How individual variation shapes ecological niches in two Pipistrellus bat species.

Niche partitioning is a crucial mechanism explaining species coexistence and biodiversity; however, the role of individual variation is less understood. As global changes reshuffle species communities, understanding coexistence mechanisms is vital. In this study, we use two co-occurring, morphologically similar bat species, Nathusius' pipistrelle (Pipistrellus nathusii) and the range-expanding Kuhl's pipistrelle (P. kuhlii), as models. We examine their niche partitioning across habitats and time, considering individual variations by analysing the spatio-temporal habitat selection of 58 radio-tracked individuals. For resource assessment, we use metabarcoding of guano samples. Our results show that individual variation in both species exceeded species-level differences. Nathusius' pipistrelle exhibits greater between-individual variation, while the range-expanding Kuhl's pipistrelle shows stronger within-individual variation, probably facilitating its expansion. This study emphasises the significance of individual variation in investigating animal niche partitioning. It suggests a contribution of within-individual variation in the range expansion of bat species, reshaping animal communities under global change.