Visitation rate of pollinators and nectar robbers to the flowers and inflorescences of Tabebuia aurea (Bignoniaceae): effects of floral display size and habitat fragmentation

Large floral displays favour pollinator attraction and the import and export of pollen. However, large floral displays also have negative effects, such as increased geitonogamy, pollen discounting and nectar/pollen robber attraction. The size of the floral display can be measured at different scales (e.g. the flower, inflorescence or entire plant) and variations in one of these scales may affect the behaviour of flower visitors in different ways. Moreover, the fragmentation of natural forests may affect flower visitation rates and flower visitor behaviour. In the present study, video recordings of the inflorescences of a tree species (Tabebuia aurea) from the tropical savannah of central Brazil were used to examine the effect of floral display size at the inflorescence and tree scales on the visitation rate of pollinators and nectar robbers to the inflorescence, the number of flowers approached per visit, the number of visits per flower of potential pollinators and nectar robbers, and the interaction of these variables with the degree of landscape disturbance. Nectar production was quantified with respect to flower age. Although large bees are responsible for most of the pollination, a great diversity of flower insects visit the inflorescences of T. aurea. Other bee and hummingbird species are highly active nectar robbers. Increases in inflorescence size increase the visitation rate of pollinators to inflorescences, whereas increases in the number of inflorescences on the tree decrease visitation rates to inflorescences and flowers. This effect has been strongly correlated with urban environments in which trees with the largest floral displays are observed. Pollinating bees (and nectar robbers) visit few flowers per inflorescence and concentrate visits to a fraction of available flowers, generating an overdispersed distribution of the number of visits per inflorescence and per flower. This behaviour reflects preferential visits to young flowers (including flower buds) with a greater nectar supply.     

Floral display size in comfrey, Symphytum officinale L. (Boraginaceae): relationships with visitation by three bumblebee species and subsequent seed set

The fecundity of insect-pollinated plants may not be linearly related to the number of flowers produced, since floral display will influence pollinator foraging patterns. We may expect more visits to plants with more flowers, but do these large plants receive more or fewer visits per flower than small plants? Do all pollinator species respond in the same way? We would also expect foragers to move less between plants when the number of flowers per plant are large, which may reduce cross-pollination compared to plants with few flowers. We examine the relationships between numbers of inflorescence per plant, bumblebee foraging behaviour and seed set in comfrey, Symphytum officinale, a self-incompatible perennial herb. Bumblebee species differed in their response to the size of floral display. More individuals of Bombus pratorum and the nectar-robbing B.?terrestris were attracted to plants with larger floral displays, but B. pascuorum exhibited no increase in recruitment according to display size. Once attracted, all bee species visited more inflorescences per plant on plants with more inflorescences. Overall the visitation rate per inflorescence and seed set per flower was independent of the number of inflorescences per plant. Variation in seed set was not explained by the numbers of bumblebees attracted or by the number of inflorescences they visited for any bee species. However, the mean seed set per flower (1.18) was far below the maximum possible (4 per flower). We suggest that in this system seed set is not limited by pollination but by other factors, possibly nutritional resources.     

Effects of patch size and density on flower visitation and seed set of wild plants: a pan-European approach

1.  Habitat fragmentation can affect pollinator and plant population structure in terms of species composition, abundance, area covered and density of flowering plants. This, in turn, may affect pollinator visitation frequency, pollen deposition, seed set and plant fitness.
2.  A reduction in the quantity of flower visits can be coupled with a reduction in the quality of pollination service and hence the plants' overall reproductive success and long-term survival. Understanding the relationship between plant population size and/or isolation and pollination limitation is of fundamental importance for plant conservation.
3.  We examined flower visitation and seed set of 10 different plant species from five European countries to investigate the general effects of plant populations size and density, both within (patch level) and between populations (population level), on seed set and pollination limitation.
4.  We found evidence that the effects of area and density of flowering plant assemblages were generally more pronounced at the patch level than at the population level. We also found that patch and population level together influenced flower visitation and seed set, and the latter increased with increasing patch area and density, but this effect was only apparent in small populations.
5.   Synthesis. By using an extensive pan-European data set on flower visitation and seed set we have identified a general pattern in the interplay between the attractiveness of flowering plant patches for pollinators and density dependence of flower visitation, and also a strong plant species-specific response to habitat fragmentation effects. This can guide efforts to conserve plant–pollinator interactions, ecosystem functioning and plant fitness in fragmented habitats.     

