Functional divergence drives the prevalence of low‐abundance species in bat assemblages

Abstract Ecological communities are structured by a few common species, while most occur at low abundance. Understanding the drivers of this widespread pattern raises fundamental questions about community assembly rules and is important for applied ecology for identifying conservation targets. We used assemblages of phyllostomid bats to answer the following questions: (i) Does a higher divergence of morphological traits and functional hypervolume from the assemblage explain the prevalence of low‐abundance species? (ii) What is the relative importance of single functional traits and functional hypervolume divergence to explain such patterns? We sampled phyllostomid bats across an urban–rural landscape and estimated species abundance, measured key morphological traits, and calculated functional hypervolumes. We then applied a Bayesian causal inference framework to identify the drivers of abundance. The divergence of functional hypervolume, flight performance, and food acquisition traits had a negative impact on the abundance of the species. This pattern holds whether assessing aggregated species abundance or when considering spatiotemporal variation in assemblage structure, implying that low‐abundance species had functional hypervolumes and morphological traits more divergent from the assemblage average. Species ranked at the quantile intervals 0%–25% and 25%–50% of abundance occupied hypervolumes 45.9% and 46.8% more divergent compared to species ranked at Q 75%–100%. Similarly, the species at Q 0%–25% and 25%–50% exhibited a 59.5% greater divergence in morphological traits compared to common species. Such divergence on specific traits and intraspecific functional space from the assemblage centroid can result in a substantial reduction (13%–57%) in species abundance. Our results indicate that low‐abundance species are linked to their trait and hypervolume functional divergence. We propose that the position of the species in the functional space and the divergence of sensory‐ and vagility‐related traits are factors that determine the structure of bat communities, which denotes niche axes that have likely been narrowed at the current human‐dominated habitat. Our findings emphasize the importance of low‐abundance species, as they occupy unique ecological niches and likely contribute to specific ecosystem processes. Read the free Plain Language Summary for this article on the Journal blog.