Predicting freshwater fish life history tactics: Filtering potential life history diversity via habitat scenarios using Ecosystem Diagnosis and Treatment

Background/Question/Methods

While ecologists tend to classify and study broad scale life history strategies of species, proximate evolutionary mechanisms act on specific life history tactics at the population level.  Within a population and life stage individuals may exhibit multiple tactics or tactics that vary at small scales.  Expressions of a tactic may have higher or lower fitness under environmental conditions that vary over space and time.  Understanding which life history tactics may be most successful under alternate future scenarios can aid in shaping management plans and predicting how populations may respond.  Using the habitat-based ecosystem model Ecosystem Diagnosis and Treatment, we ask questions about which life history tactics of freshwater fish species are most likely to be successful under alternative habitat scenarios in rivers. We examine success of life history trajectories which are modeled sequences and durations of life stages reflecting specifics of life history tactics.  We are asking questions about success of alternate life history tactics in a variety of systems (ex., Alameda Creek and the San Joaquin River in California, the Umatilla River in Oregon, the Okanagan River in B.C. and Washington) for a variety of fish species (steelhead, Chinook salmon, delta smelt). 

Results/Conclusions

Here we present results for Alameda Creek, where we compared success of seven life history tactics under restoration scenarios and found that several life history tactics completely failed.  A life history tactic that restricted fish to one specific spawning reach with favorable habitat conditions was most successful, emphasizing that even with a larger ‘genetic template’ available observed life history patterns for a particular population may be highly constrained.   Our model results indicate which reaches in a river might be most important to protect and restore when management decisions must be made, whereas the examination of specific life history tactics helps describe the mechanisms by which selection may shape behavioral and developmental diversity.