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PubMed2006

Pollination niche overlap between a parasitic plant and its host.

Niche theory predicts that species which share resources should evolve strategies to minimise competition for those resources, or the less competitive species would be extirpated. Some plant species are constrained to co-occur, for example parasitic plants and their hosts, and may overlap in their pollination niche if they flower at the same time and attract the same pollinators. Using field observations and experiments between 1996 and 2006, we tested a series of hypotheses regarding pollination niche overlap between a specialist parasitic plant Orobanche elatior (Orobanchaceae) and its host Centaurea scabiosa (Asteraceae). These species flower more or less at the same time, with some year-to-year variation. The host is pollinated by a diverse range of insects, which vary in their effectiveness, whilst the parasite is pollinated by a single species of bumblebee, Bombus pascuorum, which is also an effective pollinator of the host plant. The two species therefore have partially overlapping pollination niches. These niches are not finely subdivided by differential pollen placement, or by diurnal segregation of the niches. We therefore found no evidence of character displacement within the pollination niches of these species, possibly because pollinators are not a limiting resource for these plants. Direct observation of pollinator movements, coupled with experimental manipulations of host plant inflorescence density, showed that Bombus pascuorum only rarely moves between inflorescences of the host and the parasite and therefore the presence of one plant is unlikely to be facilitating pollination in the other. This is the first detailed examination of pollination niche overlap in a plant parasite system and we suggest avenues for future research in relation to pollination and other shared interactions between parasitic plants and their hosts.

Animals↗
PubMed2005

Adaptive plasticity of floral display size in animal-pollinated plants.

Plants need not participate passively in their own mating, despite their immobility and reliance on pollen vectors. Instead, plants may respond to their recent pollination experience by adjusting the number of flowers that they display simultaneously. Such responsiveness could arise from the dependence of floral display size on the longevity of individual flowers, which varies with pollination rate in many plant species. By hand-pollinating some inflorescences, but not others, we demonstrate plasticity in display size of the orchid Satyrium longicauda. Pollination induced flower wilting, but did not affect the opening of new flowers, so that within a few days pollinated inflorescences displayed fewer flowers than unpollinated inflorescences. During subsequent exposure to intensive natural pollination, pollen removal and receipt increased proportionally with increasing display size, whereas pollen-removal failure and self-pollination accelerated. Such benefit-cost relations allow plants that adjust display size in response to the prevailing pollination rate to increase their attractiveness when pollinators are rare (large displays), or to limit mating costs when pollinators are abundant (small displays). Seen from this perspective, pollination-induced flower wilting serves the entire plant by allowing it to display the number of flowers that is appropriate for the current pollination environment.

Adaptation, Physiological↗
PubMed2002

Ecological and evolutionary conditions for fruit abortion to regulate pollinating seed-eaters and increase plant reproduction.

Coevolved mutualisms, such as those between senita cacti, yuccas, and their respective obligate pollinators, benefit both species involved in the interaction. However, in these pollination mutualisms the pollinator's larvae impose a cost on plants through consumption of developing seeds and fruit. The effects of pollinators on benefits and costs are expected to vary with the abundance of pollinators, because large population sizes result in more eggs and larval seed-eaters. Here, we develop the hypothesis that fruit abortion, which is common in yucca, senita, and plants in general, could in some cases have the function of limiting pollinator abundance and, thereby, increasing fruit production. Using a general steady-state model of fruit production and pollinator dynamics, we demonstrate that plants involved in pollinating seed-eater mutualisms can increase their fecundity by randomly aborting fruit. We show that the ecological conditions under which fruit abortion can improve plants fecundity are not unusual. They are best met when the plant is long-lived, the population dynamics of the pollinator are much faster than those of the plant, the loss of one fruit via abortion kills a larva that would have the expectation of destroying more than one fruit through its future egg laying as an adult moth, and the effects of fruit abortion on pollinator abundance are spatially localized. We then use the approach of adaptive dynamics to find conditions under which a fruit abortion strategy based on regulating the pollinator population could feasibly evolve in this type of plant-pollinator interaction.

Animals↗
PubMed2006

Characterizing ecological generalization in plant-pollination systems.

