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

Dispersal has long been recognized as a primary determinant of species diversity in ecological communities. 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 characteristics that affect their vectors should indirectly influence the diversity of the vectored, but these relationships remain poorly understood. We investigated landscape-dispersal-diversity relationships in nectar-inhabiting bacteria that disperse via flower-visiting insects. Field observations and experiments revealed that bacterial diversity 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 the taxonomic diversity of vectored organisms tends to be maximized at an intermediate dispersal rate, especially in the widely observed situation where the vectored organisms and/or their habitat patches constitute consumable resources for their vectors.