Pollen Delivery Research Articles

Predicted thresholds for natural vegetation cover to safeguard pollinator services in agricultural landscapes

The conversion of natural vegetation into cultivated land can cause pollinator declines and thereby degrade pollination services to crops and wildflowers. The effect of landscape composition on pollinator abundance is well established, but its impact on pollination intensity and crop yield is not fully resolved. We therefore studied pollination of two crops in India, brinjal (Solanum melongena) and mustard (Brassica nigra), along a landscape-scale gradient in habitat transformation from forest-dominated natural vegetation to intensive cultivation. We quantified the pollination requirements (pollen receipt-seed set relationships) of the crops and the levels of pollen delivery by their principal pollinators, bees. Combining these with field surveys of pollinator abundance, we modelled the levels of pollination service to fields along the landscape gradient. Projected pollination services declined as the area occupied by natural vegetation decreased. We identified thresholds at which bee pollination no longer supported maximum seed set, which were landscapes with approximately one quarter (27 %) of nearby natural vegetation for brinjal fields and one fifth (18 %) for mustard. Our findings indicate that preserving or restoring the cover of natural habitats above these minimum thresholds could be a valuable strategy for maintaining pollinator abundance and safeguarding yield in these bee-pollinated crops.

The critical role of honeyeaters in the pollination of the catspaw Anigozanthos humilis (Haemodoraceae)

The pollination biology of Anigozanthos humilis (Haemodoraceae) was studied within a Banksia woodland reserve using a combination of field techniques and genetic analysis. Motion-triggered cameras were deployed on 25 flowering plants to identify visitors to flowers, quantify visitation rates and assess visitor behaviour. Entire A. humilis plants were caged to exclude potential floral visitors with six treatments: (i) bird and honey possum exclusion, allowing access by insects; (ii) bird and insect exclusion, allowing access by honey possums; (iii) total animal exclusion; (iv) open, allowing access by birds, insects and honey possums; (v) hand-pollination with cross-pollen; and (vi) hand-pollination with self-pollen. Open pollinated seed were genotyped to assess mating system parameters including outcrossing rate. From 23424 h of surveillance with camera traps, 109 visits were recorded, 106 (97%) of which were western spinebills (Acanthorhynchus superciliosus), with three visits by brown honeyeaters (Lichmera indistincta). We recorded an average of 8 (±4) visits per plant, equivalent to one visit every eleven days over the 2016 flowering season (mean = 63 days). Mean seed set per fruit was negligible (0.2–0.3 seed per fruit) for all pollination treatments except open- and hand-pollination with cross pollen. Mean seed set per fruit for hand cross-pollinated flowers (37.1 seed per fruit) was 37 times that of open pollinated flowers (1.0 seed per fruit). Outcrossing rate estimates were not significantly different to one. Our results indicate that at least for the study population and season, A. humilis was largely dependent on western spinebills for delivery of outcross pollen and resulting seed set, but visitation rates were low and pollen limitation was severe. Given the known sensitivity of western spinebills to habitat fragmentation, our results suggest flow on effects that may negatively impact on reproduction, and means that A. humilis may be particularly vulnerable to environmental changes that impact on bird pollinators.

Dominance of cropland reduces the pollen deposition from bumble bees

Intensive agricultural landscapes can be hostile for bees due to a lack of floral and nesting resources, and due to management-related stress such as pesticide use and soil tillage. This threatens the pollination services that bees deliver to insect-pollinated crops. We studied the effects of farming intensity (organic vs. conventional, number of insecticide applications) and availability of semi-natural habitats at the field and landscape scale on pollinator visits and pollen delivery to pumpkin in Germany. We found that wild bumble bees were the key pollinators of pumpkin in terms of pollen delivery, despite fivefold higher visitation frequency of honey bees. Critically, we observed that the area of cropland had stronger effects on bees’ pollen deposition than the area of seminatural habitats. Specifically, a 10% increase of the proportion of cropland reduced pollen delivery by 7%. Pumpkin provides a striking example for a key role of wild pollinators in crop pollination even at high numerical dominance of honey bees. In addition, our findings suggest that habitat conversion to agricultural land is a driver of deteriorating pollination. This underlines the importance to maintain sufficient areas of non-crop habitats in agricultural landscapes.

