Co-flowering plant species commonly share flower visitors, and thus have the potential to influence each other's pollination. In this study we analysed 750 quantitative plant-pollinator networks from 28 studies representing diverse biomes worldwide. We show that the potential for one plant species to influence another indirectly via shared pollinators was greater for plants whose resources were more abundant (higher floral unit number and nectar sugar content) and more accessible. The potential indirect influence was also stronger between phylogenetically closer plant species and was independent of plant geographic origin (native vs. non-native). The positive effect of nectar sugar content and phylogenetic proximity was much more accentuated for bees than for other groups. Consequently, the impact of these factors depends on the pollination mode of plants, e.g. bee or fly pollinated. Our findings may help predict which plant species have the greatest importance in the functioning of plant-pollination networks.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. British Ecological Society is collaborating with JSTOR to digitize, preserve and extend access to Journal of Animal Ecology. Summary 1. The insect wing appears to degenerate with use, so that wing wear increases with increased flight activity. Wing degeneration may affect an insect's mortality. 2. The rate of mortality is known to increase with age in worker bumble bees. This study examines whether wing wear can account for mortality in foraging bumble bees. 3. Workers in eight wild-foraging colonies of bumble bee (Bombus melanopygus Nylander) were divided into two treatment groups: clipped (the outer margin of each forewing trimmed, reducing wing surface area by an average of 18%) and unclipped controls. The mortality and behaviour of foraging individuals was assessed with colony watches and night censuses. 4. Treatment did not detectably affect the proportion of foraging bees, the lengths of foraging or within-nest bouts of foragers, or pollen load sizes, but wing-clipping did cause bees with the greatest amounts of initial wing wear to stop foraging. 5. Mortality was positively related to natural wing wear among unclipped bees. In addition, relative to control foragers, foragers with clipped wing margins experienced significantly reduced life expectancies. 6. These results support the hypothesis that wing wear is a proximate factor responsible for an increase in mortality in older workers. The wing-wear hypothesis therefore provides one functional reason for foragers to adopt a currency that maximizes the ratio of net benefit to cost (i.e. 'efficiency').

Organisms undergo wear and tear of their bodies as they age, as illustrated by tooth erosion, hearing loss, appendage loss and ovipositor wear (reviewed by Finch, 1990;Lalonde and Mangel, 1994). An example common to many flying insects is wing wear. Insects have no mechanism to repair damage to their wings; therefore, as an insect ages and continues to use its wings, the amount of wing wear is cumulative and progressive (Alcock, 1996;Eltz et al., 1999;Hayes and Wall, 1999;Burkhard et al., 2002;Higginson and Barnard, 2004;Lopez-Uribe et al., 2008). Many studies have used wing wear to estimate relative insect age (Mueller and Wolf-Mueller, 1993;Kemp, 2000;Burkhard et al., 2002;Richards, 2003;Inoue and Endo, 2006;Peixoto and Benson, 2008). Wing wear has consequences, which include increased wingbeat frequency (Hargrove, 1975;Kingsolver, 1999;Hedenstrom et al., 2001), changed flight speed (Fischer and Kutsch, 2002), changed flight performance (Haas and Cartar, 2008;Jantzen and Eisner, 2008;Combes et al., 2010), changed foraging behaviour (Higginson and Barnard, 2004;Foster and Cartar, 2011) and increased risk of mortality (Cartar, 1992).Many eusocial insects, particularly bees and wasps, rely on their wings to defend their nest from predators (Breed et al., 1990;Kastberger et al., 2009), maintain colony temperature and assure proper larval development (Heinrich, 1979a;O'Donnell and Foster, 2001), and acquire food for themselves and their colony (Heinrich, 1979a). Providing protection, care and food for the colony's young are the ways in which a non-reproductive forager increases its inclusive fitness. Therefore, wing wear may have important consequences for both individual and colony fitness.Risk of mortality in worker bumble bees (Bombus spp.) increases with age (Brian, 1952;Garofalo, 1978;Rodd et al., 1980;Goldblatt and Fell, 1987;Smeets and Duchateau, 2003), as it does in honey bees (Apis mellifera) (Dukas, 2008). Wing wear has been speculated to lead to an increased risk of mortality in honey bee drones (Rueppell et al., 2005) and tsetse flies (Glossina morsitans) (Allsopp, 1985). Bumble bees that either were wing-clipped or had high naturally occurring amounts of wear died earlier than did those with more pristine wings (Cartar, 1992). An increase in mortality risk with wing wear could result from a number of factors, all of which are supported only by speculation: decreased manoeuvrability, making it more difficult for a bee to escape from predators or severe weather conditions (Rodd et al., 1980), increased energy expenditure (Cartar, 1992) (but see Hedenstrom et al., 2001) and/or increased wingbeat frequency, which matters if the number of wingbeats is limited over a lifespan (Higginson and Gilbert, 2004). Regardless of how wing wear is linked with lifespan, the causes of wing wear have yet to be formally investigated in any insect.Wing wear is associated with male intra-sexual competition (Alcock, 1996), mating attempts (Ragland and Sohal, 1973), failed predator attacks (Robbins, 1981) and foraging activity...

