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Heatwaves are an increasingly common extreme weather event across the globe and are projected to surge in frequency and severity in the coming decades. Plant‐pollinator mutualisms are vulnerable due to interacting effects of extreme heat on insect pollinator foraging behaviour and their forage plants.We designed an experiment to parse the impact of extreme heat on bumblebee foraging mediated directly through air temperature and indirectly through changes in plant rewards.Temperatures simulating a moderate heatwave negatively impacted foraging bumblebees reducing the proportion of successful foraging bouts, foraging bout duration and plant and flower visitation and indirect stress through reduced nectar production that limited foraging bout duration.Our experimental results provide a mechanistic link between climate, plants and pollinators and suggest in situ conditions from heatwaves could have profound negative consequences for bumblebee colony persistence and maintenance of pollination services. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Nectar is a key resource for numerous insects. Despite its importance, nectar productivity has mainly been assessed using one sampling method, in which the volume of nectar produced by a flower is measured after 24 h of isolation from insects ('measured 24 h volume' hereafter). This method assumes that nectar removal by flower‐visiting insects does not affect nectar productivity. Hence, a linearity in the nectar production dynamic is assumed. The effect of nectar removal could lead to an actual volume of nectar produced per flower over 24 h being higher or lower than the measured 24 h volume. Whether the nectar productivity is influenced by insect activity still therefore needs to be assessed.In a field experiment, we estimated the nectar production dynamics of lavender (Lavandula hybrida) and fennel (Foeniculum vulgare) flowers and tested whether they met the linearity assumption. Then, we developed a simulation model to identify how different scenarios of insect foraging activity: nectar removal rate (average and maximum), and flower‐selection strategies (random selection or rewarding flower selection) alter the estimated 24 h volume of nectar for both crops ('estimated 24 h volume' hereafter). Finally, we tested whether the estimated 24 h volume differed from the measured 24 h volume for both crops.Lavender and fennel showed equal measured 24 h volume of nectar but the produced nectar volume over 6 h suggested that a flower of lavender was more productive than a flower of fennel. Both nectar production dynamics did not meet the assumption of linearity. The simulation models showed that the estimated 24 h volume increased with maximum nectar removal rate for lavender, and the opposite was found for fennel. Rewarding selection always increased the estimated 24 h volume for fennel while for lavender a positive effect was detected at average rate of nectar removal. We found that the estimated 24 h volume was always greater than the measured 24 h volume.Our model demonstrated that the effect of insect foraging activity on flower's nectar productivity should be considered while estimating the resources produced by plants. As an alternative, measures of produced nectar volume in short time spans may be compared with the measured 24 h volume to check the reliability of this widespread method. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Exposure to radiation is a natural part of our environment. Yet, due to nuclear accidents such as at Chernobyl, some organisms are exposed to significantly elevated dose rates. Our understanding of the effects of radiation in the environment is limited, confounded by substantial interspecific differences in radio‐sensitivity and conflicting findings.Here we study radiation impacts on bumblebees in the laboratory using principles from life‐history theory, which assume organismal investment in fitness‐related traits is constrained by resource availability and resource allocation decisions. To investigate how chronic radiation might negatively affect life‐history traits, we tested whether exposure affects bumblebee energy budgets by studying resource acquisition (feeding) and resource use (metabolic rate).We monitored metabolic rate, movement and nectar intake of bumblebees before, during and after 10 days of radiation exposure. Subsequently, we monitored feeding and body mass across a dose rate gradient to investigate the dose rate threshold for these effects. We studied dose rates up to 200 μGy/hr: a range found today in some areas of the Chernobyl Exclusion Zone.Chronic low‐dose radiation affected bumblebee energy budgets. At 200 μGy/hr nectar consumption elevated by 56% relative to controls, metabolic CO2 production increased by 18%, and time spent active rose by 30%. Once radiation exposure stopped, feeding remained elevated but CO2 production and activity returned to baseline. Our analysis indicates that elevated metabolic rate was not driven by increased activity but was instead closely associated with feeding increases. Our data suggest bumblebee nectar consumption was affected across the 50–200 μGy/hr range.We show field‐realistic radiation exposure influences fundamental metabolic processes with potential to drive changes in many downstream life‐history traits. We hypothesise that radiation may trigger energetically costly repair mechanisms, increasing metabolic rate and nectar requirements. This change could have significant ecological consequences in contaminated landscapes, including Chernobyl. We demonstrate bumblebees are more sensitive to radiation than assumed by existing international frameworks for environmental radiological protection. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Neonicotinoid pesticides in the nectar and pollen of managed crops and wildflowers contribute to the global declines of bees. These chemicals can have detrimental effects on bees' physiology, behaviour and reproduction. Floral nectar also contains secondary chemistry with its own effects on bee health. How nectar secondary chemistry may act additively or synergistically with neonicotinoids is unknown.Here, we asked how an acute exposure to a common neonicotinoid, imidacloprid (IMD) affected the longevity, immune function and behaviour of bumble bee Bombus impatiens workers maintained on diets enriched with one of three nectar secondary metabolites (NSMs; the alkaloid caffeine, the terpenoid thymol or the cardiac glycoside digoxin). A factorial design allowed us to assess the potential for additive and interactive effects of each NSM and IMD combination on multiple health outcomes.Without IMD exposure, different dietary NSMs each had positive effects on life span (caffeine), immune function (digoxin) and activity levels (caffeine, thymol), although these came with trade‐offs. A single sublethal IMD exposure overshadowed these NSM effects, and in two cases, an NSM‐enriched diet magnified the negative effects of pesticide exposure.In summary, we show that even a single acute exposure to a pesticide has the potential to reshape interactions between pollinators and plants mediated by nectar secondary chemistry. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

A fundamental question in community ecology is how the quantity of floral resources affects pollinator activity and how this relates to the structure and robustness of pollination networks. The issue has been mainly addressed at the species level, while at the community level several questions are still open.Using a species‐rich semi‐natural grassland as model ecosystem, we explored the relationship between community‐level quantity of floral resources, the number of flower visits at community level and descriptors of the structure and robustness of pollination networks. To assess whether patterns of pollination interactions were consistent when using different types of floral resources, we measured three types of floral resources, namely the volume of nectar, the number of pollen grains and the number of flowers.Community‐level pollinator visitation rate showed a hump‐shaped relationship with the quantity of floral resources. Results were consistent among models employing different measures of floral resources as independent variables. The relationship between the quantity of floral resources and the structure and robustness of the network was not consistent among different types of floral resources; only intermediate levels of nectar volume were associated with high levels of network robustness.The pattern we found is in contrast with some former studies which reported positive linear relationships between the community‐level visitation rate of pollinators and the quantity of floral resources. Rather, the observed hump‐shaped pattern resembles the relationship previously found between the quantity of floral resources of a given plant species and its visitation rate per flower. Our results highlighted that, by using specific types of floral resources (e.g. the volume of nectar and the number of pollen grains), it is possible to reveal ecological processes that would be masked by using the number of flowers as the sole measure of floral resource. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

