Successive stamen movement in Saxifraga candelabrum is responsive to weather and pollinator visits

BACKGROUND

Successive stamen movement is a complex plant behavior involving successive uplift of stamens and pollen release, which plays a role in reducing sexual interference, increasing pollen deposition and promoting pollen export. Although reported from several taxa, studies on whether the movement can be influenced by abiotic and biotic factors are scarce.

METHODS

In this study, we here for the first time described a pattern of successive stamen movement in Saxifraga candelabrum (Saxifragaceae). We then compared the rates of stamen movement in S. candelabrum under different weather and varying pollinator visits. Pollen packaging and presentation schedule of S. candelabrum were also investigated.

RESULTS

The results showed that the number of stamens bent per day in sunny days was significantly higher than overcast and rain. Flowers that receive more pollinator visits (control treatment) had significantly higher number of stamen movement than those that received fewer (removal treatment) and none (bagging treatment). Throughout the staminate phase of a flower, there was a progressive increase in both pollen quantity of individual stamens and pollen presentation during each day.

CONCLUSION

Our research demonstrates that successive stamen movement in S. candelabrum was accelerated by favorable weather and increased pollinator visits, which may promote pollen export. Moreover, incremental pollen packaging is likely an adaptation to seasonal regularity in variations of sex ratio resulting from protandry.

Periodically taken photographs reveal the effect of pollinator insects on seed set in lotus flowers

Understanding of pollination systems is an important topic for evolutionary ecology, food production, and biodiversity conservation. However, it is difficult to grasp the whole picture of an individual system, because the activity of pollinators fluctuates depending on the flowering period and time of day. In order to reveal effective pollinator taxa and timing of visitation to the reproductive success of plants under the complex biological interactions and fluctuating abiotic factors, we developed an automatic system to take photographs at 5-s intervals to get near-complete flower visitation by pollinators during the entire flowering period of selected flowers of Nelumbo nucifera and track the reproductive success of the same flowers until fruiting. Bee visits during the early morning hours of 05:00-07:59 on the second day of flowering under optimal temperatures with no rainfall or strong winds contributed strongly to seed set, with possible indirect negative effects by predators of the pollinators. Our results indicate the availability of periodic and consecutive photography system in clarifying the plant-pollinator interaction and its consequence to reproductive success of the plant. Further development is required to build a monitoring system to collect higher-resolution time-lapse images and automatically identify visiting insect species in the natural environment.

Behavioural responses by a bumble bee to competition with a niche-constructing congener

While feeding, foragers can alter their environment. Such alteration constitutes ecological niche construction (ENC) if it enables future benefits for the constructor and conspecific individuals. The environmental modification may also affect non‐constructing, bystander species, especially if they share resources with constructor species. If so, ENC could confer the constructor species a competitive advantage by both enhancing its foraging returns and reducing those of bystander species.

Expectations – (E1) ENC frequency should vary positively with the recent and current density of the constructor species, and (E2) constructors should use modifications disproportionately. In contrast, bystanders should (E3) experience intensified competition for the affected resource, and (E4) exhibit diverse, possibly mitigating, responses to ENC, depending on opportunity and relative benefits.

We investigated these expectations in Argentina for competition for Fuchsia magellanica nectar between an invasive bumble bee Bombus terrestris (terr: putative constructor), which often bites holes at the bases of floral tubes to rob nectar, and native B. dahlbomii (dahl: bystander), which normally accesses Fuchsia nectar through the flower mouth (front visits). Robbing holes constitute ENC, as they persist until the 7‐day flowers wilt. The dynamics of the incidence of robbed flowers, abundance of both bees and the number and types of their flower visits (front or robbing) were characterised by alternate‐day surveys of plants during 2.5 months.

After initially accessing Fuchsia nectar via front visits, terr switched to robbing and its abundance on Fuchsia increased 20‐fold within 10 days (E2). Correspondingly, the incidence of robbed flowers varied positively with recent and past terr abundance (E1). In contrast, dahl abundance remained low and varied negatively with the incidence of robbed flowers (E3). When terr ceased visiting Fuchsia, dahl abundance increased sixfold within 10 days (E3), possibly because many dahl previously had avoided competition with terr by feeding on other plant species (E4). While terr was present, dahl on Fuchsia used front visits (tolerance) or used existing robbing holes (adoption: E4). The diverse dahl responses suggest partial compensation for competition with terr.

ENC alters competitive asymmetry, favouring constructor species. However, bystander responses can partially offset this advantage, perhaps facilitating coexistence.

