INFLUENCE OF DRAINAGE CONNECTIVITY, DRAINAGE AREA AND REGIONAL SPECIES RICHNESS ON FISHES OF THE INTERIOR HIGHLANDS IN ARKANSAS

There has been strong recent interest in the ''macroecological'' appro ach of explaining local community phenomena as a consequence of patter ns at larger geographic scales. Various authors have suggested that if local observations can be explained by the larger-scale patterns in w hich they are embedded, there is less need to invoke local (within-sit e) processes (like competition, habitat structure, etc.) to explain co mmunity structure. We used a large database on local stream fish assem blages and species distributions in the Interior Highlands of Arkansas to test three macroecological hypotheses: (1) faunal similarities amo ng upland river basins can be predicted from the hierarchical geograph ical connectivities of those streams in the larger Mississippi River B asin drainage network; (2) faunal richness of drainages up to the size of small rivers (ca. 4000 km(2)) increases with drainage area; and (3 ) local (within-site) species richness increases in proportion to regi onal (basin) richness. These hypotheses were tested at the level of '' all species'', and within the families Cyprinidae (minnows) and Percid ae (darters). For the first hypothesis, Mantel tests comparing matrice s of faunal similarities and basin connectivity (based on number of no des separating these smaller basins within the Mississippi River Basin ) showed that similarities in composition of fish faunas among the upl and basins were predictable from the pattern of drainage connectivity. This pattern existed at the levels of ''all species'', minnows, and d arters. Upland basins separated by the fewest nodes had fish faunas th at were most similar, with all basins in the more northern White-Arkan sas river basin separating (across all taxa and within families) from the southern Ouachita river basin drainages; and lesser rivers within these basins also showed similarity generally related to their connect ivity. In rests of the second hypothesis, drainages up to small rivers in size exhibited positive, species-areas slopes at all taxonomic lev els. Species-area regression slopes (z) were 0.30 for ''all species'', and 0.36 for darters, both differing significantly from a slope of ze ro. However, minnows had a species-area regression slope of z = 0.20, which did nor differ statistically (P = 0.16) from a slope of zero. Fo r the third hypothesis, regional (basin) species richness explained li ttle of the variation in species richness at individual local sites, w ith the relationship significant at P = 0.054 for mean local number of ''all species'', and nonsignificant within the minnow and darter fami lies. Within all levels of regional (basin) species richness, there wa s great variation in number of species found at individual sites. Over all, we conclude that extrinsic macroecological hypotheses, based on p atterns at large spatial scales, differed in explaining composition of the faunas or assemblages at smaller spatial scales, leaving much var iation in local assemblage structure to be explained by local intrinsi c factors.