Flower Visitor Assemblages Research Articles

Forest conservation maximises açaí palm pollination services and yield in the Brazilian Amazon

Abstract Agricultural expansion is one of the main drivers of global pollinator loss. Paradoxically, this occurs while agriculture is becoming increasingly dependent on biotic pollination, raising concerns about food production. Integrated Crop Pollination (ICP), the use of both wild and managed pollinators in crop fields, can help conserve pollinator diversity while ensuring effective pollination services for growers. However, given the context‐dependent nature of this approach, there is an urgent need to evaluate its application across different landscapes and crops. We apply the ICP approach to açaí palm (Euterpe oleracea Mart.) production in the eastern Brazilian Amazon to explore effects of a native stingless bee, Scaptotrigona aff. postica (Apidae: Meliponini), and landscape‐level forest conservation on yield and socioeconomic outcomes for açaí fruit growers. We assessed flower visitor assemblages and fruit production on 18 plantations across a landscape forest cover gradient, with bee colonies introduced on nine plantations. Field data were combined with information from semistructured interviews of growers to estimate yield and profit per hectare under different pollinator management scenarios. Bee colonies and forest cover enhanced flower visitor abundance on palm inflorescences, but abundance increases attributed to managed bees were associated with shifts in flower visitor evenness and diversity (species richness), due to reduced visitation of wild bees near managed colonies. Fruit production on inflorescences was positively related to bee abundance and bee diversity. Consequently, overall pollination performance was lower in plantations with bee colonies. This was repeated at the hectare scale, where yield and profit were associated with surrounding forest cover and not bee colonies. Synthesis and applications. Managed bees can increase pollinator densities and fruit production, but the increased environmental and socioeconomic risks associated with this activity means açaí growers should prioritise forest conservation to safeguard pollination services and improve overall sustainability of açaí production in the eastern Brazilian Amazon.

Effects of urbanization on the structure of plant-flower visitor network at the local and landscape levels in the northern Argentinian Yungas forest

Human population and cities are growing fast, with a concomitant modification of the land surface. Urbanization is driving biodiversity loss and biological homogenization, which impacts human wellbeing. In this study, we evaluated the influence of urbanization on flower visitor assemblage using an interaction network approach. We assessed the effect of different variables at the local and landscape scales on community parameters and network metrics along a gradient of urbanization located in a subtropical montane Yungas forest. We found that local variables affected the richness of flower visitors, which increased with greater flower coverage, high stability of floral resources, and the proportion of exotic plants. Moreover, local variables affected the diversity, nestedness (NODF), and specialization (H2) of the interaction network. Landscape variables, such as altitude and proportion of impervious surface (a proxy of urbanization), affected both the richness of flower visitors and specialization. The effect of urbanization on the richness of flower visitors differed across the altitudinal gradient, with higher impact at higher altitudes. In conclusion, our results indicate that local and landscape variables affect community parameters and the structure of plant-flower visitor networks to different extents and strengths.

Flower size affects bee species visitation pattern on flowers with poricidal anthers across pollination studies

Flower size is a crucial trait for pollinator attraction. In flowers with poricidal anthers, the plant constraints the pollinator's access to the flower's rewards by enclosing pollen grains in poricidal anthers. The pollen is only released by mechanical vibrations applied mainly by bee species during buzz pollination. Although buzz-pollinated flowers exhibit a large size variation across species, their influence over patterns of flower visitation by different pollinator species remains to be elucidated. To fill such gap, we asked how flower size influences flower visitor assemblage, especially bees, across plant species and how flower size is related to body size and vibrating behavior of the most frequent bee species. We hypothesized that the assemblage of animals, especially bees, visiting larger flowers have higher taxonomic and functional diversity than smaller flowers, and the most frequent bee species visiting larger flowers have larger body size and a mandatory vibrating behavior. To test this hypothesis, we conducted a systematic review of pollination studies that reported patterns of flower visitation in plant species with poricidal anthers, describing the relationship between flower size and flower visitor metrics. We found that large-flowered species were visited by three times more species than small-flowered species, including vibrating and non-vibrating bee species. Unlike our expectations, non-vibrating bees were largely absent from small-flowered species. The most frequent bee species visiting flowers, irrespective of flower size, exhibited vibrating behavior. The most frequent bee species visiting large flowers were twice the body size of those visiting small flowers, highlighting a morphological match between flowers and pollinators. Although larger flowers are more susceptible to interactions with exploiters, reproductive success should be favored owing to the higher probability of their interaction with vibrating, large-bodied bee species. Still, a reduction in flower size probably prevents interactions with non-vibrating bees, while favoring vibrating small-bodied bee species.

