A geographical perspective on the relationship between spur lengths and bill lengths of sunbirds in Afrotropical mountains.

Trait matching-a correlation between the morphology of plants and their pollinators-has been frequently observed in pollination interactions. Different intensities of natural selection in individual regions should cause such correlations to be observable across different local assemblages. In this study, we focused on matching between spur lengths of the genus and bill lengths of sunbirds in tropical Africa. For 25 mountain and island locations, we compiled information about the composition and traits of local and sunbird assemblages. We found that assemblage mean and maximum values of bill lengths were positively correlated with mean and maximum spur lengths across locations. Moreover, our results suggest that the positive correlations hold only for forest sunbird assemblages sharing the same habitat with species. We further show that long-billed sunbirds seem to locally match the morphology of multiple plant species, not vice versa. Our observation implies that trait matching significantly contributes to structuring of sunbird pollination systems. We suggest that special habitat preferences together with spatial isolation of mountain environment might play a role in this case.