Community‐level effects of Müllerian mimicry on pollinator diversity and functioning

Müllerian mimicry, a mutualistic interaction in which harmful species evolve similar warning signals, is often accompanied by niche divergence among mimetic species. While these aspects have traditionally been studied in an evolutionary context, their community‐level implications—for species coexistence, diversity and ecosystem functioning—remain understudied. Here, we focus on bumblebee ( Bombus spp.) communities, first analysing associations between colour resemblance, species abundance and unpalatability—as predicted under Müllerian mimicry. We then test whether community‐level colour resemblance affects species coexistence, species richness and the diversity of visited plants and flower shapes. In these analyses, we account for other sources of variation, including environmental and spatial drivers, as well as potential competitive interactions driven by phylogenetic conservatism or morphological similarity. Our study supports the causal relationships predicted by Müllerian mimicry theory, namely, stronger selective pressure for convergence in warning signals when model populations are abundant and better defended (i.e. with a higher proportion of stinging females relative to undefended males). Although mimicry is imperfect—due to high within‐species variability and asymmetry in mimicry ring composition—it retains ecological significance. Mimicry modulates the effects of phylogenetic and morphological dissimilarity on community diversity. When it occurs alongside phylogenetic dissimilarity, mimicry contributes to increased bumblebee species richness; when it coincides with morphological dissimilarity, it contributes to greater diversity in floral shapes visited. Although species with similar colours do not necessarily differ in morphology, mimetic communities show a non‐random sorting of species based on morphology, consistent with reduced ecological overlap among coexisting mimics. Overall, this study provides empirical evidence that mimicry promotes species coexistence, thus acting as a positive, community‐level interaction. Beyond its direct effects on pollination‐related functions, mimicry is also associated with high pollinator species richness and ecological divergence among coexisting species—both of which are positively related to these functions. As such, mimicry may contribute more broadly to biodiversity–ecosystem functioning relationships. Read the free Plain Language Summary for this article on the Journal blog.