Phenological variation of flower longevity and duration of sex phases in a protandrous alpine plant: potential causes and fitness significance

BACKGROUND

Flower longevity plays an important role in pollen dispersal and reproductive success in plants. In dichogamous plants, the duration of anthesis as well as the time allocated to male and female functions can vary in response to intrinsic factors (e.g., flowering time and resource allocation) and pollination context along a growth season. However, the fitness consequences of phenological dynamics have rarely been examined. This study aims to unravel the potential causes driving variation in flower longevity, duration of sex phases, and phenotypic sex during a flowering season of strongly protandrous Aconitum gymnandrum, and particularly reproductive consequences of the phenological pattern.

RESULTS

Population floral sex ratio shifted from completely male at the beginning to completely female at the end of the season, as is common in other protandrous plants. Phenological dynamics of the floral sex ratio and the duration of sex phases caused a shift from femaleness to maleness in the mean phenotypic sex over the whole season. Floral longevity was negatively correlated with flower size and positively affected by temperature. Early flowers within inflorescences rather than early-flowering individuals emphasized the duration of female over male phase. Owing to the dominance of male-phase flowers, early flowering for individual flowers and plants, or female-biased sex resulted in higher pollen deposition per flower and seed set. At the flower level, flower longevity positively affected female reproductive success, while the effect of flower size was negative. By contrast, plant-level female reproductive success was negatively affected by flower longevity but positively correlated to flower size.

CONCLUSIONS

The major result of this study lies in elucidating the relationship between variation in phenological sex expression and floral longevity and their fitness consequences of protandrous A. gymnandrum. The contrasting results on female fitness for individual flowers and plants contribute to our current understanding of the adaptive significance of floral longevity.

Intraspecific variation in body size of bumblebee workers influences anti-predator behaviour

Flower-dwelling predators make flowers dangerous foraging sites for pollinators, potentially affecting their anti-predator behaviour. Moreover, predation vulnerability often varies among pollinators' body sizes with interspecific comparisons showing that smaller species are more vulnerable than larger ones. However, how intraspecific body size variation influences pollinator behaviour under predation risk is still unknown, especially under natural conditions. We hypothesized that bumblebee workers of different sizes will exhibit different foraging strategies under predation risk. We predict that (a) small workers should more often exhibit anti-predator behaviours than larger workers. We also hypothesized that the anti-predator behaviour should be influenced by predator size and reward availability; therefore, we expect (b) higher avoidance behaviour towards larger predator sizes and (c) more and longer visits to inflorescences with high nectar availability. Finally, we expect that (d) nectar availability should overcome the anti-predator behaviour in less vulnerable, large, workers. We recorded flower visitation, time spent and rejection behaviours of different sizes of Bombus terrestris (Apidae) workers (large, medium and small) to inflorescences of Alstroemeria aurea (Alstroemeriaceae) with different treatments of artificial spiders (small and large) and nectar availability (with, without). Anti-predator and foraging behaviour of bumblebees was affected by the size of the worker, the presence of artificial spiders and nectar availability. Large and medium size bumblebees strongly reduced flower visitation and time spent in the presence of artificial spiders, consistently avoiding flowers with spiders, regardless of spider size or nectar availability. Instead, small bumblebees seldom modified their behaviour when facing artificial spiders, only increasing their avoidance or decreasing their foraging time in nectarless flowers hosting large artificial spiders. This pattern of larger workers being more sensitive to predation risk than smaller ones at the intraspecific level in B. terrestris is contrary to the expected and acknowledged trend based on previous interspecific comparisons, but partially consistent with predictions of models of optimal foraging theory. Intraspecific behavioural variability was uncovered only when nectar was available, whereas artificial predator size rarely modified bumblebee anti-predator and foraging behaviour. Therefore, our findings suggest that the trade-off between maximizing resource intake and minimizing predation risk strongly varies across bumblebee worker body sizes.

