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152 Consemllion of Slreun Fishes ... upland forms. Wiley & Mayden (1985) map vicariant fishes separated by large rivers. In summary', a mixture of ecological and evolutionary processes governed by the template of watershed geometry (Leopold, Wolman, & Miller 1964; Richards 1982) is capable of producing a strong positive dependence of fish diversity on drain- age area. If diversity depends on area, drastic alteration of drainages can be expected to reduce diversity in streams remote from those directly affected by pollu- tion or impoundment (Sheldon 1987). Figure 4 contrasts species-area relationships in tribu- taries of the Mississippi with presently isolated streams draining to the Atlantic and Gulf of Mexico. All the streams lie in regions of fairly similar rainfall, runoff, and physiography. The independent coastal drainages con- sistently support fewer native fishes than intercon- nected streams of comparable area in the Mississippi system. An especially vivid demonstration of insular effects 200 100 en w u W Q. en 10 1000 Sheldon (Fig. 4) is provided by two Mississippi tributaries iso- lated by waterfalls (Stauffer et al. 1982; Hocutt et al. 1986). Although proximate ecological factors, such as water chemistry and lack of lowland habitats, may be involved, the low diversities of fishes in the New River above Kanawha Falls and the upper Cumberland river above Cumberland Falls are consistent with an hypoth- esis of extreme insularity. (Both streams contain en- demic fishes.) Even small streams having free inter- change with larger systems support many fish species. For example, Cicerello & Butler (1985) reported 73 species from Buck Creek, Kentucky (drainage area 767 km2), which is a tributary of the Cumberland below the falls. Excluding 15 species associated with the low- gradient downstream reaches, which are influenced by an impoundment on the Cumberland River, and three introduced or recently invading species, leaves a richer fauna than that of the nearby much larger upper Cum- berland. 100,000 10,000 AREA (km2) Figure 4. Species-drainage area curoes for Mississippi tributaries (0), independent Gulf and Atlantic drainages (e), and Mississippi tributaries isolated by major waterfalls (()). a. Guyandotte b. Big South Fork Cumberland c Little Kanawha d. Licking e. Big Sandy J Kentucky g. Green h. Cumberland i. Tennessee j Mobile k Santee l Pearl m. Escambia n Neuse o. York p. Rappahannock q. Cumberland above falls r. Pascagoula oS: Roanoke t. Savannah u. James v. Pee Dee w. Apalachicola x Potomac y. Susquehanna z New. <:on.av.tlon Biology Volu~ 2. No. 2.)unc 1988