Co-Flowering Species Richness Increases Pollinator Visitation to Apple Flowers

Co-flowering plants can experience an array of interactions, ranging from facilitation to competition, the direction and strength of which are often dependent on the relative abundance and diversity of the plant species involved and the foraging behavior of their pollinators. Understanding interactions between plant–pollinator networks and how they change over time is particularly important within agricultural systems, such as apples, that flower en masse and that also contain non-crop co-flowering species both within the farm and the surrounding landscape. We determined the degree of overlap between pollinator networks on two varieties of apple (Granny Smith and Pink Lady) and co-flowering plant species within orchards and the wider vegetation matrix in two apple-growing regions (Orange and Bilpin) in Australia. We surveyed plant–pollinator interactions at key stages of the cropping cycle: before mass flowering; during king, peak and late blooms; and, finally, once apple flowering had finished. Overall, we found considerable overlap in the flower visitor assemblage on apples and co-flowering species within the orchard. The introduced honeybee (Apis mellifera) was the most frequent flower visitor to all three vegetation types at all times in Orange. However, in Bilpin, both a native stingless bee (Tetragonula carbonaria) and A. mellifera were highly frequent visitors, both on- and off-crop. Numerous native bees, flies and Lepidoptera also commonly visited apple and co-flowering species within orchards in both locations. We found that native-bee and honeybee visitation to apple flowers was positively correlated with co-flowering species richness (within the orchard and the wider matrix); however, visitation by native bees decreased as the area of co-flowering species in the surrounding landscape increased. Our study highlights the importance of maintaining diverse co-flowering plant communities within the local landscape to increase and support a wide variety of pollinators in horticultural production systems.

Why honeybees are poor pollinators of a mass-flowering plant: Experimental support for the low pollen quality hypothesis.

PremiseHoneybees dominate the flower‐visitor assemblages of many plant species, yet their efficiency in terms of the quality of pollen delivered to stigmas is largely unknown. We investigated why honeybees are poor pollinators of Aloe ferox, a self‐incompatible succulent treelet with large numbers of flowers. Honeybees are very frequent visitors to flowers of this species, yet contribute very little to seed production.MethodsWe assessed pollen loads on honeybees, studied their visitation behavior, selectively excluded birds from plants to determine direct effects of bees on pollen deposition, seed set, and ovule abortion, and used a novel “split‐pollinator” method to test whether honeybees deposit mainly low‐quality self pollen. For the latter, we captured honeybees, and with their existing pollen loads, used them to either pollinate virgin flowers on the plant on which they were caught or to pollinate virgin flowers on different plants.ResultsHoneybees cumulatively deposit as much pollen on stigmas as do birds, but our experiments showed that the pollen deposited by honeybees is mostly low‐quality self pollen that leads to substantial ovule discounting and depressed seed set.ConclusionsLack of movement among A. ferox plants during individual honeybee foraging bouts is the most likely explanation for their deposition of low‐quality self pollen on stigmas. The “split‐pollinator” method is a simple and cost‐effective technique to test the quality of pollination.

Foraging Behavior and Pollen Transport by Flower Visitors of the Madeira Island Endemic Echium candicans.