Green consumerism: the influence of antioxidant parameters and socio-economic values on Tarhana consumption patterns

This study aimed to examine the production and consumption patterns of the tarhana as a green food product and its content in terms of health value in the socio-economic framework by comparing urban and rural households. To be able to assess the tarhana's health value, the addition of antioxidative parameters was analysed. We obtained the data as a result of a two-part study. The first part of the research included a structured survey conducted between September and December 2015. In the second part, three types of tarhana samples evaluated in terms of their antioxidant capacity and total phenolic content as extractable, hydrolysable, and bioaccessible phenolics to support the claim that homemade tarhana offers higher nutritional potential and healthier content than commercially produced tarhana. Organic and additive-free homemade tarhana samples have great antioxidative potential, also depending on the content and the production pattern. The results of the antioxidant capacity, total phenolic content analyses, and their bioaccessibility revealed that non-fermented homemade tarhana and cranberry-added tarhana stand out, according to production process and content. Our findings showed that participants mostly produced the tarhana at home. In cases where they could not produce it themselves, they supplied it from their family and friends. This result showed us that participants preferred homemade tarhana over industrial tarhana sold in markets. Rural areas mostly consumed tarhana for its economic value. However, tarhana consumption did not decrease in cities. Only the consumption mode and the times have changed.

Pollinator-mediated selection on flowering phenology and floral display in a distylous herb Primula alpicola

The targets and causes of phenotypic selection are crucial to understanding evolutionary ecology. However, few studies have examined selection quantitatively from multiple sources on the same trait identified the agent of natural selection experimentally. Here we quantified phenotypic selection on traits, including flowering phenology and aspects of floral display via female fitness, in the distylous perennial herb Primula alpicola. To determine the role of pollinators in generating selection effects on floral traits, we compared the phenotypic selection gradients in open-pollinated and hand-pollinated plants. Our results show that pollinator-mediated linear selection on flowering start and correlational selection on the number of flowers and scape height explains most of the net phenotypic selection on these traits suggesting pollinators played an important role in shaping floral diversity. We used path analysis and structural equation modeling (SEM) to examine how herbivores affected the relationship between floral traits and female fitness, but no significant selection was caused by seed predators. These results suggest pollinators, not herbivores maybe the significant agent of selection on flora traits.

Seasonal variation in the mating system of a selfing annual with large floral displays

BACKGROUND AND AIMS

Flowering plants display considerable variation in mating system, specifically the relative frequency of cross- and self-fertilization. The majority of estimates of outcrossing rate do not account for temporal variation, particularly during the flowering season. Here, we investigated seasonal variation in mating and fertility in Incarvillea sinensis (Bignoniaceae), an annual with showy, insect-pollinated, 'one-day' flowers capable of delayed selfing. We examined the influence of several biotic and abiotic environmental factors on day-to-day variation in fruit set, seed set and patterns of mating.

METHODS

We recorded daily flower number and pollinator abundance in nine 3 × 3-m patches in a population at Mu Us Sand land, Inner Mongolia, China. From marked flowers we collected data on daily fruit and seed set and estimated outcrossing rate and biparental inbreeding using six microsatellite loci and 172 open-pollinated families throughout the flowering period.

KEY RESULTS

Flower density increased significantly over most of the 50-d flowering season, but was associated with a decline in levels of pollinator service by bees, particularly on windy days. Fruit and seed set declined over time, especially during the latter third of the flowering period. Multilocus estimates of outcrossing rate were obtained using two methods (the programs MLTR and BORICE) and both indicated high selfing rates of ∼80 %. There was evidence for a significant increase in levels of selfing as the flowering season progressed and pollinator visitation declined. Biparental inbreeding also declined significantly as the flowering season progressed.

CONCLUSIONS

Temporal variation in outcrossing rates may be a common feature of the mating biology of annual, insect-pollinated plants of harsh environments but our study is the first to examine seasonal mating-system dynamics in this context. Despite having large flowers and showy floral displays, I. sinensis attracted relatively few pollinators. Delayed selfing by corolla dragging largely explains the occurrence of mixed mating in I. sinensis, and this mode of self-fertilization probably functions to promote reproductive assurance when pollinator service is limited by windy environmental conditions and competition from co-occurring flowering plants.

The invasion of southern South America by imported bumblebees and associated parasites

The Palaearctic Bombus ruderatus (in 1982/1983) and Bombus terrestris (1998) have both been introduced into South America (Chile) for pollination purposes. We here report on the results of sampling campaigns in 2004, and 2010-2012 showing that both species have established and massively expanded their range. Bombus terrestris, in particular, has spread by some 200 km year(-1) and had reached the Atlantic coast in Argentina by the end of 2011. Both species, and especially B. terrestris, are infected by protozoan parasites that seem to spread along with the imported hosts and spillover to native species. Genetic analyses by polymorphic microsatellite loci suggest that the host population of B. terrestris is genetically diverse, as expected from a large invading founder population, and structured through isolation by distance. Genetically, the populations of the trypanosomatid parasite, Crithidia bombi, sampled in 2004 are less diverse, and distinct from the ones sampled later. Current C. bombi populations are highly heterozygous and also structured through isolation by distance correlating with the genetic distances of B. terrestris, suggesting the latter's expansion to be a main structuring factor for the parasite. Remarkably, wherever B. terrestris spreads, the native Bombus dahlbomii disappears although the reasons remain unclear. Our ecological and genetic data suggest a major invasion event that is currently unfolding in southern South America with disastrous consequences for the native bumblebee species.

