Availability Of Floral Resources Research Articles

Distance models reveal biases associated with passive trapping methods for measuring wild bee abundance

IntroductionThere is overwhelming evidence of declines in native bee populations and therefore a need for increased monitoring to track these declines and assist in conservation and restoration efforts. Bees can be sampled non-lethally through visual surveys (e.g., distance transects) or lethally through active (e.g., hand netting) or passive (e.g., traps that lure insects from afar) methods. These lethal methods suffer from imperfect detection that is difficult to account for and can confound inferences about habitat characteristics. Additionally, evidence suggests that lethal sampling methods can even invert habitat quality patterns such that high-quality sites yield fewer individuals and low-quality sites yield more individuals.MethodsTo study potential biases associated with imperfect detection, we used hierarchical density estimation with visual surveys to estimate density of bees within 40 young forest patches across Pennsylvania, USA. We surveyed bee communities non-lethally using visual surveys and lethally using blue-vane traps and bee bowls every two weeks between May and September 2019. We collected data on blooming flowers, vegetation structure, and weather during times of survey.ResultsWe found that bee densities estimated from distance transects had a positive relationship with floral resource availability. In contrast, abundance measured via bee bowls and blue-vane traps had no relationship, or sometimes even negative trends with habitat quality, including floral resource availability. Raw bee counts within 2-m of the transect always correlated with modeled densities, showing that some methods do not share the biases of attractive traps.DiscussionOur study demonstrates that failing to account for imperfect detection can impact the interpretation of pollinator surveys and adds to a growing body of literature that acknowledges the value of distance sampling for insects like bees to better understand species’ habitat needs and to monitor populations for conservation.

A map of pollinator floral resource habitats in the agricultural landscape of Central New York

We created a spatially and temporally-explicit model of floral area in Central New York State, USA, using public data from federal and state governmental agencies and non-governmental organisations. This model incorporates remote sensing-derived natural habitat, crop and land-use data products with roads GIS data to predict land cover indicative of floral resources for pollinators. The resulting dataset provides the necessary land-cover data to quantify floral resources available within a user-specified area (e.g. 2 km radius around the location of a bee hive). When paired with phenological data of species within the communities associated with our land-cover classes, users can predict pollinator floral resources over any specified period in a year. This dataset would be of use to both researchers and practitioners, allowing them to estimate floral resource availability around crops or hive placements. It could also identify habitat restoration to most effectively boost native pollinator populations. We present the methodology for the creation of the spatial dataset and usage information.

Standardized transect walks outperform pan traps in assessing wild bee community in a Mediterranean protected area (Asinara National Park, Italy)

AbstractThe decline of pollinator insects in various parts of the world has increased the interest in studies on bee sampling. Because pollinator management and conservation policies depend on data representing their communities, knowledge of the systematic bias of sampling methods in relation to surrounding habitat is fundamental. This study examined the performance of standardized transect walks and colored pan traps considering differences in bee species richness, diversity, and composition, and the potential bias due to a different availability of floral sources throughout seasons. The study was conducted in a minor outlying island (Asinara, Italy), a natural park characterized by the prevalence of natural or semi-natural habitats and an Oceanic Pluviseasonal Mediterranean bioclimate. We found that transect and pan trap methods reflected different bee communities based on taxonomic families, genera, and species. In general, the transect method captured more varied samples than pan traps, despite the significantly lower number of individuals captured on transects. Moreover, pan traps captured more bees as floral abundance decreased, whereas transects showed greater bee abundance, richness, and diversity with increasing floral resource availability. In addition, 18 species out of the 68 observed in total were caught exclusively with pan traps, especially in July–October, when transect catches decreased due to substantial bloom reduction. Therefore, alternating the two methods according to season (i.e., transect in late winter-spring and pan trap in summer-autumn) might be the most suitable trade-off to obtain a better representation of the bee community by limiting sampling efforts and the negative impact on bee fauna.

