Generalist Pollinators Research Articles

Extreme divergence in floral scent among woodland star species (Lithophragma spp.) pollinated by floral parasites

A current challenge in coevolutionary biology is to understand how suites of traits vary as coevolving lineages diverge. Floral scent is often a complex, variable trait that attracts a suite of generalized pollinators, but may be highly specific in plants specialized on attracting coevolved pollinating floral parasites. In this study, floral scent variation was investigated in four species of woodland stars (Lithophragma spp.) that share the same major pollinator (the moth Greya politella, a floral parasite). Three specific hypotheses were tested: (1) sharing the same specific major pollinator favours conservation of floral scent among close relatives; (2) selection favours 'private channels' of rare compounds particularly aimed at the specialist pollinator; or (3) selection from rare, less-specialized co-pollinators mitigates the conservation of floral scent and occurrence of private channels. Dynamic headspace sampling and solid-phase microextraction were applied to greenhouse-grown plants from a common garden as well as to field samples from natural populations in a series of experiments aiming to disentangle the genetic and environmental basis of floral scent variation. Striking floral scent divergence was discovered among species. Only one of 69 compounds was shared among all four species. Scent variation was largely genetically based, because it was consistent across field and greenhouse treatments, and was not affected by visits from the pollinating floral parasite. The strong divergence in floral scents among Lithophragma species contrasts with the pattern of conserved floral scent composition found in other plant genera involved in mutualisms with pollinating floral parasites. Unlike some of these other obligate pollination mutualisms, Lithophragma plants in some populations are occasionally visited by generalist pollinators from other insect taxa. This additional complexity may contribute to the diversification in floral scent found among the Lithophragma species pollinated by Greya moths.

Effects of habitat fragmentation on plant reproductive success and population viability at the landscape and habitat scale

Habitat fragmentation can significantly affect plant reproductive success and ultimately population viability, but little is known about the magnitude, direction or time scale of these impacts on plant–pollinator mutualisms. In this study, four species of terrestrial orchid with specialist and generalist pollination syndromes were used to investigate the effects of fragmentation on capsule set in urban bushland remnants. Supplementary pollination showed pollination limitation, but not resource limitation, occurs across all species. Habitat and landscape scale fragmentation predictor variables were used to build parsimonious models that explained capsule set data collected over 2years. We found the sexually deceptive species, Caladenia arenicola, to be sensitive to interactions between landscape (perimeter to area ratio) and habitat scale (bare ground cover and population size) predictor variables. The effect of perimeter to area ratio was heavily tempered by the significant negative influence of bare ground cover, where values of over 40% bare ground cover resulted in reproductive failure. We found that generalist pollinated species had significant interactions at the habitat scale including significant positive interactions between capsule set and population size and litter cover. Our results suggest the effects of habitat fragmentation at the landscape and habitat scale are important drivers of population viability. Our results suggest population viability will depend on the sensitivity of the pollination syndrome and the pollinator involved. This study highlights the need for research into reproductive success across multiple spatial scales to improve and inform conservation efforts.

Pollination ecology and floral function of Brown’s peony (<i>Paeonia brownii</i>) in the Blue Mountains of northeastern Oregon

Brown’s peony, Paeonia brownii (Paeoniaceae), is one of only two peony species native to the Western Hemisphere, yet its pollination ecology and breeding system have never been documented. Using flowering individuals of an endemic colony in the Blue Mountains of Oregon, U.S., we investigated the peony’s pollination system and floral function. We also examined pollen/carpel interactions through experimental pollinations aided by fluorescence microscopy. Paeonia brownii appears to be self compatible and mostly protogynous with floral traits of a generalist pollination system. The flowers appear to attract insects by producing abundant floral nectar secreted from lobes of a perigynous disc throughout their 9-15-days of anthesis. The most common pollen vectors were wasp queens (Vespidae), the large flower fly Criorhina caudata (Syrphidae), and females of Lasioglossum spp. (Halictidae), all of which foraged exclusively for nectar. Whether collected from foraging wasps and flies, anthers, or stigmas, about half the pollen grains appeared fertile. The number of ovules per carpel was about 19. Seed set (seeds/ovule) of naturally pollinated flowers was about 20% with about 4 viable seeds per follicle. The number of fertile pollen grains transferred to the stigma under natural conditions was highly variable but generally low, which may have contributed in part to the low rate of seed set. This study raises further questions about the role of pollen sterility, floral nectar and vespid wasps in shaping a pollinator system that is unusual in Paeonia.