In many communication systems, signal receivers profit from honest signals that indicate the signaller's quality, whereas low‐quality signallers should profit from cheating. Under such a conflict of interests between signallers and signal receivers, the maintenance of honest signals presents a puzzle. In theory, honesty can represent an evolutionarily stable strategy, but the actual mechanisms have been studied in few systems only.Here, we investigate honest signalling in a plant species, Brassica rapa, that advertises nectar volumes to pollinators by two honest floral signals; corolla size and the floral volatile phenylacetaldehyde. In a series of experiments we tested for physiological constraints and pollinator behaviours related to honest floral signals and nectar volume, incorporated the result into a mathematical model, and verified its predictions experimentally.While honest floral signals attracted pollinators, the bees' flower visitation time depended on nectar volume and was associated with the number of seeds that flowers developed. Furthermore, honest floral signals and seed set without pollen limitation both increased after soil fertilisation, indicating nutrient limitation in these traits.The mathematical model which incorporates these findings showed that honest signalling in B. rapa can be maintained by a combination of pollinator behaviour and resource limitation causing differential benefits of nectar production. The study demonstrates how honest floral signalling can evolve as a stable strategy in a plant species. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

The high variability observed in floral traits has been interpreted as resulting from the adaptation of plants to pollinators, as the latter present innate preferences for specific floral traits and impose selection over them. However, some pollinators such as bees can learn to associate floral signals with rewards, thus increasing floral constancy on more rewarding flowers. The integration of all these rewards and cues is markedly important at community level, where co‐flowering species compete for pollinators.In order to verify the honesty of the above‐mentioned signals, we examined the association between floral visual signals (size, colour, symmetry and floral display) and rewards (pollen and nectar) for 98 species in a Mediterranean community. The associations between floral traits were analysed considering the phylogenetic relationship between the different species.Flower colour, size, pollen volume or amount of sucrose exhibited no phylogenetic signal, which suggests an adaptive evolution in response to different conditions in the pollinator community. Flower size was seen to constitute the most honest signal for pollinators, as this was significantly associated with quantities of pollen and nectar. In contrast, nectar concentration was observed to be positively associated with chromatic contrast. We detected no relationship between flower shape and rewards, on the one hand, nor between flower display and rewards, on the other.Our study unequivocally demonstrates the correlation between rewards and the visual signals perceived by bees, the most effective pollinators in the Mediterranean Basin. In the community studied, bees employed flower size at longer distances and chromatic contrast at shorter distances to predict rewards. The limited number of studies existing in this sense indicates that this kind of association appears to be community specific. [ABSTRACT FROM AUTHOR]

Size‐number trade‐offs in reproduction are commonly observed in nature. Bumblebee (Bombus spp.) colonies produce workers that vary considerably in size. This variation suggests that colonies face potential size‐number trade‐offs when producing workers.Here, we estimated size‐based vital rates of Bombus vosnesenskii workers using colonies reared from wild‐caught queens. We conducted a mark–recapture study to estimate worker survival as a function of body size. We also collected data on pollen and nectar loads as well as foraging trips using a radiofrequency identification system to estimate daily resource return as a function of body size. We integrated survival and daily resource return to estimate lifetime resource collection and offset these estimates by the size‐based worker production costs.We found size‐based trade‐offs among workers of different sizes. Smaller workers had higher survival, but larger workers returned with more resources per day. The largest workers made slightly fewer foraging trips per day.Overall, larger workers made the greatest lifetime contribution to both nectar and pollen collection. However, once the benefits of larger workers are offset by their higher production costs, intermediate‐sized workers were the optimal for net resource contribution according to our models. Many previous studies have found that larger workers outperformed smaller workers with foraging and in‐nest tasks, yet these studies have not integrated multiple fitness components or worker production costs to quantify net resource contribution towards colony growth.Accounting for trade‐offs between costs and performance changed our conclusions about optimal body size from being large to being near the observed average.  Similar approaches of integrating multiple vital rates may resolve apparently suboptimal life histories in other taxa. A plain language summary is available for this article. Plain Language Summary [ABSTRACT FROM AUTHOR]

Nectar is a crucial energy resource that strongly mediates the interactions between plants and animal pollinators or plant defenders. Previous research has shown that nectar is frequently colonized by microorganisms, most commonly bacteria and yeasts, which can have a strong impact on nectar chemistry. However, at present little is known about the effects of microorganisms on the fitness of animals feeding on nectar., We used three nectar bacteria representing different metabolic groups ( Asaia sp., Lactococcus sp. and Rosenbergiella sp.) and the common generalist aphid parasitoid Aphidius ervi (Haliday; Hymenoptera: Braconidae) to test the hypothesis that different nectar-dwelling bacteria affect nectar consumption and insect longevity differently by altering the chemistry of nectar., Bacteria significantly affected nectar chemistry by altering its acidity, sugar and amino acids composition/concentration and by adding compounds synthesized by the microbes. Although inoculation with bacteria did not affect nectar consumption, a significant difference in insect longevity was observed. The impact on longevity was species specific, with Lactococcus being beneficial and Asaia having a detrimental effect., Bacteria have a strong impact on nectar chemistry and changes in nectar chemistry may not only influence the foraging behaviour of flower-visiting animals and impact on plant fitness, but also influence the fitness of nectar-consuming organisms. As effects were species dependent, changes in nectar chemistry induced by different bacteria may have contrasting effects on the interactions between plants and insects. It is therefore essential to know how different microbes alter nectar chemistry to understand the relationships between plants, nectar-inhabiting microbes and nectar-consuming animals., A is available for this article. [ABSTRACT FROM AUTHOR]