Emergence of structure in plant–pollinator networks: low floral resource constrains network specialisation

Specialisation enhances the efficiency of plant–pollinator networks through the exchange of conspecific pollen transfer for floral resources. Floral resources form the currency of plant–pollinator interactions, but the understanding of how floral resources affect the structure of plant–pollinator networks remains modest. Previous theory predicts that optimally foraging animal species will specialise to improve resource acquisition under high resource availability. Although floral resource availability depends on both the plant production and animal consumption of the resources, previous work has assumed that production and availability are equivalent. This potentially may have led to erroneous inferences on the effect of resource availability on specialisation. We develop a mutualistic Lotka–Volterra consumer‐resource model to investigate the influence of floral resource availability on plant–pollinator network structure. The model incorporates animal adaptive foraging behaviour, floral resource dynamics, and density‐dependent dynamics. Specialisation, nestedness and modularity of simulated networks generated from the model under a wide range of parameters were explained using the generalised linear model. We found that the distinction between floral resource dynamics and plant density dynamics was necessary for partial specialisation of plant–pollinator networks. This is because floral resource dynamics constrained animal preference due to its depletion by animal species. Floral resource abundance had a positive effect on network specialisation, but animal density had a negative effect on network specialisation. Floral resource dynamics thus play key roles in the structure of plant–pollinator networks, distinctive from plant species density dynamics.

Pollen load, pollen species diversity and conspecific pollen carried by pollinators across 24-hour cycles

Plant-pollinator interactions are key for the reproduction of wild plants and for food security. However, the role nocturnal pollinators play in wild plant communities is not yet clear. Specifically, it has rarely been studied whether nocturnal pollinators are comparable to diurnal ones in the pollination services they deliver in plant communities. We tested whether nocturnal pollinators have the potential to provide high pollination services to the plants they visit by carrying high conspecific pollen loads. We studied pollen loads carried by nocturnal and diurnal pollinators captured over 24-hour cycles in co-flowering plant communities in Swiss ruderal meadows. Pollen load was less diverse at night, and the proportion of conspecific pollen carried by nocturnal pollinators was higher than that of diurnal ones. Because the majority of plant species visited at night were also visited during the day, floral resource availability could drive the observed patterns in pollen load and amount of conspecific pollen. Nevertheless, nocturnal pollinators do not only carry pollen but can remove and potentially deposit conspecific pollen to the plants they visit. Therefore, pollinators active at night might be an important pollination vector for more plant species than previously thought and should not be neglected in pollination studies.

Agave distribution and floral display influence foraging rates of an endangered pollinating bat and implications for conservation.

Wildlife conservation involves making management decisions with incomplete knowledge of ecological relationships. Efforts to augment foraging resources for the endangered Mexican long-nosed bat (Leptonycteris nivalis) are progressing despite limited knowledge about the species' foraging behavior and requirements. This study aimed to understand L. nivalis responses to floral resource availability, focusing on individual agave- and local-scale characteristics influencing visitation rates to flowering agaves. We observed bat visitation at 62 flowering agaves around two roosts in northeast Mexico on 46 nights in the summers of 2017 and 2018. We found visitation rate had positive relationships with two agave-scale characteristics: the number of umbels with open flowers and the lower vertical position on the stalk of those umbels (i.e., earlier phenological stages of flowering). However, these factors exhibited strong negative interaction: with few umbels with open flowers, the position of flowering umbels had little effect on visitation rate, but when umbels with open flowers were abundant, visitation rate was more strongly related to the lower flowering umbel position. We also found relationships between visitation rate and two local-scale characteristics: negative for the density of flowering conspecifics within 30 m of the focal agave and positive for the density of dead standing agave stalks within 30 m. Our findings suggest opportunities to augment foraging resources for L. nivalis in ways that are consistent with their foraging behavior, including: increasing the supply of simultaneously blooming flowers by planting agave species that tend to have more umbels with simultaneously open flowers; planting multiple species of agaves with different flowering times to increase the availability of agaves with open flowers on lower-positioned umbels throughout the period when bats are present in the region; planting agaves in clusters; and keeping dead standing agave stalks on the landscape. Our study points to useful management strategies that can be implemented and monitored as part of an adaptive management approach to aid in conservation efforts.