Simple SummaryThe successful conservation of many endangered island plants depends on the pollination services provided by animals. In this study, we identify the flower visitors of Echium candicans, a charismatic plant exclusive to the island of Madeira, and also evaluate their performance as pollinators by analyzing their behavior on the flowers and the pollen they transport on their body. We found that many different animals visit this plant’s flowers, from insects to reptiles, but bees were the most frequent visitors. Large bees visited more flowers and transported more pollen of Echium candicans compared to other pollinators, like butterflies and hoverflies. However, by visiting many flowers in the same plant large bees might contribute to inbreeding, whilst the other animals visited fewer flowers in each plant favoring outcrossing. We conclude that the different flower visitors of Echium candicans provide complementary services as pollinators and highlight the importance of having diverse communities of pollinators to ensure successful pollination in many island plants.The study of flower visitor behavior and pollen transport dynamics within and between plants can be of great importance, especially for threatened or rare plant species. In this work, we aim to assess the flower visitor assemblage of the Madeiran endemic Echium candicans and evaluate the performance of the most common visitors through the analysis of their foraging behavior and pollen loads. The flower visitor assemblage of E. candicans is diverse, including several insect groups and the endemic lizard Teira dugesii, but bees are the most common visitors. In general, large bees (Amegilla quadrifasciata, Apis mellifera, and Bombus spp.) had the highest average visitation rates (>18 flowers/min) and their pollen loads had higher percentages of homospecific pollen (>66%) when compared with butterflies and hoverflies. The honeybee (Apis mellifera) and two bumblebees (Bombus terrestris and B. ruderatus) were the most efficient flower visitors of E. candicans, but their foraging behavior seems to favor geitonogamy. Other visitors, such as butterflies and the small bee Lasioglossum wollastoni, may have a complementary role to the honeybee and bumblebee species, as their high mobility is associated with fewer flower visits on each plant and may promote xenogamy. Two non-native bees (A. mellifera and B. ruderatus) are important flower visitors of E. candicans and may contribute mostly to self-pollination rendering the endemic plant more vulnerable to inbreeding effects.

Community-level plant–pollinator interactions in a Palaeotropical montane evergreen oak forest ecosystem

ABSTRACT The montane terrain of northern Laos is covered by species-rich subtropical evergreen oak forests, home to endemic tree genera such as Mytilaria (Hamamelidaceae), and characterised by the coexistence of several honeybee and bumblebee species. We explored community-level plant–pollinator interactions of this unique little-known ecosystem. Extensive direct observations on flowering phenology and flower-visitor assemblages of 288 plant species of 82 families were conducted in a montane forest ecosystem in Houaphanh and Xiangkhouang Provinces, Laos, from 2005 until 2016. Based mainly on the extensive flower-visit data, we assessed the pollination system of each plant species. Five sympatric honeybee species (Apis dorsata, A. laboriosa, A. cerana, A. florea and A. andreniformis) were common on various types of flowers, and floral preferences differed among species. Long-tongued bees belonging to Bombini and Anthophorini (Apidae) were species-rich and frequent visitors on various deep flowers, especially Acanthaceae, Balsaminaceae, Lamiaceae, Rubiaceae and Zingiberaceae. Character displacement by tongue length was observed among the bee species, and many relaxed species-specific and species-semispecific interactions were observed between the bees and the deep-flowers. Four plant species, in the genera Mytilaria, Chloranthus, Dioscorea and Cryptocarya, were visited exclusively by thrips. Two plant species, in the genera Lysimachia and Thladiantha, had oil-secreting flowers, which were specifically visited by the oil-collecting bees Macropis and Ctenoplectra, respectively. The dominant pollination system assessed was general insect pollination (31%), followed by long-tongued bee, small bee, honeybee, dipteran, lepidopteran, beetle, wasp, carpenter bee, thrips (e.g. the endemic genus Mytilaria), bird and hemipteran pollination. Our results suggest that the plant–pollinator interactions in the Palaeotropic montane ecosystem are characterised by significant contribution of the five honeybee species and species-rich, morphologically diverse long-tongued bees, both of which have contributed to shaping the remarkable diversity of angiosperms with deep flowers.

Urbanization Affects Composition but Not Richness of Flower Visitors in the Yungas of Argentina.

Urban areas represent a spatially small impact in relation to other land-uses such as livestock and agriculture, but they undergo rapid changes. Such changes involve their size, shape, interconnectivity, and composition of natural patches. Habitat loss generated by urbanization affects the diversity and abundance of bees and other flower visitors in many sites. In general, the presence of urban areas represents a strict boundary to flower visitors and restricts their movement between natural and suburban habitat patches. The aim of this work is to evaluate how the flower visitor assemblage change along an urban-natural gradient in northwest Argentina. We established five areas in the Yungas ecoregion and sampled three sites with different degrees of urbanization (urban, suburban, and natural), at each area, reaching 15 sites. At each site, we sampled flower visitors during 5-min observation periods done over flowering plants. We found 197 morphospecies of flower-visiting insects along the gradient and an invariant richness, abundance, and Shannon diversity. The assemblage presented the same taxonomic group distributions in the three categories established. However, in urban sites, solitary bees and bees with soil borrowing nesting type predominate, while eusocial and cavity nesting bees were the main flower visitors in suburban sites. Our results suggest that the cities of northwestern Argentina are not a strict boundary for flower visitors; however, urbanization seems to be selecting and favoring certain flower-visitor species traits.

