Pollination crisis Down-Under: Has Australasia dodged the bullet?

Since mid-1990s, concerns have increased about a human-induced "pollination crisis." Threats have been identified to animals that act as plant pollinators, plants pollinated by these animals, and consequently human well-being. Threatening processes include loss of natural habitat, climate change, pesticide use, pathogen spread, and introduced species. However, concern has mostly been during last 10-15 years and from Europe and North America, with Australasia, known as Down-Under, receiving little attention. So perhaps Australasia has "dodged the bullet"? We systematically reviewed the published literature relating to the "pollination crisis" via Web of Science, focusing on issues amenable to this approach. Across these issues, we found a steep increase in publications over the last few decades and a major geographic bias towards Europe and North America, with relatively little attention in Australasia. While publications from Australasia are underrepresented, factors responsible elsewhere for causing the "pollination crisis" commonly occur in Australasia, so this lack of coverage probably reflects a lack of awareness rather than the absence of a problem. In other words, Australasia has not "dodged the bullet" and should take immediate action to address and mitigate its own "pollination crisis." Sensible steps would include increased taxonomic work on suspected plant pollinators, protection for pollinator populations threatened with extinction, establishing long-term monitoring of plant-pollinator relationships, incorporating pollination into sustainable agriculture, restricting the use of various pesticides, adopting an Integrated Pest and Pollinator Management approach, and developing partnerships with First Nations peoples for research, conservation and management of plants and their pollinators. Appropriate Government policy, funding and regulation could help.

Floral nectar production: what cost to a plant?

Floral nectar production is central to plant pollination, and hence to human wellbeing. As floral nectar is essentially a solution in water of various sugars, it is likely a valuable plant resource, especially in terms of energy, with plants experiencing costs/trade-offs associated with its production or absorption and adopting mechanisms to regulate nectar in flowers. Possible costs of nectar production may also influence the evolution of nectar volume, concentration and composition, of pollination syndromes involving floral nectar, and the production of some crops. There has been frequent agreement that costs of floral nectar production are significant, but relevant evidence is scant and difficult to interpret. Convincing direct evidence comes from experimental studies that relate either enhanced nectar sugar production (through repeated nectar removal) to reduced ability to produce seeds, or increased sugar availability (through absorption of additional artificial nectar) to increased seed production. Proportions of available photosynthate allocated by plants to nectar production may also indicate nectar cost. However, such studies are rare, some do not include treatments of all (or almost all) flowers per plant, and all lack quantitative cost-benefit comparisons for nectar production. Additional circumstantial evidence of nectar cost is difficult to interpret and largely equivocal. Future research should repeat direct experimental approaches that relate reduced or enhanced nectar sugar availability for a plant with consequent ability to produce seeds. To avoid confounding effects of inter-flower resource transfer, each plant should experience a single treatment, with treatment of all or almost all flowers per plant. Resource allocation by plants, pathways used for resource transfer, and the locations of resource sources and sinks should also be investigated. Future research should also consider extension of nectar cost into other areas of biology. For example, evolutionary models of nectar production are rare but should be possible if plant fitness gains and costs associated with nectar production are expressed in the same currency, such as energy. It should then be possible to understand observed nectar production for different plant species and pollination syndromes involving floral nectar. In addition, potential economic benefits should be possible to assess if relationships between nectar production and crop value are evaluated.

Flower Color Evolution and the Evidence of Pollinator-Mediated Selection.

The evolution of floral traits in animal-pollinated plants involves the interaction between flowers as signal senders and pollinators as signal receivers. Flower colors are very diverse, effect pollinator attraction and flower foraging behavior, and are hypothesized to be shaped through pollinator-mediated selection. However, most of our current understanding of flower color evolution arises from variation between discrete color morphs and completed color shifts accompanying pollinator shifts, while evidence for pollinator-mediated selection on continuous variation in flower colors within populations is still scarce. In this review, we summarize experiments quantifying selection on continuous flower color variation in natural plant populations in the context of pollinator interactions. We found that evidence for significant pollinator-mediated selection is surprisingly limited among existing studies. We propose several possible explanations related to the complexity in the interaction between the colors of flowers and the sensory and cognitive abilities of pollinators as well as pollinator behavioral responses, on the one hand, and the distribution of variation in color phenotypes and fitness, on the other hand. We emphasize currently persisting weaknesses in experimental procedures, and provide some suggestions for how to improve methodology. In conclusion, we encourage future research to bring together plant and animal scientists to jointly forward our understanding of the mechanisms and circumstances of pollinator-mediated selection on flower color.

