Maximum foraging ranges in solitary bees: only few individuals have the capability to cover long foraging distances

Climate change is altering the phenology of species across the world, but what are the consequences of these phenological changes for the demography and population dynamics of species? Time-sensitive relationships, such as migration, breeding and predation, may be disrupted or altered, which may in turn alter the rates of reproduction and survival, leading some populations to decline and others to increase in abundance. However, finding evidence for disrupted relationships, or lack thereof, and their demographic effects, is difficult because the necessary detailed observational data are rare. Moreover, we do not know how sensitive species will generally be to phenological mismatches when they occur. Existing long-term studies provide preliminary data for analysing the phenology and demography of species in several locations. In many instances, though, observational protocols may need to be optimized to characterize timing-based multi-trophic interactions. As a basis for future research, we outline some of the key questions and approaches to improving our understanding of the relationships among phenology, demography and climate in a multi-trophic context. There are many challenges associated with this line of research, not the least of which is the need for detailed, long-term data on many organisms in a single system. However, we identify key questions that can be addressed with data that already exist and propose approaches that could guide future research.

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The effects of phenological mismatches on demography

Recent declines of bee species have led to great interest in preserving and promoting bee populations for agricultural and wild plant pollination. Many correlational studies have examined the indirect effects of factors such as landscape context and land management practices and found great variation in bee response. We focus here on the evidence for effects of direct factors (i.e., food resources, nesting resources, and incidental risks) regulating bee populations and then interpret varied responses to indirect factors through their species-specific and habitatspecific effects on direct factors. We find strong evidence for food resource availability regulating bee populations, but little clear evidence that other direct factors are commonly limiting. We recommend manipulative experiments to illuminate the effects of these different factors. We contend that much of the variation in impact from indirect factors, such as grazing, can be explained by the relationships between indirect factors and floral resource availability based on environmental circumstances.

The Role of Resources and Risks in Regulating Wild Bee Populations

Recent evidence highlights the value of wild-insect species richness and abundance for crop pollination worldwide. Yet, deliberate physical importation of single species (eg European honey bees) into crop fields for pollination remains the mainstream management approach, and implementation of practices to enhance crop yield (production per area) through wild insects is only just beginning. With few exceptions, studies measuring the impacts of pollinator-supporting practices on wild-insect richness and pollination service success – particularly in relation to long-term crop yield and economic profit – are rare. Here, we provide a general framework and examples of approaches for enhancing pollinator richness and abundance, quantity and quality of pollen on stigmas, crop yield, and farmers' profit, including some benefits detected only through long-term monitoring. We argue for integrating the promotion of wild-insect species richness with single-species management to benefit farmers and society.

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From research to action: Enhancing crop yield through wild pollinators

There is evidence that in Europe and North America many species of pollinators are in decline, both in abundance and distribution. Although there is a long list of potential causes of this decline, there is concern that neonicotinoid insecticides, in particular through their use as seed treatments are, at least in part, responsible. This paper describes a project that set out to summarize the natural science evidence base relevant to neonicotinoid insecticides and insect pollinators in as policy-neutral terms as possible. A series of evidence statements are listed and categorized according to the nature of the underlying information. The evidence summary forms the appendix to this paper and an annotated bibliography is provided in the electronic supplementary material.

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A restatement of the natural science evidence base concerning neonicotinoid insecticides and insect pollinators

Summary

1. Solitary bees are central place foragers returning to their nests several times a day with pollen and nectar to provision their brood cells. They are especially susceptible to landscape changes that lead to an increased spatial separation of suitable nesting sites and flower rich host plant stands. While knowledge of bee foraging ranges is currently growing, quantitative data on the costs of foraging flights are very scarce, although such data are crucial to understand bee population dynamics.



2. In this study, the impact of increased foraging distance on the duration of foraging bouts and on the number of brood cells provisioned per time unit was experimentally quantified in the two pollen specialist solitary bee species Hoplitis adunca and Chelostoma rapunculi. Females nesting at different sites foraged under the same environmental conditions on a single large and movable flowering host plant patch in an otherwise host plant free landscape.