Complex interactions among biocontrol agents, pollinators, and an invasive weed: a structural equation modeling approach

Herbivores, seed predators, and pollinators can exert strong impacts on their host plants. They can also affect the strength of each other's impact by modifying traits in their shared host, producing super- or sub-additive outcomes. This phenomenon is especially relevant to biological control of invasive plants because most invaders are attacked by multiple agents. Unfortunately, complex interactions among agents are rarely studied. We used structural equation modeling (SEM) to quantify the effect of two biocontrol agents and generalist pollinators on the invasive weed Centaurea solstitialis, and to identify and quantify the direct and indirect interaction pathways among them. The weevil Eustenopus villosus is both a bud herbivore and a predispersal seed predator; the fly Chaetorellia succinea is also a predispersal seed predator; Apis mellifera is the primary pollinator. We conducted this work at three sites spanning the longitudinal range of C. solstitialis in California (USA) from the coast to the Sierra Nevada Mountains. SEM revealed that bud herbivory had the largest total effect on the weed's fecundity. The direct effect of bud herbivory on final seed set was 2-4 times larger in magnitude than the direct effect of seed predation by both agents combined. SEM also revealed important indirect interactions; by reducing the number of inflorescences plants produced, bud herbivory indirectly reduced the plant's attractiveness to ovipositing seed predators. This indirect, positive pathway reduced bud herbivory's direct negative effect by 11-25%. In the same way, bud herbivory also reduced pollinator visitation, although the magnitude of this pathway was relatively small. E. villosus oviposition deterred C. succinea oviposition, which is unfortunate because C. succinea is the more voracious of the seed predators. Finally, C. succinea oviposition indirectly deterred pollinator visitation, thereby enhancing its net effect on the plant. This study demonstrates the powerful insights that can be gained from the SEM approach in understanding the multiple direct and indirect interactions among agents and pollinators and their effects on an invasive weed. Such an approach may improve our ability to manage weeds with biocontrol agents by identifying pathways that could be exploited by future agents and minimizing the possibility of interference with established agents.

Improving species distribution models using biotic interactions: a case study of parasites, pollinators and plants

Biotic interactions have been considered as an important factor to be included in species distribution modelling, but little is known about how different types of interaction or different strategies for modelling affect model performance. This study compares different methods for including interspecific interactions in distribution models for bees, their brood parasites, and the plants they pollinate. Host–parasite interactions among bumble bees (genus Bombus: generalist pollinators and brood parasites) and specialist plant–pollinator interactions between Centris bees and Krameria flowers were used as case studies. We used 7 different modelling algorithms available in the BIOMOD R package. For Bombus, the inclusion of interacting species distributions generally increased model predictive accuracy. The improvement was better when the interacting species was included with its raw distribution rather than with its modeled suitability. However, incorporating the distributions of non‐interacting species sometimes resulted in similarly increased model accuracy despite their being no significance of any interaction for the distribution. For the Centris‐Krameria system the best strategy for modelling biotic interactions was to include the interacting species model‐predicted values. However, the results were less consistent than those for Bombus species, and most models including biotic interactions showed no significant improvement over abiotic models. Our results are consistent with previous studies showing that biotic interactions can be important in structuring species distributions at regional scales. However, correlations between species distributions are not necessarily indicative of interactions. Therefore, choosing the correct biotic information, based on biological and ecological knowledge, is critical to improve the accuracy of species distribution models and forecast distribution change.