Pollinators utilize floral resources that vary in colour, scent and reward quality. Variation in such traits, including nectar rewards, in addition to cues associated with their quality, can influence pollinator foraging decisions with consequences for pollinator reproductive success. Nectar is commonly subject to colonization by micro-organisms capable of affecting a suite of traits important for pollinator attraction and fitness; yet, links between microbial presence and changes in pollinator preference and performance remain few., Here, we evaluated the effects of a nectar-inhabiting micro-organism on pollinator foraging behaviour and reproduction using the common eastern bumblebee Bombus impatiens and the cosmopolitan nectar yeast Metschnikowia reukaufii. Using a combination of choice and no-choice behavioural and feeding assays, we manipulated the presence and viability of M. reukaufii in nectar and assessed bumblebee foraging and reproductive responses., Bombus impatiens workers responded positively to the presence of yeasts. Foragers trained to associate yeast presence with flower colour visited a significantly greater proportion of flowers inoculated with yeast when subject to a colour discrimination test. Moreover, foragers naïve to nectar yeasts incorporated more yeast-inoculated flowers into initial foraging bouts when presented with a novel floral array. In addition, bees spent significantly longer foraging on yeast-inoculated flowers compared to yeast-free flowers. However, when we manipulated yeast presence and viability in microcolonies of queenless workers, we found no effect of yeast on components of bumblebee reproduction, such as initiation of egg laying and number of eggs laid. This lack of an effect of yeast persisted even under conditions of pollen limitation., Taken together, these results suggest that nectar yeasts can enhance floral signalling and alter pollinator foraging behaviour at individual flowers, though they may not directly affect pollinator performance. Thus, nectar yeasts may play a significant role in mediating pollinator foraging behaviour, with consequences for plant fitness and evolution of floral traits. [ABSTRACT FROM AUTHOR]

The ecological function of secondary metabolites in plant defence against herbivores is well established, but their role in plant-pollinator interactions is less obvious. Nectar is the major reward for pollinators, so the occurrence of defence chemicals in the nectar of many species is unexpected. However, increasing evidence supports a variety of potential benefits for both plant and pollinator from these compounds., Beneficial effects may include: (i) mediating specialization in plant-pollinator interactions, (ii) protecting nectar from robbery or larceny and (iii) microbial activity including preservation of nutrients in nectar from degradation and reduction in disease levels in pollinators., Secondary metabolites in nectar can be toxic or repellent to flower visitors, but equally they can go undetected or even make nectar more apparent or attractive. These biological effects are concentration dependent, so must be considered at a range of ecologically relevant doses. For example, caffeine occurs in nectar and improves honeybee memory for odours associated with food rewards, which enhances pollen transfer at naturally occurring concentrations but is repellent to honeybees at higher concentrations., This review synthesizes evidence from recent literature that supports selection for secondary metabolites in floral nectar as an adaptation that drives the co-evolution between plants and their pollinators. However, their presence in nectar could still simply be a consequence of their defensive role elsewhere in the plant (pleiotropy). We highlight the need for more studies demonstrating measurable benefits to the plant, the importance of exposure levels and effects on target species beyond the current emphasis on alkaloids and bees., A is available for this article. [ABSTRACT FROM AUTHOR]

Proboscis length has been proposed as a key dimension of plant pollination niches, but this niche space has not previously been explored at regional and global scales for any pollination system. Hawkmoths are ideal organisms for exploring pollinator niches as they are important pollinators in most of the biodiverse regions of the earth and vary greatly in proboscis length, with some species having the longest proboscides of all insects., Using data sets for nine biogeographical regions spanning the Old and New World, we ask whether it is possible to identify distinct hawkmoth pollination niches based on the frequency distribution of proboscis length, and whether these niches are reflected in the depths of flowers that are pollinated by hawkmoths. We also investigate the levels of specialization in hawkmoth pollination systems at the regional and community level using data from interaction network studies., We found that most regional hawkmoth assemblages have bimodal or multimodal distributions of proboscis length and that these are matched by similar distributions of floral tube lengths. Hawkmoths, particularly those with longer proboscides, are polyphagous and at the network level show foraging specialization equivalent to or less than that of bees and hummingbirds. In the case of plants, shorter-tubed flowers are usually visited by numerous hawkmoth species, while those that are longer-tubed tend to exclude shorter-proboscid hawkmoths and thus become ecologically specialized on longer-proboscid hawkmoth species. Longer-tubed flowers tend to have greater nectar rewards, and this promotes short-term constancy by long-proboscid hawkmoths., Our results show that pollinator proboscis length is a key niche axis for plants and can account for the patterns of evolution in functional traits such as floral tube length and nectar volume. We also highlight a paradoxical trend for nectar resource niche breadth to increase according to proboscis length of pollinators, while pollinator niche breadth decreases according to the tube length of flowers., A is available for this article. [ABSTRACT FROM AUTHOR]

Invasive species are considered a main driver of pollinator declines, yet the direct effects of invasive alien plants on pollinators are poorly understood., Abundant, invasive plant species can provide a copious nectar resource for native pollinators. However, the nectar of some plants contains secondary compounds, usually associated with defence against herbivores. The impacts of these compounds on pollinators are often unknown., We compared how consumption of grayanotoxin I and III, natural secondary compounds in the nectar of invasive Rhododendron ponticum L., affected three native bee species: a honeybee, ( Apis mellifera L.), a solitary mining bee ( Andrena carantonica, Pérez) and a bumblebee, ( Bombus terrestris, L.)., Survival of the solitary bee and the bumblebee species was not affected by either grayanotoxin, but honeybees were ∼20× more likely to die when fed solutions containing grayanotoxin I. Furthermore, solitary bees were deterred from feeding and exhibited malaise behaviours indicative of sublethal toxicity in response to consumption of grayanotoxin I. In contrast, grayanotoxins did not affect bumblebee survival or behaviour, even when bees were subjected to multiple stressors (parasite infection or food stress)., Our experiments suggest that while R. ponticum provides abundant floral nectar, it is only available as a food resource to pollinators that tolerate grayanotoxins. Pollinators whose health is negatively affected by grayanotoxins may experience negative impacts from R. ponticum invasion directly (if they consume R. ponticum nectar) or indirectly (if native floral resources are replaced by R. ponticum)., Our study makes a novel comparison of the effects of a natural nectar secondary compound on three pollinator species and clearly demonstrates drastic variation in the responses of different key pollinator taxa to a nectar toxin. Our findings are thus in congruence with literature demonstrating the varying effects of invasive plant chemistry on native foliar herbivores, and our work demonstrates that nectar chemistry should be taken into account when determining the impacts of plant invasion for native pollinators. [ABSTRACT FROM AUTHOR]