Shared traits make flies and bees effective pollinators of oilseed rape (Brassica napus L.)

One of the major aims of pollination ecology has been to understand the role and relative importance of different pollinator species in both natural and agricultural systems. This study explores how the quantity of pollen delivered in a single visit to a stigma (SVD) differs across insect species from a wide range of taxa (Orders: Hymenoptera, Diptera and Coleoptera) and assesses the morphological and behavioural traits that lead to differences in pollen delivery. We used oilseed rape (OSR) (Brassica napus L.), an economically important crop with open self-fertile flowers, as a test system. Behavioural traits and SVD were measured in the field for individuals of all frequent flower-visiting species of OSR. Individuals were collected and morphological traits were measured in the laboratory. The quantities of free pollen on different body parts of flower visitors, or ‘pollen load’, were also measured. Behavioural and morphological traits were then assessed as predictors of SVD. The individuals that delivered most pollen were (in order of greatest median number of pollen grains delivered): bumblebees (Bombus spp.), mining bees (Andrenidae) and honeybees (Apis mellifera). However, all but one family of flies tested delivered a significantly greater median number of pollen grains than the control, and most delivered more than sweat bees (Halictidae). Behavioural and morphological traits were important in determining pollen delivery, with greater body length, hairiness and visit duration all resulting in greater SVD. Pollen load was measured for a proportion of individuals and we found that for momentary flower visits, a greater quantity of pollen on the head of the flower visitor was linked to a greater SVD. This study demonstrates that, while bees are important pollinators in this system, many fly taxa are also effective at delivering pollen and this is linked to morphological and behavioural traits found in both groups.

The most effective pollinator principle applies to new invasive pollinators.

G. L. Stebbins' most effective pollinator principle states that when pollinators are not limiting, plants are expected to specialize and adapt to the most abundant and effective pollinator species available. In this study, we quantify the effectiveness of bees, hummingbirds and hawkmoths in a Chilean population of Erythranthe lutea (Phrymaceae), and examine whether flower traits are subject to pollinator-mediated selection by the most effective pollinator species during two consecutive years. Unlike most species in the pollinator community, the visitation rate of the recently arrived Bombus terrestris did not change substantially between years, which together with its high and stable pollen delivery to flower stigmas made this species the most important in the pollinator assemblage, followed by the solitary bee Centris nigerrima Flower traits were under significant selection in the direction expected for short-tongue bees, suggesting that E. lutea is in the initial steps of adaptation to the highly effective exotic bumblebee. Our results illustrate the applicability of Stebbins' principle for new invasive pollinators, and stress their importance in driving flower adaptation of native plant species, a critical issue in the face of biotic exchange and homogenization.

Exotic flies maintain pollination services as native pollinators decline with agricultural expansion

Abstract Globally, conversion of natural habitat to agricultural land is a primary driver of declines in critical ecosystem services, including pollination. However, exotic species are often well‐adapted to human‐modified environments and could compensate for ecosystem services that are lost when native species decline. We measured pollination services (pollen delivery to stigma) provided by wild insects to a mass flowering crop, pak choi Brassica rapa at 12 sites across a gradient of increasing agricultural land use (agricultural expansion) in New Zealand. We found that pollination services increased as the proportion of agricultural land in the surrounding landscape increased; pollination from exotic species exceeded the loss of pollination from native species. However, pollination service delivery became increasingly dominated by a few exotic fly species that were active throughout the day, compared to native species, which had more constrained activity patterns. Synthesis and applications. The best way to ensure continued sufficient crop pollination is to protect and restore diverse natural habitats on or around farms, as species‐rich pollinator communities are relatively resilient to further environmental change. However, we show that where human‐driven disturbance has caused loss of native pollinator species, exotic pollinators can maintain sufficient pollination. Therefore, in areas where native species loss cannot easily be reversed, decisions about pesticide use and habitat provision that foster populations of beneficial exotic species are likely to maintain pollination service delivery, at least in the short term. This highlights the need for land managers to identify the pollinator communities that are present on their farms, whether native or exotic, and make decisions to support these important communities accordingly.

