How Common are Cycles in Animal Populations

Although they seem unusual and dramatic, cyclic dynamics in animal populations are not particularly uncommon. Approximately 30% of all animals display significant cycles in population size, which is substantially greater than the 5% expected by chance alone. These

Table 1 Examples of herbivores with strong cyclic population dynamics

Herbivore Period (years) Synchronous area (km) Dominant process order Mechanisms

Voles 3-5 500 2 Predation

Snowshoe hare 9-11 1500 2 Predation

LBM 9-10 1000 2 Induced plant susceptibility, parasitoids

Cycle periods, maximum spatial extent of cycle synchrony, important mortality factors, and dominant order of population dynamics are presented.

cycles typically occur in disturbed temperate and boreal biomes, while cycles in tropical insects are much less common. Mammals and fish are the two major taxa that have the highest proportion of cyclic populations (0.33 and 0.43, respectively). It is likely that as more data are collected, examples of either separate populations or whole species that exhibit cyclic population dynamics may become more prevalent than we had realized. Latitudinal gradients in propensity to cycle are common, but are only statistically detectable in mammalian taxa.

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