Omnivory enables animals to fill more than one trophic niche, providing access to a wider variety of food resources with potentially higher nutrient value, particularly when resources become scarce. Animals can achieve omnivory using different strategies, for example opportunistic foraging, or switching between multiple trophic niches., The Neotropical bat Glossophaga soricina (Pallas, 1766) is a common and widespread species known for nectar feeding, but it also eats fruit and insects. Approaching stationary objects (flowers and fruits) or moving objects (insects) poses different sensory tasks and should require different echolocation behaviours. Here we tested the contrasting hypothesis that G. soricina can approach both stationary and moving objects using the same echolocation behaviour, thus feeding at different trophic levels by a single sensory mechanism., Using DNA barcoding, we demonstrate that G. soricina eats beetles (Coleoptera), flies (Diptera) and noctuid moths with bat-detecting ears. Laboratory observations show that G. soricina actively hunts for prey so insect consumption does not appear to be opportunistic. After capture, individuals consumed prey while perched and manipulated them with jaw, thumb, wrist and wing movements, but food handling was longer and chewing rate slower than in obligate insectivores., In contrast to most insectivorous bats, the echolocation calls of G. soricina are of high frequency and low intensity, and G. soricina did not produce feeding buzzes when approaching insects. An acoustic model of detection distances shows that its low-intensity calls fail to trigger the auditory neurons of eared moths, allowing G. soricina to overcome auditory prey defences., Individuals achieved niche flexibility using a unique but generalist behavioural approach rather than employing two different specialist methods. Our findings provide a novel insight into the functional mechanisms of insect capture in G. soricina and highlight the importance of considering niche flexibility in classifying trophic links in ecological communities. [ABSTRACT FROM AUTHOR]

Nectar-bearing flowers are characterized by many different shapes, sizes and orientations, which may affect the way hummingbirds feed from them. Many hummingbird-pollinated flowers are oriented downwards, thereby requiring that trochilids feed while hovering with the bill oriented vertically upward., We measured body orientations, wingbeat kinematics and hovering metabolic rates for Anna's Hummingbirds ( Calypte anna) feeding from artificial flowers that were oriented horizontally, tilted 45° downwards and pointing vertically downwards., When feeding from vertically oriented flowers, hummingbirds employed an upright body position combined with dorsal head flexion. Additional kinematic adjustments included an increased stroke plane angle relative to the longitudinal body axis and an increased stroke amplitude deriving from increases in the minimum positional angle of the wingbeat., By contrast, wingbeat frequency, the stroke plane angle relative to horizontal, the ratio of the minimum to maximum positional angles of the wingbeat and the upstroke/downstroke ratio did not vary during feeding from different flower orientations., Metabolic rates increased by an average (±SD) of 10·8 (±8·8)% for feeding from vertically compared to horizontally oriented flowers., Feeding from pendent flowers comes with a substantial metabolic cost that may influence floral selection by hummingbirds and thus the evolution of associated pollination syndromes. [ABSTRACT FROM AUTHOR]

The 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 of Asclepias. 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 of Asclepias., We found that the average cardenolide concentrations in nectar, leaves and flowers of the 12 Asclepias species 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. [ABSTRACT FROM AUTHOR]

1. Many plant species have two inducible indirect defences against herbivores, emission of volatile organic compounds (VOCs) and secretion of extrafloral nectar (EFN). Moreover, herbivore-induced VOCs can serve as airborne signals in plant-plant communication, inducing and/or priming defences in undamaged neighbouring plants. However, it remains largely unknown, particularly in woody plants, whether herbivore-induced VOCs induce and/or prime these two indirect defences simultaneously. 2. We investigated the VOC-mediated induction and priming of VOC emission and EFN secretion in the woody plant hybrid aspen ( Populus tremula × Populus tremuloides) in the context of plant-plant communication. Hybrid aspen saplings were exposed to VOCs released either from herbivore-infested or uninfested conspecifics and subsequently challenged by herbivores. VOCs and EFN from exposed plants were collected throughout experiments. Additionally, local and systemic EFN induction was investigated. 3. Exposure to VOCs from infested plants directly induced secretion of EFN sugars but not emission of volatile terpenes. Upon subsequent herbivore attack, however, plants previously exposed to herbivore-induced VOCs released significantly more terpenes than unexposed plants, whereas EFN secretion was not increased, indicating that herbivore-induced VOCs prime VOC emission but not EFN secretion. This switching in the indirect defence priority from induced EFN secretion to primed VOC emission may reflect the potential fitness disadvantages of VOC emission and EFN secretion on their own. In addition, feeding by Epirrita autumnata larvae reduced EFN sugar production both locally and systemically, which disagrees with previous findings and suggests that EFN secretion varies depending on plant and herbivore species. 4. Thereby, our work has parallels and divergences from the most significant previous studies. Nevertheless, it suggests that plants can respond differently to early warning signals and ensuing herbivory and in doing so fine-tune their different indirect defences timely to achieve optimal use of resources. [ABSTRACT FROM AUTHOR]

Summary 1. Many floral displays are visually complex, transmitting multi-coloured patterns that are thought to direct pollinators to nectar rewards. These 'nectar guides' may be mutually beneficial, if they reduce pollinators' handling time, leading to an increased visitation rate and promoting pollen transfer. Yet, many details regarding how floral patterns influence foraging efficiency are unknown, as is the potential for pollinator learning to alter this relationship. 2. We compared the responses of bumblebee ( Bombus impatiens Cresson) foragers to artificial flowers that either possessed or lacked star-like patterns. By presenting each bee with two different foraging scenarios (patterned flowers rewarding/plain flowers unrewarding, plain flowers rewarding/patterned flowers unrewarding) on different days, we were able to assess both short- and long-term effects of patterns on bee foraging behaviour. 3. Bees discovered rewards more quickly on patterned flowers and were less likely to miss the reward, regardless of whether corollas were circular or had petals. Nectar guides' effect on nectar discovery was immediate (innate) and persisted even after experience, although nectar discovery itself also had a learned component. We also found that bees departed patterned flowers sooner after feeding. Finally, when conditions changed such that flowers no longer provided a reward, bees visited the now-unrewarding flowers more persistently when they were patterned. 4. On the time-scale of a single foraging bout, our results provide some of the first data on how pollinators learn to forage efficiently using this common floral trait. Our bees' persistent response to patterned flowers even after rewards ceased suggests that, rather than being consistently mutually beneficial to plant and pollinator, nectar guide patterns can at times promote pollen transfer for the plant at the expense of a bee's foraging success. [ABSTRACT FROM AUTHOR]

1. Plants with open flowers and exposed nectar should attract a wide diversity of flower visitors, yet, for reasons that are not yet well understood, some plants with these ‘generalist’ floral traits have highly specialized pollination systems. 2. We investigated this problem in the African milkweed Pachycarpus grandiflorus which has open flowers that produce copious amounts of exposed and concentrated nectar, yet is visited almost exclusively by spider-hunting wasps in the genus Hemipepsis. 3. These wasps were the only visitors found to consistently carry pollinaria and a cage experiment showed that they are capable of successfully pollinating this plant. Furthermore, experimental hand-pollinations showed that P. grandiflorus is genetically self-incompatible and thus reliant on pollinators for seed set. 4. We investigated the roles of chemical (nectar and floral scent) and spectral properties in the selective attraction of wasps and the filtering out of other potential flower visitors. Nectar palatability experiments showed that the nectar is unpalatable to honeybees but palatable to the wasps. Choice experiments conducted in the field and using a Y-maze in the laboratory showed that wasps are attracted primarily by scent rather than visual cues. Analysis of scent using Gas Chromatography-Mass Spectrometry showed that these inflorescences produce 36 different compounds, mostly monoterpenes and aliphatics. Analysis of spectral reflectance showed that flowers have similar colouring to the background vegetation. 5. We conclude that P. grandiflorus is specialized for pollination by Hemipepsis wasps, and in the absence of morphological filters, achieves specialization through unpalatable nectar, cryptic colouring and scent as a selective pollinator attractant. 6. This study demonstrates that plants whose flowers are not morphologically adapted to exclude particular floral visitors can achieve specialization through non-morphological filters. [ABSTRACT FROM AUTHOR]