Salvage of floral resources through re-absorption before flower abscission.

Plants invest floral resources, including nectar and pigment, with likely consequent reproductive costs. We hypothesized that plants, whose flowers abscise with age, reabsorb nectar and pigment before abscission. This was tested with flowers of Rhododendron decorum, which has large, conspicuous white flowers that increasingly abscise corollas as flowers age. As this species is pollinated by bees, we also hypothesized that nectar concentration would be relatively high (i.e., > 30% wt/vol) and petals would contain UV-absorbing pigment. Floral nectar volume and concentration were sampled on successive days until abscission (up to ten days old, peak at five days) and for sub-sample of four-day-old flowers. Flowers just abscised were similarly sampled. Flower colours were measured using a modified camera, with recordings of spectral reflectance for abscised and open non-abscised flowers. Pigment content was summed values of red, green, blue channels of false color photos. As expected, flowers reabsorbed almost all nectar before abscission, separately reabsorbing nectar-sugar and nectar-water, and petals contained UV-absorbing pigment. However, flowers did not reabsorb pigment and nectar-concentration was < 30% wt/vol. That flowers reabsorb nectar, not pigment, remains unexplained, though possibly pigment reabsorption is uneconomical. Understanding floral resource reabsorption therefore requires determination of biochemical mechanisms, plus costs/benefits for individual plants.

Changes in floral nectar are unlikely adaptive responses to pollinator flight sound.

Under noiseless experimental conditions, sugar concentration of secreted floral nectar may increase after flower exposure to nearby sounds of pollinator flight (Veits et al. 2019). However, we reject the argument that this represents adaptive plant behaviour, and consider that the appealing analogy between a flower and human ear is unjustified.

Nectar mimicry: a new phenomenon.

Nectar is the most common floral reward for flower-visiting flies, bees, bats and birds. Many flowers hide nectar in the floral tube and preclude sensing of nectar by flower-visitors from a distance. Even in those flowers that offer easily accessible nectar, the nectaries are mostly inconspicuous to the human eye and the amount of nectar is sparse. It is widely accepted that many flowers display nectar guides in order to direct flower-visitors towards the nectar. Using false colour photography, covering ultraviolet, blue and green ranges of wavelength, revealed a yet unknown conspicuousness of nectar, nectaries and false nectaries for bees due to concordant reflection in the ultraviolet range of wavelength. Nectars, many nectaries and false nectaries have glossy surfaces and reflect all incident light including UV-light. In most cases, this is not particularly conspicuous to the human eye, but highly visible for UV-sensitive insects, due to the fact that the glossy areas are often positioned in UV-absorbing central flower parts and thus produce a strong UV-signal. The optical contrast produced by the glossiness of small smooth areas in close proximity to nectar holders represents a widespread yet overlooked floral cue that nectarivorous flower-visitors might use to locate the floral nectar.

Patterns of floral nectar standing crops allow plants to manipulate their pollinators.

'Pollination syndromes' involving floral nectar have eluded satisfactory evolutionary explanation. For example, floral nectars for vertebrate-pollinated plants average low sugar concentrations, while such animals prefer high concentrations, perplexing pollination biologists and arousing recent controversy. Such relationships should result from evolutionary games, with plants and pollinators adopting Evolutionarily Stable Strategies, and nectar manipulating rather than attracting pollinators. Plant potential to manipulate pollinators depends on relationships between neighbouring flowers within plants, for all nectar attributes, but this has not been investigated. We measured nectar volume, concentration and sugar composition for open flowers on naturally-growing Blandfordia grandiflora plants, presenting classic bird-pollinated plant syndrome. To evaluate potential pollinator manipulation through nectar, we analysed relationships between neighbouring flowers for nectar volume, concentration, proportion sucrose, log(fructose/glucose), and sugar weight. To evaluate potential attraction of repeat-visits to flowers or plants through nectar, we compared attributes between successive days. Nearby flowers were positively correlated for all attributes, except log(fructose/glucose) as fructose≈glucose. Most relationships between nectar attributes for flowers and plants on successive days were non-significant. Nectar-feeding pollinators should therefore decide whether to visit another flower on a plant, based on all attributes of nectar just-obtained, enabling plants to manipulate pollinators through adjusting nectar. Plants are unlikely to attract repeat pollinator-visits through nectar production. Floral nectar evolution is conceptually straightforward but empirically challenging. A mutant plant deviating from the population in attributes of nectar-production per flower would manipulate, rather than attract, nectar-feeding pollinators, altering pollen transfer, hence reproduction. However, links between floral nectar and plant fitness present empirical difficulties.

