Landscape fragmentation constrains bumblebee nutritional ecology and foraging dynamics

Habitat fragmentation is modifying landscapes and the distribution of floral resources, possibly shaping also pollinator resource acquisition. Here, using urban parks as field laboratories for the dramatic contrast around, we aimed to clarify how fragmentation and local flower availability shape bumblebee foraging dynamics by characterizing several components: the nutritional content and plant composition of collected pollen pellets, the foraging rate and the plant-nutrition association along a fragmentation gradient. We found mostly negative linear or non-linear relationships between nutritional quality and fragmentation, tight plant composition-nutrition associations interpretable as low access to alternative resources, and shorter foraging time in smaller green areas, showing behavioral limits by the landscape. Thus, fragmentation can constrain all aspects of bumblebee foraging by compromising resource accessibility. This study illuminates the link between landscape features and the nutritional ecology of pollinators, a key aspect for understanding pollinator foraging dynamics and even for outlining mitigation measures in urban contexts.