1. The evolution of flowering plants has undoubtedly been influenced by a pollinator’s ability to learn to associate floral signals with food. Here, we address the question of ‘why’ flowers produce scent by examining the ways in which olfactory learning by insect pollinators could influence how floral scent emission evolves in plant populations. 2. Being provided with a floral scent signal allows pollinators to learn to be specific in their foraging habits, which could, in turn, produce a selective advantage for plants if sexual reproduction is limited by the income of compatible gametes. Learning studies with honeybees predict that pollinator-mediated selection for floral scent production should favour signals which are distinctive and exhibit low variation within species because these signals are learned faster. Social bees quickly learn to associate scent with the presence of nectar, and their ability to do this is generally faster and more reliable than their ability to learn visual cues. 3. Pollinators rely on floral scent as a means of distinguishing honestly signalling flowers from deceptive ones. Furthermore, a pollinator’s sensitivity to differences in nectar rewards can bias the way that it responds to floral scent. This mechanism may select for flowers that provide olfactory signals as an honest indicator of the presence of nectar or which select against the production of a detectable scent signal when no nectar is present. 4. We expect that an important yet commonly overlooked function of floral scent is an improvement in short-term pollinator specificity which provides an advantage to both pollinator and plant over the use of a visual signal alone. This, in turn, impacts the evolution of plant mating systems via its influence on the species-specific patterns of floral visitation by pollinators. [ABSTRACT FROM AUTHOR]

1. The complexity of ecological communities can often hinder understanding their structural features. With the recent application of network theory, the structure of previously neglected mutualistic communities has begun to be elucidated. 2. Mutualistic communities have now been shown to follow particular power distributions in their degree, that is, the number of species interactions per species. However, predictive variables of degree and other structures of mutualistic networks remain largely unexplored. 3. Here, we show that body size of ants is positively correlated with their degree in mutualistic networks comprised of ant interactions with extrafloral nectar (EFN) bearing plants in the Sonoran Desert. This pattern in body size and the number of plant species with which ants interact occurred among all eight sampled communities, a relationship which was not contingent upon phylogenetic history among ant species. 4. These results indicate that further study of body size in ant–plant and other mutualistic networks may yield promising insights into the processes influencing their structure. Moreover, the degree–body size relationship for ant–plant mutualistic communities is consistent with that of predator–prey food webs, possibly suggesting similar underlying processes at work. [ABSTRACT FROM AUTHOR]

1. Most animal-pollinated flowering plants offer nectar as a reward for their pollinators. Some 20 000 species, however, offer only pollen and rely on pollen-foraging bees for pollination. This creates a dilemma since pollen grains contain the male gametes and should be protected from becoming bee food. Darwin was the first to hypothesize that a ‘division-of-labour’ among stamens could solve this dilemma, with some stamens providing pollen as food, others providing pollen for fertilization. This hypothesis can only be tested if pollen grains from the two sets of stamens can be distinguished and their fates determined to the point of attachment on the stigma. 2. We tested Darwin's hypothesis in Melastoma malabathricum (Melastomataceae), a pollen-only flower with conspicuously differentiated stamens, an inner set that is short and yellow and an outer set that is much longer and purple with small yellow spurs. Pollen release is through terminal anther pores. Taking advantage of different exine patterns on the pollen produced by the two sets of stamens, we carried out a series of experimental manipulations to compare pollinator foraging behaviour and pollen pathways from anthers to stigmas. 3. The results demonstrate that in spite of all 10 stamens being buzzed simultaneously by the carpenter bees that pollinate M. malabathricum, pollen from the purple ‘fertilization’ stamens is dramatically more likely to land on stigmas than pollen from the yellow ‘feeding’ stamens. Removal experiments showed that the yellow ‘feeding’ stamens also attracted pollinators from a distance. Flowers that had their anther pores plugged received fewer buzzing bouts per visit, indicating that bees assessed the amount of pollen received per bout. Surprisingly, there was no significant difference in pollen loads on stigmas of flowers that had their anthers plugged and stigmas of controls, demonstrating the efficiency of vector-assisted cross-pollination and the lack of vector-assisted self-pollination. 4. The unexpectedly precise placement of pollen grains even with buzz pollination, with a large proportion of the grains deposited out of the bees’ grooming reach, helps explain the evolutionary persistence of pollen as a reward in spite of the bees’ ability to assess the amount of pollen received during foraging bouts. Together, these results strongly support Darwin's division-of-labour hypothesis. [ABSTRACT FROM AUTHOR]

1. Although it is well established that different plant species vary considerably in the quality of pollinator rewards they offer, it is unclear how plant reproductive systems, in particular an obligate dependence on insects for pollination, might influence the evolution of pollinator rewards. Moreover, unlike the interaction between nectar reward and pollinator visitation, we have a limited understanding of the way in which pollen quality influences pollinator foraging behaviour. 2. We quantified the pollen protein and amino acid content for 23 NW European plant species. Pollen quality was compared with breeding system (facultative- vs. obligate insect-pollinated). A subset of 18 plants was sampled from a single habitat. For these we compared the proportion of pollen collection visits made by bumblebees with the quality of pollen offered. 3. We found a significant association between pollen quality and reproductive system; pollen of obligate insect-pollinated species contained higher protein content. We also found a significant relationship with pollinator use; plants most frequently visited by pollen-collecting bumblebees produced the highest-quality pollen. 4. We discuss how the close relationship between pollen quality and bumblebee attraction may have important benefits for plant reproductive success. However, we also show how the disruption of this mutualism can have detrimental consequences for plant and pollinator alike. [ABSTRACT FROM AUTHOR]