The effects of floral display on pollinator visitation vary among populations ofPhacelia linearis (Hydrophyllaceae)

Summary Individual plants in gynodioecious populations ofPhacelia linearis (Hydrophyllaceae) vary in flower gender, flower size, and flower number. This paper reports the effects of variation in floral display on the visitation behaviour of this species' pollinators (mainly pollen-collecting solitary bees) in several natural and three experimental plant populations, and discusses the results in terms of the consequences for plant fitness. The working hypotheses were: (1) that because female plants do not produce pollen, pollen-collecting insects would visit hermaphrodite plants at a higher rate than female plants and would visit more flowers per hermaphrodite than per female; and (2) that pollinator arrival rate would increase with flower size and flower number, the two main components of visual display. These hypotheses were generally supported, but the effects of floral display on pollinator visitation varied substantially among plant populations. Hermaphrodites received significantly higher rates of pollinator arrivals and significantly higher rates of visits to flowers than did females in all experimental populations. Flower size affected arrival rate and flower visit rate positively in natural populations and in two of the three experimental populations. The flower size effect was significant only among female plants in one experimental population, and only among hermaphrodites in another. The effect of flower number on arrival rate was positive and highly significant in natural populations and in all experimental populations. In two out of three experimental populations, insects visited significantly more flowers per hermaphrodite than per female and visited more flowers on many-flowered plants than on few-flowered plants, but neither effect was detected in the third experimental population. Because seed production is not pollen-limited in this species, variation in pollinator visitation behaviour should mainly affect the male reproductive success of hermaphrodite plants. These findings suggest that pollinator-mediated natural selection for floral display inP. linearis varies in space and time.     

Size and sex of floral displays affect insect visitation rates in the dioecious Australian alpine herb, Aciphylla glacialis

Differences in floral display size between male and female plants in dioecious species are often considered to be the result of competition within and between male and female plants to attract insects, although this hypothesis is rarely tested. In a field study of the alpine dioecious herb Aciphylla glacialis , insect visitation rates were found to increase with increasing floral display, as predicted. Dipterans were the most common visitors to male and female inflorescences, both in terms of individuals visits (2083 out of 2581 total visits by insects), and species number (20 morphospecies, potentially 22 species). Larger male inflorescences attracted 1.7 times as many insects in total, and 3.1 times more visits by the most common flower visitor, Musca vetustissima than did female inflorescences, but equal number of visits by the next most common flying visitors, Poecilohetaerus aquilius and Tephritis poenia. There was no difference in the amount of time M. vetustissima individuals spent on male and female inflorescences, even though male inflorescences have more flowers. Larger displays (four and eight inflorescences) of either sex attracted more visits than smaller ones (one inflorescence), although the rate of increase in visitation rate with increasing floral display declined. The response of insects to increasing floral display does not support the predicted escalating or proportionate increasing rate of visitation of some models for the evolution of dimorphism in floral displays in dioecious plants.     

THE EVOLUTION OF INSECT-MEDIATED SELF-POLLINATION FROM AN OUTCROSSING SYSTEM IN CALYPTRIDIUM (PORTULACACEAE)

Calyptridium monospermum (Portulacaceae) comprises two biological races visited by different groups of insects. One race, pollinated by a bumblebee, Bombus vosnesenskii (Apidae), is outcrossing, while the other race is pollinated casually by a variety of other insects whose visits result in insect-mediated self-pollination and geitonogamy within the inflorescence. Insect-mediated selfing is also the mode of pollination in the closely related species, C. umbellatum. While all plants of both species are self-compatible, insect visitation is necessary for good seed set. Selfing populations of C. monospermum exhibit many floral adaptations for insect-mediated self-pollination which parallel those of the selfing C. umbellatum, while retaining vegetative characteristics typical of C. monospermum. These floral traits involve flower color and odor, style and stamen orientation, size of stigmatic surfaces, number of pollen grains produced, density of open flowers on inflorescences, and presence or absence of protogyny. Artifical pollination experiments show that these floral adaptations are effective in increasing the probability of insect-mediated self-pollination. Insect-mediated selfing in C. umbellatum and in some populations of C. monospermum is encouraged and probably made necessary by the inconstant pollinating behavior of the insects which visit these plants, as shown by the large percentage of non-Calyptridium pollen recovered from the bodies of insects captured while visiting these plants.     

