Henrik Smith

Environmental heterogeneity in forest understories creates microhabitat niches that differ both spatially and temporally in light intensity and temperature. Do animal communities segregate in relation to these niche dimensions, and can this be explained by functional traits? Answering these questions is particularly important for insect pollinators, as they play a critical role in maintaining flowering plant biodiversity. Bumblebees are essential pollinators of high altitude/latitude ecosystems and are particularly sensitive to climate change. In early spring, they forage on bilberry, a keystone species in heterogeneous habitats – hemi-boreal forests. We capitalised on these conditions to study a species-specific selection of foraging niches in relation to abiotic conditions. We combined full-day monitoring of bumblebee communities foraging in bilberry-dominated forests with joint species distribution modelling, which showed that temperature conditioned species occurrence, while light intensity explained species abundance. The inclusion of functional traits did not improve the overall explanatory and predictive power of the models. Our results suggest that temperature acts as a first filter of the local species pool and that species, once present, partition along a light intensity gradient. This study confirms and extends upon previous findings that microhabitat partitioning may act as a mechanism underpinning bumblebee coexistence. It highlights the importance of focusing on micro-scales when studying how species interact with their environment, as this could, for example, help improve our ability to predict the consequences of global changes.