Differences in sex expression and mating systems in three pollination morphs of Cimicifuga simplex

AbstractCimicifuga simplex (Ranunculaceae) has three genetically distinct pollination morphs. Here, we report that each of the three pollination morphs of C. simplex differs from the others with regard to sex expression and mating system: morph I consists mostly of ramets with hermaphroditic flowers and ramets with only female flowers, morph II consists of ramets with hermaphroditic flowers and ramets with hermaphroditic and male flowers, and morph III consists mostly of ramets with hermaphroditic flowers. A microsatellite analysis of seed DNA showed that morph III has a high self‐fertilization rate. Flowering season and flower visitor assemblages, which also differ among the three morphs, may influence the evolution and maintenance of the differences in sex expression and mating systems in the morphs.

Geography is essential for reproductive isolation between florally diversified morning glory species from Amazon canga savannahs

The variety, relative importance and eco-evolutionary stability of reproductive barriers are critical to understanding the processes of speciation and species persistence. Here we evaluated the strength of the biotic prezygotic and postzygotic isolation barriers between closely related morning glory species from Amazon canga savannahs. The flower geometry and flower visitor assemblage analyses supported pollination by the bees in lavender-flowered Ipomoea marabaensis and recruitment of hummingbirds as pollinators in red-flowered Ipomoea cavalcantei. Nevertheless, native bee species and alien honeybees foraged on flowers of both species. Real-time interspecific hybridization underscored functionality of the overlap in flower visitor assemblages, questioning the strength of prezygotic isolation underpinned by diversification in flower colour and geometry. Interspecific hybrids were fertile and produced offspring in nature. No significant asymmetry in interspecific hybridization and hybrid incompatibilities among offspring were found, indicating weak postmating and postzygotic isolation. The results suggested that despite floral diversification, the insular-type geographic isolation remains a major barrier to gene flow. Findings set a framework for the future analysis of contemporary evolution of plant-pollinator networks at the population, community, and ecosystem levels in tropical ecosystems that are known to be distinct from the more familiar temperate climate models.

Global-scale drivers of crop visitor diversity and the historical development of agriculture.

Understanding diversity in flower-visitor assemblages helps us improve pollination of crops and support better biodiversity conservation outcomes. Much recent research has focused on drivers of crop-visitor diversity operating over spatial scales from fields to landscapes, such as pesticide and habitat management, while drivers operating over larger scales of continents and biogeographic realms are virtually unknown. Flower and visitor traits influence attraction of pollinators to flowers, and evolve in the context of associations that can be ancient or recent. Plants that have been adopted into agriculture have been moved widely around the world and thereby exposed to new flower visitors. Remarkably little is known of the consequence of these historical patterns for present-day crop-visiting bee diversity. We analyse data from 317 studies of 27 crops worldwide and find that crops are visited by fewer bee genera outside their region of origin and outside their family's region of origin. Thus, recent human history and the deeper evolutionary history of crops and bees appear to be important determinants of flower-visitor diversity at large scales that constrain the levels of visitor diversity that can be influenced by field- and landscape-scale interventions.

Are insect flower visitor assemblages distinguishable between Brassica napus and B. rapa?

Brassica napus and Brassica rapa are grown across six continents for purposes including oilseed, biofuel, vegetables and livestock fodder. Hybridisation between the two can downgrade seed quality reducing grower returns. We assess the similarity of flower visitor assemblages of both species to determine the applicability of pollinator management strategies to both. Insect taxa were collected using window traps placed within ten peak-flowering fields, five each of B. napus and B. rapa (one cultivar/species) located in South Canterbury, New Zealand. Both crops contained similar flower visitor assemblages with 25 of 29 taxa in common. Of the 1549 insects counted, Apis mellifera was most abundant (~40% of individuals in both crops). Bombus terrrestris and the flies Delia platura, and Oxysarcodexia varia were also common. Crop location more likely influenced assemblage composition than crop species. Strategies to boost the role of bee and non-bee pollinators have potential benefits for both crops; however, a broader understanding of pollinator movement between crops is required to optimise seed purity and crop spacing.