Despite the development of diversity indices in community ecology that incorporate both richness and evenness, pollination biologists commonly use only pollinator richness to estimate generalization. Similarly, while pollination biologists have stressed the utility of pollinator importance, incorporating both pollinator abundance and effectiveness, importance values have not been included in estimates of generalization in pollination systems. In this study, we estimated pollinator generalization for 17 plant species using Simpson's diversity index, which includes richness and evenness. We compared these estimates with estimates based on only pollinator richness, and compared diversity estimates calculated using importance data with those using only visitation data. We found that pollinator richness explains only 57-65% of the variation in diversity, and that, for most plant species, pollinator importance was determined primarily by differences in visitation rather than by differences in effectiveness. While simple richness may suffice for broad comparisons of pollinator generalization, measures that incorporate evenness will provide a much more accurate understanding of generalization. Although incorporating labor-intensive measurements of pollinator effectiveness are less necessary for broad surveys, effectiveness estimates will be important for detailed studies of some plant species. Unfortunately, at this point it is impossible to predict a priori which species these are.

Animals↗
PubMed2004

Flower color microevolution in wild radish: evolutionary response to pollinator-mediated selection.

Evolutionary ecologists are fundamentally interested in how species interactions affect evolutionary change. We tested the degree to which plant-pollinator interactions affect the frequency of flower color morphs of Raphanus sativus. Petal color in R. sativus is determined by two independently assorting loci, producing four petal colors (yellow, white, pink, and bronze). We assessed the impact of pollinator discrimination on changes in flower color variation by comparing the frequency of colors produced in the presence (open pollination) versus absence (null pollination) of pollinator discrimination. We also assessed the impact of postpollination and developmental effects on progeny colors using equal pollinations with all four color morphs. Our results from open pollinations found an overrepresentation of yellow progeny in the next generation, when compared with both null pollinations and cumulative ratios based on Hardy-Weinberg and linkage equilibria assumptions. When these results were combined with those from equal pollinations, the overrepresentation of yellow could be attributed to selection from pollinators. Yet, surveys in the field the following year found no flower color frequency changes in the next generation. These results illustrate that flower color microevolution can be driven by both pollinator discrimination and other nonpollinator selective forces acting during the seed-to-adult transition, countering selection imposed by pollinators.

Animals↗
PubMed2003

The pollination ecology of an assemblage of grassland asclepiads in South Africa.

The KwaZulu-Natal region of South Africa hosts a large diversity of asclepiads (Apocynaceae: Asclepiadoideae), many of which are endemic to the area. The asclepiads are of particular interest because of their characteristically highly evolved floral morphology. During 3 months of fieldwork (November 2000 to January 2001) the flower visitors and pollinators to an assemblage of nine asclepiads at an upland grassland site were studied. These observations were augmented by laboratory studies of flower morphology (including scanning electron microscopy) and flower colour (using a spectrometer). Two of the specialized pollination systems that were documented are new to the asclepiads: fruit chafer pollination and pompilid wasp pollination. The latter is almost unique in the angiosperms. Taxa possessing these specific pollination systems cluster together in multidimensional phenotype space, suggesting that there has been convergent evolution in response to similar selection to attract identical pollinators. Pollination niche breadth varied from the very specialized species, with only one pollinator, to the more generalized, with up to ten pollinators. Pollinator sharing by the specialized taxa does not appear to have resulted in niche differentiation in terms of the temporal or spatial dimensions, or with regards to placement of pollinaria. Nestedness analysis of the data set showed that there was predictability and structure to the pattern of plant-pollinator interactions, with generalist insects visiting specialized plants and vice versa. The research has shown that there is still much to be learned about plant-pollinator interactions in areas of high plant diversity such as South Africa.

Animals↗
PubMed2004

Heteromorphic incompatibility and efficiency of pollination in two distylous Pentanisia species (Rubiaceae).

BACKGROUND AND AIMS: Distyly has been hypothesized to promote cross-pollination by reducing intrafloral and geitonogamous self-pollination, and enhancing intermorph pollination. Distylous plants typically display both reciprocal herkogamy and a heteromorphic incompatibility system, which allows mating only between morphs. Distyly and its pollination consequences were examined in two Pentanisia species with long-tubed flowers which are pollinated almost exclusively by butterflies. METHODS: Anther and stigma heights were measured to quantify reciprocal herkogamy. The type of incompatibility system was determined by observing pollen tubes and seed production following controlled hand pollination. Pollen loads on pollinators and stigmas were also examined to assess the efficiency of intermorph pollen flow. KEY RESULTS: Pentanisia prunelloides and P. angustifolia exhibit reciprocal herkogamy and a host of ancillary dimorphisms, including pollen colour, exine sculpturing, stigmatic papilla shape and floral-tube pubescence. Controlled hand-pollinations revealed the presence of a strong heteromorphic incompatibility system in both species. The site of incompatibility differed between the morphs; intramorph pollen tubes were blocked in the style of the short-styled morph and on the stigmatic surface of the long-styled morph. Butterflies carried pollen from the short- and long-styled morphs primarily on their head and proboscis, respectively. Natural pollination resulted in a higher proportion of pollen transfer from long- to short-styled plants than vice versa. Nevertheless, fruit set did not differ between morphs. CONCLUSIONS: Both Pentanisia species are fully distylous. Reciprocal herkogamy results in pollen from the two morphs being carried on different locations on pollinators' bodies, which in turn promotes intermorph pollination. Intramorph pollination does not result in fertilization, because of an effective heteromorphic incompatibility system.