Pesticide hazard, floral resource availability and natural enemies interactively drive the fitness of bee species depending on their crop fidelity

Pesticides, loss of floral resources and parasitism are considered drivers of wild bee decline in agroecosystems, but their interactions are poorly understood under field conditions. Negative impacts are predicted to vary across species of distinct crop fidelity because of the associated consequences for pesticide exposure and dependence on wild flowers. We experimentally established populations of two solitary bee species in apple orchards with distinct pesticide hazard and flower availability in surrounding landscapes. The number of nesting females, their reproduction and offspring survival and parasitism rate were tracked throughout apple bloom. We show that in the solitary bee Osmia cornuta, which showed a strong preference to forage in apple orchards, the number of females remaining at nesting sites towards the end of apple bloom and the overall reproductive success of the released bees declined with pesticide hazard. In contrast, the closely related Osmia bicornis, which showed a lower preference for apple, was not affected by pesticide use in orchards. Floral resource distribution furthermore modulated parasitism rates in both species: while large amounts of locally available resources reduced offspring parasitism, it increased with relatively higher food availability in the landscapes surrounding focal orchards, probably due to the bees foraging on a larger scale and thus longer periods during which nests remained unattended. Our findings provide novel insights into the complex interplay of pesticide exposure, flower availability and parasitism risk driving population dynamics of bees in agroecosystems. They show that in particular the most reliable crop pollinator species are especially harmed by high pesticide use in crops. Our study underpins the key role of reducing pesticide risks for pollinators through effective regulation of potentially hazardous agrochemicals and the promotion of alternative pest regulation approaches along with conserving and restoring flower-rich habitats to sustain pollinator populations in agroecosystems.

Seed mix design and floral resources drive multitrophic interactions in prairie restoration

Abstract Ecological restoration often targets plant community recovery, but restoration success may depend on the recovery of a complex web of biotic interactions to maintain biodiversity and promote ecosystem services. Specifically, management that drives resource availability, such as seeding richness and provenance, may alter species interactions across multiple trophic levels. Using experimentally seeded prairies, we examine three key groups—plants, pollinators and goldenrod crab spiders (Misumena vatia, predators of pollinators)—to understand the effects of species richness and admixture seed sourcing of restoration seed mixtures on multitrophic interactions. Working with prairie plants, we experimentally manipulated seed mix richness and the number of seed source regions (single‐source region or admixture seed sourcing). In each experimental prairie, we surveyed floral abundance and richness, pollinator visitation and plant–M. vatia interactions. A high richness seed mix increased floral abundance when seeds were sourced from a single geographic region, and floral abundance strongly increased pollinator visitation, M. vatia abundance and prey capture. Seeding richness and admixture seed sourcing of the seed mixture did not affect floral species richness, but floral species richness increased pollinator visitation. Pollinators interacted with different floral communities across seeding treatments, indicating a shift in visited floral species with restoration practices. Synthesis and applications. Long‐term success in prairie restoration requires the restoration of plant–arthropod interactions. We provide evidence that seed mix richness and admixture seed sourcing affect arthropod floral associations, but effective restoration of plant–arthropod interactions should consider total floral resource availability. Incorporating a food web perspective in restoration will strengthen approaches to whole ecosystem restoration.

Floral resources enhance fitness of the parasitoid Hadronotus pennsylvanicus (Hymenoptera: Scelionidae) but not biological control of its host Leptoglossus zonatus (Heteroptera: Coreidae).

The diet of adult parasitoid wasps is vital for their survival and reproduction. However, the availability of food resources, such as plant nectar, can vary widely in cropping systems, potentially affecting parasitoid fitness and thereby biological control of pests. The egg parasitoid Hadronotus pennsylvanicus (Ashmead) (Hymenoptera: Scelionidae) is a potential biological control agent of the pistachio pest Leptoglossus zonatus (Dallas) (Heteroptera: Coreidae). While H. pennsylvanicus is known to attack L. zonatus eggs in California, USA, parasitism rates in orchards are highly variable. Floral resource provisioning has the potential to enhance parasitoid longevity and thus improve parasitism rates, leading to reduced pest densities. Here, a combination of field and laboratory studies was used to assess the influence of flowering groundcovers on the reproductive fitness of H. pennsylvanicus and the abundance of L. zonatus. Evaluated groundcovers included oat (Avena sativa L.), cowpea (Vigna unguiculata L.), white mustard (Sinapis alba L.), and buckwheat (Fagopyrum esculentum Moench). Under laboratory conditions, buckwheat and mustard provided the greatest benefit to female H. pennsylvanicus longevity. However, females provided a buckwheat diet produced the greatest number of offspring over the course of their lifetime. In field trials, flowering groundcovers did not influence the abundance of H. pennsylvanicus nor parasitism rates on L. zonatus. While the availability of floral resources can improve the reproductive fitness of H. pennsylvanicus, the use of groundcovers in pistachio did not enhance biological control of L. zonatus.

