Selective Consequences of Catastrophes on Growth Rates in a Stream-Dwelling Salmonid

Rapid environmental change occurring at an unprecedented rate calls for analyses of life-history evolution in highly variable environments. It has been shown that optimal life‑histories in a fluctuating environment with no episodes of massive mortality are likely to differ from those optimal in a constant environment. Catastrophic disturbances substantially alter population dynamics of affected populations, but little has been done to investigate how catastrophes may act as a selective agent for life-history traits. We use a life-history model of population dynamics of the stream-dwelling salmonid marble trout (Salmo marmoratus) to investigate how trade-offs between growth and mortality of individuals and density-dependent body growth can lead to the maintenance of a wide or narrow range of individual variation in body growth rates in the case of environments that are constant (i.e., only demographic stochasticity), variable (i.e., environmental stochasticity), or variable with catastrophic events (e.g., floods) causing massive mortalities. We find occasional episodes of massive mortality can substantially reduce persisting variability in intrinsic growth rates. The reduction of population density reduces density-dependence and allows for higher fitness of more opportunistic strategies (rapid growth and early maturation) during the recovery period.