The interplay between inflorescence development and function as the crucible of architectural diversity

BACKGROUND

Most angiosperms present flowers in inflorescences, which play roles in reproduction, primarily related to pollination, beyond those served by individual flowers alone. An inflorescence's overall reproductive contribution depends primarily on the three-dimensional arrangement of the floral canopy and its dynamics during its flowering period. These features depend in turn on characteristics of the underlying branching structure (scaffold) that supports and supplies water and nutrients to the floral canopy. This scaffold is produced by developmental algorithms that are genetically specified and hormonally mediated. Thus, the extensive inflorescence diversity evident among angiosperms evolves through changes in the developmental programmes that specify scaffold characteristics, which in turn modify canopy features that promote reproductive performance in a particular pollination and mating environment. Nevertheless, developmental and ecological aspects of inflorescences have typically been studied independently, limiting comprehensive understanding of the relations between inflorescence form, reproductive function, and evolution.

SCOPE

This review fosters an integrated perspective on inflorescences by summarizing aspects of their development and pollination function that enable and guide inflorescence evolution and diversification.

CONCLUSIONS

The architecture of flowering inflorescences comprises three related components: topology (branching patterns, flower number), geometry (phyllotaxis, internode and pedicel lengths, three-dimensional flower arrangement) and phenology (flower opening rate and longevity, dichogamy). Genetic and developmental evidence reveals that these components are largely subject to quantitative control. Consequently, inflorescence evolution proceeds along a multidimensional continuum. Nevertheless, some combinations of topology, geometry and phenology are represented more commonly than others, because they serve reproductive function particularly effectively. For wind-pollinated species, these combinations often represent compromise solutions to the conflicting physical influences on pollen removal, transport and deposition. For animal-pollinated species, dominant selective influences include the conflicting benefits of large displays for attracting pollinators and of small displays for limiting among-flower self-pollination. The variety of architectural components that comprise inflorescences enable diverse resolutions of these conflicts.

Herbivores affect natural selection for floral-sex ratio in a field population of horsenettle, Solanum carolinense

Although aspects of a plant's breeding system are generally believed to have evolved in response to selection for effective pollination, herbivores may also play a selective role. Here we report on a field experiment involving 960 transplanted ramets of the andromonoecious herb Solanum carolinense in which the pattern of natural selection for an important breeding-system trait was influenced by naturally occurring herbivores. As the level of flower and fruit herbivory increased, the pattern of selection on floral-sex ratio went from stabilizing (with an optimum of 29% male flowers), to directional toward a lower proportion of males, with the optimum bottoming at 0% male. This pattern of selection likely helped generate the broad-sense genetic correlation (r = 0.42) between floral-sex ratio and resistance to herbivory. These results contribute to the growing awareness that herbivores can be important influences not only on plant resistance traits, but also on the evolution of their hosts' breeding system.

Floral adaptation and diversification under pollen limitation

Pollen limitation (PL) of seed production creates unique conditions for reproductive adaptation by angiosperms, in part because, unlike under ovule or resource limitation, floral interactions with pollen vectors can contribute to variation in female success. Although the ecological and conservation consequences of PL have received considerable attention in recent times, its evolutionary implications are poorly appreciated. To identify general influences of PL on reproductive adaptation compared with those under other seed-production limits and their implications for evolution in altered environments, we derive a model that incorporates pollination and post-pollination aspects of PL. Because PL always favours increased ovule fertilization, even when population dynamics are not seed limited, it should pervasively influence selection on reproductive traits. Significantly, under PL the intensity of inbreeding does not determine whether outcrossing or autonomous selfing can evolve, although it can affect which response is most likely. Because the causes of PL are multifaceted in both natural and anthropogenically altered environments, the possible outcrossing solutions are diverse and context dependent, which may contribute to the extensive variety of angiosperm reproductive characteristics. Finally, the increased adaptive options available under PL may be responsible for positive global associations between it and angiosperm diversity.

