How does wing length relate to distribution patterns of stoneflies (Plecoptera) and mayflies (Ephemeroptera)?

Short wings, and hence a potential for reduced dispersal capacity, can be one of several reasons for rarity in freshwater insects. To test this hypothesis, I compared wing lengths, standardised for body length differences, of stoneflies and mayflies based on published Swedish material. Taking 25% presence as the limit between rare and not rare, rare species indeed had shorter wings than those that were classified as not rare. Wing length was not the sole explanation for rarity as seen in the presence of rare species along the entire range of wing to body lengths. In both stoneflies and mayflies wing lengths were positively related to range sizes. Occupancy showed a positive relationship with wing size in mayflies, whereas in stoneflies the relationship was not significant, probably because there was no difference in wing lengths over a range of occupancy values in the common species. Implications for conservation include the importance to identify poor dispersers among these groups and describe their habitats, since it can be expected that recolonisation by poor flyers can be very uncertain and slow after local extinction. Therefore, localities with rare, poorly-dispersing species should be protected but if extinction occurs, re-introduction might offer a possibility to re-establish such insects. (C) 2000 Elsevier Science Ltd. All rights reserved.