Although the largest perturbations to lake commu- nities and ecosystem processes probably occur soon after fishless lakes are stocked for the first time, our analyses show that continued stocking only serves to exacerbate the original effects. For example, some large invertebrate species (for example, Hes- perodiaptomus spp.) may coexist with low densities of introduced trout, especially in large and deep lakes (Donald and others 1994). However, many Sierra Nevada lakes with self-sustaining trout pop- ulations are still being stocked (R. A. Knapp unpub- lished), thereby increasing populations above den- sities that would normally result from natural reproduction. Such increased densities can increase predation intensity and further reduce the
