The ecologist is assuming that there are no replacements for these resources and that technology will not necessarily fill the void. His/her premise does not include the possibility of substitutes, much the same as the extinction of a species. The economist looks at past occurrences and assumes such breakthroughs will continue due to economic pressure (increased commodity price=increased innovation) This is probably the most realistic view based on modern history. He/she is assuming that there is some substitute/alternative but is relying on past case histories to predict the future, which is logical but not always correct.