Earlier Flowering Phenology and Pollinator Visitation on Urban Green Roofs Compared to Ground-Level Gardens

Urban green space, green infrastructure, and horticultural installations are gaining recognition for their potential to foster biodiversity. Green roofs are challenging growing environments for plants, characterized by extreme substrate temperatures, high light intensity, limited moisture availability, and limited substrate depth. Plants have a variety of physiological responses to these unique conditions, but little is known about how green roof growing conditions affect ecological characteristics like plant flowering phenology. Meanwhile, studies are only just uncovering the degree to which green roofs can provide habitat and support urban pollinator biodiversity. We evaluated the flowering phenology and made in situ pollinator observations of 15 plant taxa growing both on green roof systems and at ground level in Denver, Colorado, over two growing seasons. We found that flowering phenology occurs substantially earlier on green roofs compared to ground level among the observed plant taxa and observed a greater number of pollinators on green roofs early in the season, compared to ground level, presumably due to the availability of floral resources among the observed plant taxa. We observed significantly higher substrate temperatures along with wider diurnal temperature amplitude during the growing season that may contribute to the observed phenological patterns. Divergence in flowering phenology between individual plants of the same species on green roofs and plants at ground-level may have implications for organisms that rely on floral resources in urban environments. Earlier flower initiation on green roofs may provide pollinators with unique foraging opportunities and aid targeted conservation where early-season floral resources are limited.

Bridging the Gap between Field Experiments and Machine Learning: The EC H2020 B-GOOD Project as a Case Study towards Automated Predictive Health Monitoring of Honey Bee Colonies.

Honey bee colonies have great societal and economic importance. The main challenge that beekeepers face is keeping bee colonies healthy under ever-changing environmental conditions. In the past two decades, beekeepers that manage colonies of Western honey bees (Apis mellifera) have become increasingly concerned by the presence of parasites and pathogens affecting the bees, the reduction in pollen and nectar availability, and the colonies' exposure to pesticides, among others. Hence, beekeepers need to know the health condition of their colonies and how to keep them alive and thriving, which creates a need for a new holistic data collection method to harmonize the flow of information from various sources that can be linked at the colony level for different health determinants, such as bee colony, environmental, socioeconomic, and genetic statuses. For this purpose, we have developed and implemented the B-GOOD (Giving Beekeeping Guidance by computational-assisted Decision Making) project as a case study to categorize the colony's health condition and find a Health Status Index (HSI). Using a 3-tier setup guided by work plans and standardized protocols, we have collected data from inside the colonies (amount of brood, disease load, honey harvest, etc.) and from their environment (floral resource availability). Most of the project's data was automatically collected by the BEEP Base Sensor System. This continuous stream of data served as the basis to determine and validate an algorithm to calculate the HSI using machine learning. In this article, we share our insights on this holistic methodology and also highlight the importance of using a standardized data language to increase the compatibility between different current and future studies. We argue that the combined management of big data will be an essential building block in the development of targeted guidance for beekeepers and for the future of sustainable beekeeping.

Bees go up, flowers go down: Increased resource limitation from late spring to summer in agricultural landscapes

Abstract The loss of floral resources is a leading cause of wild bee decline in agricultural landscapes, but little is known about the temporal aspects of floral resource limitation for both social and solitary bees. Understanding when floral resources are most needed is crucial for the optimal design of pollinator conservation measures. We surveyed bees and flowers in 160 semi‐natural habitat patches multiple times per year (May–July) for 5 years. We identified the seasonality of floral resources and wild bees and examined inter‐ and intra‐annual patterns of floral resource limitation at both local and landscape scales. Floral resource availability varied across years but generally peaked in late May, after which it declined and remained low through July. Bumblebee and solitary bee abundances increased across the season, leading to stronger floral resource limitation for both groups later in the season. Bumblebee abundance was marginally positively associated with the cumulative amount of landscape‐scale floral resources as well as the floral resources of the previous year. Solitary bee abundance was only predicted by local‐scale floral resources. Synthesis and applications: Our results indicate that agri‐environmental management should target the provision of summer floral resources for both social and solitary bees. Local‐scale enhancement of floral resources can likely benefit solitary bees, but bumblebees probably require the management of floral resources at the landscape scale. Increasing the floral resources and the flowering period of herbaceous habitats that cover large proportions of the landscape, such as pastures, has the greatest potential to improve summer floral resources for bees.

