FACTORS AFFECTING COMPETITIVE DOMINANCE OF RAINBOW-TROUT OVER BROOK TROUT IN SOUTHERN APPALACHIAN STREAMS - IMPLICATIONS OF AN INDIVIDUAL-BASED MODEL

We used an individual-based model to examine possible explanations for the dominance of rainbow trout Oncorhynchus mykiss over brook trout S alvelinus fontinalis in southern Appalachian streams. Model simulation s were used to quantify the effects on interspecific competition of (1 ) competitive advantage for feeding sites by rainbow trout, (2) latitu dinal differences in stream temperatures, flows, and daylight, (3) yea r-class failures, (4) lower fecundity of brook trout, and (5) reductio ns in spawning habitat. The model tracks the daily spawning, growth, a nd survival of individuals of both species throughout their lifetime i n a series of connected stream habitat units (pools, runs, or riffles) . Average densities of each species based on 100-year simulations were compared for several levels of each of the five factors and for sympa tric and allopatric conditions. Based on model results and empirical i nformation, we conclude that more frequent year-class failures and the lower fecundity of brook trout are both possible and likely explanati ons for rainbow trout dominance, that warmer temperatures due to latit ude and limited spawning habitat are possible but unlikely explanation s, and that competitive advantage for feeding sites by rainbow trout i s an unlikely explanation. Additional field work should focus on compa rative studies of the reproductive success and the early life stage mo rtalities of brook and rainbow trout among Appalachian streams with va rying rainbow trout dominance.