Since discovered by Elton, long-term population cycles have been a major focus in ecology given their implications for population regulation and impacts on ecosystem dynamics. Studies of long-term population cycles have identified various influential factors, from species interactions to species’ life history. Few, if any, common factors governing cyclicity are known to apply across species and environments. Here, we aim to explain heterogeneity in long-term population cycles across the full range of animal species that exhibit these dynamics. We examine the extent to which species’ generation time, and thus body mass and temperature, may explain differences in cycle period for diverse primary consumer species (insects, protists, zooplankton, mammals, birds) based on predictions from metabolic scaling theory. We perform a broad-scale analysis on extensive published data from both wild and laboratory populations.
We find that long-term population cycles are sublinearly related to generation time across groups (R2=0.87), yet scale with body mass and temperature approximately as expected from metabolic scaling theory. Combined, the power-law relationship of cycle period to mass, and the exponential relationship to temperature, explain 89% of the variation in cycle periods across groups. The latter relationship of cycle periods with temperature shows that periods are roughly cut in half with a 10 oC increase in environmental temperature among ectotherms. We conclude that the period of cycles in primary consumer populations are strongly influenced by the factors governing generation time, namely size and temperature. Thus, these results point to possible changes to the period of cycles with changes in the size structure or body temperature of populations. By showing how generation time sets the pace of cycles, they also provide a point of departure for understanding the various causal factors driving long-term population cycles across species and environments.