Flowers↗
PubMed2004

Influence of brood, vent screening, and time of year on honey bee (Hymenoptera: Apidae) pollination and fruit quality of greenhouse tomatoes.

Greenhouse tomatoes, Lycopersicon esculentum Miller (Solanaceae), are autogamous, but facilitated pollination results in increased fruit size and set. Previous research examining honey bee pollination in greenhouse tomato crops established that fruit quality resulting from honey bee visitation is often comparable to bumble bees (Bombus spp.) and significantly better than in flowers that receive no facilitated pollination. However, management alternatives have not been studied to improve tomato fruit quality when honey bees are the only pollination option available for the high-value greenhouse industry. We investigated whether the quantity of brood (eggs, larvae, and pupae) in a honey bee colony in the winter and screening on greenhouse vents in the summer would encourage honey bee foraging on tomato flowers. We also established the influence of time of year on the potential for honey bees to be effective pollinating agents. We constructed small honey bee colonies full of naive forager bees with either two frames of brood ("brood colonies") or two empty frames ("no-brood") and compared total fruit set and the number of tomato seeds resulting from fruit potentially visited by honey bees in each of these treatments to bagged flowers that received no facilitated pollination. There was no significant difference in the quality of fruit resulting from honey bees from "brood" and "no-brood" colonies. However, these fruits produced significantly more seeds than bagged flowers restricted from facilitated pollination. Honey bees from brood and no-brood colonies also resulted in 98% fruit set compared with 80% fruit set in bagged flowers that received no facilitated pollination. During the summer, the number of seeds per fruit did not differ significantly between unbagged flowers potentially visited by honey bees in screened greenhouses and unscreened greenhouses and bagged flowers that received no facilitated pollination. However, time of year did have a significant influence on the quality of fruit produced by honey bees compared with flowers that received no facilitated pollination, because no difference in seed number was observed between the treatments after mid-April. The results from this study demonstrate that the management of brood levels and vent screening cannot be used to improve the quality of fruit resulting from honey bee pollination and that honey bees can be a feasible greenhouse pollination alternative only during the winter.

Agriculture↗
PubMed2007

Importance of pollinators in changing landscapes for world crops.

The extent of our reliance on animal pollination for world crop production for human food has not previously been evaluated and the previous estimates for countries or continents have seldom used primary data. In this review, we expand the previous estimates using novel primary data from 200 countries and found that fruit, vegetable or seed production from 87 of the leading global food crops is dependent upon animal pollination, while 28 crops do not rely upon animal pollination. However, global production volumes give a contrasting perspective, since 60% of global production comes from crops that do not depend on animal pollination, 35% from crops that depend on pollinators, and 5% are unevaluated. Using all crops traded on the world market and setting aside crops that are solely passively self-pollinated, wind-pollinated or parthenocarpic, we then evaluated the level of dependence on animal-mediated pollination for crops that are directly consumed by humans. We found that pollinators are essential for 13 crops, production is highly pollinator dependent for 30, moderately for 27, slightly for 21, unimportant for 7, and is of unknown significance for the remaining 9. We further evaluated whether local and landscape-wide management for natural pollination services could help to sustain crop diversity and production. Case studies for nine crops on four continents revealed that agricultural intensification jeopardizes wild bee communities and their stabilizing effect on pollination services at the landscape scale.

Agriculture↗
PubMed2006

Functional diversity of plant-pollinator interaction webs enhances the persistence of plant communities.

Pollination is exclusively or mainly animal mediated for 70% to 90% of angiosperm species. Thus, pollinators provide an essential ecosystem service to humankind. However, the impact of human-induced biodiversity loss on the functioning of plant-pollinator interactions has not been tested experimentally. To understand how plant communities respond to diversity changes in their pollinating fauna, we manipulated the functional diversity of both plants and pollinators under natural conditions. Increasing the functional diversity of both plants and pollinators led to the recruitment of more diverse plant communities. After two years the plant communities pollinated by the most functionally diverse pollinator assemblage contained about 50% more plant species than did plant communities pollinated by less-diverse pollinator assemblages. Moreover, the positive effect of functional diversity was explained by a complementarity between functional groups of pollinators and plants. Thus, the functional diversity of pollination networks may be critical to ecosystem sustainability.

