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Identifying resource preference is considered essential for developing targeted conservation plans but, for many species, questions remain about the best way to estimate preference. Resource preferences for bees are particularly difficult to determine as the resources they collect, nectar and pollen, are challenging to estimate availability and collection. Resources are traditionally measured at the flower or inflorescence level, but these measures of availability do not correspond to the resources actually used by bees. Additionally, it is unclear as to whether common models including availability are appropriate for bees which may target resources regardless of available quantities. Here we first compare two common hypotheses of resource use - the 'random use hypothesis' and the 'linear preferences hypothesis' - using three different measures of availability (pollen, flower and inflorescence) - to determine if one measure of availability was better for understanding bee pollen use. Next, the superior model using availability was compared to a novel model of bee pollen use the 'target use hypothesis'. This model assumes that bees target some resources regardless of how much of each resource is available (but assuming resources are present at a site), and thus models preference without availability data. Of the models including availability, the linear preference model using inflorescence availability best explained the pollen use data. This suggests that bumblebee pollen use is non-random and that cues to identify and locate resources (i.e. display size and quantity) may be more important than the quantity of the resource available (i.e. pollen availability). Additionally, in most cases the target use model explained the data equal to or better than the other models suggesting bee resource use may be better modeled without measured availability data compared to linear models. These results could be important for expanding resource use analysis of bees that are difficult to quantify availability. [ABSTRACT FROM AUTHOR]

The influence of space on the structure (e.g. modularity) of complex ecological networks remains largely unknown. Here, we sampled an individual-based plant-pollinator network by following the movements and flower visits of marked bumblebee individuals within a population of thistle plants for which the identities and spatial locations of stems were mapped in a 50 × 50 m study plot. The plant-pollinator network was dominated by parasitic male bumblebees and had a significantly modular structure, with four identified modules being clearly separated in space. This indicated that individual flower visitors opted for the fine-scale division of resources, even within a local site. However, spatial mapping of network modules and movements of bumblebee individuals also showed an overlap in the dense center of the plant patch. Model selection based on Akaike information criterion with traits as predictor variables revealed that thistle stems with high numbers of flower heads and many close neighbours were particularly important for connecting individuals within the modules. In contrast, tall plants and those near the patch center were crucial for connecting the different modules to each other. This demonstrated that individual-based plant-pollinator networks are influenced by both the spatial structure of plant populations and individual-specific plant traits. Additionally, bumblebee individuals with long observation times were important for both the connectivity between and within modules. The latter suggests that bumblebee individuals will still show locally restricted movements within sub-patches of plant populations even if they are observed over a prolonged time period. Our individual-based and animal-centered approach of sampling ecological networks opens up new avenues for incorporating foraging behaviour and intra-specific trait variation into analyses of plant-animal interactions across space. [ABSTRACT FROM AUTHOR]

Although the practice of cultivating mass flowering crops (MFCs) is seen as a means of counteracting the widespread decline of insect pollinators, no study to-date has evaluated whether the increased pollinator abundance associated with MFCs influences pollinator visits to assemblages of adjacent native, non-crop plant species (pollinator 'spill-over'). In this study we quantified bumblebee abundance along hedgerow transects in MFC (field bean) vs non-MFC (wheat) margins. Surveys were conducted on east and west-facing margins twice daily (morning and afternoon) for three or four days during the main MFC flowering period (June) over four years involving paired bean and wheat fields in Devon and Cornwall, southwest England. Although no single bumblebee species showed any consistent change in relative frequency, when taken across all years and bumblebee species combined, we observed twice as many bumblebees visiting flowers adjacent to the MFC. However, when we compared bumblebee activity along hedgerow transects two weeks after bean flowering, there was no difference between crops. We thus conclude that although there is evidence for pollinator spill-over from the bean MFC to nearby semi-natural habitat, the effect is comparatively short lived and not specific to any single bumblebee species. We also suggest that while pollinator services to native plant species might be briefly enhanced by MFC cultivation, the possible repercussions of bumblebee spill-over from MFCs to semi-natural habitats and the other pollinator groups they support should be evaluated before MFC cultivation is considered as a means of conserving declining bumblebee populations. [ABSTRACT FROM AUTHOR]

We studied pollinator visitation rates and movement patterns in experimental arrays of irises at two sites within a Louisiana iris hybrid zone. Arrays contained single-flowered stems of red-flowered Iris fulva, blue-flowered I. hexagona, and purple-flowered F1 hybrids. At one site, where I. hexagona was the only wild-growing iris, queen bumble bees were the most common pollinator, and the rank order of pollinator visit rates was I. hexagona > F1 < I. fulva. At a second site, where I. fulva predominated in the wild, hummingbirds were the most common pollinators, and this order was reversed: I. hexagona < F1 > I. fulva. Thus, at both sites, the naturally occurring iris was visited most frequently and F1 flowers were visited more frequently than the non-native species. Pollinators used both long-distance and short-distance cues to discriminate among flowers, and differences in visit rates seemed to be based on differences in the ease of access to pollen and nectar rewards on flowers of different size. Analysis of movement patterns between flowers showed that pollinators were more likely to make parental-F1 transitions than heterospecific transitions. These data suggest that pollinator behavior acts as a partial barrier to initial hybridization, although this barrier largely breaks down after F1 formation. Our results help to explain the existence of many introgressed populations of Louisiana iris, despite the fact that F1s are extremely rare in the wild.. [ABSTRACT FROM AUTHOR]

Pollinators collect resources that are patchy, since flowers are usually aggregated on several spatial scales. Empirical studies have established that pollinators almost invariably visit a smaller proportion of flowers as patch size increases. This has not been adequately explained. Here I present data on the payoff curve achieved by bumblebees, Bombus lapidarius, when visiting patches containing different numbers of inflorescences, and use the marginal value theorem to predict the optimum duration of stay within patches. The data demonstrate that visiting a declining proportion of inflorescences as patch size increases is an optimal strategy, if we assume that bees are attempting to maximise their rate of reward acquisition. I argue that this occurs because searching for the remaining unvisited inflorescences is easier in a small patch. On large patches, bees visited more inflorescences per patch than predicted (although still visiting a declining proportion). I suggest that this may occur because bees are using simple departure rules which result in near-optimal behaviour. I show that a departure rule based on two successive encounters with empty inflorescences closely predicts observed behaviour. [ABSTRACT FROM AUTHOR]