How shrub encroachment under climate change could threaten pollination services for alpine wildflowers: A case study using the alpine skypilot, Polemonium viscosum.

Under climate change, shrubs encroaching into high altitude plant communities disrupt ecosystem processes. Yet effects of encroachment on pollination mutualisms are poorly understood. Here, we probe potential fitness impacts of interference from encroaching Salix (willows) on pollination quality of the alpine skypilot, Polemonium viscosum. Overlap in flowering time of Salix and Polemonium is a precondition for interference and was surveyed in four extant and 25 historic contact zones. Pollinator sharing was ascertained from observations of willow pollen on bumble bees visiting Polemonium flowers and on Polemonium pistils. We probed fitness effects of pollinator sharing by measuring the correlation between Salix pollen contamination and seed set in naturally pollinated Polemonium. To ascertain whether Salix interference occurred during or after pollination, we compared seed set under natural pollination, conspecific pollen addition, and Salix pollen addition. In current and past contact zones Polemonium and Salix overlapped in flowering time. After accounting for variance in flowering date due to latitude, Salix and Polemonium showed similar advances in flowering under warmer summers. This trend supports the idea that sensitivity to temperature promotes reproductive synchrony in both species. Salix pollen is carried by bumble bees when visiting Polemonium flowers and accounts for up to 25% of the grains on Polemonium pistils. Salix contamination correlates with reduced seed set in nature and when applied experimentally. Postpollination processes likely mediate these deleterious effects as seed set in nature was not limited by pollen delivery. Synthesis: As willows move higher with climate change, we predict that they will drive postpollination interference, reducing the fitness benefits of pollinator visitation for Polemonium and selecting for traits that reduce pollinator sharing.

How efficient is the Asian honey bee, Apis cerana in pollinating mustard, Brassica campestris var. toria? Pollination behavior, pollinator efficiency, pollinator requirements and impact of pollination

Brassica campestris var. toria (mustard) is an insect attractive crop with ample pollen and nectar, so is predominantly insect pollinated. Rate of pollinator visitation, delivery of pollen to stigmas and seed-set are various factors to assess the importance of a pollinator. The Asian honey bee, Apis cerana was found to occupy a share of 39.33% of all the flower visitors to mustard in natural habitat. Pollination behavior in terms of peak activity, flowers handled per unit time, time spent per flower and time spent in search of flowers were studied separately for both pollen and nectar foragers. Pollination efficiency of A. cerana in mustard, measured by means of seed set per flower at defined number of bee visits was 0.41 and 2.44 visits per flower required for optimum seed set. Impact of A. cerana bee pollination on mustard seed production was studied in two different villages for two years. An increase of 20.8% in siliqua/panicle, 9.4% of seeds/siliqua and 17.1% in seed yield were noticed in planned honey bee pollinated mustard with respect to those grown in natural habitats. For assessing the requirement of pollinators to pollinate a one ha area of mustard, flower availability and the flower handling time of both the pollen and nectar forager are taken into consideration. A forager was estimated to pollinate 10,146 flowers a day, but mustard needs 2.44 visits for optimum seed set. Thus, 1,530 bee foragers or 2.2 colonies are needed to effectively pollinate a 1 ha mustard crop at peak flowering.