Floral interventions enhance flower visitor communities and pollination services in moringa plantations

Abstract Pollination is a crucial ecosystem service contributing to global food security. Moringa (Moringa oleifera) is an economically important tropical crop, mostly cultivated by smallholder farmers. Well‐established approaches of planting flower‐rich patches used in temperate agroecosystems for pollination enhancement were adapted to tropical moringa systems. Based on existing evidence, we hypothesised that floral interventions would improve flower visitor diversity and abundance in the crop, thereby increasing pollination services and moringa yield and quality. We used standardised methods to survey flower visitors on moringa and assess economically relevant measures of crop yield quality and quantity. We selected 24 moringa fields in Tamil Nadu, India, to compare fields with and without floral interventions. We planted red gram, Cajanus cajan as a border crop, and marigold, Tagetes erecta as an intercrop on moringa fields to enhance floral resource availability for pollinators. These interventions were co‐designed with local farmers to ensure additional benefits to their community. We found that flower visitor abundance and species richness were significantly (50% for abundance and 33% for species richness) greater in fields with floral interventions compared with control fields. We also found that the percentage of flowers that resulted in harvestable fruits were significantly (30%) greater in fields with floral intervention. Production benefits in yield and quality were significantly positively correlated with the abundance and species richness of flower visitors. Synthesis and applications. Our results provide clear evidence that floral interventions in the form of intercropping and border cropping can enhance pollinator communities and services they provide in tropical smallholder systems. These findings underpin a practical management option for farmers to enhance flower visitor communities and pollination services, which can potentially also provide additional co‐benefits to farmers, improving livelihoods and sustainable production.

Enhancing Coccinella Beetle Biological Pest Control via a Floral Approach in Cucumber Greenhouse.

Flower-rich habitats are crucial for promoting biodiversity and ecosystem services within agricultural ecosystems, such as pollination and pest control. The present study investigates the efficacy of employing floral structures as a criterion for the selection of plant species in order to enhance the attraction of natural enemies within cucumber greenhouses, consequently augmenting floral resources. The results of our study provide evidence that flower strips have a beneficial effect on the fitness of critical natural predators, while not facilitating the proliferation of detrimental insect species. These findings exhibit potential for enhancing pest-management services in the agricultural sector. The findings of our study demonstrate that pest levels within greenhouse environments closely resemble those observed in real-world commercial cropping systems. As a result, the introduction of Coccinella septempunctata and Menochilus sexmaculatus biocontrol agents is confirmed to be a reliable and efficient method for pest management. The phenomenon of predator-prey density dependency is recognized as a crucial element in the implementation of biological control strategies. Furthermore, we investigate the impact of floral resources on the reproductive capacity of indigenous predators. The impact of Coriandrum sativum on fertility is substantial, indicating that the presence of a varied plant assortment with overlapping flowering periods can prolong the availability of floral resources. This study highlights the significance of flower-rich habitats and deliberate plant selection in augmenting biodiversity, ecosystem services, and pest management within agricultural settings. The implementation of conservation biological control technologies presents supplementary ecological advantages, thus offering practical implications for the promotion of sustainable agricultural practices.

Examining spatial and temporal drivers of pollinator nutritional resources: evidence from five decades of honey bee colony productivity data

Pollinators are an essential component of terrestrial food webs and agricultural systems but are threatened by insufficient access to floral resources. Managed honey bees, as generalist foragers that hoard nectar as honey, can act as bioindicators of floral resources available to pollinators in a given landscape through their accumulation of honey. Honey yields across the United States have decreased appreciably since the 1990s, concurrent with shifts in climate, land-use, and large-scale pesticide application. While many factors can affect honey accumulation, this suggests that anthropogenic stressors may be having large-scale impacts on the floral resources that pollinators depend on for their nutrition. We used hierarchical partitioning on five decades of state-level data to parse the most important environmental factors and likely mechanisms associated with spatial and temporal variation in honey yields across the US. Climatic conditions and soil productivity were among the most important variables for estimating honey yields, with states in warm or cool regions with productive soils having the highest honey yields per colony. These findings suggest that foundational factors constrain pollinator habitat suitability and define ecoregions of low or high honey production. The most important temporally varying factors were change in herbicide use, land use (i.e. increase in intensive agriculture and reduction in land conservation programs that support pollinators) and annual weather anomalies. This study provides insights into the interplay between broad abiotic conditions and fine temporal variation on habitat suitability for honey bees and other pollinators. Our results also provide a baseline for investigating how these factors influence floral resource availability, which is essential to developing strategies for resilient plant–pollinator communities in the face of global change.