Conservation and the 4 Rs, which are rescue, rehabilitation, release, and research.

Vertebrate animals can be injured or threatened with injury through human activities, thus warranting their "rescue." Details of wildlife rescue, rehabilitation, release, and associated research (our 4 Rs) are often recorded in large databases, resulting in a wealth of available information. This information has huge research potential and can contribute to understanding of animal biology, anthropogenic impacts on wildlife, and species conservation. However, such databases have been little used, few studies have evaluated factors influencing success of rehabilitation and/or release, recommended actions to conserve threatened species have rarely arisen, and direct benefits for species conservation are yet to be demonstrated. We therefore recommend that additional research be based on data from rescue, rehabilitation, and release of animals that is broader in scope than previous research and would have community support.

Larvivorous fish for preventing malaria transmission.

BACKGROUND: Adult female Anopheles mosquitoes can transmit Plasmodium parasites that cause malaria. Some fish species eat mosquito larvae and pupae. In disease control policy documents, the World Health Organization (WHO) includes biological control of malaria vectors by stocking ponds, rivers, and water collections near where people live with larvivorous fish to reduce Plasmodium parasite transmission. In the past, the Global Fund has financed larvivorous fish programmes in some countries, and, with increasing efforts in eradication of malaria, policymakers may return to this option. Therefore, we assessed the evidence base for larvivorous fish programmes in malaria control. OBJECTIVES: To evaluate whether introducing larvivorous fish to anopheline larval habitats impacts Plasmodium parasite transmission. We also sought to summarize studies that evaluated whether introducing larvivorous fish influences the density and presence of Anopheles larvae and pupae in water sources. SEARCH METHODS: We searched the Cochrane Infectious Diseases Group Specialized Register; the Cochrane Central Register of Controlled Trials (CENTRAL), published in the Cochrane Library; MEDLINE (PubMed); Embase (Ovid); CABS Abstracts; LILACS; and the metaRegister of Controlled Trials (mRCT) up to 6 July 2017. We checked the reference lists of all studies identified by the search. We examined references listed in review articles and previously compiled bibliographies to look for eligible studies. Also we contacted researchers in the field and the authors of studies that met the inclusion criteria for additional information regarding potential studies for inclusion and ongoing studies. This is an update of a Cochrane Review published in 2013. SELECTION CRITERIA: Randomized controlled trials (RCTs) and non-RCTs, including controlled before-and-after studies, controlled time series, and controlled interrupted time series studies from malaria-endemic regions that introduced fish as a larvicide and reported on malaria in the community or the density of the adult anopheline population. In the absence of direct evidence of an effect on transmission, we performed a secondary analysis on studies that evaluated the effect of introducing larvivorous fish on the density or presence of immature anopheline mosquitoes (larvae and pupae forms) in water sources to determine whether this intervention has any potential that may justify further research in the control of malaria vectors. DATA COLLECTION AND ANALYSIS: Two review authors independently screened each article by title and abstract, and examined potentially relevant studies for inclusion using an eligibility form. At least two review authors independently extracted data and assessed risk of bias of included studies. If relevant data were unclear or were not reported, we contacted the study authors for clarification. We presented data in tables, and we summarized studies that evaluated the effects of introducing fish on anopheline immature density or presence, or both. We used the GRADE approach to summarize the certainty of the evidence. We also examined whether the included studies reported any possible adverse impact of introducing larvivorous fish on non-target native species. MAIN RESULTS: We identified no studies that reported the effects of introducing larvivorous fish on the primary outcomes of this review: malaria infection in nearby communities, entomological inoculation rate, or on adult Anopheles density.For the secondary analysis, we examined the effects of introducing larvivorous fish on the density and presence of anopheline larvae and pupae in community water sources, and found 15 small studies with a follow-up period between 22 days and five years. These studies were undertaken in Sri Lanka (two studies), India (three studies), Ethiopia (one study), Kenya (two studies), Sudan (one study), Grande Comore Island (one study), Korea (two studies), Indonesia (one study), and Tajikistan (two studies). These studies were conducted in a variety of settings, including localized water bodies (such as wells, domestic water containers, fishponds, and pools (seven studies); riverbed pools below dams (two studies)); rice field plots (five studies); and water canals (two studies). All included studies were at high risk of bias. The research was insufficient to determine whether larvivorous fish reduce the density of Anopheles larvae and pupae (12 studies, unpooled data, very low certainty evidence). Some studies with high stocking levels of fish seemed to arrest the increase in immature anopheline populations, or to reduce the number of immature anopheline mosquitoes, compared with controls. However, this finding was not consistent, and in studies that showed a decrease in immature anopheline populations, the effect was not always consistently sustained. In contrast, some studies reported larvivorous fish reduced the number of water sources withAnopheles larvae and pupae (five studies, unpooled data, low certainty evidence).None of the included studies reported effects of larvivorous fish on local native fish populations or other species. AUTHORS' CONCLUSIONS: We do not know whether introducing larvivorous fish reduces malaria transmission or the density of adult anopheline mosquito populations.In research studies that examined the effects on immature anopheline stages of introducing fish to potential malaria vector larval habitats, high stocking levels of fish may reduce the density or presence of immature anopheline mosquitoes in the short term. We do not know whether this translates into impact on malaria transmission. Our interpretation of the current evidence is that countries should not invest in fish stocking as a stand alone or supplementary larval control measure in any malaria transmission areas outside the context of research using carefully controlled field studies or quasi-experimental designs. Such research should examine the effects on native fish and other non-target species.

