Linaceae)

This study examines the reproductive biology of Linum lewisii Pursh. (Linaceae), a polyphilic species visited by small bees and generalist flies in montane Colorado. L. lewisii plants growing at different sites experience large temporal and spatial variations in pollinator visits. Their ability to attract both dipteran and hymenopteran pollinators allows pollination under varying conditions as pollinator pool composition changes. Although L. lewisii is self-compatible, hand-pollination studies indicate that insects are required for seed production. The relative effectiveness of fly and bee pollinators is assessed in terms of per-visit pollen deposition. Insect visitation patterns are combined with per-visit effectiveness data to evaluate the relative importance of different pollinator groups. Overall, bees tend to be more effective than flies in depositing pollen. However, in many instances flies appear to be responsible for more pollen deposition due to their higher visitation rates.