Final answer:
The interactions between the American chestnut and the parasitic fungus Cryphonectria parasitica are an example of parasitism, with severe ecological impact on North American forests.
Step-by-step explanation:
The interactions between the American chestnut and the parasitic fungus Cryphonectria parasitica exemplify the principle of parasitism, which is a type of ecological interaction where one organism benefits at the expense of another. In the early twentieth century, Cryphonectria parasitica, also known as the chestnut blight fungus, wreaked havoc on American chestnut populations, leading to dramatic ecological consequences. The American chestnut used to be a dominant canopy tree species in eastern North American forests, but the introduction of this parasitic fungus caused a severe decline in its populations, which led to significant changes in forest structure, nutrient cycling, and the extinction of species that depended on the chestnut.