Virus Specificity in Disease Systems: Are Species Redundant?

Despite our increasing recognition of the key role that microbes play in ecosystem processes (e.g., Giller et al. 1997; Mills and Bever 1998; van der Heijden et al. 1998), concern over the loss of biodiversity in ecological communities rarely focuses on microbes— particularly pathogenic microbes which are more often targeted for eradication than preservation (but see Windsor 1995). Yet it is becoming clear that disease-causing microbes may be important in shaping biotic communities (Real 1996a), and their diversity significantly influences populations, communities, and ecosystems. We are surrounded by examples of the influence of disease on the landscape. One of the most dramatic examples is the loss of mature chestnut and elm trees in European and North American deciduous forests following the introductions of chestnut blight (Cryphonectria parasitica) and Dutch elm disease (Ophiostoma ulmi/O. novo-ulmi),