Figure 1.

Ecological vs. evolutionary change in bacterial susceptibility to phages or antibiotics. Ecological processes involve interactions between organism phenotypes and their environments, whereas evolutionary processes involve changes in allele frequencies (organism genotypes) over time. Vertical evolutionary changes (parent to offspring) involve mutations, whereas horizontal evolutionary change (horizontal or lateral gene transfer) involves what is known as genetic migration. The latter, though not emphasized here, involves the acquisition especially of evolved genetic material from other populations, e.g., such as in the course of acquisition of plasmids by bacteria. Tolerance-type phenotypes that result from near-term evolutionary changes are also not emphasized here.