Patch size has no effect on insect visitation rate per unit area in garden-scale flower patches

Previous studies investigating the effect of flower patch size on insect flower visitation rate have compared relatively large patches (10–1000s m²) and have generally found a negative relationship per unit area or per flower. Here, we investigate the effects of patch size on insect visitation in patches of smaller area (range c. 0.1–3.1 m²), which are of particular relevance to ornamental flower beds in parks and gardens. We studied two common garden plant species in full bloom with 6 patch sizes each: borage (Borago officinalis) and lavender (Lavandula × intermedia ‘Grosso’). We quantified flower visitation by insects by making repeated counts of the insects foraging at each patch. On borage, all insects were honey bees (Apis mellifera, n = 5506 counts). On lavender, insects (n = 737 counts) were bumble bees (Bombus spp., 76.9%), flies (Diptera, 22.4%), and butterflies (Lepidoptera, 0.7%). On both plant species we found positive linear effects of patch size on insect numbers. However, there was no effect of patch size on the number of insects per unit area or per flower and, on lavender, for all insects combined or only bumble bees. The results show that it is possible to make unbiased comparisons of the attractiveness of plant species or varieties to flower-visiting insects using patches of different size within the small scale range studied and make possible projects aimed at comparing ornamental plant varieties using existing garden flower patches of variable area.     

Edaphic factors and plant–insect interactions: direct and indirect effects of serpentine soil on florivores and pollinators

Edaphic factors can lead to differences in plant morphology and tissue chemistry. However, whether these differences result in altered plant–insect interactions for soil-generalist plants is less understood. We present evidence that soil chemistry can alter plant–insect interactions both directly, through chemical composition of plant tissue, and indirectly, through plant morphology, for serpentine-tolerant Mimulus guttatus (Phrymaceae). First, we scored floral display (corolla width, number of open flowers per inflorescence, and inflorescence height), flower chemistry, pollinator visitation and florivory of M. guttatus growing on natural serpentine and non-serpentine soil over 2 years. Second, we conducted a common garden reciprocal soil transplant experiment to isolate the effect of serpentine soil on floral display traits and flower chemistry. And last, we observed arrays of field-collected inflorescences and potted plants to determine the effect of soil environment in the field on pollinator visitation and florivore damage, respectively. For both natural and experimental plants, serpentine soil caused reductions in floral display and directly altered flower tissue chemistry. Plants in natural serpentine populations received fewer pollinator visits and less damage by florivores relative to non-serpentine plants. In experimental arrays, soil environment did not influence pollinator visitation (though larger flowers were visited more frequently), but did alter florivore damage, with serpentine-grown plants receiving less damage. Our results demonstrate that the soil environment can directly and indirectly affect plant–mutualist and plant–antagonist interactions of serpentine-tolerant plants by altering flower chemistry and floral display.     

Native birds and insects,and introduced honey bees visiting Echium wildpretii (Boraginaceae) in the Canary Islands

In this paper, we report observations of flower visitors of the endemic Echium wildpretii in Tenerife, Canary Islands. This plant inhabits the high altitudinal sub-alpine zone, which is characterized by a harsh climate, low species diversity and a short growing season. Echium wildpretii is a monocarpic perennial, producing a 2–3 m column-shaped, red-flowered, nectar-rich inflorescence. Although these floral traits have previously been suggested as being typical of ornithophilous flowers, this is the first study reporting observations of native birds (Phylloscopus collybita and Serinus canarius) in addition to insects visiting the flowers for nectar. The purposes of this study were firstly to investigate levels of visitation by native birds, native insects, and introduced honey bees. Secondly, we studied the influence of floral display (plant height and number of flowers), nearest neighbours (distance and size) and local vegetation structure on visitation rate. Finally, we discuss the evolution of ornithophily in an otherwise entomophilous plant lineage. We found that the level of bird visitation was relatively high early in the flowering season, but decreased in mid/late season, while the opposite pattern was found for introduced honey bees. For native insects, the frequency of visits was similar in early and late season. Bird visits were correlated with floral display. In the early season, visitation rates of honey bees and the two most common native bee species were correlated with size of the plant or its nearest neighbours, consistent with preference patterns for larger resource patches. Since only insects visit the flowers of other species in the Echium clade, E. wildpretii appears to have evolved from a truly insect-pollinated lineage.     