Spatio-temporal complementarity of floral resources sustains wild bee pollinators in agricultural landscapes

Targeted conservation and promotion of wild bees in agroecosystems requires understanding of relationships between different groups of bees and available floral resources across land-use types during the season and at the landscape scale. Here, we quantified floral resource amount and diversity across habitat types at different times during the season at the scale of entire landscapes (500 m radius) across 20 different agricultural landscapes. Moreover, we examined whether floral resource metrics obtained from these high-resolution floral resource maps are more suitable to assess and predict abundance and species richness of different bee pollinator groups, including rare species and important crop pollinators, sampled in these agricultural landscapes compared to traditional land-cover metrics. Floral resource availability shifted from flower-rich woody vegetation early in the season to herbaceous vegetation such as grasslands and crops later in the season, which was associated with a ten-fold decline in overall floral resource availability. Forest edges had highest per-area floral contributions in spring, whereas floral diversity of grasslands, in particular if extensively managed, was continuously high. Total wild bee species richness, as well as rare species richness and abundance of important crop pollinators, increased with floral resource availability and/or diversity contributed by forest edges and floral diversity of permanent grasslands. Rare bee richness was also positively related to floral resource amount provided by crops. Total bee richness and important crop pollinator abundance, but not rare bee richness, were positively related to overall floral resource amount, but not floral diversity, in the landscape. Floral resource maps based on floral resource supply by major habitat types early or late in the season predicted wild bee species richness (R2 =0.61) better than traditional descriptors of landscape composition such as proportion of semi-natural habitat. The pronounced temporal shifts in floral resource availability for pollinators from woody towards herbaceous vegetation during the season highlights the importance of taking a landscape-scale perspective on pollinator conservation. Our findings indicate that both rare bees and important crop pollinators benefit from complementary floral resources of forest edges and grasslands in agroecosystems. This reveals a potential synergy between the conservation of endangered species and the landscape scale management to promote pollination services. Our study also highlights that floral resource maps are useful tools in supporting more targeted pollinator conservation and pollination service management at the landscape level.

Diversity matters: Diet of Apis cerana in southeast India includes one consistently occurring and several seasonally available floral sources

Little is known about the agroecological implications of the Asian honey bee Apis cerana Fabricius in its vast native range including southeast India. To identify the foraging preferences of this generalist species, we collected 388 corbicular pollen samples over three years at Merveille, an eco-restoration site in Puducherry region, southeast India. Pollen was collected twice or thrice weekly from March 2018 to December 2021 in three locations within the site. We used canonical correspondence analysis to evaluate how average daily temperature, humidity and other meteorological changes over the years would influence A. cerana’s diet. We show that (1) A. cerana has a large dietary niche (87 pollen taxa), but essentially feeds on Cocos nucifera (all year long) and on Borassus flabellifer, Turnera, Acacia, Mollugo/Trianthema, Leucaena/Prosopis, Portulaca, Poaceae, Syzygium-t, Dodonaea viscosa and Boerhavia seasonally; these were most frequently and abundantly foraged at all locations. (2) In all locations, bees preferentially feed on arboreal plants (44 taxa). (3) Bees' pollen diet varies in composition according to seasons. It is also least diverse in the hottest and driest months (March-May) with 2–4 taxa against 7–13 taxa in other months. (4) In 2021, which was more humid and slightly cooler than 2018 and 2019, bee diet included more pollen of Cyperaceae, Dodonaea viscosa, Liliaceae and fallow land weeds such as Boerhavia and Mimosa pudica. In conclusion, corbicular pollen loads of Apis cerana provide a long and continuous record of the bee’s diet and its changes through time and space. The diet changed according to subtle changes in humidity and temperature as also drastic changes in rainfall at the study site, likely reflecting changes in the floral resource availability and the bees’ preference. The sustained presence of this bee species within its native ranges can be a bellwether of pollinator friendly habitats.

Landscape-scale floral resource discontinuity decreases bumble bee occurrence and alters community composition.

