Fungi may be selective in their source of a food base or may be restricted in terms of resource exploitation by competition with other fungal species. Providing the resource contains carbohydrates for energy and nutrients for growth, however, this resource can come from living or dead plant or animal tissue or merely from chemicals in the atmosphere (Wainwright et al., 1997). This leads to another property of fungi, their pathogenicity to both plants and animals, whereby the fungi "eat" living organisms. The role of fungal pathogens in agriculture has been
the subject of considerable research over many years. Indeed, the potato blight in Ireland (1843-1846) could be regarded as a classic example of the magnitude of the effect of a fungus on ecosystems (Austin Bourke, 1964). The fungal-induced potato crop failure not only reduced crop yield, it reduced the population of grazing fauna (humans) and caused one of the largest emigrations of fauna from an infected area (the movement of thousands of Irish to the United States). The economic loss of crops has resulted in the development of a large agrochemical industry to provide effective fungicides to combat fungal diseases of plants. In addition to the loss of plant biomass, other effects of pathogens result in the reduction of the fitness of the host organism. This fitness can be measured in terms of loss of reproductive capacity. This reduced fitness has important consequences on the population of the organism and/or its competitive abilities within the community. Fungi are thus involved in the regulation of the community structure of organisms and the population of individual species. Chapter 5 will discuss the role of fungi in influencing animal and plant populations and community structure, but will consider mainly natural ecosystems rather than the agricultural implications.
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