Most hermaphroditic, many‐flowered plants should suffer reduced fitness from within‐plant selfing (geitonogamy). Large inflorescences are most attractive to pollinators, but also promote many flower visits during a single plant visit, which may increase selfing and decrease pollen export. A plant might avoid the negative consequences of attractiveness through modification of the floral display to promote fewer flower visits, while retaining attractiveness. This report shows that increasing only the variance in nectar volume per flower results in fewer flower visits per inflorescence by wild hummingbirds (Selasphorus rufus) and captive bumble bees (Bombus flavifrons) foraging on artificial inflorescences. Inflorescences were either constant (all flowers contained the same nectar volume) or variable (half the flowers were empty, the other half contained twice as much nectar as in the constant flowers). Both types of inflorescence were simultaneously available to foragers. Risk‐averse foraging behaviour was expressed as a patch departure preference: birds and bees visited fewer flowers on variable inflorescences, and this preference was expressed when resource variability could be determined only by concurrent sampling. When variance treatments were clearly labelled with colour and offered to hummingbirds, the departure effect was maintained; however, when preference was measured by inflorescence choice, birds did not consistently prefer to visit constant inflorescences. The reduced visitation lengths on variable inflorescences by both birds and bees documented in this study imply that variance in nectar production rates within inflorescences may represent an adaptive trait to avoid the costs of geitonogamy.

This study considers how a forager moves through its environment when food is patchily distributed and the patches differ in quality. One possibility is to move directionally among patches, staying longer in the best patches (the “Local‐Experience Hypothesis”). Additionally, when foragers reuse patches in a regenerating environment, they can potentially benefit from remembering the most profitable patches, and return preferentially to these (the “Memory Hypothesis”). Both hypotheses were tested with foraging bumble bees (Bombus spp.) collecting nectar in the foothills and mountains of southwest Alberta, Canada. Individually marked worker bumble bees were observed visiting flowers on focal plants of five species visited primarily by bumble bees. In three plant species (Epilobium angustifolium, Hedysarum alpinum, and Penstemon confertus), variation in nectar secretion rate was experimentally induced by defoliation and fertilization of individual plants. In the other two species (H. sulphurescens and Oxytropis monticola), bees' responses to natural variation in plant‐level nectar secretion were measured. Considering the bee population as a whole, plants with higher nectar production rates attracted more bees (three of five plant species) and had more of their flowers visited (three of five plant species). The Local‐Experience Hypothesis was supported in three of the five plant species: individual bees stayed longer by visiting more flowers on plants with higher rates of nectar production. The Memory Hypothesis was supported in four of the five plant species; individual bees were more likely to return to plants with higher rates of nectar secretion. Overall, there was a positive correlation between the extent to which individual plants differed in their rate of nectar secretion (a species‐level trait), and the strength of support for the Memory Hypothesis (measured as a standardized effect size). That is, individual bumble bees more strongly adjusted their visitation rate based on plant quality as the magnitude of natural differences in plant quality increased. Support for the Memory Hypothesis may explain why bumble bees often revisit the same plants on successive foraging trips: memory for good plants gives them a fitness advantage over naïve bees using the same area. Bumble bees appear to use a relatively sophisticated spatial memory in resource tracking, which may constrain the evolution of empty‐flower strategies of plant nectar secretion.

