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Methods for sampling ecological assemblages strive to be efficient, repeatable, and representative. Unknowingly, common methods may be limited in terms of revealing species function and so of less value for comparative studies. The global decline in pollination services has stimulated surveys of flower-visiting invertebrates, using pan traps and net sampling. We explore the relative merits of these two methods in terms of species discovery, quantifying abundance, function, and composition, and responses of species to changing floral resources. Using a spatially-nested design we sampled across a 5000 km(2) area of arid grasslands, including 432 hours of net sampling and 1296 pan trap-days, between June 2010 and July 2011. Net sampling yielded 22% more species and 30% higher abundance than pan traps, and better reflected the spatio-temporal variation of floral resources. Species composition differed significantly between methods; from 436 total species, 25% were sampled by both methods, 50% only by nets, and the remaining 25% only by pans. Apart from being less comprehensive, if pan traps do not sample flower-visitors, the link to pollination is questionable. By contrast, net sampling functionally linked species to pollination through behavioural observations of flower-visitation interaction frequency. Netted specimens are also necessary for evidence of pollen transport. Benefits of net-based sampling outweighed minor differences in overall sampling effort. As pan traps and net sampling methods are not equivalent for sampling invertebrate-flower interactions, we recommend net sampling of invertebrate pollinator assemblages, especially if datasets are intended to document declines in pollination and guide measures to retain this important ecosystem service.

Animals visit flowers to access resources and by moving pollen to conspecific individuals act as pollinators. While biotic pollinators can increase the seed set of plants, other flower visitors can reduce seed set directly by damaging vital reproductive organs and indirectly by affecting the way the plant interacts with subsequent flower visitors. It is, therefore, vital to understand the varied effects of all visitors and not only pollinators on plant fitness, including those visitors that are temporally or spatially rare. We document the first known case of flower visitation by small mammals to C rotalaria cunninghamii ( Fabaceae), a plant species morphologically suited to bird pollination. During a rain-driven resource pulse in the Simpson Desert in 2011, the rodents M us musculus ( Muridae) and P seudomys hermannsburgensis ( Muridae) visited flowers to remove nectar by puncturing the calyx. We investigated the effects of this novel interaction on the reproductive output of C . cunninghamii. Compared with another recent resource pulse in 2007, plants flowering during mammal visitation had five times as many inflorescences per plant, 90% more flowers per inflorescence, and two to three times more nectar per flower, but this nectar was 30% less sugar rich. Concurrently, rodent plagues were up to three times larger during this rain-driven resource pulse than during a previous pulse in 2007. Up to 75% of flowers had evidence of small mammal florivory, but this was not necessarily destructive, as up to 90% of fruit had the remains of florivory. Through a series of exclusion experiments, we found that small mammal florivory did not directly reduce seed set. We conclude that rain-driven resource pulses led to a unique combination of events that facilitated the novel florivory interaction. Our findings emphasize the dynamic nature of biotic interactions and the importance of testing the role of all visitors to pollination services. [ABSTRACT FROM AUTHOR]

Mutualistic networks display distinct structural and organizational features such as nestedness, power-law degree distribution and asymmetric dependencies. Attention is now focused on how these structural properties influence network function. Most plant-pollinator networks are constructed using records of animals contacting flowers, which is based on the assumption that all visitors to flowers are pollinators; however, animals may visit flowers as nectar robbers, florivores, or to prey upon other visitors. To differentiate potential pollinator interactions from other interaction types, we examined individual bees that had visited flowers to detect if they carried pollen. Using these data, we constructed visitation and pollen-transport networks for a spinifex-dominated arid zone grassland. To determine how the structure of the visitation network reflects pollen transport, we compared the two networks using a null model approach to account for differences in network size. Differences in number of species, nestedness and connectance observed between the visitation and pollen-transport networks were within expected ranges generated under the null model. The pollen-transport network was more specialized, had lower interaction evenness, and fewer links compared to the visitation network. Almost half the number of species of the visitation network participated in the pollen-transport network, and one-third of unique visitation interactions resulted in pollen transport, highlighting that visitation does not always result in pollination. Floral visitor data indicate potential pollen transporters, but inferring pollination function from visitation networks needs to be performed cautiously as pollen transport resulted from both common and rare interactions, and depended on visitor identity. Although visitation and pollen-transport networks are structurally similar, the function of all species cannot be predicted from the visitation network alone. Considering pollen transport in visitation networks is a simple first step towards determining pollinators from non-pollinators. This is fundamental for understanding how network structure relates to network function. [ABSTRACT FROM AUTHOR]

Recent work on the ecosystem service of biodiversity suggests that higher pollinator diversity could lower pollen limitation, but these two aspects of plant-pollinator communities have only rarely been causally connected. Here we present a review of studies that produced quantitative assessments of both pollinator diversity and evenness as well as pollen limitation of focal plant species. Although pollen limitation is expected to be lower when pollinator diversity is high, our analysis suggests this relationship is weak. The relationship may be obscured when features of the plant species (e.g., average level of specialization) are confounded with features of the plant communities (e.g., habitat). We encourage researchers investigating pollen limitation to consider including measures of diversity of the floral visitors, and their effectiveness. These data would permit a more powerful test of the relationships among these variables and improve our understanding of the critical elements of stable plant-pollinator networks. [ABSTRACT FROM AUTHOR]

Complete dichogamy occurs when temporal separation prevents any overlap in male and female function within and among flowers of one or more inflorescences. Although dichogamy may increase outcrossing and prevent inbreeding, it also results in the presentation of inflorescences with different floral resources. Pollinators may prefer one gender over the other based on these differences, which can reduce the transfer of pollen to conspecific stigmas and reduce floral resources for effective pollinators. We investigated whether the insect visitors of Trachymene incisa (Apiaceae), an Australian herb demonstrating complete protandry at the umbel level, show a preference for male or female umbels. The male phase umbels present pollen and nectar, whereas the female phase umbels offer nectar only. Therefore, we expect pollen-collecting insects to favour male umbels, whereas insects that forage only for nectar will favour female umbels. In natural patches that exhibited a male umbel bias, insects showed a preference for male phase umbels at Agnes Banks in 2003 and at Myall Lakes in both 2003 and 2004. By contrast, insects showed no preference for umbel phases, visiting umbels at a similar frequency to which they occurred, at Agnes Banks in 2004 and at Tomago in both 2003 and 2004. This suggests spatial and temporal variation in insect preferences for umbel phases that differ in floral rewards. In experimental arrays where the umbel gender ratio was equal, there were no significant differences between male and female umbels in terms of insect visitation during a foraging trip and mean foraging time per visit. The differing patterns of preference may be due to a differential response by insects when the umbel ratios vary, where a male bias in umbel genders leads to a preference for male umbels, whereas an equal umbel gender ratio leads to equal visitation to male and female phase umbels. [ABSTRACT FROM AUTHOR]