Flowering phenology influences seed production and outcrossing rate in populations of an alpine snowbed shrub, Phyllodoce aleutica: effects of pollinators and self-incompatibility

BACKGROUND AND AIMS

Because of differences in snowmelt time, the reproductive phenologies of alpine plants are highly variable among local populations, and there is large variation in seed set across populations. Temporal variation in pollinator availability during the season may be a major factor affecting not only seed production but also outcrossing rate of alpine plants.

METHODS

Among local populations of Phyllodoce aleutica that experience different snowmelt regimes, flowering phenology, pollinator availability, seed-set rate, and outcrossing rate were compared with reference to the mating system (self-compatibility or heterospecific compatibility with a co-occurring congeneric species).

KEY RESULTS

Flowering occurred sequentially among populations reflecting snowmelt time from mid-July to late August. The visit frequency of bumble-bees increased substantially in late July when workers appeared. Both seed set and outcrossing rate increased as flowering season progressed. Although flowers were self-compatible and heterospecific compatible, the mixed-pollination experiment revealed that fertilization with conspecific, outcrossing pollen took priority over selfing and hybridization, indicating a cryptic self-incompatibility. In early snowmelt populations, seed production was pollen-limited and autogamous selfing was common. However, genetic analyses revealed that selfed progenies did not contribute to the maintenance of populations due to late-acting inbreeding depression.

CONCLUSIONS

Large variations in seed-set and outcrossing rates among populations were caused by the timing of pollinator availability during the season and the cryptic self-incompatibility of this species. Despite the intensive pollen limitation in part of the early season, reproductive assurance by autogamous selfing was not evident. Under fluctuating conditions of pollinator availability and flowering structures, P. aleutica maintained the genetic composition by conspecific outcrossing.

Effects of flowering plant density on pollinator visitation, pollen receipt, and seed production in Delphinium barbeyi (Ranunculaceae)

Variation in flowering plant density can have conflicting effects on pollination and seed production. Dense flower patches may attract more pollinators, but flowers in those patches may also compete for pollinator visits and abiotic resources. We examined how natural and experimental conspecific flowering plant density affected pollen receipt and seed production in a protandrous, bumble bee-pollinated wildflower, Delphinium barbeyi (Ranunculaceae). We also compared floral sex ratios, pollinator visitation rates, and pollen limitation of seed set from early to late in the season to determine whether these factors mirrored seasonal changes in pollen receipt and seed production. Pollen receipt increased with natural flowering plant density, while seed production increased across lower densities and decreased across higher flower densities. Experimental manipulation of flowering plant density did not affect pollinator visitation rate, pollen receipt, or seed production. Although pollinator visitation rate increased 10-fold from early to late in the season, pollen receipt and seed set decreased over the season. Seed set was never pollen-limited. Thus, despite widespread effects of flowering plant density on plant reproduction in other species, the effects of conspecific flowering plant density on D. barbeyi pollination and seed production are minor.

Displacement of a native by an alien bumblebee: lower pollinator efficiency overcome by overwhelmingly higher visitation frequency

Biological invasions might constitute a major threat to mutualisms. Introduced pollinators might competitively displace their native counterparts, which in turn affects the pollination of native plants, if native and alien visitors differ in pollinator effectiveness. Since its invasion in 1994 into south-west Argentina, the introduced European bumblebee Bombus ruderatus has continuously increased in abundance, along with a simultaneous decrease in the abundance of the native Bombus dahlbomii. The latter is the only native bumblebee species of the temperate forests of southern South America, and the main pollinator of the endemic herb Alstroemeria aurea. In order to evaluate the impact of the ongoing displacement of the native by the alien bumblebee, we compared the pollinator effectiveness (i.e., the combination of pollinator efficiency per visit and visitation frequency) between both bumblebee species, as well as related pollinator traits that might account for potential differences in pollinator efficiency. Native Bombus dahlbomii, which has a larger body and spent more time per flower, was the more efficient pollinator compared to Bombus ruderatus, both in terms of quantity and quality of pollen deposited per visit. However, Bombus ruderatus was a much more frequent flower visitor than Bombus dahlbomii. As a consequence, Bombus ruderatus is nowadays a more effective pollinator of A. aurea than its native congener. Despite the lack of evidence of an increase in seed set at the population level, comparisons with historical records of Bombus dahlbomii abundances prior to Bombus ruderatus' invasion suggest that the overall pollination intensity of A. aurea might in fact have risen as a consequence of this invasion. Field experiments like these, that incorporate the natural variation in abundance of native and alien species, are powerful means to demonstrate that the consequences of invasions are more complex than previous manipulated and controlled experiments have suggested.

