no. 3602 CRAYFISHES — HOBBS, HOLT, AND WALTON 5 



structs tunnels in the bordering banks. As might be expected, none 

 of the three recognizes any absolute limits such as suggested, and 

 occasional individuals of each may invade the ecological niche of the 

 other two. To what extent these invasions are due to individual 

 wanderings, intraspecific population pressures, or interspecific pres- 

 sures, is not known. Of the three there seems to be little doubt that 

 C. I. longulus is ecologically more restricted than either of the other 

 two. At lower elevations, particularly in the larger streams in which 

 there are larger rocks in the riffle areas, C. acuminatus not only 

 appears to compete with C. I. longulus but frequently replaces it. 

 C. b. bartonii undoubtedly has the broadest ecological tolerance, and 

 in the New River drainage, where it is not in competition with C. I. 

 longulus, it is as abundant in the riffle areas as in the pools and marginal 

 portions of the stream. Furthermore, in the tidewater areas of 

 Virginia, C. b. bartonii is found not only living in the smaller streams 

 but also burrowing in swampy areas along the margins of streams. 

 In the Roanoke drainage system, the ecological distribution of C. b. 

 bartonii, C. I. longulus, and C. acuminatus is not unlike that indicated 

 in the James River drainage above; however, the headwater streams 

 are not at such high elevations. 



The fourth species, Orconectes juvenilis, occurs in two quite dissimilar 

 habitats in the Mountain Lake area. At the present time it is the 

 only crayfish found in Mountain Lake itself, and apparently it is 

 found in most of the littoral zone, where adequate cover exists in the 

 form of stones and rubble. In the single Potts Creek locality, it 

 occurs primarily in precisely the same types of habitats in which 

 C. acuminatus is found elsewhere in the James drainage, and in addi- 

 tion it has invaded the riffle zones frequented by C. I. longulus. In 

 the portion of the New River system treated here, 0. juvenilis is 

 restricted to Mountain Lake, having been introduced there in 1933 

 (Hobbs and Walton, 1966a). Cambarus b. bartonii and C. sciotensis 

 share the remainder of the watershed in the area. As in the James 

 drainage, C. b. bartonii is the sole inhabitant of the headwater streams, 

 and downstream, where it encounters populations of C. sciotensis, it 

 is confined to the marginal regions, but even there, apparently it 

 competes for cover with the latter. In Little Stony Creek, both 

 species occur up to the level of station 44, where the cascades serve 

 as a barrier to C. sciotensis (and probably to the upstream migration 

 of C. b. bartonii as well) ; above the cascades, C. b. bartonii is the sole 

 crayfish inhabitant and it occupies all portions of the stream bed. 

 In accessible areas of the New River system, it appears that C. 

 sciotensis vicariates for C. acuminatus and in part for C. I. longulus. 



While all the crayfishes of the area demonstrate some burrowing 

 tendencies, only C. carolinus spends the greater part of its life living 