Alien plants have greater impact than habitat fragmentation on native insect flower visitation networks

AbstractAimHabitat fragmentation and alien species are among the leading causes of biodiversity loss. In an attempt to reduce the impact of forestry on natural systems, networks of natural corridors and patches of natural habitat are often maintained within the afforested matrix, yet these can be subject to degradation by invasion of non‐native species. Both habitat fragmentation and alien invasive species disrupt the complex interaction networks typical of native communities. This study examines whether an invasive plant and/or the fragmented nature of the forestry landscape influences natural flower visitation networks (FVNs), flower–visitor abundance and richness or flower/visitor species composition.LocationThe species rich and diverse grasslands in the KwaZulu‐Natal Midlands, South Africa is under threat from transformation, particularly by commercial forestry plantations, restricting much of the remaining untransformed grasslands into remnant grassland patches (RGPs). Remaining patches are under additional threat from the invasive Rubus cuneifolius Pursh (bramble). Sites were established in RGPs and in a nearby protected area (PA), with and without brambles present for both areas.ResultsFlower abundance and flower area of native plant species were greater within RGP than in PA, but only in the absence of R. cuneifolius. Flower–visitor assemblages differed between invaded and uninvaded sites and also differed between PA and RGP sites. Both areas lost specialist flower–visitor species in the presence of brambles. Network modularity was greatly reduced by the presence of bramble, indicating a reduction in complexity and organization. The structure of FVNs was otherwise unaffected by presence of bramble or being located in RGPs or the PA.Main conclusionsThe RPGs contribute to regional biodiversity conservation through additional compositional diversity and intact FVNs. Rubus cuneifolius reduces ecological complexity of both RGPs and PAs, however, and its removal must be prioritized to conserve FVNs.

Functional consequences of plant-animal interactions along the mutualism-antagonism gradient.

Plant-animal interactions are pivotal for ecosystem functioning, and usually form complex networks involving multiple species of mutualists as well as antagonists. The costs and benefits of these interactions show a strong context-dependency directly related to individual variation in partner identity and differential strength. Yet understanding the context-dependency and functional consequences of mutualistic and antagonistic interactions on individuals remains a lasting challenge. We use a network approach to characterize the individual, plant-based pollination interaction networks of the Canarian Isoplexis canariensis (Plantaginaceae) with a mixed assemblage of vertebrate mutualists (birds and lizards) and invertebrate antagonists (florivores, nectar larcenists, and predispersal seed predators). We identify and quantify interaction typologies based on the sign (mutualistic vs. antagonistic) and strength (weak vs. strong) of animal-mediated pollination and test the relationship with individual female reproductive success (FRS). In addition, we document pollinator movement patterns among individual plants to infer events of pollen transfer/receipt that define the plant mating networks and test the relationship with FRS. We identify six interaction typologies along a mutualism-antagonism gradient, with two typologies being over-represented involving both mutualists and antagonists and influencing FRS. Plants showing strong mutualistic interactions, but also (weak or strong) interactions with antagonists are relatively better connected in the mating network (i.e., with higher potential to transfer or receive pollen). Thus, mixed flower visitor assemblages with mutualists and antagonists give plants increased their importance in the mating networks, promote outcrossing and increasing both female and male fitness. Our approach helps characterize plant-animal interaction typologies, the context-specificity of diversified mutualisms, and a better forecasting of their functional consequences.

