Practice question

“Bell-shaped curve” for a plot of dn/dt as a function of population density shows. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. Population ecology links individual births, deaths, immigration, and emigration to changes in abundance. Per-capita rates determine the direction of change, while density dependence creates feedback when crowding alters survival or reproduction. The remaining alternatives—“Rectangular hyperbola”, “Negative exponential”, “Linear increase”—refer to different states, processes, or scales and therefore do not express the same causal relationship. Interpretation must distinguish absolute population change from a per-capita rate and must state the time interval and population boundary. Age structure, dispersal, environmental variation, and delayed responses can all make observed trajectories depart from a simple model. Field observations could test this account by measuring the proposed driver and the demographic or ecosystem response while controlling plausible confounding factors.