Stigmatic pollen delivery by flies and bees: Methods comparing multiple species within a pollinator community

A wide variety of insect species provide pollination services in natural and agricultural ecosystems, but in order to quantify their contribution it is necessary to evaluate their effectiveness. An important component of this is to determine their ability to transfer pollen to stigmas which typically requires observers to wait for insects to visit focal flowers (static approach); a time-consuming process not amenable to obtaining measures for pollinating species of low local abundance. An alternative method (active approach) is to detach test flowers and present them to the targeted flower visitor. This offers a number of advantages (e.g. increased speed and flexibility), but may alter insect behaviour. We compared pollen deposition within flowering onion crops using three bee (Apoidea) and three fly (Diptera) species. The two approaches resulted in similar numbers of pollen grains being deposited onto stigmas for each insect species, thereby supporting the validity of the active as an alternative to the static approach in our test crop. The ability to rapidly assess stigmatic pollen deposition of a broad range of insects using the active approach can greatly assist assessments of pollinator contribution within plant pollinator assemblages.

Specialist pollinators deplete pollen in the spring ephemeral wildflower Claytonia virginica.

Pollinators that collect pollen – and specifically, pollen‐specialist bees – are often considered to be the best pollinators of a (host) plant. Although pollen collectors and pollen specialists often benefit host plants, especially in the pollen that they deliver (their pollination “effectiveness”), they can also exact substantial costs because they are motivated to collect as much pollen as possible, reducing the proportion of pollen removed that is subsequently delivered to stigmas (their pollination “efficiency”). From the plant perspective, pollen grains that do not pollinate conspecific stigmas are “wasted”, and potentially costly. We measured costs and benefits of nectar‐collecting, pollen‐collecting, and pollen‐specialist pollinator visitation to the spring ephemeral Claytonia virginica. Visits by the pollen‐specialist bee Andrena erigeniae depleted pollen quickly and thoroughly. Although all pollinators delivered roughly the same number of grains, the pollen specialist contributed most to C. virginica pollen delivery because of high visitation rates. However, the pollen specialist also removed a large number of grains; this removal may be especially costly because it resulted in the depletion of pollen grains in C. virginica populations. While C. virginica appears to rely on pollen transfer by the pollen specialist in these populations, nectar‐collecting visitors could provide the same benefit at a lower cost if their visitation rates increased. Pollen depletion affects a pollinator's value to plants, but is frequently overlooked. If they lower the effectiveness of future floral visitors, visits by A. erigeniae females to C. virginica may be more detrimental than beneficial compared to other pollinators and may, in some circumstances, reduce plant fitness rather than increase it. Therefore, A. erigeniae and C. virginica may vary in their degree of mutualism depending on the ecological context.

Invasion status and phylogenetic relatedness predict cost of heterospecific pollen receipt: implications for native biodiversity decline

SummaryUnderstanding the mechanisms by which invasive species affect native plants is a central challenge. Invasive plants have been shown to reduce pollinator visitation to natives and increase pollen quantity limitation. However, visitation and conspecific pollen delivery are the only two components of the pollination process; post‐pollination interactions on the stigma (heterospecific pollen [HP] receipt) could intensify pre‐pollination responses to invasion.Here, we used meta‐analysis to test the hypotheses that invasive plants are more detrimental asHPdonors than natives ones and thatHPdonors that are closely related to the recipients have stronger effects on fruit and seed production compared to distantly related ones.InvasiveHPdonors reduced fruit and seed production of recipients to a greater degree than native ones, and this was more intense forHPdonors closely related to natives. Related donors were more detrimental overall.Synthesis. These results suggest that the total effect of invasive plants on native plant reproductive success could be greater than what is inferred from visitation and conspecific pollen transfer alone. Furthermore, these results indicate that invasive species can reduce reproductive success of native species even if pollinator visitation rates remain unaltered. Thus, we highlight the need to evaluate pre‐ and post‐pollination processes in order to fully understand the potential effects of invasive species on the reproductive success and maintenance of native plant populations.