Arbuscular mycorrhizal fungi affect phytophagous insect specialism

The majority of phytophagous insects eat very few plant species, yet the ecological and evolutionary forces that have driven such specialism are not entirely understood. The hypothesis that arbuscular mycorrhizal (AM) fungi can determine phytophagous insect specialism, through differential effects on insect growth, was tested using examples from the British flora. In the UK, plant families and species in the family Lamiaceae that are strongly mycorrhizal have higher proportions of specialist insects feeding on them than those that are weakly mycorrhizal. We suggest that AM fungi can affect the composition of insect assemblages on plants and are a hitherto unconsidered factor in the evolution of insect specialism.     

接种AM真菌对短命植物生长发育及矿质养分吸收的影响

 采用分室培养方法研究接种幼套球囊霉(Glomus etunicatum,BEG168)、摩西球囊霉(G. mosseae, BEG167)、混合菌剂(M)对两种沙漠早春短命植物小车前(Plantago minuta)和尖喙牻牛儿苗（Erodium oxyrrhynchum）生长发育及矿质养分吸收的影响。结果表明,接种AMF处理的小车前和尖喙牻牛儿苗根系形成了典型的菌根结构,侵染率为22 %～60%;接种AMF提高了小车前和尖喙牻牛儿苗两种植物的生物量、株高及N、P养分吸收量。小车前单独接种BEG167、BEG168以及混合接种都显著提高了单株种子数量,其增幅分别 为67%、50%和78%。上述结果说明,在极端贫瘠和干旱的古尔班通古特沙漠中,丛枝菌根真菌对于早春短命植物小车前和尖喙牻牛儿苗的生态适应性的贡献表现为促进营养生长、提高后代（种子）繁殖数量。     

Reconstructing the pollinator community and predicting seed set from hydrocarbon footprints on flowers

The measurement of insect visits to flowers is essential for basic and applied pollination ecology, but is often fraught with difficulty. Floral visitation is highly variable and observational studies are limited in scope due to the considerable time needed to acquire reliable data. Our study investigates whether the analysis of hydrocarbon residues (footprints) deposited by insects during flower visits allows the reconstruction of the visitor community and the prediction of seed set for large numbers of plants. In three consecutive years we recorded bumblebee visitation to wild plants of comfrey, Symphytum officinale, and later used gas chromatography/mass spectrometry (GC/MS) to quantify bumblebee-derived unsaturated hydrocarbons (UHCs) extracted from flowers. The UHCs washed from corollae were most similar to the tarsal UHC profile of the most abundant bumblebee species, Bombus pascuorum, in all 3 years. The species compositions of the bumblebee communities estimated from UHCs on flowers were also similar to those actually observed. There was a significant positive correlation between the observed number of visits by each of three bumblebee species (contributing 3–68% of the flower visits) and the estimated number of visits based on UHC profiles. Furthermore, significant correlations were obtained separately for workers and drones of two species. Seed set of comfrey plants was positively correlated with overall bumblebee visitation and the total amount of UHCs on flowers, suggesting the potential for pollen limitation. We suggest that quantifying cumulative footprint hydrocarbons provides a novel way to assess floral visitation by insects, and that this method can be used to predict seed set in pollen-limited plants.     

Pollination of Euphorbia dendroides by lizards and insects: Spatio-temporal variation in patterns of flower visitation

The patterns of flower visitation by lizards (Podarcis lilfordi, Lacertidae) and insects (mainly flies, bees and wasps) on the shrub Euphorbia dendroides, were studied in the island of Cabrera (Balearic Islands) during the flowering seasons of 1995 and 1996. Lizards act as true pollinators of the plant, moving large quantities of pollen within and among shrubs. To our knowledge, this is the first time that pollination by lizards has been empirically demonstrated. Variation in the quantitative component of pollination (frequency of visits × flower visitation rate) by the two groups of pollinators (lizards and insects) is documented at both spatial (within a plant population) and temporal scales (throughout the flowering season and between seasons). Variation in lizard density on a small spatial scale (within c. 200 m), presumably due to differences in vegetation cover, strongly affected their frequency of flower visitation. Insects were rather scarce, mainly because the plant flowers at a time (mid-March) when temperatures are still low. At the site where lizards were abundant, their frequency of flower visits was more than 3 times that of insects, they stayed on the shrubs about 3 times longer and visited about 8 times more cyathia per minute than did insects. Fruit and seed set were greater at this site, and this is attributed to the different frequency of flower visits by lizards, as shrubs are similar in size and produce similar amounts of cyathia in the two sites compared. Both, lizards and insects went more frequently to plants with large flower crops. However, flower crop was not associated with seed viability. We found no evidence for pollinator-mediated selection on plant traits related to fitness. Received: 28 August 1996 / Accepted: 26 February 1997     

