Testing models of bee foraging behavior through the analysis of pollen loads and floral density data

The composition of social bees' corbicular pollen loads contains information about both the bees' foraging behavior and the surrounding floral landscape. There have been, however, few attempts to integrate pollen composition and floral landscape to test hypotheses about foraging behavior. Here, we present an individual-based model that generates the species composition of pollen loads given a foraging model and a spatial distribution of floral resources. We apply this model to an existing dataset of inflorescence counts and bumble bee pollen loads sampled at different field sites in California. For two out of three sites, a foraging model consisting in correlated random walks with constant preferences for each plant species provides a plausible fit for the observed distribution of pollen load content. Pollen load compositions at the third site could be explained by an extension of the model, where different preferences apply to the choice of an initial foraging patch and subsequent foraging steps. Since this model describes the expected level of pollen load differentiation due solely to the spatial clustering of conspecific plants, it provides a null hypothesis against which more complex descriptions of behavior (e.g. flower constancy) can be tested

The Changing Role of Plant-Soil Feedback Loops in Maintaining Coexistence in the Face of Drought

My goal was to explore the influence of drought and soil biota on plant growth via plant-soil feedbacks, and thus to examine potential implications for stable coexistence for similar plants within overlapping species ranges. I carried out a greenhouse experiment to determine the effect of drought and soil biota on the relative fitness of two milkweed species. The project consisted of harvesting soil samples of each species from the field, further training the soil in the greenhouse to cultivate soil organisms, then growing each milkweed species in trained soil in a fully reciprocal experiment that included watering regiment and soil biota as treatments. There were strong conspecific negative feedbacks in both species, but these diminished under drought treatments. These results were driven by the growth of below ground biomass and were likely due to an increase in pathogenic soil microbes cultivated on the roots of conspecific plants. However, conspecific soil allowed for more growth in Asclepias syriaca compared to Asclepias sullivantii, suggesting that A. syriaca is less limited by pathogens. Additionally, these negative effects disappeared in treatments were the inoculum was sterilized. Synthesis. My findings suggest that biotic soil interactions play a significant role in plant growth, which complicates the possibility of coexistence in plants with overlapping ranges beyond resource competition. As drought intensifies under climate change, the effect of drought on soil-feedback mechanisms will complicate future range predictions beyond the physiological stresses of the drought-intensive summers predicted by climate change models, requiring an increase in knowledge of plant-soil interactions so that future ranges can be more accurately predicted

Data from: Estimating resource preferences of a native bumblebee: the effects of availability and use-availability models on preference estimatess

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

Filtering across Spatial Scales: Phylogeny, Biogeography and Community Structure in Bumble Bees

<div><p>Despite the expansion of phylogenetic community analysis to understand community assembly, few studies have used these methods on mobile organisms and it has been suggested the local scales that are typically considered may be too small to represent the community as perceived by organisms with high mobility. Mobility is believed to allow species to mediate competitive interactions quickly and thus highly mobile species may appear randomly assembled in local communities. At larger scales, however, biogeographical processes could cause communities to be either phylogenetically clustered or even. Using phylogenetic community analysis we examined patterns of relatedness and trait similarity in communities of bumble bees (<i>Bombus)</i> across spatial scales comparing: local communities to regional pools, regional communities to continental pools and the continental community to a global species pool. Species composition and data on tongue lengths, a key foraging trait, were used to test patterns of relatedness and trait similarity across scales. Although expected to exhibit limiting similarity, local communities were clustered both phenotypically and phylogenetically. Larger spatial scales were also found to have more phylogenetic clustering but less trait clustering. While patterns of relatedness in mobile species have previously been suggested to exhibit less structure in local communities and to be less clustered than immobile species, we suggest that mobility may actually allow communities to have more similar species that can simply limit direct competition through mobility.</p> </div

Z scores and p-values of relatedness and tongue length for various scales and measures of similarity.

<p>Local assemblages (n = 110) represent co-occurring species and the species pool is the regional gridcell the assemblage is within. Regional assemblages (n = 45) are the species in each grid cell compared to a species pool of all Nearctic Species. The continental assemblage (n = 1) consists of all Nearctic species compared to all <i>Bombus</i> globally.</p