Caenorhabditis elegans is a species of soil-dwelling nematode (roundworm) that feeds on soil bacteria, including Bacillus thuringiensis. B. thuringiensis is a virulent bacterial pathogen that produces BT toxin, a protein that can kill different invertebrate species, including C. elegans. In a laboratory experiment, C. elegans and B. thuringiensis were cultured individually (control) or together (experimental) for 150 days. Under optimal conditions, the generation time of C. elegans is approximately 3.5 days and the generation time of B. thuringiensis is approximately 25 minutes. At the end of the experiment, the change in virulence of B. thuringiensis and the change in resistance of C. elegans to BT toxin were determined. The researchers found that after 150 days, the magnitude of the change in both B. thuringiensis virulence and C. elegans resistance was less when they were cultured individually (control) than when they were cultured together (experimental). Provide ONE reason for the difference in results between the two treatments.