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Population growth over time is depicted for three functions (A-C) and for experimental data (D). In panel A, the characteristic concave-up curve of exponential growth is shown (solid line). The shape of this function changes with increasing (dotted line) or decreasing (dashed line) growth rates. In Panel B, the incorporation of resource limitation into the population growth model tempers growth rates at higher densities, giving a distinctive S-shaped curve (solid line). Increasing (dotted line) or decreasing (dashed line) growth rate will shift the curve to the right or left, but they both approach the same maxima, the carrying capacity. Reducing resources will have the effect of reducing maximal carrying capacity (dash-dot line). Panel C shows Lotka-Volterra style predator (dashed line) and prey (solid line). Predator numbers usually correspond to prey numbers with a slight lag and a reduced magnitude. VoMs behave differently in that their numbers usually exceed that of their 'prey.' Panel D (modified from Marston et al., 2012) shows the population dynamics al a bacterium, Synechococcus (black circles), and a virus, RIM8 (open circles), in a chemostat (top third). For reference, the dashed line is bacterial abundance in the control, virus-free chemostat. The middle and bottom panels show host and virus phenotypes found at six time points. Host-range mutants are numbered in their order of infectivity (e.g. ¢1-¢12), with higher numbers indicating the ability to infect a greater number of hos! phenotypes. Host phenotypes are labelled by their ability to resist infection by each host-range mutant. For example, S (sensitive to RIM8) is the ancestral host, and R0-2 is resistant to ¢0, ¢1, and ¢2. Dashed lines are hypothetical evolutionary histories based on the most parsimonious interpretation of the data. Reprinted with permission from Marston et al. (2012).
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