Expanding the limits of the pollen-limitation concept: effects of pollen quantity and quality

Pollination commonly limits seed production, as addition of pollen to stigmas often increases fecundity. This response is usually interpreted as evidence that plants' stigmas receive too few pollen grains to maximize ovule fertilization (quantity limitation); however, many genetic studies demonstrate that poor-quality pollen can also reduce seed production (quality limitation). We explore both aspects of pollen limitation theoretically with a dose-response model that incorporates a saturating negative-exponential relation of seed production to pollen receipt. This relation depends on aspects of ovule production, pollen import, pollen-pistil interactions and seed development, all of which can contribute to pollen limitation. Our model reveals that quantity limitation is restricted to the lowest range of pollen receipt, for which siring success per pollen grain is high, whereas quality limitation acts throughout the range of pollen receipt if plants do not import the highest-quality pollen. In addition to pollinator availability and efficiency, quantity limitation is governed by all post-pollination aspects of seed production. In contrast, quality limitation depends on the difference in survival of embryos sired by naturally delivered pollen vs. by pollen of maximal quality. We briefly illustrate the distinction between these two components of pollen limitation with results from the mistletoe Tristerix corymbosus. Our model also shows that the standard pollen-supplementation technique neither estimates the total intensity of pollen limitation nor distinguishes between its quantity and quality components. As an alternative, we propose a methodological protocol that requires both measurement of seed production following excess pollination with only outcross pollen and quantification of the dose-response relation of seed output to pollen receipt. This method estimates both the total extent of pollen limitation and its two components. Finally, we consider the influences on quantity and quality limitation, which reveals that quantity limitation probably occurs much less often than has been inferred from pollen-supplementation experiments. These interpretations suggest that an expanded perspective that recognizes the fecundity consequences of pollination with poor-quality pollen would promote ecological understanding of pollen limitation.

Seasonal changes in pollinator activity influence pollen dispersal and seed production of the alpine shrub Rhododendron aureum (Ericaceae)

In alpine ecosystems, microscale variation in snowmelt timing often causes different flowering phenology of the same plant species and seasonal changes in pollinator activity. We compared the variations in insect visitation, pollen dispersal, mating patterns, and sexual reproduction of Rhododendron aureum early and late in the flowering season using five microsatellites. Insects visiting the flowers were rare early in the flowering season (mid-June), when major pollinators were bumblebee queens and flies. In contrast, frequent visitations by bumblebee workers were observed late in the season (late July). Two-generation analysis of pollen pool structure demonstrated that quality of pollen-mediated gene flow was more diverse late in the season in parallel with the high pollinator activity. The effective number of pollen donors per fruit (N(ep)) increased late in the season (N(ep) = 2.2-2.7 early, 3.4-4.4 late). However, both the outcrossing rate (t(m)) and seed-set ratio per fruit were smaller late in the season (t(m) = 0.89 and 0.71, seed-set ratio = 0.52 and 0.18, early and late in the season, respectively). In addition, biparental inbreeding occurred only late in the season. We conclude that R. aureum shows contrasting patterns of pollen movement and seed production between early and late season: in early season, seed production can be high but genetically less diverse and, during late season, be reduced, possibly due to higher inbreeding and inbreeding depression, but have greater genetic diversity. Thus, more pollinator activity does not always mean more pollen movement.

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.

Seasonal changes in pollen-packaging schedules in the protandrous plant Chamerion angustifolium

The rate at which pollen is presented varies widely both among and within species of flowering plants. Although several studies have tried to explain between-species variation in this trait, few explanations exist for the variation that exists among individuals of the same species. I used protandrous fireweed, Chamerion angustifolium (Onagraceae), to examine seasonal changes in pollinator visitation, population sex ratio, and pollen presentation schedules. Most studies that make predictions about optimal pollen presentation assume conditions are constant throughout the flowering season. However, data presented here show that pollen presentation schedules vary seasonally: in early season flowers, anthers dehisce over a number of days, while late season flowers present all anthers simultaneously. I show that pollinator visitation rates to individual plants are higher but more variable early in the season than late in the season. Furthermore, per-male availability of female-phase flowers increases over the course of the flowering season in this population. I suggest that seasonal differences in the variability of pollinator visitation and the availability of female flowers has played an important role in selection for pollen presentation schedules.