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Interaction webs, or networks, define how the members of two or more trophic levels interact. However, the traits that mediate network structure have not been widely investigated. Generally, the mechanism that determines plant-pollinator partnerships is thought to involve the matching of a suite of species traits (such as abundance, phenology, morphology) between trophic levels. These traits are often unknown or hard to measure, but may reflect phylogenetic history. We asked whether morphological traits or phylogenetic history were more important in mediating network structure in mutualistic plant-pollinator interaction networks from Western Canada. At the plant species level, sexual system, growth form, and flower symmetry were the most important traits. For example species with radially symmetrical flowers had more connections within their modules (a subset of species that interact more among one another than outside of the module) than species with bilaterally symmetrical flowers. At the pollinator species level, social species had more connections within and among modules. In addition, larger pollinators tended to be more specialized. As traits mediate interactions and have a phylogenetic signal, we found that phylogenetically close species tend to interact with a similar set of species. At the network level, patterns were weak, but we found increasing functional trait and phylogenetic diversity of plants associated with increased weighted nestedness. These results provide evidence that both specific traits and phylogenetic history can contribute to the nature of mutualistic interactions within networks, but they explain less variation between networks.

Can. Ent. 123: 283-293 (1991) Bumble bees rely on stored nectar to maintain high colony temperatures. This study examines some of the costs associated with exhausting stored nectar for a day in confined colonies of Bombus occidentalis Greene and B. melanopygus Nylander. Workers from energy-deprived colonies ceased incubating and allowed brood temperatures to drop to ambient levels. Workers from energy-rich colonies responded to a simulated vertebrate predator by actively moving about and buzzing loudly (apparently searching for the source of disturbance), but those from energy-depleted colonies mostly remained stationary on the comb. Workers from energy-rich colonies responded to an intruding social parasite (a Psithyrus insularis Smith queen) by chasing and attacking it, whereas those from energy-depleted colonies adopted stationary threat postures. In both cases, the more successful defensive strategy of simultaneous attack by several workers was not employed by nectar-depleted colonies. Cooling of final-instar larvae and pupae added to their development times (disproportionately so in the case of pupae), but low temperature per se did not affect their probability of survival. Hence, the costs of shortterm energy shortfall include increased susceptibility to predators and parasites and a lengthened period of development. These costs probably relate to energy stores in a nonlinear manner, providing the foundation upon which risk-sensitive foraging decisions can be based. RCsumeLes abeilles dependent de rCserves de nectar afin de maintenir de hautes tempkratures pour leur colonies. Cette Ctude examine certains prix associCs B la p6nurie de rkserves quotidiennes de nectar encourus par des colonies confinCes de Bombus occidentalis Greene et de B. melanopygus Nylander. Les ouvrikres des colonies dont les sources d'Cnergie sont limitCes cessent d'incuber et laissent baisser au niveau ambient la temp6rature des couvains. Les ouvrieres des colonies riches en Cnergie rCpondent B une simulation d'attaque de la part d'un prkdateur vertCbrC en se dCplapnt activement et en bourdonnant fortement (cherchant apparemment la source de perturbation), tandis que celles des colonies B budget CnergCtique limite demeurent en majeure partie stationnaires sur les rayons. Les ouvrieres des colonies i budget CnergCtique non limit6 kpondent B l'intrusion d'un parasite social (une reine Psithyrus insularis Smith) en chassant ce dernier et en l'attaquant, tandis que celles des colonies B budget rCduit adoptent des postures de menace stationnaires. Aux deux cas, la stratkgie de dCfense la plus fructueuse, l'attaque en groupe, n'est pas employCe par les colonies dCprivCes de nectar. Le refroidissement des larves en stade larvaire terminal et des pupes prolonge la d u r k de leur dCveloppement (d'une f a~o n disproportionnke au cas des pupes) mais n'affecte pas la probabilitk de survie. Ainsi, les prix B courte CchCance du manque d'Cnergie incluent une plus grande susceptibilitk aux prkdateurs et aux parasites et une p6riode de dC...