Effects of Pathogens on Terrestrial Ecosystem Function

Many studies have demonstrated that pathogens can have strong effects on the per for mance of individual organisms, population dynamics, and community interactions. A more limited set of studies suggests that pathogens can alter a wide range of ecosystem functions in terrestrial systems; however, we are lacking a framework to predict the type and magnitude of ecosystem effects that a given pathogen will have. In this chapter, we present a number of general principles that determine how pathogens infl uence ecosystems over time, based on the welldeveloped fi elds of disturbance ecol ogy and the ecosystem effects of species composition. Our focus is not only on pathogens as disturbances but also as drivers of ecosystem pro cesses, even when their presence is not readily apparent.