ECOLOGY AND SYSTEMATICS OF FRESHWATER FISHES

the problems identified on a world-wide scale also impact our local aquatic flora and fauna. the distribution of the fishes within pennsylvania was initially related to plate tectonics, physiography, and geomorphology of the region. fenneman (1938) recognized the coastal plain, piedmont, blue ridge, ridge and valley, and appalachian plateau as distinct provinces of the region. it is generally conceded that the appalachian mountains evolved in the taconic (ordovician), acadian (devonian) and appalachian (primarily permian) orgogenies. contemporary thinking (e.g., judson 1976, cook et al. 1980) strongly suggests that these three major peaks of mountain building were a direct consequence of the actions of plate tectonics that characterized the paleozoic from ordovician through permian times. relative to the formation of these barriers to fish dispersal, schmidt (1986) hypothesized that five disjunct refugia contributed to the fauna of the northern appalachian region. the two refugia that would have most influenced the fauna within the region that is now pennsylvania are the mississippi valley and the atlantic coastal plain. the mississippi river basin is hypothesized to be the primary center of origin and dispersal of fishes east of the rocky mountains; thus, the high diversity of fishes found in these drainages relative to the atlantic coastal plain is expected. the overflow caused by melting glaciers probably would have been important in the dispersal of fishes from more northern regions into the susquehanna, delaware, and potomac basins of the atlantic slope, and caused stream reversal and dispersal of the great lakes fauna into the allegheny and monongahela rivers, and vice versa. there is no doubt that these events determined the original distribution of fishes with the commonwealth. more recently, however, anthropogenic influences have greatly altered the current arrangement of fish distribution patterns within pennsylvania. such influences include the direct transport of fishes through intentional or accidental introductions and changes in water quality caused by direct input of toxins into our waterways or by landscape alterations, which in turn change the physico-chemical parameters of run-off.the quantification of biodiversity, for the most part, hinges on the number of species present in a particular system. thus, the concept of species has long influenced the way in which humans view the diversity of life (ruffing et al. 2002). the goal to define the species category has provoked more discussions and arguments than perhaps any other topic in comparative or evolutionary biology (eldridge 1995). darwin (1859) recognized the difficulty in delimiting species when he noted that many forms considered by competent scientists as varieties are ranked as species by other competent researchers.i recently redescribed the brook trout (salvelinus fontinalis) from the type locality on long island, new york and designated a neotype, since a holotype was never preserved. my students and i are now working on the systematics of the 'brook trout' from pennsylvania and great smoky mountains national park in tennessee and north carolina. our preliminary conclusions indicate that brook trout do not occur in pa, but are in fact other species in salvelinus.