1. Understanding avian diet preferences reveals a great deal about the birds’ digestive physiology and relationships with food plants, and can make a valuable contribution towards directing physiological and ecological research. Importantly, diet preferences are likely to reflect physiological constraints and therefore mechanisms of digestion. 2. We assessed the interaction between diet concentration and sugar-type preferences of three Australian nectarivorous bird species. Each individual bird was offered paired energetically-equivalent diets: a sucrose solution and hexose (1 : 1 mixture of glucose : fructose) solution over a range of diet concentrations from 0·075 to 2 mol L−1 Sucrose Equivalents (SE). 3. Similar patterns were found for all three species. Intake on the most dilute diets was insufficient to maintain energy balance, suggesting that these birds faced physiological constraints on such diets. 4. All three species demonstrated a preference for hexose over sucrose when offered dilute diets, and sucrose (or none) preference on more concentrated diets. The three species differed in terms of when this switch from hexose to sucrose preference took place. Rainbow lorikeets (Psittacidae, c. 135 g body mass) demonstrated hexose preference for diets up to and including 0·75 mol L−1 SE; sucrose was preferred on 2 mol L−1 SE diets. Red wattlebirds (Meliphagidae, c. 105 g) showed hexose preference on only the most dilute (0·075 mol L−1 SE) diet, and sucrose preference on 1 and 2 mol L−1 SE diets. New Holland honeyeaters (Meliphagidae, c. 22 g) preferred hexose on 0·075 and 0·1 mol L−1 SE diets, and their selectivity for sucrose was not statistically significant. We suggest that the switch from hexose preference may be directly related to the digestive capacity of different taxa. 5. Accumulating evidence suggests similar patterns of sugar preferences in various nectarivorous bird lineages. A switch from hexose preference on dilute diets to sucrose preference on concentrated diets has now been shown for hummingbirds, flowerpiercers, sunbirds, honeyeaters and lorikeets. Hexose preference on dilute diets suggests that reduced digesta retention time and low sugar concentration influences sucrose hydrolysis efficiency, whilst absorption rate of monosaccharides is less limiting. Sucrose preference on concentrated diets is more puzzling, but may reflect preference for diets with lower osmolality. Varying preferences suggest that the co-evolutionary relationships between birds and nectar sugar composition are likely to be similarly dynamic and situation dependent. [ABSTRACT FROM AUTHOR]

1. Secondary compounds such as phenolics, usually present in floral nectar, may act in combination with sugar components to influence the evolution of pollination mutualism. 2. Previous work on the significance of secondary compounds in nectar considers honey bee responses to those compounds alone, but neglects sugar. Our experiments demonstrated that phenolic sugar syrups were attractants to free-flying Asian Apis cerana Fab. when sugar concentrations were 15–35%, but were deterrents below or above this range. 3. Synergism between nectar phenolics and sugar may thus provide a novel mechanism for plants to encourage pollinating bees and reduce energy investment in nectar, operating as exaptations by co-opting defence mechanisms against herbivores. [ABSTRACT FROM AUTHOR]

1. Animal-pollinated plants influence their mating success through characteristics of their individual flowers and the arrangement of flowers into inflorescences. Previous studies of inflorescence function have focused on flower number, so the influences of traits of individual flowers on pollinator attraction and self-pollination between flowers remain unknown. 2. To investigate the effects of flower size and number on pollinator attraction and behaviour on inflorescences, we reduced the perianth size of flowers of Delphinium bicolor Nuttall and Delphinium glaucum S. Watson. 3. Reduction in flower size decreased the number of visits per inflorescence by bumble bees ( Bombus spp.), but increased the number of probes per visit. In contrast, both attraction and probes per visit increased in a decelerating manner with number of open flowers. The average number of probes per flower, which combines the effects of pollinator attraction and behaviour on inflorescences, did not differ significantly between small- and large-flowered plants, or with flower number. 4. The absence of significant variation among plants with different floral and inflorescence characteristics in visits per flower and nectar standing crop per flower indicate that bees achieved an ideal free distribution. 5. Our results suggest that large flowers reduce the incidence of geitonogamous pollination without reducing the frequency of probes per flower. [ABSTRACT FROM AUTHOR]

1. One route to a deeper understanding of the life history of organisms is to identify how resources are acquired and used for reproduction. This may be particularly relevant for insects such as nectar-feeding butterflies, which change diets during the life cycle. 2. Nitrogenous resources used for reproduction in nectar-feeding butterflies come principally from the juvenile diet and are stored in abdominal reserves. Juvenile resources are also used to build the soma of the adult. Consequently somatic and reproductive investment will trade off and constrain the amount of resources available for egg and spermatophore production. Recent findings show a pronounced decrease in thorax resource content and suggest that nitrogen from somatic tissue can be reallocated to reproduction and thus alleviate the resource limitation upon reproduction. 3. In this paper we test the prediction that the observed decrease in thorax nitrogen content is related to the expenditure of resources in spermatophore production in Pieris napi males. By comparing thorax nitrogen content over the life span between males mated 0–3 times, we show that mating history is an important factor in explaining the observed decrease in nitrogen content. 4. These results support the hypothesis that thoracic resources are used for reproduction in male nectar-feeding butterflies. [ABSTRACT FROM AUTHOR]

1. Spatio-temporal variation in resource availability is often large and unpredictable. When animals need to find and sample novel foods, therefore they may prefer to choose food sources with feeding conspecifics or odour left by the conspecifics. This behaviour (local enhancement) would be favoured, especially if it decreases the time spent on food-finding and subsequent decision-making. In laboratory experiments we tested if naive bumble bees use local enhancement, and to what degree it could reduce the time spent on finding and sampling novel flowers. 2. When naive bees were presented with a pair of equally rewarded artificial or real flowers in a flight cage, they preferred to land and feed on the flower where a dead conspecific was attached. The presence of conspecifics reduced the time spent on detecting floral reward, which was significant only when bees chose between real flowers. In a similar pairwise choice, bees landed on artificial flowers with a dead conspecific wrapped in plastic more frequently than on flowers with the same-sized plastic wrap including no bees, which suggests that visual cues have important influences on the bees’ flower choice. 3. Effects of conspecifics on flower choice and food detection time were most evident when they were attached to real flowers, and least evident when they were wrapped in plastic. These results suggest that the presence of conspecifics on flowers has stronger effects on bees’ decision-making as the attractiveness of flowers increases, and that bees use both visual and non-visual cues to recognize conspecifics on flowers. 4. If the benefit of saving time were universal, the use of local enhancement would also be advantageous when bees switch between focal flower species or sites in response to temporal changes in resource availability. [ABSTRACT FROM AUTHOR]