Patterns of diversity of flower-visitor assemblages to the understory Araceae in a tropical mountain forest in Colombia

In the Araceae, pollination biology has been extensively evaluated in several genera mainly in lowland tropical areas. However, the influence of physical factors such as elevation or precipitation on plant/flower-visitor interactions at the community level remains challenging for this plant family, specifically in tropical mountain forests. The aim of this study was to analyze how the species diversity and abundance of flowering Araceae and their flower-visitor assemblages change along an elevation gradient and through time, in response to changes in mean monthly precipitation in a tropical mountain forest located in Jardin, Antioquia, Colombia. Eighteen flowering Araceae species and floral visitors belonging to seven orders were recorded. Flower-visitor diversity decreased with elevation. A trend of increasing flowering Araceae and flower-visitor abundance richness at intermediate levels of precipitation was observed. Diptera were dominant in the lower part and Thysanoptera were dominant in the upper part of the gradient. The pattern of plant species distribution along the elevation and the amount of precipitation influenced the availability of flower resources, and, as a consequence, affected the spatial and temporal composition of flower-visitor assemblages. Local strategies for the conservation of the diversity of insect flower-visitors and their interactions should be focused on the implementation of agricultural practices that reduce the use of pesticides within adjacent commercial plantations and the avoidance of illegal clearings, maintaining unbroken elevational gradients of forest, which is the only way to protect the flowering resources for anthophilous insects. At the same time, continuous forest promotes the maintenance of macro and microclimatic conditions, preserving the stability of insect populations and diversity amongst several functional groups.

Functional homogenization of flower visitor communities with urbanization.

Land‐use intensification and resulting habitat loss are put forward as the main causes of flower visitor decline. However, the impact of urbanization, the prime driver of land‐use intensification in Europe, is poorly studied. In particular, our understanding of whether and how it affects the composition and functioning of flower visitor assemblages is scant, yet required to cope with increasing urbanization worldwide. Here, we use a nation‐wide dataset of plant‐flower visitor (Coleoptera, Diptera, Hymenoptera, Lepidoptera) interactions sampled by citizen scientists following a standardized protocol to assess macroecological changes in richness and composition of flower visitor communities with urbanization. We measured the community composition by quantifying the relative occurrence of generalist and specialist flower visitors based on their specialisation on flowering plant families. We show that urbanization is associated with reduced flower visitor richness and a shift in community composition toward generalist insects, indicating a modification of the functional composition of communities. These results suggest that urbanization affects not only the richness of flower visitor assemblages but may also cause their large‐scale functional homogenization. Future research should focus on designing measures to reconcile urban development with flower visitor conservation.

Flower-visitor selection on floral integration in three contrasting populations of Lonicera implexa.

Geographic differences in flower visitor assemblages might lead to among-population differences in the magnitude and pattern of floral integration. However, the role of current pollinator visitation in shaping the magnitude and pattern of floral trait correlations is still controversial. We used individual-level data on floral morphology, flower visitation, and fitness to assess if floral integration (at flower and floral-module level) and the covariance structure of floral traits varied among three populations of Lonicera implexa differing in the importance of long-tongue (hawk moths) and short-tongue (bees and small beetles) pollinators; and to assess whether this variation was related to the selection pressures exerted by flower visitors. Short-tongue pollinators preferentially visited plants with floral traits that enhanced flower accessibility; consequently, there was directional selection for accessibility (integration at floral-module level) in the populations where they dominated or codominated. In the population with both short- and long-tongue pollinators, disruptive selection on corolla width and directional selection against whole-flower integration was also found. Dominance by long-tongue pollinators (hawk moths) resulted in disruptive selection on whole-flower integration. Overall, the conflicting selection pressures that were found matched among-population differences in covariance structure: populations with short-tongue pollinators showed correlations between corolla-tube width and other floral traits that were absent in the population pollinated primarily by hawk moths. Conflicting selection on floral integration mediated by floral visitors can occur even in nearby populations of a species with restricted floral morphology.

Natural habitat loss and exotic plants reduce the functional diversity of flower visitors in a heterogeneous subtropical landscape

