Pollinators contribute to biodiversity and are vital for ecosystem functioning. In the last decades, a global decline of pollinator species and individuals has been observed. In intensively used agricultural areas, pollinators suffer from habitat loss and fragmentation, exposure to pesticides and declining food sources. Thus, land use intensity represents a major threat for pollinators in such landscapes. These stressors can affect pollinator health, resulting in developmental changes (e.g. wing asymmetry), physiological changes (change of pheromone composition) or increased viral loads. In return, such changes in pollinator health may cause changes of foraging activity or behaviour, what can ultimately result in a loss of pollination services. Therefore, it is important to disentangle the links between land use intensity, pollinator health and pollination services in order to preserve pollination services and ecosystem functioning in our agricultural landscapes.
In this project we pursue two major goals: (I) identification of the effects of land use intensity on pollinator health and (II) disentangle how connections of land use and pollinator health affect pollination services. We will focus on two species, Bombus lapidarius and Episyrphus balteatus, which represent two major pollinator groups: bumble bees and syrphid flies. For this purpose, we will collect field data on pollinator health and pollinator behaviour of the pollinator species in the grassland plots of the Exploratories and conduct lab- and common garden experiments.
Effects of land use intensity on pollinator health
We will investigate the effects of land use intensity on several pollinator health indicators, such as asymmetric wing development, body size, viral loads and composition of cuticular pheromones. For the analysis we will use the land use index (LUI), pesticide use, data on plant abundance and diversity and land cover types in the surrounding as surrogates for land use intensity.
- Viral loads and asymmetric wing development are positively correlated with increasing land use intensity.
- The amount of cuticular pheromones decreases and their composition changes with increasing land use intensity.
Up to ten individuals of B. lapidarius and E. balteatus will be collected in all 150 grassland plots of the Exploratories and analyzed for pollinator health indicators. In a fully-crossed two-factorial labour experiment we will simulate different intensities of land use by exposing the pollinator species to different diets and pesticide amounts to identify underlying mechanisms between land use intensity and pollinator fitness.
Effects of land use intensity and pollinator health on pollination services
To disentangle links between land use intensity, pollinator health and pollination services, we will conduct pollen analysis and observations on pollinator behaviour.
- The amount of collected pollen decreases and its composition changes with increasing land use intensity and decreasing pollinator health.
- Foraging behaviour changes and pollinator efficiency decreases with increasing land use intensity and decreasing pollinator health.
We will conduct analysis on pollen amounts and diversity with the pollinator individuals collected in the field. Additionally, we will perform observations on pollinator behaviour in all grassland plots of the Exploratories. Amongst others, we will investigate the visit duration, flight distance between two plant individuals and floral constancy (number of plant species visited in a certain period). In common garden experiments, we will make observations on pollinator behaviour of B. lapidarius und E. balteatus in flight cages under simulation of different land use intensities to uncover causal correlations between land use, pollinator health and pollination services.
Temporal patterns of land use intensity and pollinator health
To investigate, whether correlations between pollinator health and land use intensity are stable over time, we will use land use intensity data and B. lapidarius and E. balteatus individuals collected in previous projects (2008 and 2012, "Arthropods II: Pollinators" and “Response", PI: Blüthgen and “Landscapes”, PI: Westphal) and compare it with our collected data. Here, we will focus on the analysis of asymmetric wing development and body size as surrogates for pollinator health.
- Wing asymmetry is positively, and body size negatively correlated with increasing land use intensity.
- Relations between land use intensity and pollinator health are stable across years, e.g. increasing land use intensity results in decreased pollinator health.