Species richness of eriophyid mites on Finnish trees and shrubs

Host plant use and species richness of eriophyid mites (Arthropoda, Acarina, Eriophyiidae) on Finnish trees and shrubs was studied on the basis of published data. The number of eriophyid species ranged from 0 (Picea) to 15 (Alnus). Most of these mites were concentrated on two species-rich, host plant families, Betulacea and Salicacea. The two families harbor 42% of the total eriophyid fauna of Finnish trees and shrubs. However, Tilia cordata, the only species of the Tiliaceae family, had six species of eriophyids. We used the geographic range, average and total frequency (abundance) of the host plant, host plant height, leaf size and the number of host plant relatives (other plants in the same family) as explaining variables in a regression model. Species richness of eriophyid mites was best explained by the leaf size and number of relatives of host plants. These two factors explained 42% of the variation in species richness. When conifers (which have a low number of eriophyid species) were excluded, the host plant abundance and leaf size explained 66% of the variation in species richness. The results indicate that resource availability (both leaf size and abundance) is an important factor in increasing the probability of random colonization and adaptive radiation on eriophyid mites living on trees and shrubs.