Shifts in pollinator composition and behavior cause slow interaction accumulation with area in plant–pollinator networks

Although ecologists have a solid understanding of the positive species-area relationship, little is known about how and why variation in habitat area influences the richness, structure, and function of species interaction networks. To address this, we investigated plant-pollinator interaction networks of the herbaceous rocky outcrop communities in Ozark glades (Missouri, USA) of different areas. We quantified the degree to which the increase in the number of species interactions with area differed from a null model based on sampling, where numbers of individuals increase with area. Although plant-pollinator interactions were expected to increase more steeply with area than species richness as a result of sampling, the observed rate of increase was considerably lower than expected. Two mechanisms could lead to this pattern: a higher proportion of specialist species in larger glades or generalist pollinators becoming more selective in their diets in larger glades. We found support for the former hypothesis, and those changes in species composition were strong enough to outweigh behavioral changes in the opposite direction; generalist pollinators were more selective in smaller glades. If these results are general, larger habitats may be needed to conserve interactions than would be thought based on species accumulation curves.

Adaptive foraging allows the maintenance of biodiversity of pollination networks

Pollination systems are recognized as critical for the maintenance of biodiversity in terrestrial ecosystems. Therefore, the understanding of mechanisms that promote the integrity of those mutualistic assemblages is an important issue for the conservation of biodiversity and ecosystem function. In this study we present a new population dynamics model for plant–pollinator interactions that is based on the consumer–resource approach and incorporates a few essential features of pollination ecology. The model was used to project the temporal dynamics of three empirical pollination network, in order to analyze how adaptive foraging of pollinators (AF) shapes the outcome of community dynamics in terms of biodiversity and network robustness to species loss. We found that the incorporation of AF into the dynamics of the pollination networks increased the persistence and diversity of its constituent species, and reduced secondary extinctions of both plants and animals. These findings were best explained by the following underlying processes: 1) AF increased the amount of floral resources extracted by specialist pollinators, and 2) AF raised the visitation rates received by specialist plants. We propose that the main mechanism by which AF enhanced those processes is (trophic) niche partitioning among animals, which in turn generates (pollen vector) niche partitioning among plants. Our results suggest that pollination networks can maintain their stability and diversity by the adaptive foraging of generalist pollinators.

Variation and constraints of local adaptation of a long‐lived plant, its pollinators and specialist herbivores

Summary Due to geographically variable species interactions, plants may become locally adapted to their sympatric herbivores and pollinators. However, adaptation to the abiotic environment may significantly affect plant interactions with herbivores and pollinators. Local adaptation to the abiotic environment may constrain local adaptation to herbivores and pollinators under contrasting selection pressures, resulting in trade‐offs in local adaptation. We studied local adaptation of a perennial herb, Vincetoxicum hirundinaria, in a reciprocal transplant experiment among four populations and measured plant fitness, pollination success and resistance to two specialist herbivores. We also estimated local adaptation of these two herbivores and generalist pollinators to their sympatric plant populations. Local adaptation was compared with within‐population genetic variation, genetic and geographical divergence, and with divergence in terms of population size, environmental conditions and plant secondary chemistry. We further compared local adaptation to the environment, to local adaptation to herbivores and pollinators to detect possible trade‐offs in local adaptation. The existence and degree of local adaptation varied among the plant populations. Plants from two populations were locally adapted to their sympatric leaf herbivores and plants from two populations were locally adapted to their abiotic environment. Herbivores from one population were locally adapted to their sympatric plant population. Local adaptation of V. hirundinaria to the seed predator increased with increasing among‐population divergence in precipitation and temperature. Local adaptation to the seed predator and the environment increased with increasing population genetic variation. Local adaptation of V. hirundinaria in fitness and in herbivore resistance also correlated positively, suggesting lack of trade‐offs in local adaptation. Synthesis. These results demonstrate that species interactions can lead to a mosaic of locally adapted plant, herbivore and pollinator populations. In addition to natural enemies, genetic variation, the abiotic environment and mutualistic interactions contribute to the evolution of local adaptation in long‐lived plants. These results provide new insights into the patterns and causes of variation in local adaptation and are among the first to demonstrate that conflicting selection pressures within a population do not constrain local adaptation in multiple traits.

