Figure 42.8: Per Capita Growth Rate Decreases with Population Density (A) The decline in r as population density increases, as measured in a population of a small crustacean, Daphnia pulex (see Figure 42.10). (B) Schematic representation of density-dependent growth, in which r declines linearly with population density. This graph is an idealization—few species follow it exactly. For example, close inspection of (A) suggests that the decline in r for Daphnia pulex is not precisely linear.