Exploring the source-to-sink residence time of terrestrial pollen deposited offshore Westland, New Zealand

The occurrence of terrestrial palynomorphs in Quaternary marine sedimentary sequences allows for direct land–sea correlations and provides a means for transferring Marine Isotope Stage chronologies to terrestrial records that extend beyond the range of radiocarbon dating. Both of these important applications require an implicit assumption that the lag between pollen release and final deposition on the seafloor – here referred to as source-to-sink residence time – is negligible in relation to the chronological resolution of the sedimentary sequence. Most studies implicitly assume zero lag, and where studies do take palynomorph residence time into account, its magnitude is rarely quantified. In Westland, New Zealand, fluvial transport is the main source of delivery of terrestrial pollen offshore to the adjacent East Tasman Sea. We radiocarbon-dated organic matter carried and deposited by contemporary Westland rivers that drain catchments with varying degrees of disturbance. The ages obtained ranged widely from essentially modern (i.e., −57±22calyr BP) to 3583±188calyr BP, suggesting that precisely constraining the residence time in this region is unlikely to be achieved. We also compared the timing of four palynomorph events characterising Westland's late Pleistocene, along with the well-dated Kawakawa/Oruanui Tephra (KOT), between marine core MD06-2991 and four terrestrial records from Westland. Critically, all palynomorph events and the KOT are chronologically indistinguishable with respect to the independently dated marine and terrestrial records, supporting the general principle of transferring the marine chronology onto the terrestrial records in this setting. In other regions, particularly those lacking the high soil production and erosion rates that characterise Westland, we suggest that similar tests of marine residence time should be conducted before assumptions of zero or negligible lag are invoked.

Floral symmetry affects bumblebee approach consistency in artificial flowers

Bilateral symmetry has evolved from radial symmetry in several floral lineages, and multiple hypotheses have been proposed to account for the success of this floral plan. One of these hypotheses posits that bilateral symmetry (or, more generally, a reduced number of planes of floral symmetry) allows for more precise pollen placement on pollinators. Greater precision would maximize the efficacy of pollen transfer to conspecifics, while minimizing reproductive interference amongst plant species. Despite the intuitiveness of this hypothesis, it has little experimental support. Here, we tested whether a reduction in the number of floral planes of symmetry (as in the transition from radial to bilateral symmetry) increases the potential precision of pollen placement. We analyzed video recordings of bumblebees (Bombus impatiens) visiting artificial flowers to determine whether consistency in flower entry angle differed between radial (round) and disymmetric (rectangular) “flowers”. We observed more consistent entry angles for disymmetric flowers than for radial flowers, with entry angles to radial flowers 43% more variable on average (standard deviations of 30° vs. 21°). Bees trained on flowers with an intermediate (square) morphology exhibited a slight, non-significant preference for radial symmetry over disymmetry. Our results show that disymmetry—an evolutionarily intermediate form of floral symmetry—has the potential to increase pollen transfer to conspecific stigmas, relative to radial symmetry. Thus, evolutionary reduction in the number of planes of floral symmetry likely provides benefits in terms of pollen delivery, as suggested by the pollen-placement-accuracy hypothesis. These findings offer insight into the evolution of floral symmetry.

Vegetation dynamics from a coastal peatland: insights from combined plant macrofossil and pollen data

ABSTRACTThis paper reports the results of plant‐macrofossil investigations from a peat layer buried within coastal alluvium at the Caburn, a site adjacent to the English chalkland. The data collected are compared against a published mid‐Holocene pollen sequence with the macrofossil record providing greater taxonomic resolution and establishing a local presence for many taxa. Alnus glutinosa pollen is abundant and Alnus macrofossils are recorded continuously over a c. 3000 cal year period. Fluctuations in the number of Alnus propagules and the presence of seeds of light‐demanding herbaceous plants suggest that regeneration occurred at a local scale, a process which is likely to have been promoted by a rising water table and sediment consolidation. Taxus baccata macrofossils were also recovered, indicating that the high pollen values previously reported may be the result of yew being present within the wetland area. The Tilia macrofossils establish the presence nearby of T. cordata, T. × europaea and T. platyphyllos. High pollen values for Quercus, Tilia and Alnus coincide with the occurrence of their anthers. Deposition within inflorescences is therefore likely to have been an important mode of pollen delivery. The usefulness of both techniques in studies that utilize peats derived from fen carr vegetation are discussed.

