. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. Nearctic Dolomedes Spiders • Carico 441. Map 1. Speciation among six nearctic species of the genus Dolomedes. The diagonally hatched area (6) represents the combined distributions of the widely distributed eastern species: Dolomedes scr/ptus, D. vittotus, and D. tenefarosus. The isolated populations of D. gertschi (3) and D. holti (4) are separated from the eastern populations (6) by a xeric barrier (1) which probably became established in the Pleistocene. The Florida species, D. okefinokensis (5), was probably isolat
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. Nearctic Dolomedes Spiders • Carico 441. Map 1. Speciation among six nearctic species of the genus Dolomedes. The diagonally hatched area (6) represents the combined distributions of the widely distributed eastern species: Dolomedes scr/ptus, D. vittotus, and D. tenefarosus. The isolated populations of D. gertschi (3) and D. holti (4) are separated from the eastern populations (6) by a xeric barrier (1) which probably became established in the Pleistocene. The Florida species, D. okefinokensis (5), was probably isolated from the eastern populations (6) by a sea barrier (2) also at some time during the Pleistocene. The black arrows show probable dispersal routes into the isolated areas from the eastern populations. Another kind of passive dispersal is trans- portation by flowing water in streams. This would not be of interest in terms of geo- graphic isolation because freshwater connec- tions would potentially provide continuous connections between populations, and sim- ilarly between their gene pools. Many changes in streams which affect the distri- bution of stricth" aquatic animals (, stream capture and fishes) would not apply to Dolomedes. Active means of dispersal is here meant to include primarily directional movements of the spider by walking. Again, as stated before, water dependency seems to restrict Dolomedes to a wet, or at least a moist en\"ironment; therefore, species of Dolo- medes are not found walking in arid areas, and are probably not capable of living in such conditions for \er\' long. Within a drainage system, however, these animals might be expected to move long distances relatively quickly. Areas of ocean water are also a barrier to dispersal. The apparent absence of Dolo- medes from most islands off the coast of. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and ap
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