Animals↗
PubMed1999

Wind pollination and reproductive assurance in Linanthus parviflorus (Polemoniaceae), a self-incompatible annual.

Wind pollination was experimentally demonstrated in Linanthus parviflorus (Polemoniaceae), a predominantly beefly-pollinated, self-incompatible annual. Seed set in plants enclosed in mesh tents that excluded pollinators but allowed airborne pollen flow provided evidence for wind pollination, and the extent of seed set due to wind pollination was compared to that in open-pollinated controls and pollen-supplemented treatments. Additional controls were included to test for possible confounding effects of the mesh tent. Mean seed number in open-pollinated plants was 72.8-81.1% of that in pollen-supplemented plants, while wind pollination alone produced 49.5-52.2%, a smaller but substantial proportion of seed set with pollen supplementation. Further evidence for wind pollination was found in a comparison of sites differing in the extent of wind exposure in two populations of L. parviflorus. Airborne pollen counts were higher in exposed sites than in protected sites, and the difference was marginally significant. Seed set was significantly pollen limited in protected sites, but not in exposed sites. Taken together, the data suggest that wind pollination provides some reproductive assurance in this obligately outcrossing species. Wind pollination is hypothesized to represent an alternative to selfing as an evolutionary solution to the problem of temporal or spatial variation in pollination visitation.

Journal Article↗
PubMed2000

Pollination biology of two chiropterophilous agaves in Arizona.

I studied the pollination biology of two closely related species of agave, Agave palmeri and A. chrysantha (Agavaceae), which exhibit several chiropterophilous (bat-pollinated) traits. Floral studies, floral visitor observations, and pollination studies were conducted over four summers at six different sites to examine floral traits and determine the relative importance of diurnal vs. nocturnal pollinators. Agave chrysantha appears to have developed minor shifts in several floral characters that enhance diurnal pollination. Although floral shifts towards diurnal pollination were fewer in A. palmeri, stigmas were diurnally receptive and copious floral rewards were available in the morning, indicating that some adaptations exist to allow for multiple pollinators. Differences in fruit and seed set between naturally day- and night-pollinated umbels for both species were either not significant or significantly higher in day-pollinated plants. Bats were not important pollinators of A. chrysantha, and the mutualistic relationship between A. palmeri and the lesser long-nosed bat was found to be asymmetric. "Bat-adapted" floral traits appear to be flexible enough to respond to the climatic and pollinator unpredictability experienced by agaves at the northern edge of their distribution. This variability may be a more important factor affecting evolution of floral characters than a particular pollinator.

Journal Article↗
PubMed2003

[Study on the pollination characteristic of Cistanche deserticola].

OBJECTIVE: To study the Pollination Characteristic of C. deserticola. METHOD: Four pollination methods were used, cross pollination coming different plant, cross pollination in one plant, wind pollination and no-pollination. RESULT: Cross pollinations coming different plant are fructiferous. The average fructication rate of cross pollination coming different plant is 94.1%; the average fructication rate of cross pollination in one plant is 52.2%; The seed qulitity of cross pollination coming different plant is better than the cross pollination in one plant. CONCLUSION: Cross pollinations coming different plant have a high quantity and quality of seeds of C. deserticola.

Cistanche↗
PubMed2005

The effect of pollination on floral fragrance in thistles.

We investigated postpollination changes in fragrance composition and emission rates, as well as pollinator discrimination in hand-pollinated flower heads of two thistle species: Canada thistle (Cirsium arvense) and sandhill thistle (C. repandum). Following pollination, neither species emitted any novel compounds that could function as repellents. Scent emission rates declined in pollinated plants of both species by approximately 89% within 48 hr. This decline was evident in all 13 scent components of C. arvense. Apis mellifera, the dominant pollinator in the study population of C. arvense, was nearly three times more likely to visit an unpollinated rather than a pollinated flower head. A more complex pattern was observed for C. repandum, whose scent comprised 42 compounds. Quantities of aromatic and sesquiterpenoid volatiles declined after pollination, whereas two classes of scent compounds, fatty acid derivatives and monoterperpenoids, continued to be emitted. In C. repandum, discrimination against pollinated flower heads by Papilio palamedes (its primary pollinator) was not as marked. Unpollinated control plants of both species maintained moderate levels of scent production throughout this experiment, demonstrating that senescence and floral advertisement may be delayed until pollination has occurred. We expect postpollination changes in floral scent contribute to communication between plants with generalized pollinator spectra and their floral visitors. This study provides the first field study of such a phenomenon outside of orchids.