Comment on "Cognition-mediated evolution of low-quality floral nectars".

Nachev et al (Reports, 6 January 2017, p. 75) present dilute nectar in bat-pollinated plants as "paradoxical" because bats prefer concentrated nectar, but paradox disappears with realistic assumptions about nectar evolution. We argue that they make unrealistic assumptions about the cognitive abilities of bat pollinators, invoke Weber's law inappropriately, and cannot predict observed nectar concentrations of bat flowers or negative correlations between pollinator body size and average concentration.

Floral Nectar: Pollinator Attraction or Manipulation?

The literature suggests that floral nectar acts principally to attract pollinator visitation (and/or revisitation), thereby enhancing plant reproductive success. However, floral nectar also manipulates pollinator behaviour during and immediately following plant visits, affecting pollen transfer, and plant reproduction. I argue that floral nectar should really be viewed as a pollinator manipulant rather than attractant, thus potentially explaining why its concentration is not generally high and why it decreases with increasing pollinator body size. Otherwise, such patterns may remain mysterious and unexplained.

Larvivorous fish for preventing malaria transmission.

BACKGROUND: Adult anopheline mosquitoes transmit Plasmodium parasites that cause malaria. Some fish species eat mosquito larvae and pupae. In disease control policy documents, the World Health Organization includes biological control of malaria vectors by stocking ponds, rivers, and water collections near where people live with larvivorous fish to reduce Plasmodium parasite transmission. The Global Fund finances larvivorous fish programmes in some countries, and, with increasing efforts in eradication of malaria, policy makers may return to this option. We therefore assessed the evidence base for larvivorous fish programmes in malaria control. OBJECTIVES: Our main objective was to evaluate whether introducing larvivorous fish to anopheline breeding sites impacts Plasmodium parasite transmission. Our secondary objective was to summarize studies evaluating whether introducing larvivorous fish influences the density and presence of Anopheles larvae and pupae in water sources, to understand whether fish can possibly have an effect. SEARCH METHODS: We attempted to identify all relevant studies regardless of language or publication status (published, unpublished, in press, or ongoing). We searched the following databases: the Cochrane Infectious Diseases Group Specialized Register; the Cochrane Central Register of Controlled Trials (CENTRAL), published in The Cochrane Library; MEDLINE; EMBASE; CABS Abstracts; LILACS; and the metaRegister of Controlled Trials (mRCT) until 18 June 2013. We checked the reference lists of all studies identified by the above methods. We also examined references listed in review articles and previously compiled bibliographies to look for eligible studies. SELECTION CRITERIA: Randomized controlled trials and non-randomized controlled trials, including controlled before-and-after studies, controlled time series and controlled interrupted time series studies from malaria-endemic regions that introduced fish as a larvicide and reported on malaria in the community or the density of the adult anopheline population. In the absence of direct evidence of an effect on transmission, we carried out a secondary analysis on studies that evaluated the effect of introducing larvivorous fish on the density or presence of immature anopheline mosquitoes (larvae and pupae forms) in community water sources to determine whether this intervention has any potential in further research on control of malaria vectors. DATA COLLECTION AND ANALYSIS: Three review authors screened abstracts and examined potentially relevant studies by using an eligibility form. Two review authors independently extracted data and assessed risk of bias of included studies. If relevant data were unclear or were not reported, we wrote to the trial authors for clarification. We presented data in tables, and we summarized studies that evaluated the effects of fish introduction on anopheline immature density or presence, or both. We used GRADE to summarize evidence quality. We also examined whether the