PARENT SESSION
Oral Session #16: Disturbance in diverse systems: Flooding and other. Presiding: T. Stohlgren.
Monday, August 6, 2001. 1:00 PM to 5:00 PM. Hall of Ideas G.
Disturbance theory and restoration of natural flow regimes.
Lytle, David1,2, 1 2
ABSTRACT- Flow regimes play an important role in structuring aquatic communities and maintaining native biodiversity within ecosystems. In systems historically dominated by floods and droughts, amelioration of extreme flows by dams and water diversions may facilitate invasion of non-native taxa. Using desert rivers and streams as an example, I present evidence that adaptations for surviving extreme flows (floods or droughts) may be more widespread among native taxa than previously realized. Thus, extreme flows could be used as a selective "sieve" for removing non-native taxa. Disturbance theory provides a useful framework for identifying managed flow regimes that achieve this. I present a model that combines disturbance dynamics (frequency, timing, severity and predictability of extreme flows) with standard life history models that describe population dynamics over time (Leslie and Lefkovitch matrices). Within this framework managed flow regimes can be identified that favor population growth (and thus long-term persistence) of native taxa and minimize population growth of non-natives. The model results suggest that the spatial scale of disturbance relative to population structure is important; extreme flows occurring synchronously across multiple drainages will remove non-natives more rapidly than comparable flows occurring asynchronously in a patch dynamics setting. However, the results also warn that if extreme flows are reintroduced too suddenly, even well-adapted native taxa are likely to be extirpated by chance if initial population sizes are small.
KEY WORDS: natural flow regime, stage structured model, invasive species, disturbance