丛枝菌根真菌与植食性昆虫的相互作用

丛枝菌根(arbuscular mycorrhizal AM)真菌与昆虫均是陆地生态系统中的重要组分,同植物关系密切,对植物的影响和作用是巨大的。生态系统中则以AM真菌-植物-昆虫互作体系参预食物网与生态过程。早在20世纪80年代,人们已开始研究AM真菌对昆虫的影响。进入21世纪人们越来越重视AM真菌与昆虫的相互作用。总结了AM真菌对昆虫取食偏好、生长、繁殖和对植物危害等方面的影响、以及昆虫对AM真菌侵染、扩展和产孢的影响;分析了植物营养状况、昆虫性别、昆虫龄期和AM真菌种类等对AM真菌与昆虫相互作用的影响特点;探讨了AM真菌与昆虫相互作用的机制;展望了利用AM真菌抑制植食性害虫、及促进天敌昆虫和部分传粉昆虫作用的可能性,旨在丰富菌根学研究内容、促进AM真菌与昆虫互作领域的深入研究、为探索生物防控农林业害虫的新途径提供依据。     

A test of the effect of floral color change on pollination effectiveness using artificial inflorescences visited by bumblebees

Floral color change has been recognized as a pollination strategy, but its relative effectiveness has been evaluated insufficiently with respect to other floral traits. In this study, effects of floral color change on the visitation pattern of bumblebees were empirically assessed using artificial flowers. Four inflorescence types were postulated as strategies of flowering behavior: type 1 has no retention of old flowers, resulting in a small display size; type 2 retains old flowers without nectar production; type 3 retains old flowers with nectar; and type 4 retains color-changed old flowers without nectar. Effects of these treatments varied depending on both the total display size (single versus multiple inflorescences) and the pattern of flower-opening. In the single inflorescence experiment, a large floral display due to the retention of old flowers (types 2–4) enhanced pollinator attraction, and the number of flower visits per stay decreased with color change (type 4), suggesting a decrease in geitonogamous pollination. Type-4 plants also reduced the foraging time of bees in comparison with type-2 plants. In the multiple inflorescence experiment, the retention of old flowers did not contribute to pollinator attraction. When flowering occurred sequentially within inflorescences, type-4 plants successfully decreased the number of visits and the foraging time in comparison with type-2 plants. In contrast, floral color change did not influence the number of visits, and it extended the foraging time when flowering occurred simultaneously within inflorescences but the opening of inflorescences progressed sequentially within a plant. Therefore, the effectiveness of floral color change is highly susceptible to the display size and flowering pattern within plants, and this may limit the versatility of the color change strategy in nature.     

Analogous effects of arbuscular mycorrhizal fungi in the laboratory and a North Carolina field

Although arbuscular mycorrhizal (AM) fungi are ubiquitous symbionts of plants, the mutualism has rarely been tested in nature. In experiments designed to explore the ecological relevance of associations between different fungal and plant species in a natural environment, plant species were infected with different species of fungi and grown in separate trials in the laboratory and a North Carolina (USA) field. The benefits to plants varied dramatically as plant species were grown with different species of AM fungi. Effects of mycorrhizal fungi in nature were generally correlated to effects in the growth chamber, suggesting that laboratory data do reflect dynamics between plants and AM fungi in the field. Initial size at transplant and experimental block were also significant predictors of plant growth in the field. Correlation statistics between laboratory and field data were weaker when analyses involved plant species less responsive to infection by any AM fungus, suggesting that the response of a species to inoculation is a good predictor of its sensitivity to specific AM fungi in the field. AM fungal identity appears to influence the growth and reproduction of plants in the field.     

Spatial variation in selection in a plant-pollinator system in the wadis of Sinai,Egypt

We studied an insect-plant pollination system in adjacent steep-sided wadis and a connecting plain in the mountains of southern Sinai (Egypt): this environment creates a strongly divided habitat, which may promote the local differentiation of sub-populations. We tested for spatial differences in phenotypic reproductive characters of the only plant flowering abundantly in early spring, Alkanna orientalis (Boraginaceae), and its major pollinator at that time of year, Anthophora pauperata (Apoidea, Anthophoridae). There were significant morphological differences between sub-populations of Alkanna, mainly between plants from the narrower wadis and those on the interconnecting plain. Flowers on the plain were larger, with wider corollas and more nectar standing crop; these plants retained more flowers on the inflorescence, but received many fewer visits to flowers. There was a significant selection gradient between flower size and maternal fitness (seed set) in the plain, but not elsewhere. Natural selection may have increased resources devoted to attracting insect visitors in response to fewer pollinating visits in the plain. Consistent with this explanation, by experimentally manipulating flower number per plant, we showed that within a wadi having more flowers on a plant secured more visits.     

