Browsing by Author "Hardwick, Bess"

A parabiologist is an assistant in biological research without formal academic training. In this study, I use volunteer parabiologists to conduct a national survey of oak cynipid gall wasps, tribe Cynipini (Hymenoptera: Cynipidae). My objectives were to produce an updated list of Finnish oak cynipid species, to map the distribution of these species, and to examine factors that could have an effect on local species richness and on the regional distribution and local abundance of individual species. I also wanted to examine whether the two generations of a species tend to occur on the same or on different individual trees. Empirical data on local gall wasp assemblages were collected by over a hundred volunteers from all over Finland, mostly people with a general interest in nature. Since most gall wasps occur as two discrete generations, volunteers sampled oak trees twice during the summer of 2007, with the spring round encompassing 218 trees and the autumn one 180. From each tree, five half-metre branches were examined, followed by a ten-minute scan of the rest of the branches. The recovered samples were then sent to me for identification. Based on tree-specific information supplied by the volunteers, I used generalised linear models to examine the effects of the number of neighbouring oaks, of oak circumference and of sampling location on the species richness of gall wasps, on the local incidence of species and on their local abundance. The survey produced data on 16 oak cynipid species, two of which were new to Finland. These new records bring the total number of species recorded in Finland up to 21. The centre of oak cynipid species richness was in the southwest, but some species were found as far north as Ostrobothnia. Within some species, different generations occurred on different individual trees. For this reason, I separated the generations in the distribution maps and statistical analyses. Against a backdrop of large-scale clines in species richness, local species richness was affected by the number of neighbouring oaks and by tree circumference. Large oaks that are surrounded by many other oaks support the most species-rich communities of oak cynipids, and the local incidence of certain species and of generations within species exhibit similar patterns. To conclude, oak cynipids are suitable targets for sampling by parabiologists, and this survey has improved our knowledge of the Finnish oak cynipid fauna. Oak cynipids have successfully spread beyond the host plant's narrow natural distribution and colonised the planted trees in the north. Since large oaks close to other oaks exhibit the most diverse gall wasp communities, the natural old oak forests in the southwest of Finland are particularly important to these species.