Rodent cycles in relation to biomass and productivity of ground vegetation and predation in the Palearctic

Abstract

The authors have synthesized the data on population dynamics and densities of rodents in seven biomes of the Palearctic, and related them to the data on standing crop of biomass and net productivity of ground vegetation (as rough indicators of food availability to rodents). Analysis of 44 long-term (≥5 yr) series of rodent trapping showed that there was a continuum from highly cyclic to non-cyclic populations. Standing crop of biomass of ground vegetation correlated positively with latitude; it was highest in the northern tundra and decreased towards South. Net productivity of ground vegetation (30 data points) did not show latitudinal trends. It was lowest in desert, tundra, and all types of forests, and highest in open habitats of the temperate zone and steppes. Mean densities of rodents were lowest in tundra, desert, and all types of forests (8-29 rodents/ha). The highest average densities were recorded in the farmlands of temperate zone and steppe (143-490 rodents/ha). Dichotomy between seasonal (non-cyclic) and multiannual (cyclic) fluctuations in rodent numbers was not found. Results of the long-term study on predation on rodents in the temperate deciduous forests did not support the hypothesis on the role of specialist and generalist predators in shaping rodent dynamics. Based on the observed vegetation-rodent correlations, the authors have proposed an interpretation of the mechanisms of rodent population dynamics in the Palearctic biomes. A prerequisite for rodent cycles to occur is abundant winter food, which enables rodents to continue an increase phase beyond one growing season (by winter breeding). Habitats with mean standing crop of ground vegetation of over 4000 kg dry weight/ha in summer are expected to harbour cyclic populations of rodents.