Detailed information with literature references can be gained from our papers.
Specialized solitary bee species with size and host plant genus
Bee species used Size Host plant genus
Hylaeus punctulatissimus small Allium
Chelostoma florisomne medium Ranunculus
Chelostoma rapunculi medium Campanula
Hoplitis adunca large Echium
The selected bee species naturally nest in beetle burrows in dead wood, what renders them suitable for artificial breeding. These bee species are of different body sizes, fitting the categories small, medium-sized and large. These species harvest pollen exclusively on a single plant genus or family. These features ren-der the selected species highly suitable for novel experimental designs in agriculturally used landscapes.
“Chartering” agricultural landscapes
The basic concept was to simulate fragmented and de-fragmented landscapes by using long or short distances between the two key resources for the bees (i.e. nesting site and flowering host plant patch). To reliably quantify the distances covered by the bees, we used landscapes that lacked the species-specific host plants either completely, or that were deprived of the few existing ones.
To make agriculturally used landscapes available for our intense experiments, we first had to identify suitable landscapes in Switzerland, which was not an easy task due to the small-scale structure of our landscapes, and then we had to negotiate with each individual farmer to assure that he/she would keep their land devoid of the host plants. We identified such landscapes near Berlingen, Thurgau and near Selzach, Solothurn (Fig. 1 and 2; Zurbuchen et al. 2010a). We made a total of 33 contracts with farmers and reimbursed them for their services. All farmers in both landscapes fully supported our initiative, which is a strong and positive signal from the stakeholders.
Fig. 1. The wild bee Chelostoma florisomne could overcome major landscape barriers such as forests while foraging on Ranunculus flowers (Picture Albert Krebs, Winterthur).
Fig. 2. Maximum forage distance of the the large species Hoplitis adunca amounted to 1400 m, but only few individuals reached this distance. The distance covered by 50 % of the individuals amounted to 300 m only, underlining the importance of a close neighbourhood of nesting site and pollen sources in the landscape (Picture Albert Krebs, Winterthur).
Experiments on foraging distances and reproductive output
Basically, we manipulated the distances between artificial bee nesting sites (fixed stands of bamboo stems) and host plants for the representative set of native bee species (see Table above). Bees were marked individually with paint, and observers registered bee arrivals at the plant patch as well as at the nesting site. In Zurbuchen et al. 2010a, we used natural host plant patches (i.e. flowering meadows containing the host species) and measured the distances from the nest to the different foraging sites, where we recorded marked bee individuals. In Zurbuchen et al. 2010b, c, we used patches of portable host plants and arranged them at distinct distances from the nesting site, or in distinct spatial distribution patterns. All these experiments were very labor-intensive, as they required a minimum of 2 or 4 observers simultaneously.
Analyses of chemical host plant cues
Field-collected flowers and pollen from two selected host plant species listed in the Table above were used. Headspace volatiles were collected using a dynamic sampling system. These volatiles were identi-fied and quantiidenti-fied using thermal desorption-gas chromatography-mass spectrometry. Furthermore, pollenkitt surface lipids were extracted from pollen samples with the solvent hexane, and analyzed with gas chromatography-mass spectrometry. To assess reliability of the volatile cues and the pollenkitt-based contact cues, we statistically analyzed the variability among the different samples (Piskorski et al. 2011).
Innovation, gains, new insights and main results thanks to ENHANCE
Innovation
Our studies delivered novel quantified information on:
– the reliability of pollenkitt for host recognition in specialized solitary bees, – overcoming landscape barriers
– maximum distance covered by foraging bees and the respective within-population frequency distribu-tion based on direct measurements, as well as
– cost of foraging distances on offspring production based on a novel method.
The specific role of CCES ENHANCE
Interactions within CCES ENHANCE strengthened in particular three aspects:
Firstly, landscape barriers are now recognized as a key topic to be considered and understood as a basis for meaningful de-fragmentation initiatives. This prominent point was raised within CCES ENHANCE in parallel for agricultural habitats with bees and for riparian habitats with fish, and more recently also for urban habitats with hedgehogs. The respective exchange with colleagues from EMPA and WSL was very inspiring.
Secondly, the combination of behavioral experiments with population genetic studies on bees at land-scape level has been recognized as an innovative approach already in the preparatory phase of the project proposal. Data from behavioral experiments were provided on schedule to the colleague scientists within CCES ENHANCE. To complement the data set with data from molecular analyses is a task remain-ing for the future.
Thirdly, to take a comprehensive approach comprising ecological, social and economic aspects is impor-tant. At a scientific level, a sequential rather than a parallel investigation of these aspects might be most promising to interlink the different projects in an optimal way. At the practical level, the present ecological project demonstrated that a respectful social interaction with stakeholders was an important premise for our advances: farmers are not the problem for nature conservation, they are part of the solution.
References
Piskorski, R., Kroder, S. and Dorn, S., 2011. Can pollen headspace volatiles and pollenkitt lipids serve as reliable chemical cues for bee pollinators? Chemistry and Biodiversity 8: 577–586.
Zurbuchen, A., Bachofen, C., Müller, A., Hein, S. and Dorn, S., 2010a. Are landscape structures insurmountable barriers for foraging bees? A mark-recapture study with two solitary pollen specialist species. Apidologie 41: 497–508.
Zurbuchen, A., Landert, L., Klaiber, J., Müller, A., Hein, S. and Dorn, S., 2010b. Maximum foraging ranges in solitary bees:
only few individuals have the capability to cover long foraging distances. Biological Conservation 143: 669–676.
Zurbuchen, A., Cheesman, S., Klaiber, J., Müller, A., Hein, S. and Dorn, S., 2010c. Long foraging distances impose high costs on offspring production in solitary bees. Journal of Animal Ecology 79: 674–681.
Zurbuchen, A., Müller, A., and Dorn, S., 2010d. Kurze Flugdistanzen zwischen Nist- und Nahrungshabitaten fördern eine reiche Wildbienenfauna. Agrarforschung Schweiz 1: 360–365.