Cardenolides in nectar may be more than a consequence of allocation to other plant parts: a phylogenetic study ofAsclepias

SummaryThe primary function of secondary plant metabolites is thought to be defence against herbivores. The frequent occurrence of these same noxious compounds in floral nectar, which functions primarily to attract pollinators, has been seen as paradoxical.Although these compounds may have an adaptive purpose in nectar, they may also occur as a nonadaptive consequence of chemical defence in other plant parts. If nectar chemistry reflects physiological constraints or passive leakage from other tissues, we expect that the identity and relative concentration of nectar cardenolides to be correlated with those of other plant parts; in contrast, discordant distributions of compounds in nectar and other tissues may suggest adaptive roles in nectar.We compared the concentrations and identities of cardenolides in the nectar, leaves and flowers of 12 species from a monophyletic clade ofAsclepias. To measure putative toxicity of nectar cardenolides, we then examined the effects of a standard cardenolide (digoxin) on the behaviour of bumblebees, a common generalist pollinator ofAsclepias.We found that the average cardenolide concentrations in nectar, leaves and flowers of the 12Asclepiasspecies were positively correlated as predicted by nonadaptive hypotheses. However, significant differences in the identities and concentrations of individual cardenolides between nectar and leaves suggest that the production or allocation of cardenolides may be independently regulated at each plant part. In addition, cardenolide concentrations in leaves and nectar exhibited no phylogenetic signal.Surprisingly, bumblebees did not demonstrate an aversion to digoxin‐rich nectar, which may indicate that nectar cardenolides have little effect on pollination.Although the idea that discordant patterns of secondary metabolites across tissue types may signal adaptive functions is attractive, there is evidence to suggest constraint contributes to nectar secondary chemistry. Further work testing the ecological impacts of such patterns will be critical in determining the functional significance of nectar cardenolides.

Pollination and fruit set in the main neotropical mangrove species from the Southwestern Caribbean

To increase our understanding of pre-dispersal reproduction of neotropical mangrove species we studied pollination effectiveness of flower visitors (potential to be pollen vector and to induce fruit development), pollination specialization and fruit set. Rhizophora mangle exhibited ambophilous pollination, a fruit set of 7.2%, and a highly effective pollinator, the hoverfly Copestylum sp. 1. Laguncularia racemosa had three highly effective pollinators, a fruit set of 7.9%, and the most specialized pollination system among the three species. Avicennia germinans showed the least specialized pollination, with four highly effective pollinators. This species showed the highest recruitment potential, with a fruit set of 29%. Although R. mangle is considered to be predominantly wind pollinated, our results indicate that the role of insect pollination has been underestimated. Likewise, our findings show that A. germinans has effective pollinators and vectors in several taxonomic groups. On small islands, where low insect diversity is expected, the level of pollination generalization found in R. mangle and A. germinans is higher than previously suggested. Competition for pollination resources appears to be low among the species studied.

Floral traits and reproduction of Avicennia schaueriana Moldenke (Acanthaceae): a generalist pollination system in the Lamiales

AbstractPollination systems may vary in their degree of specialization from generalist to specialist and this is associated with the frequency and efficiency of pollinators. Self‐compatibility and a generalist pollination system appear to be adaptations that enhance the ability for colonizing new areas, which is typical of mangrove species. Avicennia schaueriana is a western mangrove species included in Acanthaceae, Lamiales, an order known to have specialized pollination. We aimed to describe the floral morphology and analyze the pollination and reproductive systems of A. schaueriana in a mangrove area on the northern coast of the state of Pernambuco, Brazil, to analyze the possible adaptations of this species to the environment. Avicennia schaueriana is self‐compatible; however, pollination activity is essential because there is no spontaneous formation of fruit. Reproductive efficacy was high, indicating pollinator efficiency. Some floral attributes of A. schaueriana suggest specialization; however, the broad spectrum of pollinators observed suggests that it has a generalist pollination system. The way in which pollinators interact with flowers and the environmental conditions may have exerted a selective force on the floral attributes of A. schaueriana, characterizing an adaptive generalized pollination system, which is somewhat specialized.