authors of included studies reported on any possible adverse impact of larvivorous fish introduction on non-target native species. MAIN RESULTS: We found no reliable studies that reported the effects of introducing larvivorous fish on malaria infection in nearby communities, on entomological inoculation rate, or on adult Anopheles density.For the secondary analysis, we examined the effects of introducing larvivorous fish on the density and presence of anopheline larvae and pupae in community water sources. We included 12 small studies, with follow-up from 22 days to five years. Studies were conducted in a variety of settings, including localized water bodies (such as wells, domestic water containers, fishponds, and pools; six studies), riverbed pools below dams (two studies), rice field plots (three studies), and water canals (two studies). All studies were at high risk of bias.The research was insufficient to determine whether larvivorous fish reduce the density of Anopheles larvae and pupae (nine studies, unpooled data, very low quality evidence). Some studies with high stocking levels of fish seemed to arrest the increase in immature anopheline populations, or to reduce the number of immature anopheline mosquitoes, compared with controls. However, this finding was not consistent, and in studies that showed a decrease in immature anopheline populations, the effect was not consistently sustained. Larvivorous fish may reduce the number of water sources with Anopheles larvae and pupae (five studies, unpooled data, low quality evidence).None of the included studies reported effects of larvivorous fish on local native fish populations or other species. AUTHORS' CONCLUSIONS: Reliable research is insufficient to show whether introducing larvivorous fish reduces malaria transmission or the density of adult anopheline mosquito populations.In research examining the effects on immature anopheline stages of introducing fish to potential malaria vector breeding sites (localized water bodies such as wells and domestic water sources, rice field plots, and water canals) weak evidence suggests an effect on the density or presence of immature anopheline mosquitoes with high stocking levels of fish, but this finding is by no means consistent. We do not know whether this translates into health benefits, either with fish alone or with fish combined with other vector control measures. Our interpretation of the current evidence is that countries should not invest in fish stocking as a larval control measure in any malaria transmission areas outside the context of carefully controlled field studies or quasi-experimental designs. Research could also usefully examine the effects on native fish and other non-target species.

Local geographic distributions of bumble bees near Crested Butte, Colorado: competition and community structure revisited.

Surveys in 1974 of bumble bee species distributions along elevational gradients (Pyke 1982) were revisited to reevaluate the original conclusion that coexistence of bumble bee species can be ascribed to niche differentiation, primarily on the basis of proboscis lengths and the associated corolla lengths of visited flowers. Each bee species largely visited a few plant species, which were preferred relative to other species. Bee proboscis length was correlated with average corolla length of visited flowers, but not when species with relatively long and short proboscises were considered separately. Bumble bee abundance was affected by presence or absence of major plant species and, contrary to the interpretation of Pyke (1982), elevation, with neither factor dominating. Multimodal distributions of proboscis lengths and altitudinal replacement of bee species of similar proboscis length were consistent with the original hypothesis that bumble bee species compete for floral resources, especially nectar, and cannot coexist if proboscis lengths are too similar, unless one species is a "nectar robber" and hence has exclusive use of some floral resources. However, observed overlap in elevational distributions of bumble bee species with similar proboscis length cannot be reconciled with this hypothesis unless other phenomena are invoked.

Biological collections and ecological/environmental research: a review, some observations and a look to the future.

