Microclimatic Diversity: Investigating Bumblebee Community Composition and Morphological Variations Across a Temperature Gradient

Sammanfattning

Bumblebee’s ability to thermoregulate through physiological and morphological adaptations haveenabled them to become the most important pollinators in Northern Europe. Their large body size alongwith a long and dense hair insulation layer allows bumblebees to reduce heat loss and maintain their bodytemperature above the flight-muscles’ temperature threshold. In the context of climate warming, thesecold-adapted pollinators are facing elevated risks of heat stress, reflected by the increased populationdeclines recorded worldwide. In agricultural landscapes, forested macrohabitats occupied by bumblebeesare thought to play an important role in their conservation due to their ability to buffer temperatureincreases. Using a transect-based longitudinal approach in a forest, forest edge and open field, this studyexplored how ambient temperature and seasonality impact bumblebee community variables likeabundance, species richness and Shannon diversity index. This study also explored how temperature andseasonality drive variations in thermal functional traits (body size, hair length and hair density) betweenbumblebee castes and species, as well as within species. The results showed that abundance and speciesrichness increased with temperature in low flower diversity environments, whereas the Shannon diversityindex increased with both environmental factors. The use of the three macrohabitats by different speciesshifted throughout the season, revealing the thermal importance of forests in agricultural landscapes.Temperature had no effect on bumblebee’s thermal functional traits, except for a negative relationshipwith worker hair length. However, the observed caste-specific variations in thermal functional traitsbetween and within species reveal diverging thermoregulatory strategies. Differences in caste phenotypesmay be related to the interplay between life history and temperature, whereas interspecific phenotypicvariations are likely associated with seasonal and thermal niche differences. In the context of climatechange, these findings provide a framework to better understand how thermal pressure shapes pollinatormorphology and behaviour.