Rapid Shift in Pollinator Communities Following Invasive Species Removal

Ecological restoration is increasingly used to reverse degradation of rare ecosystems and maintain biological diversity. Pollinator communities are critical to maintenance of plant diversity and, in light of recent pollinator loss, we tested whether removal of invasive glossy buckthorn (Frangula alnus L.) from portions of a prairie fen wetland altered plant and pollinator communities. We compared herbaceous plant, bee, and butterfly abundance, diversity, and species composition in buckthorn invaded, buckthorn removal, and uninvaded reference plots. Following restoration, we found striking differences in plant and pollinator abundance and species composition between restored, unrestored, and reference plots. Within 2 years of F. alnus removal, plant species diversity and composition in restored plots were significantly different than invaded plots, but also remained significantly lower than reference plots. In contrast, in the first growing season following restoration, bee and butterfly abundance, diversity, and composition were similar in restored and reference plots and distinct from invaded plots. Our findings indicate that a diverse community of mobile generalist pollinators rapidly re‐colonizes restored areas of prairie fen, while the plant community may take longer to fully recover. This work implies that, in areas with intact pollinator metapopulations, restoration efforts will likely prevent further loss of mobile generalist pollinators and maintain pollination services. On the other hand, targeted restoration efforts will likely be required to restore populations of rare plants and specialist pollinators for which local and regional species pools may be lacking.

Gone with the wind: understanding evolutionary transitions between wind and animal pollination in the angiosperms

Gone with the wind: understanding evolutionary transitions between wind and animal pollination in the angiosperms

Reproductive biology of Australian acacias: important mediator of invasiveness?

AbstractAim Reproductive traits are important mediators of establishment and spread of introduced species, both directly and through interactions with other life‐history traits and extrinsic factors. We identify features of the reproductive biology of Australian acacias associated with invasiveness.Location Global.Methods We reviewed the pollination biology, seed biology and alternative modes of reproduction of Australian acacias using primary literature, online searches and unpublished data. We used comparative analyses incorporating anAcaciaphylogeny to test for associations between invasiveness and eight reproductive traits in a group of introduced and invasive (23) and non‐invasive (129) species. We also explore the distribution of groups of trait ‘syndromes’ between invasive and non‐invasive species.Results Reproductive trait data were only available for 126 of 152 introduced species in our data set, representing 23/23 invasive and 103/129 non‐invasive species. These data suggest that invasives reach reproductive maturity earlier (10/13 within 2 years vs. 7/26 for non‐invasives) and are more commonly able to resprout (11/21 vs. 13/54), although only time to reproductive maturity was significant when phylogenetic relationships were controlled for. Our qualitative survey of the literature suggests that invasive species in general tend to have generalist pollination systems, prolific seed production, efficient seed dispersal and the accumulation of large and persistent seed banks that often have fire‐, heat‐ or disturbance‐triggered germination cues.Conclusions Invasive species respond quicker to disturbance than non‐invasive taxa. Traits found to be significant in our study require more in‐depth analysis involving data for a broader array of species given how little is known of the reproductive biology of so many taxa in this species‐rich genus. Sets of reproductive traits characteristic of invasive species and a general ability to reproduce effectively in new locations are widespread in Australian acacias. Unless there is substantial evidence to the contrary, care should be taken with all introductions.