Animals↗
PubMed2005

Buzziness as usual? Questioning the global pollination crisis.

Concerns have been raised that invertebrate pollinators of crops and wild plants are in decline as a result of modern agricultural practices, habitat degradation, and introduced pests and diseases. This has led to demands for a response by land managers, conservationists and political decision makers to the impending 'global pollinator crisis'. In questioning this crisis, it becomes apparent that perceptions of a pollinator crisis are driven mainly by reported declines of crop-pollinating honeybees in North America, and bumblebees and butterflies in Europe, whereas native pollinator communities elsewhere show mixed responses to environmental change. Additionally, few staple food crops depend on pollinator services, and most crops that do are grown at small scales in diversified agro-ecosystems that are likely to support healthy pollinator communities, or in highly managed systems that are largely independent of wild pollinators. Consequently, justifying conservation action on the basis of deteriorating pollinator services might be misplaced. Nevertheless, existing initiatives to monitor pollinators are well founded, given the uncertainty about the dynamics of pollinator populations.

Journal Article↗
PubMed2004

Floral traits and pollination systems in the Caatinga, a Brazilian tropical dry forest.

BACKGROUND AND AIMS: Pollination is a critical stage in plant reproduction and thus in the maintenance and evolution of species and communities. The Caatinga is the fourth largest ecosystem in Brazil, but despite its great extent and its importance few studies providing ecological information are available, with a notable lack of work focusing on pollination biology. Here, general data are presented regarding the frequency of pollination systems within Caatinga communities, with the aim of characterizing patterns related to floral attributes in order to make possible comparisons with data for plant communities in other tropical areas, and to test ideas about the utility of syndromes. This paper also intends to provide a reference point for further studies on pollination ecology in this threatened ecosystem. METHODS: The floral traits and the pollination systems of 147 species were analysed in three areas of Caatinga vegetation in northeastern Brazil, and compared with world-wide studies focusing on the same subject. For each species, floral attributes were recorded as form, size, colour, rewards and pollination units. The species were grouped into 12 guilds according to the main pollinator vector. Analyses of the frequencies of the floral traits and pollination systems were undertaken. KEY RESULTS: Nectar and pollen were the most common floral resources and insect pollination was the most frequent, occurring in 69.9 % of the studied species. Of the entomophilous species, 61.7 % were considered to be melittophilous (43.1 % of the total). Vertebrate pollination occurred in 28.1 % of the species (ornithophily in 15.0 % and chiropterophily in 13.1 %), and anemophily was recorded in only 2.0 %. CONCLUSIONS: The results indicated that the pollination systems in Caatinga, despite climatic restrictions, are diversified, with a low percentage of generalist flowers, and similar to other tropical dry and wet forest communities, including those with high rainfall levels.

Animals↗
PubMed2001

Pollination mode in fig wasps: the predictive power of correlated traits.

The over 700 species of Ficus are thought to have co-speciated with their obligate pollinators (family Agaonidae). Some of these wasp species pollinate figs actively, while others are passive pollinators. Based on direct observations of mode of pollination in 88 species, we show that mode of pollination can confidently be predicted from fig traits only (anther-to-ovule ratio) or from wasp traits only (presence of coxal combs). The presence of pollen pockets is not a predictor of mode of pollination. Data, direct and indirect, on 142 species, demonstrate numerous cases of the loss of active pollination and suggest one or few origins of active pollination. Hence, active pollination, an impressive example of the sophisticated traits that may result from mutualistic coevolution, depends on selective forces that can be overcome in some species, allowing reversions. Despite frequent loss, active pollination remains the predominant mode of pollination in Ficus.

Animals↗
PubMed2003

Contrasting flowering phenology and species richness in abiotically and biotically pollinated angiosperms.

Biotic pollination is thought to correlate with increased interspecific competition for pollination among plants and a higher speciation rate. In this study we compared patterns of flowering phenology and species richness between abiotically (wind) and biotically pollinated plants, using phylogenetically independent contrasts. We compiled phenological data from eight local seasonal floras, in which we found geographically overlapping sister clades. Of 65 documented origins of wind pollination, we were able to use up to 17 independent contrasts. In contrast to previous studies we found no difference in global species richness between wind- and biotically pollinated sister clades. Regarding phenology, we found wider phenological spread in biotically pollinated clades, earlier flowering onset in wind-pollinated trees, but no difference in duration of flowering between pollination modes. These results corroborate previous views that niche space is more constrained for wind-pollinated species, and that niche partitioning is less important between wind-pollinated plants compared to plants pollinated by animals.

Biodiversity↗