Size-dependent pollination efficiency in Anchusa officinalis (Boraginaceae): causes and consequences

Summary Bumblebees foraging on the self-incompatible Anchusa officinalis fly between near neighbour plants and between near neighbour inflorescences within plants. Although many-flowered plants attracted most bumblebees these plants received fewer visits on a per flower basis than smaller plants, and each bumblebee visited a smaller proportion of the flowers. The calculated effective visitation rate per flower was highest on plants of an intermediate size. If pollen-carryover was assumed to be limited the most efficient plant was predicted to be smaller since the proportion of fertilized flowers per bumblebee visit is expected to decrease further on the largest plants in relation to the total flower number. These predictions were tested by measuring fruit-set in the field. The percentage fruit-set decreased with plant size at all sizes that were investigated. That the most efficient plant was small indicates that pollen-carryover was indeed limited. However, the low percentage fruit-set associated with large size did not present a serious problem since the total estimated seed production per plant still increased with size. Selection favoring smaller plants may be low or absent in Anchusa.     

Reconstructing the pollinator community and predicting seed set from hydrocarbon footprints on flowers

The measurement of insect visits to flowers is essential in basic and applied pollination ecology studies but often fraught with difficulty. Floral visitation is highly variable, and observational studies are limited in scope due to the considerable time necessary to acquire reliable data. The aim of our study was to investigate whether the analysis of hydrocarbon residues (footprints) deposited by insects during flower visits would allow reconstruction of the visitor community and prediction of seed set for large numbers of plants. In 3 consecutive years, we recorded bumblebee visitation to wild plants of comfrey, Symphytum officinale, and later used gas chromatography/mass spectrometry (GC/MS) to quantify bumblebee-derived unsaturated hydrocarbons (UHCs) extracted from flowers. We found that the UHCs washed from corollas were most similar to the tarsal UHC profile of the most abundant bumblebee species, Bombus pascuorum, in all 3 years. The species composition of the bumblebee communities estimated from UHCs on flowers were also similar to those actually observed. There was a significant positive correlation between the observed number of visits by each of three bumblebee species (contributing 3-68% of flower visits) and the estimated number of visits based on UHC profiles. Furthermore, significant correlations were obtained separately for workers and drones of two of the study species. Seed set of comfrey plants was positively correlated to overall bumblebee visitation and the total amount of UHCs on flowers, suggesting the potential for pollen limitation. We suggest that quantifying cumulative footprint hydrocarbons provides a novel way to assess floral visitation by insects and can be used to predict seed set in pollen-limited plants.     

Temporal changes in floral resource availability and flower visitation in a butterfly

Foraging affects survival and reproductive success in animals, including flower-visiting insects. Plant-derived floral food resources (i.e. nectar and pollen) may be rapidly changing in space and time and pollinators may need to quickly switch to new resources. Butterflies are suitable model organisms to investigate foraging behaviour of insect pollinators, because they can be easily monitored under natural conditions. We studied flower visitation patterns in the Clouded Apollo butterfly Parnassius mnemosyne in relation to the abundance of available floral resources. We recorded flower visitation daily in individually marked butterflies, listed flowering species and estimated flower abundance categories every 3 days in a single meadow, during five consecutive flight periods. Butterflies visited 35 nectar plants from the 71 species available. Few nectar plants were frequently visited (visit ratios for the annually most visited species: 37–60%), many were scarcely visited and no visits were observed on several abundant species. Flower abundance and visit ratio varied among years and within flight periods. The number of visits increased with flower abundance in the seven most frequently visited plant species, but not in the occasionally visited ones. Beside their choosiness, Parnassius mnemosyne butterflies were able to adjust foraging behaviour to rapidly changing resource distributions. Diet selectivity in adults might increase the vulnerability of this species. However, visitation plasticity may mitigate the effect of the lack of some nectar plants, as complementary resources can be used as alternatives.