3. The number of brood cells provisioned per time unit by H. adunca was found to decrease by 23%, 31% and 26% with an increase in the foraging distance by 150, 200 and 300 m, respectively. The number of brood cells provisioned by C. rapunculi decreased by 46% and 36% with an increase in the foraging distance by 500 and 600 m, respectively.



4. Contrary to expectation, a widely scattered arrangement of host plants did not result in longer mean duration of a foraging bout in H. adunca compared to a highly aggregated arrangement, which might be due to a reduced flight directionality combined with a high rate of revisitation of already depleted flowers in the aggregated plant arrangement or by a stronger competition and disturbance by other flower visitors.



5. The results of this study clearly indicate that a close neighbourhood of suitable nesting and foraging habitats is crucial for population persistence and thus conservation of endangered solitary bee species.

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2656.2010.01675.x

Long foraging distances impose high costs on offspring production in solitary bees

To investigate whether landscape structures act as insurmountable barriers for foraging bees, we conducted mark-recapture studies with two pollen-specialist solitary species. Foraging options of the bees were confined to host plant stands across different landscape structures. Differences in altitude of more than 130 m were overcome and forests covering a distance of up to 480 m were crossed by Chelostoma florisomne. A broad river and a motorway with intense traffic did not represent insurmountable barriers for Hoplitis adunca. For C. florisomne, total foraging distances of up to 650 m were measured, but foraging females were recorded predominantly on host plant patches available in relatively close vicinity to their nesting site. While landscape structures might impede foraging in endangered bees, the investigated landscape structures clearly did not act as insurmountable physical barriers for the two common solitary bee species tested in our study.

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Are landscape structures insurmountable barriers for foraging bees? A mark-recapture study with two solitary pollen specialist species

Wildbienenschutz: Von der Wissenschaft zur Praxis

Les abeilles sauvages sont d'indispensables pollinisatrices de la flore sauvage et cultivee. Elles sont ainsi d'une grande utilite sur le plan ecologique et economique. Cependant, la moitie environ des 600 especes d'abeilles sauvages presentes en Suisse sont menacees. L'exploitation continue des surfaces et l'intensification de l'agriculture ont pour consequence une perte de milieux propices a la nidification et au butinage. Les abeilles doivent ainsi parcourir des distances de plus en plus longues pour collecter le pollen et le nectar. Le present travail cherche a determiner la distance de butinage maximale que peuvent parcourir certaines especes d'abeilles sauvages et a analyser l'impact de l'allongement des distances de butinage sur la reproduction. Des especes strictement infeodees a un genre de plante ont donc ete obligees a butiner dans un environnement n'hebergeant aucune plante-hote appropriee. En guise de ressource florale, des pots de fleurs ont ete places a diverses distances des nids. Quelques individus des especes Hoplitis adunca et Hylaeus punctulatissimus ont parcouru de longues distances, soit plus de 1000 metres, entre le nid et les plantes nourricieres. Toutefois, la majorite des individus a abandonne ses activites de nidification lorsque la distance etait de 100 a 300 metres deja. L'accroissement des distances de butinage semble avoir des couts eleves. En effet, a partir de 150 metres supplementaires, la performance de reproduction est substantiellement reduite, tant chez Hoplitis adunca que chez Chelostoma rapunculi. Ainsi, des distances courtes entre les milieux propices a la nidification et ceux propices au butinage pourraient contribuer de maniere notable a favoriser la diversite des especes et l'accroissement des populations d'abeilles sauvages.

Antonia Zurbuchen

Papers

Maximum foraging ranges in solitary bees: only few individuals have the capability to cover long foraging distances

Long foraging distances impose high costs on offspring production in solitary bees

Are landscape structures insurmountable barriers for foraging bees? A mark-recapture study with two solitary pollen specialist species

Wildbienenschutz: Von der Wissenschaft zur Praxis

La proximité entre sites de nidification et zones de butinage favorise la faune d'abeilles sauvages