Summary Functional diversity (FD) of pollinators can increase plant reproductive output and the stability of plant‐pollinator communities. Yet, in times of world‐wide pollinator declines, effects of global change on pollinator FD remain poorly understood. Loss of natural habitat and exotic plant invasions are two major drivers of global change that particularly threaten pollinator diversity. In a subtropical South African landscape, we investigated changes in the FD of flower visitor assemblages on native and exotic plants along gradients of natural habitat loss and relative abundance of exotic plants. We used a data set of 1434 flower visitor individuals sampled on 131 focal plants and calculated the FD in three flower visitor traits that are strongly related to plant–flower visitor interactions and pollination processes: proboscis length, proboscis diameter and body length. Multivariate FD of flower visitors decreased with both increasing natural habitat loss and relative exotic abundance. Importantly, changes in FD went beyond those in flower visitor richness. Furthermore, flower visitor richness was not related to either natural habitat loss or relative exotic abundance. Loss in multivariate FD seemed to be mediated by complementary reductions of FD in proboscis length with natural habitat loss and of FD in body length with both global change drivers. Correspondingly, we recorded lower abundances of long‐tongued flower visitors with natural habitat loss and reduced variance in body size with both drivers. In contrast, FD in proboscis diameter was unaffected by either driver. All effects of the two global change drivers were non‐interactive. Our results show that both natural habitat loss and exotic plants negatively affect flower visitor FD, which may imperil pollination of specialized plant species in degraded habitats. In contrast, flower visitor richness may not cover all facets of flower visitor FD that are relevant to pollination processes. Distinct responses of visitor traits to the two drivers suggest limited options to infer relations of one trait to another. Finally, additive effects of natural habitat loss and exotic plant invasions highlight the need to consider multiple drivers of global change when investigating ecosystem processes at a community scale.

Can the pollination biology and floral ontogeny of the threatened Acacia carneorum explain its lack of reproductive success?

AbstractMany Acacia species in arid areas of eastern Australia have been severely impacted by grazing, habitat degradation and fragmentation. These factors have been at the core of proposed explanations for the reproductive failure and numerical decline of Acacia carneorum and other threatened acacias. Paradoxically, the sympatric Acacia ligulata is thriving and highly fecund. Although these species have superficially similar floral displays, differences in sexual reproductive success may reflect interactions between flower and inflorescence ontogeny and pollinator assemblages. We compared the floral biology and flower visitor assemblages of A. carneorum and A. ligulata at four sites per species. Both species displayed similar floral ontogeny and synchronicity of display, with inflorescences simultaneously hermaphroditic for 4–5 days. However, A. ligulata displayed a higher density of flowers than A. carneorum and, while both species received a range of flower visitors, A. ligulata was visited by relatively few species and was serviced primarily by the non‐native honeybee Apis mellifera, which typically made many within‐plant movements during foraging bouts. In contrast, A. carneorum was visited by a diverse suite of native insects that carried little pollen and made fewer within plant movements. On average, Apis mellifera carried 98.4 % A. ligulata pollen, whereas the native insect visitors of A. carneorum carried only 45 % A. carneorum pollen. Differing floral ontogeny or lack of native pollinators does not explain the reproductive failure of A. carneorum. The success of A. ligulata may reflect pollination services provided by A. mellifera and interactions with plant mating systems.

Differences in the diversity and composition of the pollinator assemblage of two co-flowering congeneric alpine wallflowers, Erysimum nevadense and E. baeticum

Many alpine plants display a generalist pollination system where almost any available flower visitor could act as a legitimate pollinator. Co-flowering related plant species displaying a generalized pollination system can decrease their fitness due to interspecific mating. In this study, we determine the difference in diversity and composition of the pollination systems of two co-occurring species endemic to the alpine region of the Sierra Nevada (SE Spain), Erysimum nevadense Reut. and Erysimum baeticum baeticum (Heywood) Polatschek (Brassicaceae), and check for the potential role of floral and plant traits in explaining the observed differences. For this, we labeled 30 plants in two populations of each plant species located in the same area. We determined flower visitor assemblage by sampling all insects approaching the flowers and contacting the sexual organs during 60-min surveys. We found that the diversity of the pollinator assemblage was similar between the two studied wallflower species, both species showing a much generalized pollination system. However, the composition of the pollinator assemblage was different, since the flowers of E. nevadense were visited mostly by beetles and in a lesser extent by hover-flies, whereas the flowers of E. baeticum baeticum were visited mostly by ants and bees. Interestingly, flower traits varied between species, with E. nevadense displaying yellow, smaller and shallower flowers and E. baeticum baeticum displaying purple, large and deeper flowers. These findings suggest that differences in floral traits can explain the observed differences in the composition of the pollinator assemblage between both wallflower species.