Sexual Dimorphism in the Flowers of <I>Aegiphila odontophylla</I> (Lamiaceae)

Abstract Little is known about the sexuality of the woody Neotropical genus Aegiphila. For a long time species of Aegiphila were thought to be heterostylous, but more recently it has been reported that a few species are dioecious and suggested that likely most Aegiphila are functionally dioecious. In this note, dioecy is confirmed in Aegiphila odontophylla from live plants in the Talamanca mountains in Costa Rica. Further, comparison of total flower size revealed that male and female reproductive structures are displayed at similar heights, likely resulting in accurate pollen uptake and delivery by pollinators. The length of the corolla tube as an estimate of flower showiness on the other hand was significantly different between male and female individuals. Male individuals had longer corolla tubes, suggesting a possible role for sexual selection in the evolution of floral dimorphism in this species.

Morphological and Nectar Traits in Echeveria Rosea Lindley (Crassulaceae) Linked to Hummingbird Pollination in Central Veracruz, Mexico

Abstract: Flowers have evolved suites of traits that are associated with the attraction, reward and utilization of particular pollinator types. Specialization on particular pollinator functional group results in a particular combination of floral traits with consequences on plant fitness through efficient pollen delivery and pollen receipt at the population and species level. The aim of this study was to describe the floral morphology, nectar production patterns, floral visitors and natural fruit set in a population of Echeveria rosea Lindley (Crassulaceae) in central Veracruz, Mexico. The floral traits of Echeveria rosea correspond to the typical hummingbird pollination syndrome. The diurnal pattern of accumulated nectar (volume and amount of sugar) produced by the species corresponds to values reported for other hummingbird-pollinated species. Based on observations of foraging behavior, the Garnet-throated Hummingbird (Lamprolaima rhami) seems to be a more effective pollinator than the White-eared Hummi...

Pollen limitation and reduced reproductive success are associated with local genetic effects in Prunus virginiana, a widely distributed self-incompatible shrub

A vast quantity of empirical evidence suggests that insufficient quantity or quality of pollen may lead to a reduction in fruit set, in particular for self-incompatible species. This study uses an integrative approach that combines field research with marker gene analysis to understand the factors affecting reproductive success in a widely distributed self-incompatible species, Prunus virginiana (Rosaceae). Twelve patches of P. virginiana distributed within three populations that differed in degree of disturbance were examined. Two of the sites were small (7-35 km(2)) remnants of forest in an intensively used agricultural landscape, while the third was continuous (350 km(2)) and less disturbed. Field studies (natural and hand cross-pollinations) were combined with marker gene analyses (microsatellites and S-locus) in order to explore potential factors affecting pollen delivery and consequently reproductive success at landscape (between populations) and fine scales (within populations). Reductions in reproductive output were found in the two fragments compared with the continuous population, and suggest that pollen is an important factor limiting fruit production. Genetic analyses carried out in one of the fragments and in the continuous site suggest that even though S-allele diversity is high in both populations, the fragment exhibits an increase in biparental inbreeding and correlated paternity. The increase in biparental inbreeding in the fragment is potentially attributable to variation in the density of individuals and/or the spatial distribution of genotypes among populations, both of which could alter mating dynamics. By using a novel integrative approach, this study shows that even though P. virginiana is a widespread species, fragmented populations can experience significant reductions in fruit set and pollen limitation in the field. Deatiled examination of one fragmented population suggests that these linitations may be explained by an increase in biparental inbreeding, correlated paternity and fine-scale genetic structure. The consistency of the field and fine-scale genetic analyses, and the consistency of the results within patches and across years, suggest that these are important processes driving pollen limitation in the fragment.