1. The effect of floral display size (number of open flowers per plant) on subsequent plant choice by bumble bees, Bombus hypocrita sapporensis (Cockerell), was investigated using artificial inflorescences with blue or yellow flowers representing different ‘species’. 2. Bees flew to an inflorescence of the same colour (constant flight) more often after visiting a large inflorescence. This response occurred when the nectar volume per flower was constant (larger inflorescence offered more nectar), and when nectar volume per inflorescence was constant (nectar volume per flower varied with display size). These results indicate that bees did not exhibit higher constancy after visiting larger inflorescences because they extracted more nectar than from smaller ones. 3. Bees spent more time during visits to large vs small inflorescences. Possibly information about the last-visited inflorescence fades from short-term memory during longer visits, which strengthens colour constancy. 4. Selection on floral display size is thought to balance the attraction benefits of large displays with the cost of geitonogamy. However, in habitats with several competing plant species, selection for colour constancy may provide a further reason for selection to favour large floral displays. [ABSTRACT FROM AUTHOR]

1. For many adult nectar-feeding parasitoids food and moisture are essential for survival in the field. Early in the season, when floral nectar is not yet available in cotton, extrafloral nectar (EFN) is already present on young cotton plants. 2. The parasitoid Microplitis croceipes (Cresson) can use EFN cotton plants as an only food source. The longevity and reproduction of EFN-fed female wasps was comparable to wasps fed with honey and water provided on nectariless (NL) cotton plants, and was significantly higher compared with wasps kept on NL plants with no additional food source. 3. Wasps that were given preflight experiences on EFN cotton plants choose EFN cotton over NL cotton plants in two choice experiments in the flight tunnel. The parasitoids are more willing to search on an EFN plant at their second and third encounter with a plant previously visited, compared with an NL cotton plant. 4. Wasps can locate EFN from short distances by its odour alone, and find it almost as fast as honey, but much faster than odourless sucrose, which is only found randomly. Experience with EFN increased the retention ability of parasitoids on a flower model. [ABSTRACT FROM AUTHOR]

1. Small nectar-feeding birds have high energy turnover and must respond rapidly to changes in food concentration or feeding opportunities. A previous study showed that Rufous Hummingbirds ( Selasphorus rufus) were unable to adjust their intake rates after a midday fast and thus ended the day with energy deficits that necessitated the use of torpor. 2. We examined the ability of Whitebellied Sunbirds ( Nectarinia talatala) to cope with a similar loss of foraging time (lights out from 10.00 h to 12.00 h). During the experiment, birds were kept at 10 °C and fed 20% w/w sucrose solution. 3. In contrast to hummingbirds, sunbirds increased their rate of afternoon feeding following the fast, consuming 14·3 ± SD 10·0% ( n = 8) more than on the afternoon of the control day, and maintaining evening body mass at control levels. However, morning body mass on the third day was significantly lower than on the previous 2 days, indicating that compensation for reduced feeding time was probably incomplete. Nectar-feeding birds show varied and flexible responses to energy challenges. [ABSTRACT FROM AUTHOR]

1. Genotype by environment interactions for nectar production in Echium vulgare were studied. Nectar production was measured under high and low-water treatments for high and low nectar-producing genetic lines in a growth chamber. In the field the response of nectar production and pollinator behaviour to water availability for potted plants chosen from field populations was studied. 2. Plants selected from high-nectar lines produced significantly more nectar than those selected from low-nectar lines. Nectar production thus had a heritable component. 3. Under high water conditions plants produced more nectar than under low water conditions. The increase in nectar production under high water availability was strongest for the low-nectar plants, demonstrating a genotype by environment interaction. Only under dry conditions, which usually prevail during the flowering period of E. vulgare, high and low-nectar plants differ in nectar production. 4. Plants selected from high-nectar lines had a significantly higher root mass and root : shoot ratio. This suggests that they are less affected by low water availability and thus able to maintain high nectar production under dry conditions. 5. In the field, high-nectar plants produced significantly more nectar but did not receive more pollinator visits. Watered plants produced significantly more nectar and did receive an enhanced pollinator service. When watered, nectar production and pollinator service was similar for high and low-nectar plants. Functional Ecology (2005) 19, 000–000 [ABSTRACT FROM AUTHOR]

1. Adult parasitoids depend on sugar-rich foods such as nectar and honeydew to meet their energy requirements. Many laboratory studies have established fitness benefits of sugar feeding for parasitoids.2. Nevertheless, we know little about the nutritional ecology of parasitoids in the field, chiefly because of the limited specificity of methods applicable for field studies.3. Here we use high-performance liquid chromatography (HPLC) analysis to study the sugar profile ofCotesia glomerataL. andMicroplitis mediatorHaliday relative to feeding-treatment. We identify the overall sugar level and the ratio of glucose to fructose as two parameters that in combination unambiguously characterize an individual's nutritional state and feeding history.4. Unfed parasitoids contained low total sugar levels and glucose levels that typically exceeded fructose levels more than five-fold. Parasitoids with constant access to sucrose had high overall sugar levels with a balanced glucose–fructose ratio.5. The marked shift of the glucose–fructose ratio after feeding was still evident inC. glomerataindividuals whose total sugar content had decreased to unfed levels after 3 days of starvation. This makes it possible to distinguish between unfed individuals and those that did feed several days ago.6. In addition to revealing past feeding events, HPLC analysis also enables the identification and quantification of a wide spectrum of sugars present in each specimen. When food sources contain specific sugars this can provide additional information about the type of sugar source consumed.7. HPLC analyses revealed that trehalose, considered to be the‘insect haemolymph sugar’, is not present in the two species investigated here.8. Overall, HPLC sugar analysis provides a powerful tool to investigate energy status, feeding history and nutritional physiology of field-collected parasitoids.Functional Ecology(2004)18, 812–819 [ABSTRACT FROM AUTHOR]

1. The bird-flower element of the Canary Islands is a group of endemic plants having traits characteristic of bird pollination, and some are visited by opportunistically nectar-feeding passerine birds.2. We investigated evolutionary changes in nectar sugar composition in seven Canarian lineages of ornithophilous plant species and their entomophilous relatives.3. We hypothesized that nectar sugar composition evolved in response to the main pollinator group of a plant. Specialist nectarivores can assimilate sucrose, whereas some opportunistic nectar-feeders digest only the simple hexoses.4. Sugar composition of nectars was analysed using high pH anion exchange chromatography.5. Evolution of nectar type was correlated with mode of pollination. Generally, sucrose nectars were associated with insect visitation and hexose nectars with bird visitation. Nectar sugar composition was an evolutionary labile trait within a lineage. Hence, nectar characteristics may have evolved readily, perhaps in response to opportunistically nectarivorous birds living in the Canary Islands.Functional Ecology(2004)18, 670 –676 [ABSTRACT FROM AUTHOR]