The Neuroecology of a Pollinator's Buffet: Olfactory Preferences and Learning in Insect Pollinators

Plants and their pollinators are excellent examples of mutualistic associations that range in specialization, from obligate to generalized mutualisms, with many pollinators interacting with diverse species of flowers while still maintaining specialized associations. Although floral odors have been implicated in mediating these interactions, identification of the odors-and how the odors are represented in the olfactory system-has been elusive, and the manner in which olfactory learning mediates the generalized plant-insect interactions in the field remains unclear. This review details the composition of floral bouquets that elicit strong attraction in pollinators, demonstrating that for some species of plants the composition of the bouquet plays an important role in exploiting the insect's olfactory system, thereby driving innate attraction, whereas other bouquets can be learned as an associative cue for the nectar reward. By associative learning of nonattractive floral odors with a nectar reward-through octopamine-associated modulation of neurons in the antennal lobe-insects have the ability to exploit alternate floral resources when their preferred flowers are no longer present. Such neural mechanisms, present in specialist and generalist pollinators, provides the means by which pollination associations can range from specialized to generalized while permitting insects to exist within a dynamic floral environment.

Relative contributions to seed production by floral visitors of slickspot peppergrass, Lepidium papilliferum (Brassicaceae)

Assessing the relative contributions to seed production made by different types of floral visitors is fundamental to understanding the evolution of floral morphology and the influence that particular pollinator taxa have on plant fitness and reproduction. This 3-year study examined the pollinator activity and the seed production in three populations of Lepidium papilliferum, a threatened mustard endemic to sagebrush-steppe habitat in southwest Idaho. Relative amounts of time visitor taxa spent foraging on flowers, visitation rates (number of flowers visited per unit time during a foraging bout), and pollination effectiveness (fruit set per single visit to a virgin flower) were recorded for each of 12 insect taxa that visited L. papilliferum flowers. Relative contributions to seed production were calculated as the product of relative interaction frequencies (the relative number of flowers visited by each taxon—the “quantity” component of pollination) and pollination effectiveness (fruit set per single visit to a virgin flower—the “quality” component of pollination). Despite the superiority of some insect taxa in terms of pollination effectiveness, estimates of relative pollinator contributions to seed production were influenced primarily by an insect taxon’s interaction frequency with flowers. Pollinator assemblages varied widely both spatially and temporally, which suggest that L. papilliferum is not under strong selective pressure to shift from its generalist pollination strategy toward greater specialization. For this threatened plant, reliance on a diverse assemblage of insect pollinators may serve as an important buffer against disruption in reproductive success caused by fluctuations in population sizes of individual pollinator taxa.

The role of asymmetric interactions on the effect of habitat destruction in mutualistic networks.

Plant-pollinator mutualistic networks are asymmetric in their interactions: specialist plants are pollinated by generalist animals, while generalist plants are pollinated by a broad range involving specialists and generalists. It has been suggested that this asymmetric –or disassortative– assemblage could play an important role in determining the observed equal susceptibility of specialist and generalist plants under habitat destruction. At the core of the analysis of the phenomenon lies the observation that specialist plants, otherwise candidates to extinction, could cope with the disruption thanks to their interaction with a few generalist pollinators. We present a theoretical framework that supports this thesis. We analyze a dynamical model of a system of mutualistic plants and pollinators, subject to the destruction of their habitat. We analyze and compare two families of interaction topologies, ranging from highly assortative to highly disassortative ones, as well as real pollination networks. We found that several features observed in natural systems are predicted by the mathematical model. First, there is a tendency to increase the asymmetry of the network as a result of the extinctions. Second, an entropy measure of the differential susceptibility to extinction of specialist and generalist species show that they tend to balance when the network is disassortative. Finally, the disappearance of links in the network, as a result of extinctions, shows that specialist plants preserve more connections than the corresponding plants in an assortative system, enabling them to resist the disruption.

