Vildbiet guldsandbi (Andrena marginata F.) har en central roll i jordbrukslandkapet som en viktig pollinatör av grödor och vilda växter. I Sverige hotas artens fortlevnad av biotopförlust, habitatfragmentering och födobrist. En av de viktigaste näringskällorna är växten ängsvädd (Succisa pratensis M.) som tidigare var vanligt förekommande men som nu minskar i sin utbredning. Syftet med denna studie var att utreda om populationsstorlekarna av guldsandbi och ängsvädd är relaterade. Guldsandbinas observationsbaserad populationsstorlek uppskattades samt att ängsväddens bestånd inventerades vid fyra lokaler i Övre Klarälvsdalen, i norra Värmland. Binas populationsstorlek uppskattades genom transektinventeringar mellan 30 juli och 11 augusti 2013. Under perioden observerades totalt 286 honor och per observationsdag noterades ett medelvärde på 40,86 (± 8,1 SE, 95% konfidensintervall; n=7) honor. Ängsväddpopulationen uppskattades till totalt 2328 växter från alla fyra områden. Det fanns inget statistiskt samband mellan populationsstorlekarna av ängsvädd och guldsandbin. En jämförelse mellan den för biet förväntade populationsstorleken, baserad på förekomst av näringsväxten, och den observerade populationsstorleken, korrigerad för inventeringsbias, visade bra överensstämmelse vid två av fyra områden (8,4% respektive 5,7% från det teoretiska värdet) och dålig överensstämmelse vid de andra två områdena. Det kan mycket väl vara så att det finns en relation mellan populationerna i Övre Klarälvsdalen, men man måste öka antalet lokaler och ta hänsyn till ytterligare miljöfaktorer som påverkar både bina och växterna för att kunna dra säkrare slutsatser om ett samband. / The wild-bee Andrena marginata has a key function as an important pollinator of crops and wild plants in agriculture landscapes. The species’ persistence is threatened in Sweden due to loss of habitat, fragmentation and food scarcity. One of the most important food sources is the plant Succisa pratensis, which previously was very common but now has declining populations. The purpose of this study was to analyse if there was a relation between the population sizes of A. marginata and S. pratensis. The population size of the bees was estimated and the plant population was surveyed at four sites in the upper valley of the River Klarälven, Värmland. Bee population size was estimated by visual transect surveys conducted between 30 July and 11 August 2013. In this period a total of 286 females was observed, with a mean of 40,86 (± 8,1 SE, 95% confidence interval; n=7) per day. The total population size of S. pratensis from the four sites was estimated to 2328 plants. There was no significant correlation between the population sizes of the bees and the host plant. A comparison between the bee’s predicted theoretical population size, based on the number of host plants, and the observed population size, corrected for observer bias, showed good agreement for two of the sites (within 8,4% and 5,7% of the theoretical value) and poor agreement at the other two sites. There may well be a relation between the bee and plant populations in the upper valley of Klarälven, but one needs to increase the number of sites and take into account additional environmental factors that affect both the bees and the plants to draw a firmer conclusion about such a relationship.

<p>In recent decades, the development of strategies to prevent or slow the loss of biodiversity has become an important task for ecologists. In most terrestrial ecosystems wild-bees play a key role as pollinators of herbs, shrubs and trees. The scope of this thesis was to study 1) pollinator effectiveness of specialist bees vs. generalist flower-visitors, 2) critical floral resources for wild-bees, and 3) methods to estimate the size of wild-bee populations. The wild-bee species <i>Andrena hattorfiana </i>and <i>A. marginata </i>were used as model species. These two species are specialized on pollen from the plant family Dipsacaceae.</p><p>The bee <i>A. hattorfiana </i>was found to be a frequent visitor but a poor pollinator of its preferred food-plant <i>Knautia arvensis</i>. The female bees exert such a strong preference for pollen-producing inflorescences that they likely have deleterious effects on the plant, harvesting valuable pollen that could have been transferred to conspecific stigmas by other flower-visitors. To explore the relationship between wild-bees and their food-plants, the concept of pollen budget was developed. We quantified pollen production in the food-plant population and pollen consumption of wild-bee nests. A survey of the visitation by all flower-visitor taxa indicated that the degree of utilization (the fraction of the total pollen amount that is harvested and utilized by <i>A. hattorfiana</i>) varied from 12% to 80% among <i>K. arvensis</i> populations (N=26). The bee <i>Andrena marginata</i> utilized 44% of the pollen production in a population of <i>Succisa pratensis</i>. The pollen budget suggests that with an average flower-visitor diversity and abundance, 330 individuals of the food-plant <i>K. arvensis </i>are required to sustain a population of 20 <i>A. hattorfiana </i>♀ (the approximate median natural population size). Based on a study of <i>A. hattorfiana</i>, considerable simplifications were proposed for the commonly used mark-recapture design for measuring wild-bee population size. For this species, population size estimated based on mark-recapture data was strongly correlated with the number of observations per survey-walk. The results suggest that large-scale surveys of solitary bee species can be simplified by performing survey-walks.</p><p>The pollen budget and the method proposed for estimating the size of bee populations have the potential to become valuable tools for monitoring and management of wild-bee populations.</p>

In recent decades, the development of strategies to prevent or slow the loss of biodiversity has become an important task for ecologists. In most terrestrial ecosystems wild-bees play a key role as pollinators of herbs, shrubs and trees. The scope of this thesis was to study 1) pollinator effectiveness of specialist bees vs. generalist flower-visitors, 2) critical floral resources for wild-bees, and 3) methods to estimate the size of wild-bee populations. The wild-bee species Andrena hattorfiana and A. marginata were used as model species. These two species are specialized on pollen from the plant family Dipsacaceae. The bee A. hattorfiana was found to be a frequent visitor but a poor pollinator of its preferred food-plant Knautia arvensis. The female bees exert such a strong preference for pollen-producing inflorescences that they likely have deleterious effects on the plant, harvesting valuable pollen that could have been transferred to conspecific stigmas by other flower-visitors. To explore the relationship between wild-bees and their food-plants, the concept of pollen budget was developed. We quantified pollen production in the food-plant population and pollen consumption of wild-bee nests. A survey of the visitation by all flower-visitor taxa indicated that the degree of utilization (the fraction of the total pollen amount that is harvested and utilized by A. hattorfiana) varied from 12% to 80% among K. arvensis populations (N=26). The bee Andrena marginata utilized 44% of the pollen production in a population of Succisa pratensis. The pollen budget suggests that with an average flower-visitor diversity and abundance, 330 individuals of the food-plant K. arvensis are required to sustain a population of 20 A. hattorfiana ♀ (the approximate median natural population size). Based on a study of A. hattorfiana, considerable simplifications were proposed for the commonly used mark-recapture design for measuring wild-bee population size. For this species, population size estimated based on mark-recapture data was strongly correlated with the number of observations per survey-walk. The results suggest that large-scale surveys of solitary bee species can be simplified by performing survey-walks. The pollen budget and the method proposed for estimating the size of bee populations have the potential to become valuable tools for monitoring and management of wild-bee populations.