Pollen limitation, fruit abortion, and autonomous selfing in three populations of the perennial herb Ruellia nudiflora

AbstractMultiple factors determine plant reproductive success and their influence may vary spatially. This study addresses several factors influencing female reproductive success in three populations of Ruellia nudiflora, specifically we: (i) determine if fruit set is pollen‐limited and if pollinator visitation rates are related to this condition; (ii) estimate fruit set via autonomous self‐pollination (AS) and relate it to the magnitude of herkogamy; and (iii) evaluate if fruit abortion is a post‐pollination mechanism that determines the magnitude of pollen limitation. At each site we marked 35 plants, grouped as: unmanipulated control (C) plants subjected to open pollination, plants manually cross‐pollinated (MP), and plants excluded from pollinators and only able to self‐pollinate autonomously (AS). Fruit set was greater for MP relative to C plants providing evidence for pollen limitation, while a tendency was observed for lower fruit abortion of MP relative to C plants suggesting that fruit set is influenced not only by pollen delivery per se, but also by subsequent abortion. In addition, although pollinator visits varied significantly among populations, the magnitude of pollen limitation did not, suggesting that pollinator activity was not relevant in determining pollen limitation. Finally, fruit set tended to decrease with the degree of herkogamy for AS plants, but this result was inconclusive. These findings have contributed to identify which factors influence reproductive success in populations of R. nudiflora, with potentially relevant implications for population genetic structure and mating system evolution of this species.

Pollination studies in large cardamom ( Amomum subulatum Roxb.) of Sikkim Himalayan region of India

Pollination studies in large cardamom were carried out at the research farm of ICAR Sikkim Centre, Gangtok, Sikkim, India during 2009–2010 to assess the effectiveness and efficiency of pollinators. Polleniferous flowers (65,890 ± 11,346.5 pollen/anther) of large cardamom produce spherical, large (108.64 μm × 96.32 μm) and echinate pollen with high pollen/ovule ratio (585.2 ± 134.8). Native bumblebee ( Bombus braviceps Smith.), a nectar forager, was identified as the most effective pollinator in terms of pollination potential index score (0.88), pollen removal (55.39%) and deposition rate (4.5%), pollination efficiency and pollen delivery mechanism whereas honey bee acted as a pollen robber. Flowers appeared to be generalized; however, functional specialization was exhibited indicating that only bumblebee is adaptable for pollination moreover, pollination mechanism was an indicative of “pollination syndrome”.

Global growth and stability of agricultural yield decrease with pollinator dependence

Human welfare depends on the amount and stability of agricultural production, as determined by crop yield and cultivated area. Yield increases asymptotically with the resources provided by farmers' inputs and environmentally sensitive ecosystem services. Declining yield growth with increased inputs prompts conversion of more land to cultivation, but at the risk of eroding ecosystem services. To explore the interdependence of agricultural production and its stability on ecosystem services, we present and test a general graphical model, based on Jensen's inequality, of yield-resource relations and consider implications for land conversion. For the case of animal pollination as a resource influencing crop yield, this model predicts that incomplete and variable pollen delivery reduces yield mean and stability (inverse of variability) more for crops with greater dependence on pollinators. Data collected by the Food and Agriculture Organization of the United Nations during 1961-2008 support these predictions. Specifically, crops with greater pollinator dependence had lower mean and stability in relative yield and yield growth, despite global yield increases for most crops. Lower yield growth was compensated by increased land cultivation to enhance production of pollinator-dependent crops. Area stability also decreased with pollinator dependence, as it correlated positively with yield stability among crops. These results reveal that pollen limitation hinders yield growth of pollinator-dependent crops, decreasing temporal stability of global agricultural production, while promoting compensatory land conversion to agriculture. Although we examined crop pollination, our model applies to other ecosystem services for which the benefits to human welfare decelerate as the maximum is approached.