Drivers of sunbird-plant interactions on Mount Cameroon: Between neutrality and niche-based processes

The drivers behind plant-pollinator interactions still need to be fully understood. Previous research has suggested that observed interactions result from either neutral interaction between species based on their abundance or from niche-based processes, which are reflected in the adaptations of both plants and pollinators. Furthermore, the importance of both scenarios can differ depending on seasonal dynamics translated into differences in resource availability. Extensive research has been conducted on New-World hummingbirds (Trochilidae), whereas much less is known about Old World nectar-feeding sunbirds (Nectariniidae). Our study aimed to explore whether sunbird-plant interactions are explained by neutral and/or niche-based processes. Thus, we tested the effects of abundance, morphology, and nectar sugar content on the observed interactions and the link between sunbirds and plant traits. Moreover, we explored the effects of robbing on these mechanisms. Finally, we investigated the partitioning of bird pollination niches, based on floral traits. We used a dataset of sunbird-plant interactions collected at Mount Cameroon during two seasons (dry and wet seasons). Our study shows that sunbird-plant interactions are influenced by both neutral and niche-based processes. Neutral processes and nectar reward were the main mechanisms underlaying the observed interactions in the dry season. However, as more ornithophilous plants bloom during the rainy season, morphological trait-matching becomes more important. We found a correlation between bill length and floral tube dimensions and observed niche overlap among the sunbird species. Considering this and other research, we suggest that plant-pollinator interactions are influenced by a combination of both neutral and niche-based processes.