Diversity of vector-dispersed microbes peaks at a landscape-defined intermediate rate of dispersal

Dispersal rate has long been considered a primary determinant of species diversity in ecological communities. However, this knowledge is mostly built on studies of organisms that disperse actively by themselves or passively via physical forces. For organisms that disperse passively via other organisms, the landscape matrix that affects their vectors should indirectly shape the diversity of the vectored, but this relationship remains poorly understood. We investigated landscape–dispersal–diversity relationships in nectar-inhabiting bacteria that disperse via flower-visiting insects. Field observation and experiments revealed that bacterial diversity and abundance peaked at an intermediate frequency of insect visits, which was in turn determined by the surrounding landscape characteristics observed at the 200-m radius scale. Based on this finding, we discuss the possibility that species diversity tends to be maximized at an intermediate dispersal rate, especially when habitat patches of vectored organisms constitute consumable resources for their vectors.