Figure 13.12 Population cycling in sheep blowflies. (a) When researchers limited food for larvae but not adults, they observed a delay between the time that the adults produced a large number of eggs and the time these eggs hatched into larvae, died from high larval competition, and failed to produce new adults. As a result, the adult population experienced regular cycles. (b) When adults were initially raised with unlimited food, but then given limited food halfway through the experiment, they began to experience density dependence without a time delay. As a result, the adult population still fluctuated but no longer experienced regular cycles.
Data from A. J. Nicholson, The self-adjustment of populations to change, Cold Spring Harbor Symposia on Quantitative Biology 22 (1958): 153–173.