It is becoming increasingly evident that plant viruses -- among the smallest units of life on Earth -- can influence the dynamics of entire ecosystems. The capability of viral pathogens to disrupt agricultural ecosystems is well documented, but the mysteries of how plant viruses can play a role in ecosystem properties and processes in natural ecosystems are emerging more slowly. Once thought to be restricted mostly to agricultural ecosystems, we now understand that plant viruses are ubiquitous in nature. This symposium will examine the ecological roles of plant viruses. The role of viruses as mutualistic agents that contribute to drought and heat tolerance in plants will be highlighted, recognizing their potential influence in adaptation to climate change. Interactions between natural and agricultural ecosystems and their reciprocal influence, including the potential impact of plant viruses on biofuel crops, will be discussed. New concepts relating to the ability of viruses to manipulate their hosts and vectors to enhance their spread will be presented. Interdisciplinary interactions among ecologists, plant biologists, pathologists, and entomologists in their study of plant viruses will generate information that will help enhance food and biofuel security. The symposium will help scientists and nonscientists broaden their awareness of the natural histories of the full range of organisms that make up our biosphere.