Agricultural practices and intensification during the past two centuries have dramatically altered the abundance and temporal continuity of floral resources that support pollinating insects such as bumble bees. Long-term trends among bumble bees within agricultural regions suggest that intensive agricultural conditions have created inhospitable conditions for some species, while other species have maintained their relative abundances despite landscape-level changes in flower availability. Bumble bee responses to spatiotemporal resource heterogeneity have been explored at the colony and behavioral level, but we have yet to understand whether these conditions drive community structure and ultimately explain the diverging patterns in long-term species trends. To explore the relationship between landscape-level floral resource continuity and the likelihood of bumble bee occurrence, we mapped the relative spatial and temporal availability of floral resources within an intensive agricultural region in the US Upper Midwest and related this resource availability with bumble bee species relative abundance. Across the bee community, we found that relative bumble bee occurrence increases in landscapes containing more abundant and more temporally continuous floral resources. Declining species, such as Bombus terricola, exhibited the strongest, positive responses to resource abundance and continuity whereas common, stable species, such as Bombus impatiens, showed no statistical relationship to either. Together with existing experimental evidence, this work suggests that efforts to increase spatiotemporal flower availability, along with overall flower abundance at landscape scales may have positive effects on bumble bee communities in the US Upper Midwest.

Pollinator competition and the structure of floral resources

The mutualism between plants and pollinators is built upon the trophic ecology of flowers and florivores. Yet the ecology of flowers‐as‐food is left implicit in most studies of plant–pollinator ecology, and it has been largely neglected in mainstream trophic ecology. This deficit is especially evident in an emerging issue of basic and applied significance: competition between pollinators for floral resources. In this synthesis, we start by exploring the notion of floral resource limitation upon which most studies concerning competition between pollinators are tacitly predicated. Both theoretical and empirical lines of evidence indicate that floral resource limitation must be understood as a complex ecological contingency; the question is not simply whether but when, where and in what regions of floral trait space resources are limiting. Based on this premise, we propose a framework for understanding floral resource availability in terms of temporal, spatial and functional structure. While this framework is conceptually intuitive, it is empirically and analytically demanding. We review existing methods for measuring and summarizing the multi‐dimensional structure of floral resources, highlight their strengths and weaknesses, and identify opportunities for future methods development. We then discuss the causal relationships linking floral resource structure to species coexistence, plant–pollinator community dynamics, and exogenous drivers like climate, land use, and episodic disturbances. In its role as both cause and effect, floral resource structure mediates the relationship between behavioral ecology, landscape ecology, and coexistence theory with respect to flowers and florivores. Establishing floral resource structure as an object of study and application will both shed light on basic questions of coexistence and guide management decisions concerning contentious issues such as the compatibility of apiculture with wild pollinator conservation and the appropriate use of floral enhancements in agri‐environment schemes.

Phenologically Targeted Grazing: A Potential Sustainable Strategy for Native Bees in Semiarid Rangelands

Rangelands may offer valuable habitat for invertebrate wildlife, helping conserve ecologically and economically significant organisms, like native bees. In some systems, livestock may affect bees by consuming or trampling blooming plants that bees rely on for food. One potential way to reduce potential negative effects of livestock on bees is to delay grazing on floristically rich parts of the landscape until after peak bloom (i.e., phenologically targeted grazing). To test the outcome of this method, we collected bees using pan traps and counted blooming stems from May to September in grazed and ungrazed sites. Our sites were located in two experimental cattle grazing systems in the Pacific Northwest, United States, in which cattle turnout did not occur until after peak forb bloom. One system was located in bunchgrass prairie, and the other was located in riparian meadows. Our objectives were to 1) quantify seasonal variation in bee and blooming plant communities and 2) measure how or if these communities responded to grazing. In both systems, bee and bloom species richness peaked in June and bloom abundance and diversity were highest in May and June. Bee abundance and diversity were more variable throughout the season. We observed significantly lower abundance, richness, and diversity of blooming species in the riparian system in response to grazing, potentially decreasing floral resource availability for bees, but did not detect a concomitant negative effect on bees. In the bunchgrass system, we observed no significant negative effects of grazing on bees or blooming plants. This suggests that for areas with high-quality bee habitat, site-specific, phenologically targeted grazing may moderate negative effects of livestock on bee and plant communities. Range managers could use alternative grazing locations (e.g., old fields, early senescing sites, more intensively managed pastures), if available, during peak bloom to mitigate potential herbivory effects on bees and blooms.