Brady Holcomb, Computational Physics and Engineering
Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6038; Voice
423-241-4915; FAX 423-576-8646; E-Mail hqo@ornl.gov
Keywords: individual-based model, coexistence, sympatric
populations, population viability, trout
Understanding the biotic and abiotic conditions under which two or more
fish species coexist is critical to successful management and accurate assessment of
potential impacts. We used an individual-based simulation model of a two-species trout
community to evaluate which aspects of the hydrologic and temperature regimes have the
greatest impact on the persistence of both species. Various combinations of actual and
artificial flow and temperature regimes were used to track the success of the rainbow and
brown trout populations during 10- to 20-year simulations. Fairly constant conditions
usually allowed one species to dominate, leading to the eventual extinction of the other,
but, as environmental variability increased, so did the likelihood of long-term
coexistence. We found that the natural temporal variability in temperature and flow and
the timing of unpredictable periodic events, such as floods, droughts, and heat waves,
temporarily changed the relative advantage of the species, favoring coexistence.
Mechanisms by which variation in flow and temperature resulted in differential effects
included species-specific differences in optimal temperatures and in timing of spawning.
Information of the type derived from this model should be useful for making decisions on
stocking strategies and introductions of new species, and for assessing potential impacts
of changes in flow and water quality.