Pollinators, pollination efficiency and fruiting success in a wild nutmeg, Myristica dactyloides

Abstract:We investigated the pollinator assemblage in Myristica dactyloides, a dioecious tree species occupying the intermediate canopy stratum of the mid- and high-elevation wet evergreen forests and endemic to Sri Lanka and the Western Ghats of India. We surveyed two populations and, in one of them, marked four male and three female trees for observations on floral display and insect foraging, and two female trees for experimental pollination. Yellow sticky traps were used to sample insects in the canopy during the flowering season of December 2007 in addition to direct observations of insect activity in 2006. Myristicaceae members from other tropical areas have been reported to be specialized to beetle pollination, but our observations provide evidence of a generalist pollination system in M. dactyloides, composed of small, diverse insects: thysanopterans (thrips), coleopterans (beetles), halictid bees and dipterans (syrphid and phorid flies). Quantifying floral display, we found that female inflorescences were smaller, offered no reward and attracted significantly fewer pollinators in comparison to male inflorescences. Fruit set was low and could be attributed to a 29% flower abscission and abortion of young fruits, but a reasonably high natural pollination efficiency combined with pollination experiments established that there was no pollination limitation in the study population.

Pollination systems, biogeography, and divergence times of three allopatric species of Schisandra in North America, China, and Japan

This study analyses the pollination systems and biogeography of three allopatric species of Schisandra (Section Euschisandra) consisting of S. glabra (North America), S. bicolor (China), and S. repanda (Japan); the clade is delimited in a phylogenetic tree of Schisandraceae constructed with nuclear and plastid genes. The male and female flowers of these species have similar floral structures, but exhibit different pollination systems. At the base of the clade, S. glabra is pollinated by a wide variety of beetles and flies in a generalist pollination system that also includes floral heat and the use of male and female flowers as brood sites for insects. In Asia, however, S. bicolor and S. repanda are pollinated exclusively by one or two different species of gall midges (Resseliella spp.) in a specialist pollination system. In this system only female, pollen-eating gall midges pollinate the flowers and breed on nearby spiderwebs. The gall midge pollination system is specialized and derived from the generalist system in S. glabra, and basal in the clade. Pollen is the main floral resource, and we hypothesize it is exploited to enrich eggs, and as a result species of gall midges could increase reproductive fitness by feeding on a single dependable food source. Subsequently the life cycles of the plants and insects evolved into a tight association in old stable plant communities in the Sino-Japanese flora. Divergence times for the plant species are presented and correlated with past distributions and migration routes.

Pollen transport differs among bees and flies in a human‐modified landscape

AbstractAim Dispersal distances of insect pollinators are critical in defining their contribution to landscape‐wide pollen movement and ultimately gene flow in natural and agricultural systems. We ask whether bee and fly pollinator taxa differ in their dispersal distances and transport of viable pollen in a human‐modified system.Location Canterbury and Otago region, South Island, New Zealand.Methods We captured pollen‐carrying insects travelling outside of a model mass‐flowering agricultural crop, Brassica rapa, using insect flight intercept traps at five distances (0, 100, 200, 300 and 400 m) from the pollen source. We examined pollen loads and pollen viability to determine whether pollen transport distance and viability differ among pollinator taxa.Results A total of 5453 insects were collected of which 717 individuals from 26 insect taxa were positively identified as dispersing pollen up to 400 m from the source. These taxa consisted of four species from two bee families (Hymenoptera: Apidae and Halictidae), and eight species from four fly families (Diptera: Bibiondae, Stratiomyidae, Syrphidae and Tachinidae). Apidae generally carried higher pollen loads and more viable pollen than most fly taxa. Taxa in the fly families Stratiomyidae and Syrphidae, however, carried pollen to 400 m, which is further than both bee families.Main conclusions A diverse array of wild and managed flower visitors can transport viable pollen from a pollen source to at least 400 m. Knowledge of the differences in transport distances among generalist pollinators in human‐modified environments is crucial to understand the potential extent to which (1) pollen transport can facilitate gene flow and (2) unwanted hybridization may occur between crops and related weeds.