A molecular genetic method for estimating nest density in bumblebee populations without explicit definition of habitat area

Bumblebee (Bombus spp.) populations have declined in recent decades in many countries. Since they are important pollinators of crops and wildflowers, their declines may have serious consequences for agriculture and wild ecosystems, and urgent conservation managements should be required for threatened bumblebee populations. In order to design effective conservation managements, nest density in a habitat is an essentially important information, since the genetically effective size of bumblebee populations is determined by the number of nests. In the present study, a novel method for estimating nest density using molecular genetic markers is proposed, by the use of the concept of neighborhood size in population genetics. Space-explicit simulation suggests that the proposed method could give a satisfactory estimate even under violation of underlaying assumptions. The proposed method is illustrated by applying to microsatellite data of a rare Japanese species B. cryptarum florilegus. Finally, usefulness and limitations of the method in the practical application are discussed, and an interpretation of the estimate is presented from a viewpoint of conservation genetics. The proposed method could contribute to conservation of bumblebee populations through giving an estimate of genetically effective population size.