1. The nectars of hummingbird- and passerine-pollinated plants differ in both sugar type and concentration. Firstly, hummingbird nectars tend to be more concentrated than passerine nectars. Secondly, sucrose dominates hummingbird nectars, whereas glucose and fructose (hexose sugars) are the prevalent sugars in nectar of almost half the passerine-pollinated plants. It has been commonly assumed that these differences can be attributed to selection pressure from birds, largely determined by avian sugar preferences and digestive physiology. 2. Intake and preferences of Whitebellied Sunbirds Nectarinia talatala (A. Smith) and Broadtailed Hummingbirds Selasphorus platycercus (Swainson) were examined across a range of sucrose and equicaloric hexose solutions at two ambient temperatures. Hummingbird energy balance was not affected by sugar type. Sunbird energy balance was only influenced by sugar type on a very dilute diet (0.1 mol l-1 sucrose equivalents, 'SE'), when the birds ingested 12% more sucrose than hexoses. Sunbirds and hummingbirds showed similar patterns in sugar preferences. Sunbirds preferred hexoses when offered dilute diets (0.1 mol l-1 SE at 21 °C) and showed slight preference for sucrose when offered more concentrated diets (significant at 0.75 mol l-1 SE). Hummingbirds showed slight (nonsignificant) hexose preference when offered a dilute diet (0.25 mol l-1 SE at 10 °C), but, in contrast to previous findings, hummingbirds showed no significant sucrose preference. 3. Our findings for Whitebellied Sunbirds and Broadtailed Hummingbirds do not support an ornithocentric explanation for nectar composition. Plant physiology and opportunist nectar feeders may also be influencing nectar sugars. To further address this question we discuss methodological considerations for researchers investigating how avian preferences and physiology may affect nectar composition. [ABSTRACT FROM AUTHOR]

Functional Ecology (2004) 18, 125–129 [ABSTRACT FROM AUTHOR]

Summary 1. Effects of anther arrangement on pollen deposition and removal in hermaphrodite flowers were experimentally quantified to assess the ecological significance of stamen structure. The anther arrangement of Brassica rapa was modified into six types with respect to anther number and the spatial arrangement of long and short stamens. Each anther treatment was combined with a nectar-intact and nectar-depleted treatment. After single visits by bumblebees in a glasshouse, the visit duration to each flower and the number of pollen grains deposited on stigmas and pollen grains remaining in long and short anthers were measured. 2. Visits were significantly shorter in nectar-depleted flowers. Short anthers also extended visit duration, but modification of the long anther arrangement had no effect. Pollen deposition on stigmas depended on the number of long anthers and on visit duration. Although an increase in long anther number accelerated self-pollination, removal of short anthers did not influence pollen deposition. 3. Pollen removal from long anthers depended on anther treatment and visit duration, but not on nectar availability. Any modification of anther arrangement tended to increase pollen removal during single visits. Long anthers contributed to the decrease in pollen removal per visit, while pollen removal from short anthers depended only on visit duration. Short anthers appeared to have a different function from the restriction of pollen removal during single visits by bumblebees. 4. Thus, long and short anthers made different contributions to pollination efficiency of nectar-feeding bumblebees. The maintenance of different types of stamens in Brassicaceae plants (tetradynamous stamens) may reflect functional advantages for a diverse pollination syndrome if the pollination efficiency of long and short anthers varies depending on the type of pollinator. [ABSTRACT FROM AUTHOR]

Summary 1. Avian nectarivores consume a simple food which is generally dilute, but may vary widely in concentration and thus in water content. 2. Energy intake over 24 h was investigated in the Whitebellied Sunbird Nectarinia talatala (A. Smith) (mean mass 9·3 ± 1·0 SD g, n = 7) fed a wide range of sucrose concentrations (0·07–2·5 m), with and without access to supplementary water. 3. On diet concentrations between 0·25 and 2·5 m sucrose, birds showed perfect compensatory feeding by adjusting volumetric intake to maintain constant energy intake. 4. However, reduced intake on the two lowest concentrations of 0·07 and 0·1 m meant that the birds could not meet their energetic requirements and lost mass. We propose that physiological constraints associated with ingestion of large volumes of preformed water restrict intake at these very low concentrations. 5. Drinking of supplementary water varied greatly among individuals, but increased as diet concentration increased. This free water consumption effectively diluted the most concentrated diets of 1·5–2·5 m sucrose to an average value of 1·05 m, thus providing an indirect assessment of the birds’ concentration preferences. [ABSTRACT FROM AUTHOR]

Analyzes the role of hummingbird flower mites on nectar secretion and reproductive output of protandrous Moussonia deppeana. Reduction of nectar availability in the presence of hummingbird flower mites; Comparison of nectar secretion between staminate phase and pistillate phase; Effect of floral mites on pollen transmission.

Abstract1. Many plants produce extrafloral nectar (EFN) to nourish ants and other animals which defend them against herbivores. We aimed to find reasons for the high variability in amounts of EFN produced by most plant species. We investigated the influence of several biotic and abiotic factors (time of day, leaf age, nectar removal and leaf damage) on secretion rates of EFN in the common south-east Asian pioneer tree species, Macaranga tanarius (L.) Muell. Arg. 2. In most experiments leaves were washed with pure water and bagged in nets to protect them against nectar-collecting insects, and nectar was collected and quantified 24 h later. Six soluble sugars and up to eight amino acids were detected in nectar samples derived from untreated, field-grown plants. Total amounts of soluble substances varied more than the relative composition of EFN. 3. Nectar secretion rates were highest on young, expanded leaves. A diurnal pattern with a secretion peak in the first 2 h after dusk was detected in the field. Nectar removal had a positive effect and its accumulation a negative effect on further EFN production. Artificial leaf damage (punching leaves with a needle or removing parts of the leaf blade with scissors) led to a significant induction of EFN production for the next 3 days. 4. Extrafloral nectar of M. tanarius was secreted in complex patterns influenced by different biotic and abiotic factors; its production appeared to be adapted temporally and spatially in order to ensure optimal use of invested resources. [ABSTRACT FROM AUTHOR]

1. A published model of constant diurnal energy accumulation by territorial hummingbirds does not accurately reflect the temporal distribution of feeding behaviour of traplining hummingbirds, Phaethornis longirostris (Long-Tailed Hermit Hummingbirds). 2. In an enclosure study, gross nectar intake by P. longirostris decreased through the day, mirroring nectar production rates in its natural food-flowers and mimicking its natural foraging patterns. 3. Using a simulation model, the energetic consequences of constant and decreasing net energy intake rates for traplining hummingbirds are compared. 4. Given natural patterns of nectar production, model birds with decreasing diurnal net intake rates met their energetic needs with fewer flowers than those with constant net intake, and spent less time foraging. 5. It is concluded that P. longirostris do not satisfy the physiological assumptions of the published model, and that in this way they are different from the territorial species on which the model has previously been tested. [ABSTRACT FROM AUTHOR]