Housed worldwide, mostly in museums and herbaria, is a vast collection of biological specimens developed over centuries. These biological collections, and associated taxonomic and systematic research, have received considerable long-term public support. The work remaining in systematics has been expanding as the estimated total number of species of organisms on Earth has risen over recent decades, as have estimated numbers of undescribed species. Despite this increasing task, support for taxonomic and systematic research, and biological collections upon which such research is based, has declined over the last 30-40 years, while other areas of biological research have grown considerably, especially those that focus on environmental issues. Reflecting increases in research that deals with ecological questions (e.g. what determines species distribution and abundance) or environmental issues (e.g. toxic pollution), the level of research attempting to use biological collections in museums or herbaria in an ecological/environmental context has risen dramatically during about the last 20 years. The perceived relevance of biological collections, and hence the support they receive, should be enhanced if this trend continues and they are used prominently regarding such environmental issues as anthropogenic loss of biodiversity and associated ecosystem function, global climate change, and decay of the epidemiological environment. It is unclear, however, how best to use biological collections in the context of such ecological/environmental issues or how best to manage collections to facilitate such use. We demonstrate considerable and increasingly realized potential for research based on biological collections to contribute to ecological/environmental understanding. However, because biological collections were not originally intended for use regarding such issues and have inherent biases and limitations, they are proving more useful in some contexts than in others. Biological collections have, for example, been particularly useful as sources of information regarding variation in attributes of individuals (e.g. morphology, chemical composition) in relation to environmental variables, and provided important information in relation to species' distributions, but less useful in the contexts of habitat associations and population sizes. Changes to policies, strategies and procedures associated with biological collections could mitigate these biases and limitations, and hence make such collections more useful in the context of ecological/environmental issues. Haphazard and opportunistic collecting could be replaced with strategies for adding to existing collections that prioritize projects that use biological collections and include, besides taxonomy and systematics, a focus on significant environmental/ecological issues. Other potential changes include increased recording of the nature and extent of collecting effort and information associated with each specimen such as nearby habitat and other individuals observed but not collected. Such changes have begun to occur within some institutions. Institutions that house biological collections should, we think, pursue a mission of 'understanding the life of the planet to inform its stewardship' (Krishtalka & Humphrey, 2000), as such a mission would facilitate increased use of biological collections in an ecological/environmental context and hence lead to increased appreciation, encouragement and support from the public for these collections, their associated research, and the institutions that house them.

Optimal body size in bumblebees.

It is hypothesized that the body size of a bumblebee will be that size which maximizes its average net rate of energy intake while collecting nectar. A mathematical model is developed with the result that the net rate of energy intake of a nectar-collecting bumblebee is expressed as a function of the body size of the bumblebee. From this model the body size which maximizes the net rate of energy intake (i.e., optimal body size) is found (as the solution of an implicit equation). In this situation the advantage of large size is that larger bumblebees fly faster and hence take less flight time than smaller bumblebees. The disadvantage of larger size is greater energetic costs.The parameters of the model are estimated using data obtained from the foraging behavior of bumblebees on monkshood (Aconitum columbianum). The optimal body size is then calculated for workers of Bombus appositus which obtained almost all their nectar from monkshood. The observed and expected (i.e., optimal) body size are found to be close and not significantly different.The model also predicts that, from the bumblebee's point of view, there should be a positive correlation between the size of the bumblebee and the average amount of nectar obtained per flower. Evidence of this correlation is presented and the possible significance of the correlation from the plant's point of view is discussed. A possible extension of the model to general relationships between predator body size, prey size and prey density is discussed.

Optimal foraging in bumblebees and coevolution with their plants.

The aims of this paper were to consider the coevolution between bumblebee movement patterns within plants and various properties of the plants such as the spatial distribution of their flowers, and to determine the extent to which the bumblebees and the plants can be considered to be maximally adaptive or optimal. Attention was restricted to plants which have flowers arranged on vertical inflorescences and to the bumblebees which visit these plants.It was found that the bumblebees tend to commence foraging at the bottom of each infloresence, that they tend to move from one flower to the closest vertically higher flower, that they miss flowers as they move upwards and that they tend to leave each inflorescence before reaching the top. It was also found for the four common plant species considered that nectar abundance per flower decreases with flower height on an inflorescence, that the flowers with receptive stigmas are restricted to the bottoms of the inflorescences while the flowers shedding pollen occur above them, and that the flowers are arranged approximately in spirals on the inflorescences.The pattern of movements of the bumblebees and the various properties of the plants appear to represent coevolved adaptations. Furthermore the bumblebees' movement patterns appear to be optimal in the sense that they result in the maximum net rate of energy gain to the bumblebees. Further studies are necessary, however, to determine whether or not the plants can be considered to be optimal.An exception to the above scheme is provided by a plant which is quite uncommon in the study area. This plant also has flowers on vertical inflorescences and appears to be pollinated by bumblebees. However, while the pattern of movements of the bumblebees on this plant species are extremely similar to those on the four common species, this plant species exhibits quite different properties from the other four. Two possible explanations for this exception are presented.